A Primer About Solar Electric
It Can Get a Little Complicated, so Here Are Some Technical Points to Help You Get Started
By Dan Fink, Colorado
Back when I was a young teenager, I saw something that changed my life forever — a solar electric panel. My parents had just bought remote, mountain property here in Colorado. Our family has always loved the outdoors, with fishing, hiking, backpacking and camping our favorite activities, and of course it’s essential to have somewhere to escape the big city as often as possible. My folks were planning to build a rustic cabin, with kerosene lamps for light, a woodstove for heat, a gasoline generator for power tools and where “running water” meant my dad had to pick up the pace a bit carrying buckets up from the spring. The nearest power lines were (and still are) 11 miles away.
After our camper was parked on the property and cabin plans were forming, we started going out to meet and greet our neighbors (always a good plan in the country). At dinner at our neighbor’s house, we were all stunned that they had electric lights and a small stereo for music and radio! All powered by a few funny looking rectangular things on the roof with solar cells in them and a couple marine batteries. No smelly, dim and dangerous kerosene lamps, and no noisy, smelly and unreliable generator banging away outside.
It wasn’t cheap — at the time, a single small 22-Watt solar panel cost more than $700 — but well worth it. Our cabin was built as planned, though we had to use a generator for the power tools. But inside, I could even do my homework and read books under real electric light instead of squinting by the dim kerosene version. Clean, quiet, natural and reliable power.
That made a huge impression on me and now, 35 years later, my own off-grid home and office on the property next door to theirs has almost all the conveniences of town: microwave, dishwasher, rice cooker, satellite TV, internet and phone and even a big electric refrigerator. You’d never know that it’s entirely off grid except for the long drive to get here, all the birds and other wildlife roaming the property and the blessed, peaceful silence. I ended up making renewable energy my career, even though it looked slightly crazy at the time to my friends and family. And I’ve never looked back—it turns out that was one of the best decisions I’ve ever made. And now almost nobody thinks I’m crazy.
Solar electric (PV) power has become very inexpensive over the last few years thanks to new technology and the economy of scale—PV panels are now a mass-production item, and are about 30 times cheaper per Watt than what my folks paid for that single panel back in the day. But it also pays to do your homework before pulling out your wallet, as it’s all too easy to order DIY equipment on the internet only to find that the all the various bits you bought don’t play nice with each other.
SOLAR ELECTRIC TERMINOLOGY
First, let’s get on the same page with terminology. “Solar panel” is a confusing generic term that can also refer to solar water or air heating technologies, so Photovoltaic (or PV) is the specific term for something you put in the sun to generate electricity. PV cells are the individual round or square pieces that are wired together and sealed under glass to form a PV module. A group of PV modules is called an array, and within the array there may be multiple groups of PV modules called strings.
There are three basic types of PV modules: monocrystalline, polycrystalline and thin film. Each has advantages and disadvantages, but the important thing to remember is that you can safely make your PV purchase decisions based mostly on dollars per watt, and then by efficiency—some PV technologies take up more space per watt generated than others. If you have limited rooftop area for an array, efficiency becomes more important, but if you have plenty of space for a ground-mounted array, you can shop almost entirely by dollars-per-watt.
Thin film has taken a bad rap recently for a variety of reasons, but still has a lot of potential. This is a coating that can be sprayed or rolled onto a surface, usually glass, but plastic, cloth and other flexible bases are possible. The main problem with thin film is that it’s not as efficient—a thin film array takes up about twice the space of poly or mono to produce the same Wattage. The big advantage is that it doesn’t have to be flat and brittle and covered with glass; curved surfaces are possible. Places you’ll likely see thin film modules are the decks of boats, and solar shade car parks.
Bad publicity didn’t help thin film technology either. Just drop the words “Solyndra” and “Abound Solar” and you’ll likely still hear all kinds of stories about the waste of government loans and how our efforts to help fund start-up companies were futile. The rest of the story is that the whole idea behind these companies was to break the “$1 per watt” barrier, and they did. Unfortunately for them, the Chinese broke that barrier with standard monocrystalline and polycrystalline modules while American thin film production was still ramping up. And as with any new technology, reliability growing pains were also an issue.
