Solar Equipment

Types of Solar Panels

Solar panels come in five flavors right now: monocrystalline silicon, polycrystalline silicon, thin-film, building-integrated photovoltaic (BIPV) and solar hot water (or solar thermal).

Monocrystalline  are currently the most common and the most efficient types of panels – you can tell mono panels by the square-ish cells (see picture at right).

Polysilicon cells are slightly cheaper to produce then monosilicon, but they’re also less efficient at turning sunlight into energy. You can tell poly cells by the mosaic-like pattern of silicon in the cells (picture at left).

Thin-film solar cells are currently the cheapest type of cells to make but they’re also the least efficient. They work really well for large utility-scale solar farms, but not so much for your roof. Researchers around the world are working to improve the efficiencies of these cell. They may be coming to a roof near you in the not-too-distant future.

Building-integrated solar panels can look like roofing tiles or shingles — solar shingles are the most common place to find BIPV installed today — but they are also less efficient than roof-mounted (or ground-mounted) solar panels, so unless you have a big, sunny roof, they may not meet your energy needs.

Finally, solar hot water — or solar thermal — are a different beast altogether. These panels don’t generate electricity, but they do heat the hot water for your home and/or pool. And some systems can provide heat and air conditioning, too.

Solar Inverters

The solar inverter is the second most important (and second most expensive) component of a solar PV system. It converts the Direct Current (DC) solar power that is produced by your solar panels into the plug-the-toaster-in Alternating Current (AC) power that comes out of your wall sockets. Inverters also have technology that maximizes the power output of that DC energy. There are two main types of inverters.

• Central Inverters

Central inverters are well-tested and reliable systems that have been around for decades. These are the most common types of inverters. With central inverters, every solar panel is wired in a string to the inverter box. The conversion from DC to AC occurs at one central location, such as your garage. Because the solar panels are wired in series, each panel’s power output depends on all of the panels working. So, if shade from a tree hits one panel, it can seriously diminish the power produced by the whole solar system until the shade clears. That’s why an accurate shade analysis is so important!

•  Micro Inverters

Micro inverters are relatively new to solar. Instead of converting the DC to AC power at onecentral location, micro inverters are installed right under each solar panel. The main advantage tis the ability of each solar panel to transmit power into your home … each panel is its own solar-powered island and keeps churning out solar watts regardless of what happening to the panel beside it. The downside of micro inverters is that they can be more expensive and take more labor cost to replace each inverter. Also, because they’re so new, micro inverter reliability is unproven outside of lab testing.

• Inverter Warranties

Central inverters typically carry a 10 year warranty and often go for 12 to 15 years or longer. The leading micro inverter company has a 15 year warranty, but the inverter(s) could last years longer. In either case, if you stay in the same house for 20+ years with your same solar panels, (which last 20 to 25 years or longer) expect to pay to replace your inverter(s) at some point. How much? Due to manufacturing advances in 15 years, probably less than the current cost of about $1200-$2000.

Solar Monitoring

Solar monitoring is a way to make sure your home solar system is working to its best capacity year-round — it offers a real-time check-in on how your panels are working. Depending on your solar installer, and if you lease or buy your solar panels, your home solar system will likely come with a solar monitoring software platform from the beginning, and many installers offer both online and mobile apps to give you a real-time look at how your panels are performing.

Energy Storage (batteries and backup) 

The home solar revolution is underway, with the number of homeowners installing solar panels growing exponentially over the past five years. The next step in this revolution is the addition of energy storage systems — batteries and backup that can store your clean energy for your use at night as well as keep your home running smoothly in the case of a widespread power outage.

Right now, there are more arguments against solar storage systems than in favor: batteries are expensive, bulky, and only rarely needed. Most home solar panel systems are grid-tied — they connect to the larger utility grid in your area — and thereby make it possible for homeowners to benefit from net metering policies. You get paid for any excess energy to send back to the electric grid. That means you likely don’t need batteries for your home energy.

However, there are plenty of companies and researchers working to improve the quality and lower the price of battery storage for solar, so the market is slowly changing, and the time will certainly come when energy storage is bundled with every solar panel system sold, truly freeing homeowners from the grid and powering the country with the sun.

Solar Panel Efficiency 

The efficiency of solar panels is the measure of how well they convert sunlight to clean electricity. Solar panel efficiency is constantly improving, but slowly.

Five years ago, the most-efficient panel available for the masses was about 15% efficient; today, the most efficient panels available are about 17.6 percent efficient. As with every aspect of solar power, companies and researchers are always working on improvements, and SunPower has recently achieved efficiencies of 21.5 percent on its X-Series solar panels. These panels are traditional monocrystalline panels; efficiency for thin-film solar panels are currently between 16 and 17 percent.

The BOS (Balance of System)

There are many other less well known and less expensive parts to a solar system. Installers typically wrap these up into “The BOS” or “Balance of System.”

The balance of system includes components such as wiring, emergency DC disconnects, system monitoring hardware, the frames or racking that hold your panels to the roof and at the right angle, nuts, bolts, roof flashing to prevent leaks, and more.

The balance of system components required to attach solar panels to your roof is covered in the Nitty-Gritty on Solar Roofing.