Submitted By: Administrator Date: Nov 28, 2025, 02:14 PM Views: 68

Summary: An introduction to photovoltaic panel solar systems.

I did my first solar installation, on my motorhome at the time, over 20 years ago. A lot has changed since then, but the basics remain the same. There are two types of solar systems; grid-tied and off-grid. Grid tied, as the name implies, is connected to the electric grid that provides your household electricity. The single advantage of this type of system is that it doesn't require storage batteries, instead pushing surplus power generated by the solar panels to the grid (where the utility company pays you for the power) and pulling power from the grid as needed (where you pay them back). Grid-tied systems must be professionally installed and cost tens of thousands of dollars, so in essence all they accomplish is replacing your monthly utility bill with a monthly system payment. Since it is connected to the utility grid, a grid-tied system can power all your household appliances, but when the power goes out, your solar system stops working. An off-grid solar system is a much simpler (and cheaper) affair, and what is discussed here. Even so, unless you build it from salvaged parts, your system will probably never save you money, but does provide the comfort of having power when the utility grid fails without having to deal with conventional generators, and the satisfaction of knowing that the sun is powering your stuff. INTERJECTION, 02 DECEMBER 2025: A solar system may never really save you money or even pay for itself, but can come in mighty handy. At 1:38 this morning, with the outside temperature at 22 degrees, my power went out. I discovered this when I woke up around 3 AM because it was too quiet; the bedroom I currently occupy doesn't get much heat, so I had an electric space heater running, and the sound of it NOT running woke me. Power finally got restored at 2 PM. I had to use a flashlight to investigate the outage because part of my house doesn't yet have solar powered LED lighting. Once I identified the problem, I plugged the electric heater into an extension cord connected to my inverter and went back to bed. I woke up to a warm house, enjoyed a hot shower, and then brewed tea on my induction cooker, got milk from the refrigerator and warmed it in the microwave, heated a pair of Pop tarts in the toaster, and started my computer. A normal day despite having no power, because my ventless propane heaters and water heater don't use electricity, and besides the lights, outlets, ceiling fans, and two of my surveillance cameras, everything electric runs on solar power! The sun's out and my batteries are charging, but even without sunlight I can run everything I need for several days. THAT's why you do solar! A basic off-grid solar system consists of one or more solar panels, a charge controller, one or more storage batteries, and usually an inverter. Let's start by briefly describing the function of each of these items. Solar Panels When I did my first install, solar panels were polycrystaline with an efficiency of about 5%, and cost about $5.00 per watt. Today most panels are monocrystaline with an efficiency pushing 25%, and can be had for under $0.50 per watt. In addition, the conductors that connect the cells (a solar panel is an array of individual photovoltaic cells) are designed to minimize losses from partial shading. In older panels, the individual cells comprising a panel were basically wired in series, so even a small shadow greatly reduced the output. Newer panels are wired with small groups of cells connected to the output conductors, so that only the cells in a group lose power when one is shaded. The higher the 'bb' number on a solar panel, the less it is affected by partial shading. Monocrystaline solar panels are also better at collecting solar energy on cloudy days. The latest development I am aware of in the solar panel market is bifacial panels. Essentially this is a solar panel without an opaque backing, supposedly more efficient because it can absorb solar energy from both sides. While this may be an advantage in some circumstances, I can't think of any offhand. In most cases, that opaque backing provides structural rigidity, not to mention keeping more sun off the roof, if that's where your panels are mounted. Solar panels generate less power when they are hot than when they are cold, which is why they are typically mounted with an inch or so of air space beneath them to aid in cooling. The solar panels designed for off-grid use are typically rated 12V, 24V or 48V. The actual voltage that they generate is greater than the rated voltage, typically around 18V for a 12V panel. Depending on the limits of the charge controller (which MUST be used to control the power going into the storage batteries), panels may be connected in parallel, series, or a combination thereof. In most cases, you want to maximize the voltage to the charge controller (within its limits) if you have a modern controller, since lower amperage allows the use of thinner wiring. Speaking of wires, the cables coming out of the panels are usually stranded 10AWG with