Another consideration for you in selecting PV modules might be the country of manufacture, and these days that can be a bit confusing. The PV cells themselves might be made overseas, then assembled into modules in the United States. You might also want to look at the longterm stability of the manufacturer. Most PV modules are warrantied for 25 years, but if the company is no longer around, that warranty isn’t worth much. Fortunately, I’ve never run into any consistently “bad” brands of PV module, other than imported eBay specials. Any module that’s UL-listed should serve you just fine for many years; without that listing you are taking a big risk of failure and fire, and in most jurisdictions it’s illegal to install non-UL listed solar equipment for your home in the first place.
All this said, when shopping by dollars per watt, at the end of the day most likely you will end up with mono- or polycrystalline modules. Pay attention to shipping options, too—standard 250- to 300-watt PV modules are too large for UPS, and have to be shipped by truck on a pallet. Residential delivery with a lift gate more than doubles shipping costs, so see if your distributor can sent them to a nearby freight depot for you to pick up. They’ll load them in your pickup with a forklift, and you can break the pallet and open the individual boxes at your convenience, at your home.
TYPES OF PV MODULES
PV MODULE RATINGS
Back in the day, PV modules came in one flavor: 12 volts. Connect a 12-volt module to a 12-volt battery and connect a 12-volt light to the battery, and you had a simple power system. If your battery bank was 24 volts, you put two modules in series and two batteries in series, four and four for 48 volts. Your solar controller (which prevents overcharging the batteries) had a switch setting inside so you could tell it what voltage to expect. The disadvantage of PV arrays wired at low voltage was the high cost of thick copper wire to the battery bank, and large or multiple charge controllers to handle the high amperage.
Those “12 volt nominal” modules actually made about 22 volts with nothing connected to them—socalled “open circuit voltage,” or Voc, and a normal operating voltage (Vmp) of about 18 volts. Advances in modern charge controller technology have completely changed how most PV arrays are designed. And instead of referring to modules by nominal voltage, you’ll see “60-cell” and “72-cell” modules advertised instead. The 60-cell versions have a Voc of around 38 volts, and Vmp of around 31 volts; the 72-cell versions run at a Voc of around 47 volts and Vmp of around 37 volts.
These numbers are important to you because modern charge controllers use a technology called Maximum Power Point Tracking (MPPT) that watches changing sunlight conditions such as cloud cover and sun angle by looking at Voc, and quickly forces the array to operate at the best possible Vmp for the conditions. Even better, MPPT allows for high-voltage PV arrays with multiple modules connected in series—no more running expensive and hard-to-bend copper wire as big around as your pinky from the array to the system control center and battery bank. With a maximum Voc of 150 volts the norm, and Voc of 200 volts, 250 volts, and even 600 or 1,000 volts available, the whole PV array can run on much thinner wire. The extra cost of these hightech controllers is usually completely offset by the reduction in copper wire cost. The downside is that if you have to mix and match PV modules, the MPPT computer will likely choose the worst available solution. In those cases, I usually recommend a plain old-school PV charge controller.
There’s another catch with MPPT, though. If your PV array ever exceeds the maximum Voc of the charge controller, it will be damaged beyond repair. And there are environmental factors that can bring module Voc to over the official rating—for example extremely cold weather, snow cover on the surrounding ground that reflects extra light, and the “cloud edge effect,” all of which can raise voltage enough to destroy a controller. Fortunately, most charge controller manufacturers provide free online “string sizing” tools to help you arrange your array. Just plug in the brand and model number of your modules plus your geographical location into the website and it will tell how to arrange your PV module strings to prevent controller damage, including all the possible environmental effects.
