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Solar

Abstract

WARNING: Don't read this if you don't believe in science, since it will only aggravate you!
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I started putting up solar panels in 2016 simply to experiment with the technology and to learn from my efforts. Just based on personal experience and observing the world around us, I've known at least since the 1960's that burning fossil fuels to obtain energy was not a good idea in the long run. Maybe it was OK for a while if I didn't blatantly waste it, and found cleaner and more efficient ways of burning it. But by the 1980's it was already perfectly obvious to anyone who cared to think about it that burning fossil fuels was not only a bad idea, but that it would have extremely dangerous consequences. This was true even if I was to use fossil fuels "responsibly," which clearly I was not. I could be worse(Insert "rolling coal" emoji here), but I could and hope to be better.

The efforts documented here are not motivated necessarily by trying to "be green" or to save the world, but by trying to improve the odds of my own survival, and of those I care about. I've encountered numerous 'wake-up calls' over the years, including the 1970's gas shortage, that tell me that it's important to pick the right horse when it comes to energy dependence. Our US government, led by both Republicans and Democrats, have admitted that dependence on (foreign) oil is a national security risk. Additionally, the Democrats understand that burning any fossil fuels, regardless of their source, poses a myriad of additional risks, including undesired climate changes and dangers to our physical health. At some point in the future, all of this will be so obvious that even the Republican leaders will be forced to admit that this is going on, in spite of an apparent continuing (this is being written in early 2022) desire to make stupidity a desireable quality. But even when that time comes, our government still won't be competent enough to get the necessary things done in a timely fashion. This will be true even if it is shamed into really trying by the likes of Al Gore and Greta Tintin Eleonora Ernman Thunberg.

Fortunately, we can get started without waiting for the government to do a thing -- other than to get and stay out of our way. If "the government" can't do the "right" thing, they should at the very least stop doing the "wrong" thing, such as subsidizing the continued misuse of fossil fuels. First, do no harm.

If you don't think that a single individual can in a few short years significantly move the sustainable energy needle in the right direction, simply google the terms "Elon Musk" and "Tesla." We don't need subsidies, we don't need tax breaks, we simply need a level playing field and a significant minority of individuals willing to do the right thing, in whatever capacity they can.

For me the first step, documented below, was reaching the goal to never buy gasoline again. As of now, our household has gotten rid of all devices that use gasoline, including a 21 year old car, a lawnmower, and a chain saw. The car has been replaced with a new battery-electric vehicle (BEV), the lawnmower by a dumpster-dive model re-purposed to be powered by ebike batteries, and the chainsaw by an electric model. The complement to this goal is to produce on-site the fuel these new items use by converting some of the sun shining on us into electricity.

... and this is why energy dependence on solar is a good strategy.
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To Grid or Not To Grid?

One of the very first questions you need to answer when considering the installation of any solar panels is whether or not they will ever be connected to "the grid" -- the local power company that supplies your electrical energy.

If the answer is "yes," then you will need to satisfy numerous requirements that have little or nothing to do with solar energy. These include the permitting process, zoning laws, rules relating to your local electric utility, and who knows what else, depending on where you are in the world. Your system will be described as "grid tied," and all equipment you use for the installation will have to have various UL listings and/or certifications. Note that most solar equipment such as inverters and micro inverters are built to automatically and instantly disconnect (disable) your solar panels when the grid is down. This means, that by default, when the grid is down, so are you -- even if the sun is shining brightly. The term anti-islanding is frequently used in this context. The most commonly stated reason for this mandatory disconnect is the safety of people working on the powerlines. In 'real life' no competent utility worker would ever work on any electric lines without making sure it's safe to do so, using techniques such as grounding the lines, etc. If necessary, they would treat the lines as 'live' and proceed under those conditions.

At any rate, if you want your solar panels to keep producing energy when the grid is down, you need a "hybrid" inverter with a "transfer switch" and some form of storage battery. The transfer switch will automatically disconnect the grid from your solar panels, and the battery will work with the hybrid inverter to keep your solar panels producing energy. As for powering your house, you'll also need to have a "critical load panel" which feeds things like your refrigerator, selected lights, and maybe your furnace fan. This critical load panel will be connected to your hybrid inverter. When the transfer switch disconnects the grid during a power outage, the hybrid inverter and the battery will supply power to the critical load panel. If you're willing and able to install enough solar panels, a hybrid inverter with enough power (kW) capacity, and a battery backup system big enough (kWhrs) to accommodate your needs, your critical load panel can be your regular house load panel. Under these circumstances, when the grid goes down, you might not even notice it since your transfer switch will in a matter of a few milliseconds connect you to your backup system.

