Reducing QRM (interference) from a Renogy 200 watt (or any other!) portable solar panel system

Figure 1:
Renogy 200 watt folding panel, in the sun
Click on the image for a larger version.

Update - 10/24: 

I recent spent most of a week in a national park where I extensively used the solar panel and charger - along with some LiFePO4 batteries - as my main power source.  The panel was set up with 3-6 feet (1-2 meters) of my portable HF antenna.  I did not notice any interference from this system at all.  I did notice a bit of QRM from my fridge/freezer cooler to which I have since added its own RF filtering.

A year or so ago I got a 200 watt foldable solar panel system.  This unit - made by Renogy - consists of two glass panels in metal frames equipped with a sort of "kickstand" assembly to allow it to be angled more favorably with the sun to improve its output.  I use this panel when "car camping" to charge the batteries to run the sorts of things that one might bring:  Lights, refrigerator, amateur radio transceivers and who knows what else.  

On that last point, I've done some "in the field" operating on the HF amateur bands while the battery is being charged and noticed that the charge controller (and not the panel itself!) produced a bit of "hash" on the radio - mostly in the form of frequent "birdies" that swished around in frequency as the solar insolation and temperature varied - as well as a general low-level noise at some frequencies.   

This problem is not specific to the Renogy panel's charge controller, but common to almost any panel+controller combination that you will find.

Nearly all "portable" and RV solar power systems cause QRM:

You will find similar systems built into RVs and campers and these are also well known (notorious, even!) for generating RFI.  The techniques described here to quiet interference from these devices applies equally to those as well - but note that one may have to "scale up" the inductors/capacitors to accommodate higher voltages and currents that may be found in those systems.

By placing the solar panel with charge controller and the battery being charged some distance away from the antenna, this interference could be reduced, but that fact that it was even there in the first place annoyed me, so I did what I have done many times before (see the links to other blog entries at the end of this article) and mitigated it by making fairly easy, reversible modifications to the panel's controller.

Portable solar panels and RFI In my travels, I've been around other users of portable solar panels of various brands and I have yet to find any commercially-available portable panel+controller combination that does NOT produce noticeable RFI on HF/VHF among the half-dozen or so brands that I have checked.  In comparison with most of the others that I've been around with radios, the Renogy is comparatively quiet - producing less overall QRM with fairly long wires between the panel/controller and battery - than the others - but I decided that I could make it even quieter!

Where does the QRM come from?

It is NOT the solar panel itself that produces the radio frequency noise, but rather the charge controller attached to it.

Modern charge controllers electronically convert the (usually higher) voltage from the solar panels down to something closer to the battery voltage and this is typically done using PWM (Pulse Width Modulation) which means that these devices contain high-power oscillators:  This is true for simple "PWM" types of charge controllers as well as those using "MPPT" techniques.  It's this oscillation / switching action that produces a myriad of harmonics that can extend through the HF spectrum - and even into VHF/UHF!

The "Antenna" in this case consists of two parts of the PV system as depicted in the drawing below:

Figure 2:
A typical solar charging system showing the separation of the two major components that can radiate interference:  The panel itself, connected to the input of the charge controller and the wires and load connected on the output side.
If there is even a slight amount of differential between the two at radio frequencies, the system will radiate.
Click on the image for a larger version.

 

In other words:

• The wires connecting to the load.  Typically a battery being charged - which can be connected to other things (e.g. vehicle, inverter, etc.)  The wires connecting the panel to these other things - and those devices themselves - act as part of the "antenna" that potentially radiates noise.
  

• The solar panel itself.  The solar panel consists of large plates of metal - not only the silicon of the panel, but any metal frame and wiring:  This large area of conductive material offers a suitably large aperture to permit radiation of HF RF.
  

The "load" and solar panel constitute two different parts of the charge controller's system when it comes to radiation of RF:  The panel is connected to the INPUT of the PWM circuitry while the wiring is connected to the OUTPUT of the PWM circuitry, effectively forming a dipole antenna.  To a degree, the electrical lengths of these two conductors - which can include power cords or even a vehicle - overall can broadly resonate, affecting certain frequency ranges more than others.

The reason for the generation of the interference is due to the fact that the PWM circuitry (which is operating at a frequency of 10s or 100s of kHz) uses square waves, rich in harmonics.  As the voltage input (from the panel) and the output (to the battery/load) are different parts of the PWM circuit, they necessarily have different waveforms on them.

Figure 3:
Charge controller with additional filtering showing added
bifilar-wound chokes/caps on both the input and output leads.
Click on the image for a larger version.

While this device does have some filtering to provide a degree of input impedance reduction (fairly high capacitance) and smoothing of the PWM waveform of the output (more capacitors and likely some inductance) the extent to which this filtering is implemented is suitable for the purpose of providing clean DC power to the load and maximize power conversion efficiency.  This filtering - and likely the controller's circuit board itself - was likely not intended to provide the high degree of RF suppression needed to make it quiet enough to avoid the conduction of RF energy onto its conductors which is then picked up by a nearby receiver.

Containing the RF energy

 

As the controller itself is potted with a silicone material, it's not practical to modify it directly to make it RF-quiet - and there is no need to do so:  Instead, we must take steps to eliminate any differential RF currents that may exist between DC Input and DC output terminals.

Ferrite alone is NOT the answer!

One may presume that the answer to this problem is the implementation of RF device such as snap-on or toroidal ferrite devices - and you would be partially correct.  Any practical inductor - such as that formed by the introduction of a ferrite device onto an existing wire - will have rather limited efficacy in quashing RF currents.

Snap-on devices (e.g. those through which a wire passes) have very limited usefulness at HF frequencies (<30 MHz) - especially on the lower bands - as they simply cannot impart a significant amount of reactance in the conductor onto which they are installed.  At higher frequencies (VHF, UHF) they can have a greater effect - but their efficacy will usually be disappointing at HF.

Using a device that can accommodate multiple turns through its center such as a toroid (or even a larger snap-on device) it may be possible to get up to a few hundred ohms of reactance on a conductor across a fairly wide frequency range - but even this will be capable of reducing the amount of RF by 10-20 dB (2-3 "S" units) at most:  Depending on the intensity of the RFI from the solar controller, this may not be enough to quash the interfering energy to inaudibility - particularly in a remote and otherwise "RF Quiet" location.

To be sure, it's worth trying just the ferrite devices by themselves to see if - in your situation - it reduces the RF interference from the controller to your satisfaction, but remember that the location where you are likely to be using this panel is probably far quieter (RF-wise) than your home QTH:  A "quiet" Solar charging system may seem quiet enough at your noisy home QTH, but could still be noisy in the middle of nowhere.

