Welcome to Jay Nugent's (WB8TKL)
Household 12-volt D.C. Solar Power System

This Primer covers how I went about wiring my house for 12-volts D.C.

Having rewired conventional 110vac light fixtures for 12-volts, using Solar panels, an MPPT Solar Charge Controller, and a small bank of Deep-Cycle batteries, my home is becoming more independent of the commercial electric grid.

Now my lighting and communications are all immune from power failures, all while reducing my monthly expenses and my Carbon Footprint.


      The purpose of this webpage is to show others how easy it is to install and operate a Solar Power system for your home. Nothing says that you must convert Solar power into 110 volts A.C. (Alternating Current) as most Solar installations do. This is costly and in my view, very inefficient. Every power conversion comes with additional expense, complexity, energy loss, and yet another point of failure. So my home power system uses the D.C. (Direct Current) power produced by the Solar panels that has been stored in a battery bank, and then used to directly power LED lights and other devices found throughout the home.

      To accomplish this, I have rewired many conventional light fixtures throughout my home to operate with either 110vac or 12vdc seperately, or at the same time. These modifications are easy to implement and don't require you to be an engineer or an electrical wizzard. The most time consuming part of the project was the fishing of 12vdc wiring through the attic, walls, and basement to get 12 VDC to each of the lights/devices safely. I strongly recommend taking some time to sit back and think through your specific needs, considering your homes construction, before running any wires. A little time spent planning will pay off in the long run if you consider all the issues and you think it through thuroughly. Having experience pulling alarm, telephone, and power cabling in my younger years, I have developed the skills and techniques to do these jobs efficently. Though at 60 years old they are NOT as easy a task as they were when I was a 20 year old!

      A benefit to 12VDC Solar Power is that my lights will never go out, even after MONTHS or even YEARS of having no commercial power. Another is that Solar Power offsets a fair chunk of my monthly DTE Energy bill by providing the 12 volts D.C. that is used to run several Ham Radio rigs (both my wife and I are Ham/Amateur Radio Operators), alarm system, and lighting throughout the house. Every little bit helps, and each month or two I add yet another improvement or expansion to the existing system. This is convienient, because I don't have to jump into a Solar power system all at once, nor lay out a bunch of cash or take on a huge wiring project, all at once. This lets my "learning curve" evolve a little at a time, thereby avoiding what could perhaps turn in to some rather expensive mistakes. Take your time and plan ahead.

      As a case in point with regard to migrating off commercial power and onto solar - I watch a fair amount of TV. While we tossed the big old energy hungry CRT TV sets awhile ago, the newer flat screen TVs are far more efficient. As it happens, they are typically powered by a "brick" power supply much like those used for laptop computers. My flat panel TV requires 19-volts DC and consumes up to 60 watts. So I acquired from Amazon a couple DC-to-DC converters that allow me *step up* the 12 volts to 19 volts to run the TV set. By getting this 60 watt load that is ON for many hours every day moved onto FREE Solar power, should result in a marked decrease in my monthly power bill!!!

      So the overall theme here is, DO SOMETHING, DO ANYTHING! Just do little baby steps toward gaining your independance from the commercial power lines. Every step forward is a step in the right direction!


      We will start with the core of the system, and that is the Battery Bank. This is where we draw power from to run all of our lights, radios, TV, Laptop, and other devices, known as "loads". The batteries are the core component of our power system. All loads run off of the batteries, while all the power we generate for free from the solar panels, is pumped into the batteries to keep them charged.

      The Battery Bank MUST be able to provide ALL of our power needs throughout the night, and on those bad weather days when the Sun is not shining due to rain, snow, or simply overcast clouds. The suggested goal is to have enough Battery Capacity to run ALL your needs for at least THREE DAYS without requiring a recharge. That can sometimes be a real feat to accomplish! I currently have only enough battery capacity for ONE day, and perhaps two if I shut off a few things and limit my usage. But start SOMEWHERE! You can always add more battery capacity later as you can afford it or as your requirements grow.