If the answer to the grid-tied question is "no", you likely won't have to deal with all the paperwork and other complexities associated with the solar installation outlined above. You'll need to decide what you want to use your solar energy for, and then design and install a system that meets your needs. This is the direction we're going in here, and all of the projects below assume that there will be no connection to "the grid".

50 Watt Array: 10 watt @ 1S5P

This five panel array is mounted on the detached garage roof, facing directly south. The panel outputs are connected in parallel (1S5P), but only after each panel's individual output is measured and recorded. The vertical angle is fairly steep, both to favor the low winter sun and to help keep snow off the panels. The only shading for these panels happens in the mornings when the sun is blocked by the four-story commercial building to east (right side of photo).
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Showing rear view; when mounted on roof, panel #1 is to the far right (East). Panels 1,2, and 5 are of the "Poly Crystalline" type, while panels 3 and 4 are not labeled as to type (are they mono crystalline?).
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The factory specifications for the two types of solar panels used in this array are almost identical. The following shows two decals attached to the back of two of the panels. These give the 'stats' for the panels, which is very typical for all commercially available solar panels. For definitions and explanations of all these properties and values, see the very thorough wikipedia entry Solar panel. This will explain why these panels are called "12 volt panels" even though the label has two voltage values of 18 and 21.6 volts.
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Note the 'chinglish' language ("Moudle", "CONDILION") used by this Chinese manufacturer.
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These 'no-name' panels have actually been performing extremely well, and their power output ratings may even be on the conservative side (see graphs showing a sample one-week output below). Panel 1 (green line) had a max power output of nearly 18.5 watts, well above its 10 watt rating. The output of each 10 watt panel in the array is individually measured and recorded before being combined with the other four outputs and sent to the 12VDC "battery farm" for use and storage. The following graph shows the array's output for one week, April 4-11, 2022. Each panel's VOLTAGE in the top series, and POWER (in "watts", which is voltage x amps) in the bottom series. The X scale is time, while the Y scale is the amount being measured. Each panel's output is represented by a different color. This graph screenshot was taken at 9:30AM on 11 April 2022, so all of the panels were still in the shadow of the big building next door (to the East), so the *power* output is just beginning to rise even though the *voltage* of each panel has been near maximum for over an hour. Note that this (Grafana) graphing software's label uses "Current" not as "amps" but contemporaneous time, as in "now".
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Looking at the graph, the takeaway is that for all practical purposes, the voltage output of a solar panel is irrelevant. On each day of the week shown, each panel's voltage output was consistently near the panel's nominal maximum limit during daylight hours. By contrast, each panel's power output varied widely by which day it was. April 5,6, and 7 were very cloudy/overcast days, and power output was very low (well below 5 watts). Looking only at the top (voltage) series, one would get the impression that the entire week was sunny, which it was not. Ultimately the only measurement that matters is the power coming from each panel. The maximum voltage output of the panel is only important when doing the wiring of all of the panels, for safety reasons.

 

Starting assembly of the original five by 10-watt solar panel array in late 2018. These panels are un-branded factory samples and are provided courtesy of Bill James of JPods Inc., [jpods.com], thanks Bill! The 'nominal' power output of this array is a total of 50 watts (1/20th of a kilowatt/kW). This nominal output would be achieved under rather ideal standard testing conditions (STC). As it turns out, these five panels are rather unusual in that they still (in 2022) frequently produce more than 50 watts on a cold, clear, sunny day here in Minnesota, around 45 degrees of latitude.
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Each panel's output has been individually monitored 24/7 for the past several years, and has been recorded in a database. A variety of displays, including this ancient iPad-1, are used to monitor the performance of the panels under varying conditions. The amount of solar energy captured by this small array is nearly inconsequential in the great scheme of things, but its teaching value is priceless.
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Showing inside the garage near where the panels are mounted outdoors. This is early in the project and the connections are in the prototyping stage, with no monitoring in place yet.
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To prevent any current from 'back feeding' the solar panels, a diode is placed in series with each of the five solar panel's outputs.
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Solar charging supercapacitors

A solar panel is a great way to charge supercapacitors (a.k.a. ultracapacitors), as long as you are careful to not exceed the voltage rating of the supercaps. This arrangement is a wonderful way to learn the difference between the concepts of "energy" and "power." Here one of the five 10 watt/12 volt panels from the array above is directly connected to a string of supercaps connected in series (to accommodate a higher total voltage). The little solar panel will slowly dribble "energy" into the supercap array until it's fully charged, at which point the supercap array has enough "power" to start a big diesel engine in below freezing temperatures.
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After sitting in bright sunshine for a while, the supercap array has risen from less than one volt to highest voltage this solar panel can muster, about 20.6 volts.x This is approximately 1 volt less than this panel's maximum (open-circuit) voltage. The array of eight supercapacitors is connected in series, so each capacitor's voltage limit of 2.7 volts is summed to allow the supercap array to be charged to an absolute maximum of 21.6 volts. These supercaps are very expensive compared to other discrete electronic devices, so even though they have a protective circuit to help avoid over-volting them, this is cutting it pretty close. Since they belong to JPods, I don't worry about smoking them [I don't really mean that, Bill!].