standardized, weatherproof plug-in connectors. In most cases you can probably get by with 10AWG stranded copper wire but I've always used 8AWG, and for systems with greater current output or longer runs, I'd step up to 6AWG. The judges are out on several variations of stranded wiring; there's pure copper, tinned copper, and copper clad aluminum (CCA). Tinned copper is supposedly more resistant to corrosion, while CCA supposedly works nearly as well as pure copper despite aluminum's higher resistance, theoretically because of the skin effect that causes the majority of the electrical charge to travel on the surface of each conductor (presumably this is why stranded wire with many individual conductors is preferred). My main reason for avoiding CCA is that I've seen how quickly aluminum oxidizes if not properly maintained. The un-tinned 8 gauge copper wires left over from my 20-years-ago install show a little darkening about an inch in from the exposed ends, but are otherwise as good as new, so my personal feeling is that in most cases pure copper is the most durable. Charge Controller The charge controller, as the name implies, regulates the power going from the solar panels to the storage batteries. The most basic controller uses pulse width modulation (PWM), essentially acting as a fast digital switch that cycles the incoming power on and off depending on the battery's present state of charge (SOC). PWM controllers are usually programmed with three preset voltage levels, the first providing the greatest current to the battery, the second maintaining the battery at an optimum voltage once fully charged, and the third raising the voltage to a point that tends to break down sulphidation on the plates in lead acid batteries. Newer controllers use a strategy called maximum power point tracking (MPPT) that works by maximizing current to the battery by constantly adjusting the voltage to slightly above that of the battery while it is less than fully charged, resulting in a roughly 30% increase in efficiency. To illustrate how this works, consider 30 Watts going into a 12V battery. If the battery is at 12.0 Volts, charging at 13.8V limits the current is 2.17A, while reducing it to 12.2V provides 2.46 Amps of current, which of course is what the battery needs. Be aware that a true MPPT controller contains one or more fairly large ferrite coils and can accept an input voltage usually of around 100V or more. If those conditions are not met, it is NOT an MPPT controller, and there are MANY fakes on Amazon. Batteries Before going any further, I should point out that all storage batteries are potentially dangerous. Like a can of gasoline, a battery can become a bomb under certain circumstances. Please do the research and understand the dangers and how to mitigate them, and never, ever, ever allow a battery to be short-circuited! The flooded lead acid batteries that are typically found in cars are generally designed to provide brief periods of high current (several hundred amps) for starting, beyond which they are meant to power the car's electrical system with the alternator providing most of the power. They are not designed to be deeply discharged, and will not last long if subjected to repeated deep discharges. Deep cycle batteries, by contrast, are designed to provide moderately large output currents for sustained periods. Typically, a battery rating of 100AH means that the battery can provide a constant 20A current for five hours. Note that to maximize the life of a lead-acid deep cycle battery, it should not be discharged below 50% capacity. In addition to flooded lead acid, there are other types of deep cycle batteries, some of which are completely sealed and thus maintenance free. The latest contender is the lithium battery. Apparently these have been around for a while, but the industry standard seems to be the lithium iron phosphate (LiFePo4) battery. This is the only one I have experience with, so I'll tell you what I know. A 12V LFP battery (LiFePo4) contains four cells with a nominal voltage of 3.2V, so 12.8V total, and a battery monitoring system (BMS) that controls charge and discharge rates. Typically, a 12V LiFePo4 battery will have a 200A BMS that limits the discharge to 200A as well as preventing charging in temperatures under around 45 degrees, which supposedly would damage the battery. The main advantage of LFP batteries is that while lead acid variations should only be discharged to 50%, the LFPs can apparently be discharged almost completely without damage. This, plus the fact that they're cheaper and lighter than lead acid batteries and supposedly have a longer lifespan is why most companies are recommending their use in solar systems instead of lead acid variants. Note that because of their different voltage patterns, lead acid and LFP batteries cannot be mixed. A typical 12V lead acid deep cycle battery is fully charged when it is between 12.6 – 12.7V, at 50% when it is between 12.0 – 12.1V (both measured at rest), and fully discharged at 11.6V. A 12V LiFePo4 battery is fully charged when it is at 14.6V while charging or 13.6V at rest, at 50% when it is at 13.0V, and fully discharged at 