The addition of capacitors to the circuit can improve the efficacy over ferrite alone by orders of magnitude.  Consider the diagram below:

Figure 4:
Diagram, including additional filtering.  L1 and L2 are the bifilar chokes seen in Figure 3, above while the capacitors (C1a, C1b, C1c and C2a, C2b and C2c) and their implementation are described below.
Click on the image for a larger version.

 

Ferrite devices L1 and L2 are comprised of bifilar-wound inductors on the DC input/output lines, respectively.  These inductors will suppress common-mode RF energy that may appear - but these alone are not likely to be quite enough.

 

In order to force the RF energy to common mode to maximize L1/L2's effectiveness, capacitors C1a, C1b do so for the "external" connections (e.g. those connected to large devices, long wires) while C2a and C2b do so for any RFI emanating from the controller itself.

 

C2c - which is placed between the DC input and output of the charge controller - effectively shunt RF energy differences between the in/out terminals to minimize the differential currents.  Figure 3 shows C2a placed between the two positive terminals, but it could have been placed in any combination (+ to -, - to -, etc.) and been just as effective since the capacitors C2a and C2b effectively short the + and - terminals together at RF frequencies.  If your OCD bothers you, could could add additional capacitor combinations, but the three shown above for C1 and C2 proved to be adequate.

 

The real work for our filtering magic is actually done by C1c.  As seen from the diagram it's shunting RF currents that might appear on the "external" sides of L1 and L2 - which will have been significantly reduced in amplitude by L1 and L2 anyway:  The low impedance of the C1c at RF (a few ohms) coupled with the high RF impedance of the conductors through L1 and L2 work together to make sure that differential RF currents that might exist between the input and output of the charge controller are minuscule, and thus there is effectively no RF energy that can be radiated.

 

Figure 5:
Three 0.1uF monolithic capacitors placed across the
controller's terminals (C2a, C2b, C2c).
Click on the image for a larger version.

Implementation

A glimpse of what was done may be seen in Figure 3.  Some 14 AWG paired copper wire (red/black) was wound on two FT140-43 ferrite toroids - about 6 bifilar turns in this case:  Individual wires could have been used other than "zip" cord - just be sure that the two parallel conductors are laid in parallel to maximize the effectiveness of the bifilar configuration.  Two of these wire/bifilar devices were constructed - one for the DC from the panel and the other for the output to the battery/load.  "Spade" lugs were installed on one end of the red/black wires - two lugs per wire/bifilar assembly.  (FT240-43 or FT240-31 toroids could also have been used, but the FT140-43 is a fraction of the cost, half the diameter, and perfectly suitable for this application.  The FT240 size may be more appropriate if such a filter network is constructed for a higher-current system with larger-gauge wire.)

On the solar controller itself, small 0.1uF, 50 volt monolithic capacitors were installed (C2a, C2b, C2c) to form part of the filter circuitry:  Minimal lead length is important for maximum effectiveness.  While monolithic ceramic capacitors are preferred because they are small (and will fit more easily in tight spaces) and have very low ESR (Effective Series Resistance) one could use disk ceramic capacitors instead.  Film/plastic capacitors are less effective at higher frequencies.

Figure 6:
Terminal strip with capacitors C1a, C1b and C1c.
As described, these capacitors do much of the "bypassing"
of RF differential currents between the input and output.
Click on the image for a larger version.

As can be seen from this picture and Figure 5, the terminals are the "clamp" type and are connected in the same manner as the lugs on the cable on the bifilar toroid assembly. - and also note that this "modification" is completely reversible as nothing at all was changed on the controller itself.

The other end of the red/black wires were soldered to a four-position screw terminal strip as seen in Figure 6 - similar to the one on the back of the charge controller.  As with the terminal strip on the controller, three 0.1uF 50 volt capacitors were soldered (C1a, C1b, C1c) on the back for RF bypassing.  It is possible to have connected the capacitors under the clamps as was done on the controller, but soldering them to the back means that they would not be prone to falling out or being lost if the cables were changed.

 

With these connections made, the wire on the toroids and the connections to the added terminal strip were covered with "Shoe Goo" - a robust rubber adhesive (which may be used to fix shoes, as the name suggests) both as mean of strain relief and to provide electrical insulation.

 

The reader may have noted that we have physically brought together the input/output cables again at this terminal strip - and this was intentional.  By keeping the leads with the bifilar inductors as short as possible and then bringing them back together, we can use the shortest-possible leads on our capacitors to effectively "short" the input and output cables together at radio frequencies, making it impossible for the wires to radiate effectively at HF.  With this, the RF energy is contained within the area of the charge controller itself and the terminal strip/cables and since this is a very small aperture at HF, it can't radiate effectively and additional metallic shielding is unneeded.

 

At VHF/UHF frequencies - where the physical size of the controller+bifilar chokes is a larger proportion of the size of the wavelength (plus the fact that the components used won't work as well at these frequencies) means that some RF energy could radiate, but testing shows that the amount of VHF/UHF RF energy conveyed by the panel and cables was reduced below the point of detection more than a few feet (a meter) or so away from the system.

Spectrum analysis plots - updated 12/24

In the original version of this post I "loosely coupled" a spectrum analyzer (the "Tiny SA Ultra") to the leads to/from the controller by wrapping them around - but this only tells part of the story, showing the worst of the interference.  In this update, I connected  to the DC leads "directly" - using a 0.0022uF capacitor as a DC block - before and after the filtering to show the difference.  (Ignore the markers in the following plots - I forgot to shut them off)

First, the bad (no filtering):

 

Figure 7:
Un-filtered 0-30 MHz spectrum from the controller, directly coupled.

Figure 7 shows what the spectrum looks like from 0 to 30 MHz - each horizontal division representing 5 MHz - covering the extent of the HF spectrum but as expected, the worst of it is found in the first several MHz as shown in the next plot:

 

Figure 8:
Un-filtered 0-10 MHz spectrum from the controller, directly coupled.

Figure 8 shows from 0 to 10 MHz - with each horizontal division representing 1 MHz - and we can see that the peak energy at around 5 MHz is stronger than -40dBm - a level which correlates with an S-meter reading of about "30 over S-9".  This plot along with that of Figure 7 show that even as high as 20 meters (14 MHz) the noise can exceed "10 over S-9".