      We start with a bank of wetted-cell lead-acid deep-cycle batteries. Though my Ham Radio batteries were originally old car batteries, I later replaced them with 55 Amp/Hour wheelchair batteries. These were better as they were meant to be discharged daily, while car batteries are not. Then as my needs continued to grow I replaced those with 6-volt Golf Cart batteries as they have MUCH more capacity (Amp/Hour Rating) and are designed for daily deep cycle use. Costco sells such Golf Cart batteries for $85 each ($100 if you don't turn in a dead battery as a "core"). A pair of 6-volt Golf Cart batteries provides me with a dependable deep-cycle supply of 210 Amp-Hous (for each 12-volt string). More "strings" can be added as money allows or needs dictate.

      In this photo (this is not my battery bank, but a nice example) you can see where three 12-volt strings of batteries have been placed in PARALLEL to combine their respective Amp/Hour rating into a much larger capacity bank. So let's say that each 6-volt Deep Cycle battery has an AH rating of 210 AH. Two batteries in SERIES gives us 12-volts, but the AH capacity of the string is still 210 AH. By putting three strings in parallel (assuming all the batteries are of the same capacity) we still have 12-volts but we now have an Amp/Hour capacity of 630 AH.

I *highly* recommend keeping battery cables tight and clean, and all cables should be of the largest wire gauge practicle. This assures the lowest losses. Smaller gauge wire will act like a resistor as large currents run through it. It is also better to extract the POSITIVE lead from one end of the bank (large RED cable in the top left of the photo) and the NEGATIVE lead from the opposite end (large WHITE wire in the lower right of the picture). This is to cause the current flow through each battery AND CABLE to be equal as much as possible. Some battery banks even cross-connect between each of the 6-volt batteries to reduce any imballances in the bank.

      Since all batteries have a bare minimum Terminal Voltage that you should NEVER discharge below, we will need to assure that the Battery Bank never discharges below that point. The rule is to NEVER let a 12-volt string discharge below 11-volts or permanant damage WILL occur! So we will keep the batteries charged using two methods. First, the FREE method, and that is to use an array of Solar Panels combined with a Solar Charge Controller which will keep the battery bank topped off at between 13.5 and 14.4 volts. This keeps everything running and provides a charge (or re-charge) to the batteries whenever we have sunlight. More on that, later.

      But sometimes you just won't get enough Sun to make ends meet (weather, shorter Winter days, etc.). So at these times we need some kind of backup system. Enter the Backup Charger. This is nothing more than a regulated power supply that keeps the batteries charged to a specific terminal voltage. A voltage of 13.2 is a "float" charge level that keeps the batteries fully charged while not causing any off gassing. Fully charged batteries under load *should* hover around 13.6 volts. But once they start to drop below this voltage, they have begun to discharge. So we like the backup charger to maintain a voltage somewhere between 13.2 and 13.6 voltsas a bare minimum.

      We cover the Charger in more detail in the next section.

Backup Charger:

      In my basement office and combined Ham Radio Shack, are my battery bank and much of my Ham Radio equipment. The batteries are close to the Ham Radio equipment because they are the largest current hog, or LOAD, that are ever put on the batteries. While transmitting I will typically draw anywhere between 5 and 20 Amps. So cabling is kept as short as possible to reduce what are called "IR Losses" (the voltage droped across the resistance of the wire).

For the same reason, the Charger is kept close to the battery bank. The Charger is a simple Astron RM-12A 12-volt 12-amp (144 watt) rack-mount power supply. This supply is able to keep the battery bank State of Charge topped off sufficiently while a number of radios are turned on or in use, and some lighting loads are also in use. This has served me well as my "Shack" power source for many many years.

The backup charger is *rarely* ever turned on, but is ready in case there has not been sufficient sunlight to keep everything running as it should. Remember, size your battery bank to support ALL your needs for THREE DAYS before the Terminal Voltage has dropped to where you need to recharge them. Then if you still don't have a clear weather day, you can always resort to turning on the Backup Charger to recharge them.

Solar (PV) Panels:

      The primary source of power comes from an array of solar panels, also known as "PV" or Photo Voltaic cells. The panels I am using are flexible (Amorphouse) rather than the typical glass/fixed panels. Each strip has 22 cells and can produce a maximum of 128 watts. They are 19-feet long and 16-inches wide and have an adhesive backing as they were intended to be installed in the troughs of metal roofing. These are not the most efficient per square foot, but the price was right - and I have plenty of roof space to fill. The PVL-128 has an "Open Circuit" voltage of 33 volts. This is the voltage the panel can output under no load. When matching a Charge Controller with your panels you MUST not exceded the maximum input voltage for the charger! You must also not excede the maximum input current. So PLAN your installation accordingly.