10.0V. Most sources state that discharging them to 12.0V (10%) will not harm them. To put storage capacity in different words, a 12V 225AH lead acid battery provides a theoretical capacity of 2.7KWH (225AH x 12V) of which only half should be used, while a 200AH LiFePo4 battery provides a theoretical capacity of 2.56KWH (200AH x 12.8V). The math is admittedly a bit subjective. Inverter An inverter converts the DC power generated by a solar system and stored in its batteries to 120V or 240V AC to power household appliances and machinery. Twenty years ago an inverter was a bistable flip-flop that fed a 10:1 step-up transformer, producing a stepped square wave that approximated a 120V RMS output. Those inverters typically drew around 100W at idle just to keeping the transformer powered. While they do provide usable household power, so-called "modified sine wave" inverters (which today are transformerless) are less than kind to delicate electronics and do a horrible job powering fans and similar motors. Pure sine wave inverters, some of which still cost as much as a small car, are rapidly becoming the norm and can be had for a hundred bucks or so. As with the Chinese charge controllers, there are lots of fakes on Amazon, so make sure it actually says pure sine wave. Most pure sine inverters have a very low idle draw, typically around 10-20W, so they can be left on without much drain on your batteries. While most sine inverters claim to be able to handle loads of up to 200% of their rated capacity for brief periods (like motor starting), in most cases the cheap ones can't handle more than 10% over rated capacity, so size appropriately. An important consideration when adding an inverter to your solar system is the wiring between the battery and the inverter. As with every wired connection in your system, it should have a disconnect switch, proper grounding, and properly sized fuses or circuit breakers, but the main priority for inverter wiring is the wire itself. An inverter MUST be wired directly to the battery bank, using the shortest run possible, and a large enough gauge to handle the huge current demand. A 12V 2000W inverter at full load draws 167 amps! To provide that kind of current, you want to use 2/0 (double aught) cables. Also notice if your system uses LFP batteries, that a 200A BMS will power a 12V 2000W inverter at full load, but not a 3000W inverter. This shouldn't be a problem if your system has more than one battery in parallel, since each BMS should be able to provide up to 200A, but this is purely speculation on my part. Sizing The System When it comes to sizing your solar system, you must first determine your daily power requirement and then calculate how much storage capacity is required to provide it (based on the assumption that the battery should be able to provide that power over a 24-hour period and the sun will recharge them tomorrow). Adding more panels will charge your batteries more quickly, but any power generated while the battery is full may be wasted. Conversely, fewer panels will take longer to recharge your battery. In most cases you will want to have between 75 and 130 watts of solar panels per 100AH of battery unless your system is idle (generating power without using any) most of the time. To determine how big to make you solar system, first check your wallet. It's a hobby, or if not it will quickly become one, and we all know how much hobbies cost. All seriousness aside, start by figuring out the maximum power you will need in a 24 hour period. As a simple example, if you want to run a 100W light bulb constantly, you need 2400 watt-hours of battery capacity, regardless of whether it's a 12V or 120V bulb. For each device you want to run, multiply the wattage by the time you plan to run it (1000W microwave for 1/2 hour, 3 times a day would be 1500 watt hours) and add all these numbers together, then divide that number by your system voltage to determine what size battery bank you need. If your total was 4000 watt-hours and you are planning a 12V system, you need a minimum of 334AH battery. To this figure, add 15% for losses and then multiply the total by the number of days of storage capacity you want your system to have, so that it will continue to power your devices on cloudy days or when your panels are covered with snow. To size that 4000 watt-hour per day system to allow for three days of no sun, you would first multiply 334 by 1.15 (losses) and then by 3, a total of 1152AH. Don't forget to factor in how deeply you plan to discharge your batteries; if you plan to use lead acid batteries and keep them above 50%, you need to double that number to 2305AH. This is why everyone is switching to lithium batteries. Before You Begin I urge you to head over to Northern Arizona Wind & Sun (https://www.solar-electric.com/) and click on their resources tab. This is the company that sold me my first solar panel, charge controller, and wire back in 2004, and more importantly, explained how everything worked and gave me tips on how to install everything in my motorhome. A lot of the stuff they sell is too rich for my blood, but they do have some bargains, and the information