Remember that we are connecting the analyzer directly to the terminals of the equipment - something that you would not normally do, but these plots give you an idea as to how much energy is available to be radiated on the wires that go between the panel and the battery:  Even if the signals at 5 MHz were down by 30dB (1000-fold) due to coupling, they would still be about "S-9" in strength (e.g. pretty strong).

Below are the same plots - this time with the filtering depicted in figures 4-6:

Figure 9:
0-30 MHz, directly coupled to the controller - after filtering.

 

This shows a dramatic decrease in the amount of RF present from 0-30 MHz and as can be seen above, the noise floor above 5 MHz is VERY much reduced.  Let's look at the 0-10 MHz range, below:

Figure 10:
0-10 MHz, directly coupled to the controller - after filtering.

 

As expected, the filtering is less effective at frequencies below 1.5 MHz (more inductance and larger capacitors could help with that) but even at 2 MHz we see that the "grunge" is attenuated by about 20dB (100-fold, around 3 S-units worth), and is further reduced to be down by roughly 40dB (10000-fold, or about 7 S-units) around 80 meters (3.5-4.0 MHz) and higher, approaching the noise floor of the spectrum analyzer (approx. -100dBm with an RBW of 100 or 300 kHz) around 7 MHz, rising slightly in the 13-16 MHz range.  As can be seen in Figure 9, the worst-case noise output anywhere above 7 MHz are only around -85 dBm (S-7) and this would be with the receiver connected directly to the solar panel leads:  Again, no-one would ever do that!

 

The above measurements show how much RF energy is inputted into the wires connecting the panel and the battery bank - both of which will act as halves of a dipole antenna - and these measurements show that we can very significantly reduce this energy, likely reducing it to the point of inaudibility. 

Figure 11:
The same filtering - this time, applied to a Renogy
Rover 20 amp MPPT solar controller.
Click on the image for a larger version.

As noted in the update at the top of this posting, I've operated the solar panel and controller right next to my HF antenna and could not hear any interference from it!

 

Figure 11 shows the techniques depicted in figures 4, 5 and 6 applied to a different Renogy controller, also using FT140-43 toroids and 0.1uF monolithic capacitors.  In this case, the only capacitors used were those attached directly to the back side of the four-screw terminal strip (C1a, C1b, C1c) which works because this particular controller already has the other set of capacitors (C2a, C2b, C2c) on its circuit board.

 

Conclusion:

 

Prior to the modification, getting within several feet/meters of the solar panel with a portable shortwave receiver equipped with SSB revealed drifting "birdies" from the controller's normal operation and holding the antenna against either the panel or the output cable made this orders of magnitude worse.

After the modification these "birdies" were inaudible on the cables:  It took holding the portable receiver's antenna within a few inches/cm of the charge controller to hear its operation.  By the addition of these nine components (two bifilar inductors, six capacitors and the terminal strip) the RF energy is confined to the (small!) physical space of the controller itself and is no longer being introduced differentially to the panel and output cable, causing it to be unable to radiate effectively at HF, making it very quiet and "Radio Friendly".

While the supplied charge controller for the Renogy panel was a simple PWM type rather than an MPPT (Maximum Power Point Tracking) and is thus somewhat less effective at extracting all-possible energy from it, there is no reason why this sort of filtering could not be applied to either types.

 

This shows how a typical portable solar panel+charge controller can be made to be RF-quiet and "POTA" or "SOTA" compatible.  This (reversible!) modification has rendered this panel completely quiet across the HF spectrum and inaudible on VHF/UHF frequencies as well at distances of more than a few feet (a meter or so) as well.

* * * * *

Related articles:

• The December 8, 2012 entry about "Reducing Switch Supply Racket racket (RF Interference) - Link 
• See also the September 4, 2013 entry, "Quieting High-Current switching supplies used in the ham shack - link
• The article "Minimizing VHF and HF RFI from electronic ballasts and fluorescent tubes - link - from December 17, 2015 may also be useful in quashing interference from these sources.
• The December 1, 2017 article "Containing RF noise from a sine wave UPS" - link - also details how interference from an RF-noisy device may be suppressed.
• Quieting an insanely noisy LED floodlight - link.  This describes how a constant-current LED supply that produced enough interference to quash HF reception was quieted down to the point of undetectability. 
• Quieting a 150 watt Samlex sine wave inverter - link.  This page talks about making an otherwise RF-noisy sine wave inverter quiet at radio frequencies. 
• Completely containing switching power supply RFI - link.  Sometimes it can be difficult to quiet a switching power supply, so it may be necessary to put it in a box with strong filtering on all of the conductors that enter/leave. 
  

This page stolen from ka7oei.blogspot.com

 

[End]

Using an inexpensive MPPT controller in a portable solar charging system

As I'm wont to do, I occasionally go backpacking, carrying (a bit too much!) gear with me - some of it being electronic such as a camera, GPS receiver and ham radio(s).  Because I'm usually out for a week or so - and also because I often have others with me that may also have battery-powered gear, there arises the need for a way to keep others' batteries charged as well.

Having done this for decades I've carried different panels with me over that time, wearing some of them out in the process, so it was time for a "refresh" and a new system using both more-current technology and based, in part, on past lessons learned.

Why 12 volt panels?

If you look about you'll find that there are a lot of panels nowadays that are designed to charge USB devices -which is fine if all you need to do is charge USB devices, but many cameras, GPS receivers, radios and other things aren't necessarily compatible with being charged from just 5 volts.  The better solution in these cases is to start out with a higher voltage - say that from a "12 volt" panel intended for also keeping a car battery afloat - and convert it down to the desired voltage(s) as needed.

After a bit of difficulty in finding a small, lightweight panel that natively produced the raw "12 volts" output from the array (actually, 16-22 volts unloaded) I found a 18 watt folding panel that weighed just a bit more than a pound by itself.  It happened to also include a USB charge socket - but can be hard to find one without that accessory!

Figure 1:
The 6-7aH LiFePO4 battery, MPPT controller and "18 watt" solar panel.
The odd shape of the LiFePO4 battery is due to its being intended to power
bicycle lighting, fitting in a water bottle holder.
Click on the image for a larger version.

By operating at "12 volts" you now have the choice of practically any charging device that can be plugged into a car's 12 volt accessory socket (e.g. cigarette lighter) and there are plenty of those about for nearly anything from AA/AAA chargers for things like GPS receivers and flashlights to those designed to charge your camera.  An advantage of these devices is that nowadays, they are typically very small and lightweight, using switching power converters to take the panels voltage down to what is needed with relatively little loss.

But there is a problem.

If you use a switching power converter to take a high voltage down to a lower voltage, it will dutifully try to maintain a constant power output - which means that it will also attempt to maintain a constant power input as well - and this can lead to a vexing problem.