      Being Amorphouse, the PVL-128 panels are only 8.5% efficient, compared to the solid glass-like Crystaline panels which can be up to 18% efficient. You can WALK on my panels, but you wouldn't try that with the Crystaline/Glass panels. These efficiencies are based on a *perfect* conversion of sunlight to electrical energy. NO panels are very efficient in this regard, and the PVL-128 panels are only about half that of a modern panel's efficiency. So if I were to put TWICE as many square feet of panels on the roof, I will have just as much power as if I were using modern Glass panels. But these were CHEAP! A THIRD the cost of a comparable panel. So when Uni-Solar was closing its doors due to bankruptcy, they were unloading these panels for only $50 each. FAR less expensive than the glass panels at that time. Still a great bang for the buck! So I scarfed up as many as I could afford. Several are on the roof of my garage, while my remaining panels are in storage for future use.

      Modern day solar panels cost in the vicinity of 50 cents to $1 per Watt. So my PVL-128 panels *should* have cost me anywhere between $65 to $128. A 250-Watt glass panel had been selling for $300 each, but now sell for much less than this, depending upon manufacturer and provider.

      You must understand that *efficiency* per square foot is ONLY important if you have very limited square footage to install panels on. I have an abundance of South-facing roof on both my garage and my home, and I can place "racks" in my side yard, if necessary. So efficiency per square foot wasn't my concern, but money out of pocket to get this project started, was!

I'll note here, that many people hold off purchasing solar equipment because the price continues to drop and the efficiency continues to go up. This is called "Market Paralysis". Where you NEVER get a solar system installed because you are constantly waiting for the next improvement in the technology or drop in price. So you totally miss the bus!!! Do SOMETHING! And do it NOW!!! Like any technology, in the future you can always buy something newer or better, then sell the older gear to a friend or neighbor who wants to get started but can't afford the latest and the greatest.

      On my gargage roof I have mounted FIVE Uni-Solar PVL-128 panels. This is only temporary as the roof is VERY worn out (shingles are curling up) and is slated to be replaced, soon. Only TWO of the panels are connected to the Charge Controller in the house via an 80-foot run of 4 conductors of 8-gauge cable. At a maximum of only 4 Amps per panel, the voltage drop across that length of 8-gauge was only about 0.5 volts (0.25 volts per conductor). This is an insignificant loss when the panels produce 33 volts or more in bright sunlight.

Solar Charge Controller:

      Every solar system should have a trustworthy way to take the energy from the solar panels and apply it to the battery back with the expectation that the batteries will receive their maximum allowable charge without concern of them becoming overcharged or damaged. The purpose of the Solar Charge Controller is to manage the voltgae and current from the panels, and apply it to the batteries in the most efficient manner to maintain to proper terminal voltage (13.5-14.4) while not exceeding the proper rate of charge (current). You've got a lot invested in the batteries and you don't want to damage them - nor any of your devices attached to the batteries.

      Some charge controllers simply pulse the FULL VOLTAGE output of the solar panels (mine put out in excess of 40 volts) into the batteries at a *duty cycle* to approximate 12 volts. This is called PWM (Pulse Width Modulation). Though the batteries will typically absorb these high pulse voltages, and will *buffer* the voltage spikes, they are rather inefficient since the pulse is off much of the time. PWM is considered only about 50% efficient. But wait! There is a better way!

      Enter MPPT (Maximum Power Point Tracking). Without going into all the "magic" that MPPT does internally, let's just say that MPPT controllers don't do the high voltage spikes and typically are 98% (or more) efficient. They get nearly ALL the energy produced by your PV panels into your battery and/or loads.

      The Solar Charge Controller I use is the "Apollo" MPPT Solar Charge Controller made by DIY Solar For U in Troy, Michigan.

Circuit Breaker Panel:

      Most circuit breakers are intended for AC use. When they disconnect, arcing across the contacts is limited because with Alternating Current, the voltage drops to zero every 16 milliseconds. So any arc across the contacts is extinguished very quickly.