Leaving this setup out in the sunshine after this point will not result in more energy being stored because the solar panel can't push any more electrons into the supercaps since they are now at the same voltage as the solar panels. Should this be thought of a wasting energy?
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Here we see the supercap array being charged by the whole 5x10 solar panel array. Note that the panels and supercaps are at 20.8 volts, very near their maximums. If you look carefully, you can see the red LED's on the supercap's protective circuits showing that they are actively balancing the supercap array and dumping any excess current going to any individual supercap.
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Closeup of the supercap's protective circuit at work:
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Solar charging lithium batteries

A solar panel is also a great way to charge lithium ion batteries. Here the same 10 watt panel is charging a lipo pack consisting of 6 18650 lipo cells connected in an 3S2P configuration. To prevent overcharging this pack, whose absolute maximum voltage is 12.6 volts (3 x 4.2 volts), a very small and cheap DC-to-DC converter is used (it's hidden in the small green pillbox at the bottom of the photo). The CellMeter 8 shown in the photo is a very useful meter which provides measurements including total pack voltage (shown as 11.83 in photo), percent of charge, each individual cell's voltage, and high/low cell voltages.
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Here the 5x10 solar panel array is charging nickel-metal-hydride (NiMH) AAA "Eneloop" cells. These Panasonic rechargeable cells are very reliable and easy to use, and are considered an upgrade from the earlier generation of nickel-cadmium (NiCAD) rechargeable cells. I use these cells to power bright flashing LED lights on my helmet when I ride my bikes.

The cells are plugged into a 'charge controller' which takes the output of the solar panels (PV) and charges the inserted batteries until they are full, and then shuts off. Here we see a slightly larger DC-to-DC converter (with the red glowing LED) connected between the PV array and the charge controller to limit the voltage to 12VDC. It turns out that the charge controller's input circuitry was designed to handle the solar panels' voltage of up to 20 volts directly, so the converter is no longer used. The meters, from top to bottom, show the direct solar panel voltage (19.6VDC), the regulated voltage from the DC-to-DC converter (12.0VDC), and the current going into the charge controller in amps (0.04A). This could be stated as 40 milliamps, or about 1/2 watt of power. This means these batteries are probably fully charged, and the current flow is likely just powering the charge controller's LED display (barely visible beneath the "1 2 3 4" labels.
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The following shows the solar panel array at its near-maximum open-circuit (Voc) of 21.6 volts directly connected to the battery charge controller labeled for a 12VDC input. Prior to doing this 'smoke test', I had opened up the charge controller and observed that the manufacturer of this "Smart Charger" had used input capacitors rated for 25V, so immediate smoke was unlikely. The input voltage is usually lower anyway when batteries are being charged because the load pulls down the panels' voltage. We now have a 12 volt battery pack that sits between the solar array and the AA/AAA battery charger, so it's no longer an issue. However, the same charger is still in use and working fine after several years of being operated over a 0 to 21 volt input range. Because it's being powered directly by solar panels, the voltage varies wildly between the two extremes. I did break off the negative terminal for the AAA battery holder in the #2 position, so I can only charge 3 AAA's at a time, but that was my fault, occurring while I was disassembling the case (and likely voiding the warranty).
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1,035 (1kW) Watt Array: 345 watt @ 1S3P

After assembling the tiny 50 watt array above, it was time to start experimenting with "real" (commercial grade), full-size, solar panels. These three 345 watt solar panels were sourced locally from "The Solar Panel Guy" who obtained them from a large scale solar 'farm' in Texas, where they had been briefly used. These 'recycled' 345 watt panels, referred to as "Q" panels, were originally designed by a German firm which was later acquired by Hanwah, a Chinese company.
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... and showing the back side of the panels. This demonstrates what NOT to do when mounting panels. Using the miscellaneous 120VAC residential electrical boxes, plugs, and cords to connect to the panels violates every safety rule in the NEC and likely other sources as well. This temporary installation method, however, was extremely quick, cheap, and effective. The maximum current output of each panel is 9.64 amps at 47.46 volts DC, measured under short circuit conditions. The 12AWG copper wires, insulated for 600VAC, can easily (and safely) carry the amount of power involved.

 


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UNDER CONSTRUCTION!!!!

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3.7kW Watt Array: 370 watt @ 5S2P


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