Take as an example of a switching power converter that is 100% efficient, charging a 5 volt device at 2 amps, or (5 volts * 2 amps =) 10 watts.

If we are feeding this power converter with 15 volts, we need (10 watts / 15 volts =) 0.66 amps, but if we are supplying it with just 10 volts, we will need (10 watts / 10 volts =) 1 amp - all the way down to 2 amps at 5 volts.  What this means is that while we always have 10 watts with these differing voltages, we will need more current as the voltage from the panel goes down.

Now suppose that we have a 15 watt solar panel.  As is the nature of solar panels, there is a "magic" voltage at which our wattage (volts * amps) will be maximum, but there is also a maximum current that a panel will produce that remains more or less constant, regardless of the voltage.  What this means is that if our panel can produce its maximum power at 15 volts where it is producing 1 amps, if we overload the panel slightly and cause its voltage to go down to, say, 10 volts, it will still be producing about 1 amp - but only making (10 volts * 1 amp =) 10 watts of power!  Clearly, if we wish to extract maximum power to make the most of daylight we will want to pick the voltage at which we can get the maximum power.

Dealing with "stupid" power converters:

Suppose that, in our example, we are happily producing 10 watts of power to charge that 5 volt battery at 2 amps.  At 15 volts, we need only 0.66 amps to get that 10 watts, but then a black cloud comes over and the panel can now produce only 0.25 amps.  Because our switching converter is "stupid", it will always try to pull 10 watts - but when it does so, the voltage on its input, from the panel, will drop.  In this scenario, our voltage converter will pull the voltage all of the way down to about 5 volts - but since the panel can only produce 0.25 amps, we will be charging with only (5 volts * 0.25 amps =) 1.25 watts.


Now, the sun comes out - but the switching converter, being stupid, is still trying to pull 10 watts, but since it has pulled the voltage down to 5 volts to charge the battery, we will need 2 amps to feed the converter the 10 watts that it will need to be happy, but since our panel can never produce more than an amp, it will be stuck there, forever, producing about only (5 volts * 1 amp =) 5 watts.

If we were to disconnect the battery being charged momentarily so that the switching converter no longer saw its load and needed to try to output 10 watts, the input voltage would go back up to 15 volts - and then when we reconnected the battery, it would happily pull 0.66 amps at 15 volts again and resume charging the battery at 10 watts - but it will never "reset" itself on its own.

What this means is that you should NEVER connect a standard switching voltage converter directly to a solar panel or it will get "stuck" at a lower voltage and power if the available panel output drops below the required load - even for a moment!

Work-arounds to this "stuck regulator" problem:


The Linear regulator

One obvious work-around to this problem where a switching regulator gets "stuck" is to simply avoid using them, instead using an old-fashioned linear regulator such as an LM317 variable regulator or a fixed-voltage regulator in the 78xx series (e.g. 7805 for our 5 volt example).  This type of regulator, if outputting 1 amp, will also require an input of 1 amp, the difference in voltage being lost as heat.  If a black cloud comes over - or it is simply morning/evening with less light - and the panel outputs less current, that lower current will simply be passed along to the load.

The problem with a linear regulator is that it can be very inefficient, particularly if the voltage is being dropped significantly.  For example, if you were to charge the 5 volt device at 1 amp from a panel producing 15 volts, your panel would be producing (15 volts * 1 amp =) 15 watts, you would be charging your device at (5 volts * 1 amp =) 5 watts, but your linear regulator would be burning up the difference -10 watts of heat - wasting most of the energy.  On the up side, it simply cannot get "stuck" like a switching converter, it is very simple, it will cause no radio interference, and it is nearly foolproof in its operation.

Figure 2:
The front of the EvilBay "5 amp MPPT charger".  This unit is
an inexpensive unit that used the "Constant Voltage" algorithm (see
below) and designed primarily to charge lithium chemistry batteries.
One of the potentiometers is used to set the final charge voltage - between
14.2 and 14.6 volts for a "4 cell" LiFePO4 - and the other is set to the "maximum
power voltage" of the panels to which it is connected.  This unit- as do most
inexpensive units -require that the MPPT voltage of the panels be 2-3 volts
higher than the final charge voltage of the battery being charged.
Click on the image for a larger version.

MPPT power controller

A better solution in terms of power utilization would be to use a more intelligent device such as an MPPT (Maximum Power Point Tracking) regulator.  This is a "smarter" version of the switching regulator that, by design, avoids getting "stuck" by tracking how much power is actually available from the solar panel and never tries to pull more current than is available.  For this discussion we'll talk about the two most common types of MPPT systems.

"Perturb and Observe" MPPT:

This method monitors both the current and voltage being delivered by the panel and internally, calculates the wattage (e.g. volts * amps) on the fly and under normal conditions, and it will change the amount of current that it is trying to pull from the panel up and down slightly to see what happens, hence the name "Perturb and Observe" (a.k.a. "P&O").

For example, suppose that our goal is to get the maximum amount of power and our panel is producing 15 volts at 1 amp, or 15 watts.  Now, the MPPT controller will try to pull, say, 1.1 amps from the panel.  If the panel voltage drops slightly to 14.5 volts so we are now supplying (1.1 amps * 14.5 volts =) 15.95 watts and we were successful in pulling more power to be delivered to our load.  Now, it will try again, this time to pull 1.2 amps from the panel, but it finds that when it does so the panel voltage drops to 12.5 volts and we are now getting (1.2 amps * 12.5 volts =) 15 watts - clearly a decrease!  Realizing its "mistake" it will quickly go back to pulling 1.1 amps to get back to the setting where it can pull more power.  After this it may reduce its current to 1 amp again to "see" if things have changed and whether or not we can get more power - or if, perhaps, the amount of sunlight has dropped - such that trying to pull less current is the optimal setting.

By constantly "trying" different current combinations to see what provides the most power it will be able to track the different conditions that can affect power output of the solar panel - namely the amount of sun hitting it, the angle of that sun and to a lesser extent, the temperature of the solar panel.

Figure 3:
Curves showing the voltage versus current of a typical solar cell.  Once
the current goes above a certain point, the voltage output of a cell
drops dramatically.  The squiggly, vertical line indicates where
the maximum power (e.g. volts * amps) is obtained along the curve.
The upper graphs depict a typical curve with larger amounts
of light while the lower graphs are for smaller amounts of
impinging light.
This graph is from the Wikipedia article about MPPT - link. 
Click on the image for a slightly larger version.

