How Solar Works
Understanding the Basic Parts and Operation of a PV System
PV panels, which typically cost around $3 to $4 per watt, are the single biggest expense. For a typical installation, PV panels comprise around 70 percent of a system cost, and they take up the most space as well.
Be aware that PV modules are temperature sensitive; when the weather gets hot, power output goes down. Systems often output more power on a cold, clear winter day than a hot, muggy summer day, despite the fact that there’s a lot more sun shine on a summer day. If you have an option between a breezy location and a stagnant location, the breezy location will give you more energy output because of convection cooling, everything else being equal.
Different types of panels are finding their way onto the market. The technologies aren’t important to you, the end user, but the configurations (how they’re combined physically will govern how much space they take, and how they take that space) may be. Some panels are flexible, and some can be mounted directly over tiled roofs. Some panels are made into roofing shingles, so you simply put them up over the trusses, and you don’t need shingles.
A lot of new technologies become available all the time, but most of them are going to need some maturation to compete with the tried-and-true flat panels. Most panels are blue; some are black. Color doesn’t matter much. You can compare the performances of individual panels, but it doesn’t do a lot of good because ultimately what you’re after is system performance, and that depends on how well the components work together and other factors.
One thing you do need to be concerned with is warranty, and in this vein, manufacturer reputation and longevity. Most PV panel warranties are for 25 years, but beware; panels degrade over time. System warranties specify only a percentage of original power output over time say 80 percent after 20 years. Over time, your system will put out less and less energy; it’s inevitable.
Ground-mounted systems are more expensive than roof-mounted systems because they require concrete posts and special frames. On the other hand, you can orient the panels any way you want, and so the extra cost may be offset by the increased production of the system.
Disconnect switches are of critical importance, and they need to be mounted within easy reach. Every member of your family should know exactly how to turn the PV system off for safety reasons. If there is any abnormal behavior in your homes electrical system, shut off the solar system first. Most disconnect switches also have fuses that will prevent equipment damage.
Inverters are the next-biggest expense after PV panels. Inverters take the low voltage, high-current signals from the PV panels and change them into 120VAC, which is directly compatible with grid power. Inverters cost around $0.60 per watt, or around $2,500 for a typical 5 to 6K installation. Some of the avaiable options for inverters and systems include the following:
Monitoring functions aren’t strictly necessary, but they’re interesting and can tell you how your system is working. The simplest are a display on the inverter that shows how much power is being produced at any given time. Then you can get a reading of total generated power, either weekly, daily, or lifetime. You can get an inverter with a remote monitoring station that you can put inside your house so that you can read it without going into the garage (or wherever the inverter is installed). And, of course, you can get a monitor that connects to your computer so that you can call up on the Internet, even when you’re at work, to find out how your system is working. These latter systems also provide you with an opportunity to do all sorts of complicated calculations on, say, how much carbon dioxide you are saving. In general, you pay more for the monitoring functions, and they don’t change your production, so they can only decrease the attractiveness of your investment.
Safety features include switches and fuses that prevent dangerous situations from turning into reality.
Expandability ports are often wise. You can purchase a larger capacity inverter than what you currently plan on installing so that later on, in a few years, you can add PV modules.
You can buy an inverter that works when the grid power is shut off, but these cost a lot more because they are not as common (no economies of scale), and the utilities don’t want them. They have do not to be manually switched into the off-grid mode, as it is done automatically, so if a power failure occurs, you will not an have interruption. If the power
failure is at night, when you have no system production because there’s no sunlight, the feature is useless unless you have a hybrid system that charges batteries during the day.
The most popular feature is a digital display that tells you exactly how much power your system is producing. Efficiency is an important factor; any inefficiency is wasted energy, which gets turned into heat. Inverters can get very hot, particularly on the sunniest summer days when production is at its maximum. Where you physically locate an
inverter may be important. If you plan to expand your system in the future, buy a larger inverter than you need.
Wiring and fuse box connections
Wiring, conduit, and connections to your household main fuse box are minor expenses, but they comprise a big chunk of the labor for installation. You want the installers to hide the conduits if they can. Long wire runs cost more because the wire is generally heavy gauge.
Utility power meters
Power meters are usually provided by the utility company when the service persons come to your house to inspect your system and connect it to the grid. Conventional power meters are capable of spinning backwards, but the utility commonly changes to a special digital meter when you connect to the grid because almost all solar customers go to the TOU rate structure, which requires more intelligent processing than a mechanical device is capable of (see the earlier section titled “Reaping net-metering rewards with time-of-use rates”).
You look at the display, and it tells you whether you’re spinning forwards or backwards (though the word spinning is obsolete with the digital meters). The utility company may charge you for the meter and the installation, as well as a hookup fee.