TRACKING AND RACKING
Don’t confuse Maximum Power Point Tracking with actual “trackers” (photo 6) that physically move the solar array to face the sun all day. The former is a purely electronic process. In most cases I don’t recommend physical trackers — they are expensive and require very sturdy pole mounts set deep in the ground in concrete, a very large extra expense. Trackers also add moving parts, which require maintenance and can fail, to an elegant system with no moving parts. Unless you have a specific application like farm water pumping for livestock or if you are located at a high latitude, adding a few extra PV modules to your array is usually more cost effective than physical trackers. The exception is seasonal trackers that you move only four times a year to match the sun’s angle a bit better. These can be highly effective, and also more cost-effective for your energy generated.
Advances in racking—the rails and feet that hold your PV array in place on the roof or on the ground—have also actually played a big part in lowering the overall price of installation. No more designing, cutting and precisely drilling holes in aluminum or steel; new racking systems use precisely extruded aluminum rails that let bolt heads slide inside, and clips instead of through bolts to lock the PV modules down. In fact, you’ll void the warranty on many modules by drilling new holes in the frames; you must use the predrilled holes or sliding clips from the racking system, which can be fastened almost anywhere on the module frame. Electrical grounding solutions are included with all these new racking solutions.
Even PV module wiring connectors have changed significantly in the last few years. Gone are the days of crimp terminals, wiring blocks and conduit between modules— now it’s all waterproof click-lock (MC-4) connectors on wires that are permanently connected to the modules. These have the advantage that it’s impossible to accidentally connect them with wrong polarity (plus or minus), but the downside is more expensive connectors and wiring harnesses, and a challenge trying to keep the wires bundled out of harm’s way.
GOING SOLAR IS CHEAPER THAN EVER
At the time this issue of Countryside goes to press, retail prices for PV modules are about $1 to $1.50 per watt—a far cry and big relief from the $32 per watt my folks paid back in the early 1980s to electrify their off-grid cabin. Prices probably won’t get much lower anytime soon, but they won’t get much higher either. PV remains the most cost-effective way to generate your own electricity. Do your homework before pulling out your wallet, but there’s little chance you’ll go wrong with PV.
THE HISTORY OF SOLAR ELECTRIC
Electricity from the sun actually dates back more than 175 years. Here’s a quick history.
1839 – 19-year-old physicist Alexandre Edmond Becquerel discovers that by shining a light on two different metals in contact with each other, electricity could be produced.
1888 – Edward Weston receives the first U.S. Patent for a “solar cell.”
1905 – Albert Einstein publishes a paper on the “photo-electric effect,” which sets the stage for his Theory of Relativity—light waves and particles and how they relate. He wins the Nobel Prize for this in 1922.
1954 – Bell Labs exhibits a highpower PV cell made from silicon.
1958 – Geophysical survey satellite Vanguard 1, about the size of a grapefruit, is successfully launched by the USA. The batteries running its main transmitter expired after only 16 days, while the PVpowered second transmitter kept working for over six years. Data from the satellite showed that Earth is not a perfect sphere, but instead an oblate spheroid. The satellite is still in orbit, and is tracked optically.
1970s – The U.S. Coast Guard powered lighted navigational buoys with non rechargeable batteries that had to be replaced regularly. The ships and crews required for this task cost far more each year than the buoys themselves. USCG officer Lloyd Lomer thought PV modules to be a far more cost effective power source, but his commanders didn’t agree. He bravely went over their heads to the U.S. Department of Energy, and a PV-powered test buoy was deployed in the worst possible solar location, off of Ketchikan, Alaska. It worked. In 1986 President Ronald Reagan gave Lomer a letter of commendation for saving millions of taxpayer dollars.
1974 – Railways began to see the potential of PV electricity to power warning lights and communications in remote areas; these systems proved essential to keeping trains running during grid power outages.
1978 – Telecom Australia was mandated in 1974 to provide telecommunications services for all citizens, no matter how remote. Managers saw the potential of PV, performed extensive reliability testing, and in 1978 started deploying PV-powered phone repeaters. They worked.
1980s – PV power for the electrification of remote areas of the world became financially viable due to increased PV module production. Water pumping was of particular concern. These systems were successful.
1980s to the present – Each year, the cost of PV modules has dropped because of increased production worldwide, and efficiency (watts per square foot) has increased each year too.