"Constant Voltage" MPPT:

If you look at the current-versus-voltage curve of a typical solar panel as depicted in Figure 3 you'll note that there is a voltage at which the most power (volts * amps) can be produced (the squiggly vertical line) - a value typically around 70-80% of the open-circuit voltage, or somewhere in the area of 15-18 volts for a typical "12 volt" solar panel made these days.

Note:

Many "12 volt" panels currently being made are intended for use with MPPT controllers and have a bit of extra voltage "overhead" as compared to "12 volt" panels made many years ago before MPPT charging regimens were common.  What this means is that a modern "12 volt" panel may have an maximum power point voltage of 16-17 volts as opposed to 14-15 volts for an "older" panel made 10+ years ago.

One thing that you might notice is that, at least for higher amounts of light, the optimal voltage for maximum power for our hypothetical is about the same - approximately 0.45 volts per cell.  We can, therefore, design an MPPT circuit that is designed to cause the panel to operate only at that optimum voltage:  If the sunlight is reduced and the voltage starts to drop, the circuit will decrease the current it is pulling, but if the sunlight increases and the voltage starts to rise, it will increase the current to pull the voltage back down.


This method is simpler and cheaper to implement than the "Perturb and Observe" method because one does not need to monitor the current from the panel (e.g. it cares only about the voltage) and there does not need to be a small computer or some sort of logic to keep track of the previous adjustments.  For the Constant Voltage (e.g. "CV") method the circuit does only one thing:  Adjust the current up and down to keep the panel voltage constant.

As can be seen from Figure 3, the method of using "one voltage for all situations" is not optimal for all conditions as the voltage at which the most power can be obtained changes with the amount of light, which also changes with the temperature of the panel, age, shading, etc.  The end result of this rather simplistic method of optimization is that one ends up with somewhat lower efficiency overall - around 80% of the power that one might get with a well-performing P&O scheme according to some research. ^{Ref. 1}

This method can be optimized somewhat if the circuit is adjusted for maximum power output under "typical" conditions that one might encounter.  For example, if the CV voltage is adjusted when the panel is under (more or less) maximum sun on a typical day, it will produce power most efficiently when the solar power production is at its highest and making the greatest contribution to the task at hand - such as charging a battery.  In this case, it won't be optimized as well when the illumination is lower (e.g. morning or evening) but because the amount of energy available during these times will be lower anyway, a bit of extra loss from the lack of optimization at those times will be less significant than the same percentage of loss during peak production time.

Despite the lower efficiency, the Constant Voltage method is often found as a single-chip solution to implement low-cost MPPT, providing better performance than non-MPPT alternatives.

Actual implementation:

I was able to find an inexpensive (less than US$10, shipped) MPPT charge control board on EvilBay (called "5A MPPT Solar Panel Regulator Battery Charging") that was adjustable to allow its use with solar panels with open-circuit voltages ranging from 9 to 28 volts and its output being capable of being adjusted from 5 to about 17 volts.  This small board had built-in current regulation set to a maximum of 5 amps - more than adequate for the 18 watt panel that I would be using.

From the pictures on the EvilBay posting - and also once I had it in-hand - I could see that it used the Consonance CN3722 MPPT chip. ^{Ref. 2}  This chip performs Constant Voltage (CV) MPPT functions and provides a current-regulated output with the components on the EvilBay circuit board limiting the current to a maximum of 5 amps.  Additionally, this board, when used to charge a battery directly, may be adjusted, using onboard potentiometers, to be optimized for the solar panel's Maximum Power voltage (typically called "Vmp" in panels' specifications) and adjusted for the finish charge voltage for the battery itself, being suitable for many types of Lithium-Ion chemistries - including the "12 volt" LiFePO4 that I was going to use.

Figure 4:
The back side of the MPPT controller showing the heat sink and connections.
The heat sink is adequate for the ratings of this unit.  To save weight and bulk,
the unit was not put in a case, but rather the wires "zip tied" to the mounting
holes to prevent fatiguing of the wires - and to permit the wires themselves to
to offer a bit of protection to the top-side components.
Click on the image for a larger version.

To this end, my portable charging system consists of the solar panel, this MPPT controller and a LiFePO4 battery to provide a steady bus voltage compatible with 12 volt chargers and devices.  By including this "ballast" battery, the source voltage for all of the devices being charged is constant and as long as the average current being pulled from the battery is commensurate with the average solar charging current, it will "ride through" wide variations in solar illumination.  This method has the obvious advantage that a charge accumulated throughout the day can be used in the evening/night to charge those devices or even be used to top off batteries when one is hiking and the panel may not be deployed.

Tweaking the "Constant Voltage" MPPT board:

As noted, the EvilBay CN3722 board had two trimmer potentiometers:  One for setting the output voltage - which would be the "finish" charge voltage for the battery and another for setting the Constant Voltage MPPT point for the panel to be used.

Setting the output voltage is pretty easy:  After connecting it to a bench supply set for 4-6 volts above the desired voltage I connected a fairly light load to the output terminal and set it for the proper voltage.  For a "12 volt" LiFePO4 battery, this will be between 14.2 and 14.6 volts while the setting for a more conventional "12 volt" LiIon battery would be between 16.2-16.8 volts, depending on the chemistry and desired finish voltage. ^{Ref. 3}  Once this adjustment has been done I connected a fully-charged battery to the output along with a light load and power-cycled the MPPT controller and watched it as it stabilized, readjusting the voltage as necessary.

Setting the MPPT voltage is a bit tricker.  In this case, a partially discharged battery of the same type and voltage that will be ultimately used as was adjusted above is connected to the output of the MPPT controller in series with an ammeter on the output.  With the solar panel that is to be used connected and laid out in full sun, the "MPPT Voltage" potentiometer is adjusted for maximum current into the battery being charged.  Again, this step requires a partially-discharged battery so that it will take all of the charging current that is available from the panel.

Note that the above procedure also presumes that the solar panel is too small to produce enough power to cause the MPPT battery charger itself to go into current limiting - in which case, the current limit is that of the panel itself - which means that the maximum current that is seen at the charging terminal of the battery reflects the maximum power that can be pulled from the panel.  For example, with a panel producing 18 watts and charging a battery at 13.5 volts we could only ever expect to see about 1.33 amps flowing into the battery due to the inability of the panel to supply more power, but maximizing this current by adjusting the "MPPT" voltage control permits optimization for that particular solar panel.