they provide is priceless. For myself, I'm more impressed with affordable than I am with name brands, so I'd rather pay $100 for an item on Amazon than ten times that (or more) for the name brand, especially since the latter is probably made with the same Chinese parts anyway. I eschew the "extended warranties", and find that maybe 5-10% of the high-tech items Amazon sells have problems, as opposed to about half that for the name brands, but Amazon's return policy is so much simpler to deal with that it just doesn't make sense to shop elsewhere. Un-american, I know, but it gets me the stuff I want without forcing me to subsist on Ramen noodles. Once you've decided on the battery capacity and panel wattage you need, you need to examine your buying options, and consider exactly where you are planning on mounting your panels and installing your battery, charge controller, and inverter. Even assuming you're doing all the work yourself, don't forget to factor in the cost of wire, breakers, connectors, mounting brackets, etc. and finding or making a suitable location for your batteries, controller and inverter. My most recent install consists of lightweight 200W panels conveniently mounted on the south-facing metal roof of my carport, but I had to get new rubber kneepads to keep from sliding off the roof! One more thing you should consider before embarking on anything more than a small solar system to power your radio: Insurance. If your system ever causes an injury or starts a fire, rest assured that your insurer will NOT accept your claim. The only option I could see would be having a professional do all the wiring, but where's the fun in that?? Recommended (Tested) Products These are the items that comprise my current solar system – actually two systems, because halfway through I decided to add more batteries and also to try a LiFePo4. Since they can't be mixed with lead acid batteries, I briefly considered selling the just-purchased Rocket batteries but then decided to keep them and make a second system. With the exception of the Rocket batteries, everything else was purchased through Amazon and is all Chinese manufacture. Although I trust Chinese manufacture less than others, as long as it doesn't connect to the Internet I'm okay with most of it. All told, I've now got 1600W of panels that produce "up to" around 8 KWh per day. As a general rule, figure on (the equivalent of) about five to six hours of maximum output on a sunny day for flat-mounted panels, more if they are angled to the south. So I spent a good chunk of money for a system that provides under a dollar a day of solar power... but, in my defense, my refrigerator, computer, TV, surveillance system, ham radio, and a couple of air conditioners are all solar powered. I recently added a fourth LFP battery and two panels to the four that were in series powering them, and converted the batteries from 3 in parallel to 2 series, 2 parallel for 24V, which allowed me to add the extra panels without overloading the charge controller. Because of that, I replaced the 2000W inverter with a 24V 4000W model. Unfortunately although the claimed maximum open circuit voltage for the six panels in series is 132V, they are spiking over 150V and causing the controller to stop charging, so I had to rewire them as 2 parallel sets of 3 in series. Other than that, though, I'm fairly happy with this system. I don't have any hard data on exactly how much power the battery bank can supply, but I recently ran my heat pump air conditioner pulling about 250W average for over ten hours, and the voltage never dropped. The theoretical capacity of the four 300AH LFP batteries is 15.36KWh! Here's a list of the actual products I purchased: 2 Rocket L-105 225 AH batteries $368.12 total (incl $40 core charges) Battery Center, 1001 W Main St., Ada, Oklahoma From Amazon: 8 Rvpozwer 12V 200A solar panels +/- $120 each, cheaper in quantity https://www.amazon.com/Rvpozwer-Efficiency-Monocrystalline-Modules-Off-Grid/dp/B0DSHQM3SM/ 4 Dumfume 12.8V 300AH batteries $329.96 each https://www.amazon.com/Dumfume-Lithium-LiFePO4-Rechargeable-Phosphate/dp/B0DS26NNJL/ 2000W Bietrun pure sine inverter $109.99 https://www.amazon.com/Inverter-Converter-Hardwire-Controller-Protection/dp/B0DRCM5SVM 1000W Vterun pure sine inverter $69.00 https://www.amazon.com/Inverter-Converter-Hardwire-Controller-Protection/dp/B0DRCM5SVM/ 60A OOYCYOO MPPT charge controller $83.69 https://www.amazon.com/OOYCYOO-Controller-Regulator-Display-Lead-Acid/dp/B07S3YRF9S/ 40A Sogticps MPPT charge controller $48.99 https://www.amazon.com/SOGTICPS-40A-MPPT-Controller-Regulator/dp/B0DNYZY8TP/ 60A Gcsoar MPPT charge controller $169.99 https://www.amazon.com/GCSOAR-Controller-Charger-Regulator-Lead-Acid/dp/B0D86YNZY6/?th=1 50' white 8AWG duplex cable $73.99 https://www.amazon.com/Shirbly-Insulated-Stranded-Automotive-Speakers/dp/B0C27RMB7K/ 24V 4000W Tageeblu inverter $199.99 https://www.amazon.com/TAGEEBLU-Inverter-Grid%E3%80%81Truck%E3%80%81Power-outlets-Display/dp/B0F6BKQNJD/ And of course various circuit breakers, connectors, cables. I'm using 2 foot 2AWG cables for the 1000W inverter and 1 foot 2/0 cables for the 2000W.