      But with Direct Current, that arc inside the breaker *can* quickly damage the internal contacts, and can sometimes arc weld them together causing the breaker to NOT break the current path! So breakers designed for DC have special mechanical designes that quench the arc mechanically, by sliding a non-conductive shield between the contacts as the current path is opened. More complex methods of arc supression exist, but are beyond the scope of this website.

Distribution Wiring:

      Obviously, wiring of low-voltage DC circuits is not harmful to life and limb. But be assured that the DC currents involved *can* cause excessive heat, resulting in the melting of wires and insulation! So we MUST take precautions to prevent and protect our wiring from scorthing our household belongings, rugs, furniture, or from burning the house down!!!

      To deliver an equivelent amount of Power over a 12 VDC circuit requires TEN TIMES as much current as does a 120 VAC circuit. Thankfully, most of our 12 VDC devices don't draw much current, so the Power oftentimes is rather low. So wiring can usually be thin, smaller gauge wiring. Still, we must ALWAYS FUSE THE CIRCUIT FOR THE GAUGE OF THE WIRE!

      "I2R Losses" need to be taken into account when planning our wiring distribution plan. ......

Modifications to Existing Lamps & Fixtures:

      There are all sorts of 12vdc LED lights available. My preferance has been those that give off as near to natural white light as possible. Many 110 volt CFL screw in bulb replacements have a yellowish tint to them, making reading under such light uncomfortable. The 110 volt LED screw in replacements are much better, and give off a more natural light, but we want to avoid needing 110 volts AC altogether.

      My prefered 12-volt LED is the type 5050. This LED has a Color Temperature close to natural white light, almost as good as the Sun shining into a room on a clear day. Lucky for us these 5050 LEDs come available on a small panel containing 48 LEDs. This panel has an adhesive back, making them very easy to attach almost anywhere. They draw approximatly 7-1/2 Watts per panel, and Amazon sells them for about $3 per pair.

      There is a smaller version of the 5050 panel containing only 15 LEDs that also sell on Amazon for about $6 for a pack of 6. These are excellent for Night Lights in stairwells, hallways, closets, pantrys, or anywhere you need enough light to see well enough not to trip over something.

      Most everyone has seen LED Strip Lights, as these decorate so many stores, bars, and public areas these days. They come in many varieties from just white to colors to colors like a rainbow that change randomly. You can get them in weatherproof as well as non-weatherproof varieties, and they also have an adhesive backing so they can be stuck nearly anywhere. I use these under my kitchen cabinets to light my counter top. By using a small $3 PWM brightness controller I can adjust the brightness to just the right amount of light! These too, are available through Amazom and typically are about $1 per foot.

The easiest way to add a 12-volt D.C. light is perhaps in a hallway, as I did here in the hallway that connects two bedrooms, the bathroom, and leads to the livingroom. There never was a light in this hallway, so this was an all-new installation.

      I started with an inexpensive $12 light fixture from Home Depot. The 110vac bulb socket was removed which left a lot of flat metal surface to attach a pair of 48-LED type 5050 flat panels. These panels have an adhesive backing so they were VERY easy to attach. Each panel uses roughly 7-1/2 Watts at 12vdc, so two panels gave off a LOT of natural white light (produced by the type 5050 LEDs) for only 15 Watts of power input.

      The 48-LED 5050 Panels were aquired through Amazon for only about $6 per pair. These come with an assortment of light socket adaptors. I snipped the connector off a couple of these and used the pre-wired connector to make an easy connection to my 22-gauge wiring, putting the two panels in parellel. The 22-gauge was then routed in the attic and down the wall to a standard "paddle" type light switch. At these low currents, the contacts in the switch should last for many tens of thousands of operations.

Halo bracket & 3-way switches
Modification of "Sputnik" lamp (from XXX to 12v LED / disconnect switching power supply)

USB outleys for cellphone, tablets, and other devices (why run a Chinese wall-wart and risk a fire?)
DC-DC Converter to run Laptops and Flat Panel TV sets
More Night Lights
12-volts water pumps for wells and whole-house water filtration system
12-volt pumps for Rain Water Catchment system to water lawns and gardens
Home Accent Lighting -- change incandescent bulbs to LED and run on 12-vdc (use an Arduino/PIC/R-Pi as timer)

"You Cannot Manage What You Cannot Measure":

      Measurements/Monitoring/Data Collection