If the panel is large enough to cause the MPPT controller to current-limit its charging current (around 5 amps for the MPPT controller that I used) then it may be that the panel is oversized slightly for the task - at least at midday, when there is peak sun.  In that case one would make the same adjustment in the morning or evening when the amount of light was low enough that the panel could not cause the charger to current-limit or simply block a section of the panel.

While this charging board would be able to connect directly to almost any rechargeable Lithium battery, it would be awkward try to adapt it for each type of battery that one might need to charge "on the trail" so I decided to carry with me a small "12 volt" LiFePO4 battery as well:  The solar panel and MPPT controller would charge that battery and then the various lightweight "12 volt" chargers for the different batteries to be charged would connect to it.

Its worth noting that MPPT power controllers use switching techniques to do the efficient conversion of voltage.  What this means is that if, attached to - or nearby - is a sensitive radio - particularly an  HF (shortwave) transceiver - the switching operation of the MPPT controller may cause interference unless the controller is enclosed in an RF-tight box with appropriate filtering on the input and output leads.  In practice I haven't found this to be an issue as any HF operation is usually done in the evening, at camp, as things are winding down and the sun isn't out, anyway, so the unit is not in service at that time.

Final comments

While the "ballast battery" method has an obvious weight and volume penalty, it has the advantage that if you need to charge a number of different devices, it is possible to find a very small and light 12 volt "car" charger for almost any type of battery that you can imagine.  The other advantage is that with a 12 volt battery that is being charged directly from the MPPT controller, it acts as "ballast", allowing the charging of this "main" battery opportunistically with the available light as well as permitting the charging of the other batteries at any time - including overnight!

The 18 watt panel weighs 519 grams (1.14 pounds), the MPPT charge controller with attached wires and connectors weighs 80 grams (0.18 pounds), a cable connecting the panel to the MPPT controller weights 60 grams (0.13 pounds) while the 6-7 amp-hour LiFePO4 battery pictured in Figure 1 . ^{Ref. 4}  weighs in at 861 grams (1.9 pounds).   The total weight of this power system is about 1520 grams (3.35 pounds) - which can be quite a bit to carry in a backpack, but considering that it can provide the power needs of a fairly large group and that this weight can be distributed amongst several people, if necessary, it is "tolerable" for all but those occasions where it is imperative that there is the utmost in weight savings.  For a "grab and go" kit that will be transported via a vehicle and carried only a short distance this amount weight is likely not much of an issue.

* * *

References:

1 - The article "Energy comparison of MPPT techniques for PV Systems" - link - describes several MPPT schemes, how they work, and provides comparison as to how they perform under various (simulated) conditions.

2 - Consonance Electric CN3722 Constant Voltage (CV) MPPT multichemistry battery charger/regulator - Datasheet link.

3 - Particularly true for LiIon cells, reducing the finish (e.g. cut off) voltage by 5-10%, while reducing the available cell capacity, can improve the cell's longevity.  What this means is that if the cut-off voltage of a typical modern LiIon cell, which is nominally 4.2 volts, is reduced to 4.0 volts, all other conditions being equal this can have the potential to double the useful working life.  While this lower cut off voltage may initially reduce the available capacity by as much as 25%, a cell consistently charged to the full 4.2 volts will probably lose this much capacity in a year or so, anyway whereas it will lose much less capacity than that at the lower voltage.  For additional information regarding increasing the longevity of LiIon cells see the Battery University web page "How to Prolong Lithium-based Batteries" - link and its reference sources.

4 - This LiFePO4 battery has been featured several times before - see these links:

• Problems with LiFePO4 batteries - link
• Follow-up:  LiFePO4 batteries revisited - equalization of cells - link

    [End]

This page stolen from "ka7oei.blogspot.com".
 

The solar saga - part 2: Getting the system online

In part one (March 2, 2016) I wrote about why I chose to use a series string inverter system.  (Hint:  It was to prevent radio-frequency interference.)  To read part one, click on the link here:  The Solar Saga - Part 1:  Avoiding Interference (Why I did not choose microinverters.)

Eventually, I was able to get the system "online" in late April even though everything solar-related had been in place for over 2 months.  Why the delay?

Figure 1:
Slip-sliding around, the work crew clearing ice and snow off
the metal garage roof.  Later, they wielded a propane
"weed burner" to loosen the remaining ice and snow and
dry the metal roof panels.
Click on the image for a larger version.

As is often the case in life, things don't always go exactly according to plan!

Installing the panels:

Going back a bit, the solar panels and inverter were actually installed in February.

In the winter.

In the snow.

Think about that for just a moment, particularly considering when the system was actually put online.

Figure 2:
The mounting rails for the solar panels, installed.  If you
look carefully in the background you can see where
someone fell hard on the ridge cap, slightly crushing it!
Click on the image for a larger version.

To be sure, there was a lot to do, but everything seemed to be going according to plan, with no obvious trouble (of which I was ever informed) with the city in pulling permits.

Part of the install actually began a few weeks before this when a survey crew came out to check out the "sun situation" where the panels were to be installed.  As soon as they arrived they placed a ladder against the garage roof and then I heard some muttering:  They'd just realized that they had left the device that analyzes the sun's path and potential shadows at the previous job some 15-20 miles north in another county.  Instead of being able to plop this device down in the locations of the solar arrays they squinted with expert eyes at the trees and sky and declared more or less "I don't think that shade will be a problem."  Who was I to argue - they were professionals!

Figure 3:
The installed eastern solar array  At the time that the picture
was taken the system was wired up, but without a net meter it
couldn't be "officially" used.
Click on the image for a larger version.

Aside from lots of slipping and sliding on the snow-covered metal roof, the installation seemed to go well with the rails having been installed the first day and the roof penetration - a set of rubber "Flasher" bushing type thing being used to seal about the electrical conduit that emerged from from within the garage itself, one for each array.

A few days later the panels were on the roof and the inverter wired up and connected to the new electrical sub-panel that I'd put in the garage a few weeks before.  While the system worked, I really couldn't use it as the "Net Meter" was not yet installed and any excess power that I produced would be charged to me just as if I'd actually used it!

Figure 4:
A screen shot of the system producing just under 1400 watts
in "Standalone" or "Island" mode - a configuration that allows
the solar electric system to produce useful energy even if the power
grid was down, unlike a microinverter system where the potential
electrical solar power from the panels is completely
inaccessible if the power is out!
Click on the image for a larger version.

While I could not do the "net meter" thing, one feature provided by the Sunny Boy inverters - but not with microinverter systems - is the "Secure Power System" or "SPS" (tm) that will allow power "islanding".  In other words, if the main breaker is shut off and a switch is flipped, the inverter will provide up to 1.5kW of power (12 amps, 125 volts) - even if the mains power is unavailable, provided that there is adequate sun, of course:  Just try that with a microinverter system!

Figure 5:
The installed Sunnyboy 5+kW inverter and the garage
sub-panel to which it is connected.   Below and
to the left of the inverter is the DC disconnect switch
for the two independent MPPT solar panel strings
(the "East" and "West") and just to the right
of it is the "SPS" or "Standalone" power outlet capable of
providing up to 12 amps at 125 volts (1.5kW) even
if the electrical grid is offline.
Click on the image for a larger version.

A problem with the electrical service entrance:


From the beginning I was informed that my main electrical panel - the place where the power from underground gets to the house - would have to be replaced.  Fortunately, this cost was "baked into" the cost of the system itself and since I'd replaced the sub-panel in my garage myself, the installers would cover it.  In asking around I determined that in my case, the typical cost for this would be in the $1000-$1500 range including all parts and labor.

The reason that the old panel had to be replaced was ostensibly due to the "20% rule", and in my case it went something like this:

My panel, originally installed when the house was new (early 1970s) was rated for 100 amps on the bus.  The "20% rule" said that it was permissible to have 20% above this value, or up to 120 amps.  The problem was that my photovoltaic system would, being capable of 5.3 kilowatts, could in theory of being capable of putting 22-24 amps (depending on voltage) on the bus and this, combined with a 100 amp main breaker, meant that I could put a total of 124 amps on the bus.

This would not pass muster - or inspection - so the panel was to be upgraded to a 125 amp unit with a 100 amp breaker which, according to the same rule, should allow a total of 150 amps on the bus.

A few days before the date in late February when the service upgrade was scheduled I got a call from the contractor saying that they couldn't do it:  The power company would not sign off because of the location of the gas line and meter with respect to the electrical panel itself.  After being informed of this I took a walk through my neighborhood and observed that about a third of the houses had their electrical panels "on top" of the gas meters.

Figure 6:
 The old meter and below it, the gas meter for the
house:  Since the solar was now connected, it was
required that the red warning tag be attached even
before the net meter was installed.
The power company ultimately determined that the
electrical panel and its underground conduit had to be
relocated to a minimum of 36" (about 92cm) distant from
the gas meter and any of its piping.  I couldn't be sure,
but it looked as though the gas meter was installed
after the electrical with the original riser pipe for the
electrical being wedged between the
house and the gas meter!
Click on the image for a larger version.

As it turns out, current code in this area requires at least a 36 inch separation between the closest part of the gas line and meter and any part of the electrical entrance.  What was surprising is that none of the contractors that had visited my place to assess the scope of work had caught this, let alone planned for it!

In my case the gas meter was literally touching the conduit from the underground power feed and the panel itself was about 3 feet above the gas meter.  Since the panel was to be upgraded, it had to meet current code so it would have to be moved.  This also meant that the underground power feed, which was a length of "direct burial" wire would also have to be redone, placed in 4" conduit and run to the location of the new meter.

All of this meant a delay - about 4 weeks, as it turned out - as the plans had to be revised and arrangements had to be made to coordinate the schedule of the electrical contractor with the schedule of the city inspector along with having "Blue Stakes" come out and mark the utilities so that yet another contractor could dig a trench in my front yard from the power junction to the location of the new meter.  While this meant that it would be another 4 weeks or so before the work would be done - and likely another 2-3 weeks after that before my "Net Meter" would be installed - it also meant that the company in charge of all of the work would end up "eating" the difference in cost which was probably something in the area of an extra $1000-$1500 on top of the already-allocated cost for panel replacement.

Comment:

There is a device called a "Connect DER" (tm) that may be used in many locales to bypass the need to upgrade or replace the house's electrical service when solar power is installed.  This device plugs into the original meter base and is sandwiched between the original panel and the power company's electrical meter so that the additional current of the solar power system does not appear on the house's electrical bus since the connections to the solar is made on the Connect DER itself with a built-in circuit breaker for electrical protection and to allow it to be disconnected.

For various reasons this sort of device was apparently not an option in my case - possibly because of the fact that the gas and electrical piping were co-located. 

Figure 7:
The narrow trench that magically appeared in my yard,
running between the underground junction from the
electrical utility to the approximate location of
the new panel.
Click on the image for a larger version.

Finally, the day arrived where there appeared a trench in my front yard (figure 7).  A few days later the electricians arrived and installed the new panel and a conduit in the trench - but I couldn't help but notice that it was only about 23" from the gas lines, a fact that I mentioned to them when they arrived the next morning (figure 8).  After a bit of digging and drilling, the new panel and conduit was suddenly another 18" or so farther away from gas meter than it had been.  At about this time the power company and city inspector showed up to disconnect the power from the mains and pull new conductors into the conduit under the watchful eye of the inspector who gave preliminary approval to the work plan.

Off came the old panel to be replaced with a weatherproof junction box, connected to the new panel with a run of conduit.  In the new junction box - at the location of the original panel - a "horse tail" of wires appeared representing the individual circuits in the house, each of which had to be spliced with a new set of conductors wired to the new panel.  After about 4 hours of work everything was turned back on and I was back in business.

Figure 8:
Oops!  That ain't no 36" separation between the gas
and electrical!  The vertical pipe on the left, against the
brick was the conduit conveying the electrical to
the old meter.
Click on the image for a larger version.

A day or two later the city inspector came back to meet with me and a representative of the contractor to survey the work done both with the installation of the new panel and the photovoltaic system.  Finding everything to his satisfaction he gave his approval which also meant that the power company was notified so that the "Net Meter" would be installed.  A couple days after this a small work crew from a landscaping company appeared, filling in the trench in the front yard and replanting the sod that had been removed.

About two and a half weeks later I came home from work to find a notice from the power company stuck to my front door indicating that the net meter had, in fact, been installed so I happily closed the necessary breakers to put the system online.  Since it was already the evening, not much power was produced that day, but it was now ready for the next days' sun!

* * *

Figure 9:
In mid-job, the "horse tail" wires from the original
breaker panel emerging from the junction box that
had been installed in the approximate location of the
original breaker panel.  New wires were run
between it and the new service entrance/breaker panel.
I have since painted the new junction box and conduit a
red color to somewhat match the brickwork.
Click on the image for a larger version.

A minor shading problem:

As of this posting it has now been about four months since the system was put online and it has been working quite well.  One minor complication - something that I would have addressed earlier had I been aware of it - has to do with the fact that some of the eastern panels were located where they get shade until a bit after noon, reducing the output of the east array by 15-20% during that time.

By late March I was noticing that the northern-most panel was starting to be shaded by a nearby pine tree and by June and July, the angle of the sun had precessed to the point where at least three panels were being completely shaded in the morning, the shade finally clearing about an hour before "local noon" - or around 12:45.  Had I been aware of this I might have requested to have the east panels arranged somewhat differently to reduce this effect as there is plenty of room on the roof to do this

Would microinverters have improved this situation?  Perhaps by only 5% or so:  The real problem is that the panels get shadowed lengthwise, equally affecting each of the three sections of the panel isolated by the built-in "shade tolerance" diodes so these diodes don't have a useful effect when shading occurs in that aspect which means that it would be more difficult to extract power from it by any means.

A month or so after installation I was able to get them to come back out and do the formal shade analysis that they hadn't done before starting the job and it confirmed what was empirically observed - plus it gave a bit of information as to what problems could arise in the future in terms of tree growth.

* * *

No RF noise at all!

As far as my one of my original concerns - that of generated RF noise - I can detect absolutely nothing from the photovoltaic system at all at any frequency.

The "quiet-ness" of the system can be borne out by the fact that even if one brings a portable receiver right up to the panels or the inverter, nothing at all can be heard from it except when its antenna gets within a few inches of the inverter's LCD panel.

Where I do get some RF noise is from sources unrelated to the solar power - switching type "wall warts" scattered throughout my house, powering various things, but most of the "problem" devices have already been quieted as described in previous postings on this blog, see:

• December 17, 2015 - Minimizing VHF (and HF) RFI from electronic ballasts and fluorescent tubes - Link
• August 18, 2014 - Completely containing switching supply RFI - Link
• September 4, 2013 - Quieting high-current switching power supplies used in the ham shack - Link
• December 2, 2012 - Reducing switching power supply racket (RF Interference) - Link

* * *

Generation of power - observations:

In the (over) four months of operation the cumulative amount of power has exceeded my actual usage by about 300 kWh so the recent power bills have been low - just the "minimum charge" of less than $10.  According to my calculations based on past and current usage I expect to use up that surplus in the winter when the "production" of the the photovoltaic system will be much lower due to the lower sun angle, shorter days, occasional snow cover and the tendency for there to be extended temperature inversions that can block sun for days at a time.

At the moment I do not have a "refrigeration" whole-house air conditioner - only an evaporative (a.k.a. "swamp") cooler and a wheel-around "room" air conditioner for those relatively rare days that it is both hot and humid, but I'm considering getting a whole-house A/C sometime in the future:  When I do that I may consider increasing the capacity of my photovoltaic system.

While the system has eighteen 285 watt panels which are theoretically capable of 5130 watts, the slant of the roof (north-south ridge line with panels mounted flat on the east and wet sides), the operating temperature of the panels (an output power reduction of 0.45% per degree C panel temperature) and the actual solar insolation (e.g. the actual amount of solar energy) has limited the peak power to around 3800 watts on hotter, crystal clear days and about 4300 watts on cooler days.

If one does the  numbers this should not be too surprising.  For example, the 285 watt panel rating assumes a cell temperature of 25C.  On a hot summer day where the ambient air temperature is around 38C and the panels themselves are around 50C (a fairly modest temperature as my roof is metal and very light-colored which keeps it quite cool) that means that assuming a temperature derating of about 0.5%/C that I have lost - from heat alone - 12.5% of power, or can expect only about 250 watts per panel, or 4500 watts from the system - and that would assume that the sun was illuminating the panel at optimal right-angles - which it really cannot at any time of year.

Since my panels are on a roof with a moderate east-west pitch, I lose another 15% or so of solar insolation on a typical summer day due to the angle, yielding a number that is actually pretty close to the 3800 watt peak.  What I have observed is that because of the east/west angle of the two strings that I have a slight "double" peak around "local" noon when, before noon the angle is nearly optimal for the east array and then similarly, after noon, for the west array.  To make matters worse, during many days of the summer in recent years the valley's air is a bit murky due to some smog and the frequent wildfires that seem to be a regular occurrence in the western U.S. these days, knocking off another 10-15% of production.

What this means is that, in theory, I could have used a 4kW inverter if I was willing to tolerate a bit of "clipping" (e.g. more available photovoltaic power than the inverter will produce) on optimal days (e.g. cool spring or fall days with clear air) and possibly have averted all of the hassle with the 20% rule and the replacement of the electrical panel, but considering the state of the older electrical distribution panel, its replacement was probably for the best! If I wished to do so, I could (in theory) add another 4 panels to my system which would just about bring it to clipping under optimal conditions and to around 4600 watts on a normal, summer day.

The other option - if I needed more capacity after, say, adding a house air conditioning unit - would be to simply install another set of panels - maybe 14-16 or so - and a separate inverter - a 3.6 kW unit, perhaps:  This would still stay within the 20% rule for the new electrical panel and add a degree added redundancy.  Since the "hard" work (e.g. update of the electrical, etc.) has already been done, such an addition would be comparatively easy.

Comment:

As of the time of this writing (mid August, 2016) it would appear that the company that I used for the installation of my system (Auric Solar) will no longer consider the use of series-string photovoltaic systems, at least for residential customers - a statement based on a conversation a friend and fellow amateur radio operator had with a company representative.  The impression given - perhaps unintentionally - was that they had enough business that they didn't necessarily need to offer flexibility or other system options to their potential customers.

What this means is that for fellow amateur radio operators who wish to avoid an "RF noisy" installation, I've recently been suggesting another company.

Update - May, 2024:

It has been about eight years since the above system was installed and I have had ZERO maintenance issues during the entire time other than occasionally trimming back tree branches that block/hang over panels.

I have since had a Tesla Powerwall 2 installed as well as increased the solar production to 10 kW - again using a SunnyBoy series string inverter, still with no interference from my own solar and only very slight interference from the Powerwall 2 when it was running on some of the lower bands:  If you want more details on this and other solar-related topics at this blog, peruse the links below.

* * * * *

Other articles at this blog on related topics:

• It *IS* possible to have an RF-quiet home PV (solar) electric system - link
  
• The Solar Saga Part 1: Avoiding Interference - (Why I did not choose Microinverters) - link
  
• Does the Tesla Powerwall 2 produce Radio Frequency Interference? - link
• Reducing RFI from the Tesla Powerwall 2 - link 
• Tesla Powerwall susceptibility to RF Transmissions - and how to deal with it - link 

[End]

This page stolen from "ka7oei.blogspot.com".