Questions About Solar Electric Power
How does a solar electric power system work?
Solar photovoltaic cells—PV cells for short—convert sunlight into electric current. This current is direct (DC) current. The electrical devices and appliances in your home operate on alternating (AC) current, so the solar electricity is run through a special device called an inverter to change the DC current into AC current. AC current is fed into your home’s main circuit breaker panel, then distributed through your house as needed.
At various times throughout the day, your solar power system may produce more electricity than your home is using. At these times, the excess solar electricity is fed back through a special utility company power meter that monitors and records how much power you are supplying to the utility power grid. A written agreement with the utility company defines how you are compensated for this excess power.
Your home uses utility-provided electricity at night, and during the day when your home’s electricity demand exceeds the power output of your solar power system (solar power systems are seldom sized to provide enough power to run a home’s central air conditioning system).
A solar power system may also have a bank of batteries to store power for nighttime or rainy weather use. However, assuming a house has readily available access to utility electric power, batteries should usually be limited to an emergency backup power role during severe weather and utility power outages.
How does a solar power system work on cloudy days?
If you have ever experienced getting a sunburn on a cloudy day at the beach, you know there is still solar energy penetrating through the cloud cover. Solar PV cells produce electricity in proportion to the amount of energy striking the solar power module. During an overcast day, a solar power system might produce about half the energy output of a clear day.
Will my system work at night?
No. No sunlight, no solar power. You use utility-provided electricity after dark.
Will I still have electric power if my neighborhood experiences a utility company power outage during daylight?
Our basic, grid-tied solar power system will not provide emergency backup power during a utility company power outage. In order to use your solar power system for emergency backup power during the daylight hours, you must add a secondary circuit breaker panel—called a critical loads sub-panel—to your home’s electrical wiring system. During a power outage, backup power from the solar power system bypasses the main breaker panel and is routed into the critical loads sub-panel to panel lights, wall receptacles, consumer electronics, ceiling fans, etc., but not big energy users like central air conditioning, hot water heating, laundry appliances, pool pump, etc.
To provide emergency backup power during severe storms, cloudy or rainy weather, and at night, you also need a bank of special storage batteries.
Can I become completely independent of the electric utility company?
Yes, but we don’t recommend it. An “off-grid” system requires considerable extra cost for (1) solar power capacity to meet 100 percent of your average 24-hour demand load, including summer air conditioning; and (2) a large bank of power storage batteries for nighttime and cloudy weather power. While your system may have batteries for emergency backup power storage, this emergency battery capacity will likely be much smaller and much less expensive than a battery bank capable of providing provide power for your home’s entire power needs—including central air conditioning. Also, batteries used in a daily “off-grid” role need to be replaced every five to 10 years. Batteries used only for emergency backup power should last 20 years or more.
Will my system produce extra power to help run my central air conditioning during the summer months?
No. Actually, your system will produce about the same amount of power every month. Here’s why: The power output of solar PV cells falls as operating temperature increases. So while more solar energy is available during the summer months, the higher air temperatures reduce a solar power system’s efficiency. And even though there is significantly less incoming solar energy available during December and January, the lower average air temperatures make a solar PV array much more efficient. In Florida’s climate, solar PV cells end up producing just about the same amount of power every month of the year.
I do not have a south-facing roof. Can a solar power system still work for me?
Yes. While south-facing is the ideal orientation for a solar power system located in North America, good performance is still possible when flush-mounting solar PV modules on an east- or west-facing roof. Mounting on a flat roof can also produce good results.
Why do solar PV systems need so much roof area?
Solar PV array surface area is determined by three factors:
- Available solar energy per square foot (or square meter) on an average day. On an average Florida day, about one-half of one kilowatt-hour of solar energy strikes one square foot of a south-facing surface tilted at about 25 to 30 degrees.
- Solar PV module efficiency. While a solar PV manufacturer’s peak power output rating might suggest that one of its PV modules will turn about 15 percent of the solar energy striking the module into electricity, the actual percentage of incoming solar energy that ends up as usable alternating current (AC) power is usually closer to 10 percent.
- Amount of power needed. If we have about half of one kilowatt-hour of solar energy available, per square foot of surface area, and we can turn about 10 percent of this energy into usable AC electric power—about 1/20 of one kilowatt-hour per day—then once we estimate how much power we want to deliver, we know that we will need about 20 square feet of roof area for each kilowatt-hour of AC power desired. (A more precise number is 21.75 square feet of solar PV array for each kilowatt-hour of daily AC power output desired.)
Daytime power requirements for a more or less typical Florida home—not including power for central air conditioning, hot water heating, or a swimming pool pump—are usually between 7 and 15 kilowatt-hours. The roof area needed to supply this much power is between 7 x 20 = 140 square feet and 15 x 20 = 350 square feet.
Some actual numbers: Our standard 2 kW solar power system needs 157 square feet of roof surface and produces about 7.2 kilowatt-hours on an average Florida day. Our 5 kW system needs 392 square feet and produces about 18 kilowatt-hours on an average day. 392 square feet is just a bit smaller than the floor area of a two-car garage.
I’ve heard that if a solar PV module is partially shaded, the whole module stops working. Is this true?
Well, not precisely true. But it is true that when some portion of a solar PV module is shaded, the performance of PV cells still exposed to direct sunlight is significantly reduced. The reason has to do with the way individual PV cells in a module are wired together.
Will hurricane winds or hail damage solar PV modules?
In all but the most severe cases, no. Our solar PV modules are engineered to withstand 125 mph winds, with a safety factor that should keep panels intact on a roof during a Category 4 hurricane. These modules are also engineered to withstand impact by a one-inch hailstone at 50 mph.
How will I know how much power my system is producing?
Your system will include a power meter, so you will always be able to check and see exactly how much electricity your solar power system is producing.
What sort of maintenance and parts replacement does a solar power system require?
Very little. The major system components have no moving parts and your PV panels should continue to produce their designed power output for 25 years or more. If you add deep cycle power storage batteries to your system, these batteries should last for 20 years or more if used only in an emergency backup role. Batteries used for regular nighttime power may last only five to 10 years.
Dirt, dust and debris (leaves and twigs, for example) that collect on the PV modules can affect system performance, so it is a good idea to have someone spray the modules with a garden hose three or four times a year.
It’s a good idea to have us come out once a year to inspect connections and make sure all your modules are operating correctly.
Can my homeowners association prevent me from installing a large solar PV array if, for example, the front of my house is the only large south-facing roof area?
No. Homeowners associations usually have a right to review and approve any addition that will change the exterior appearance of a home; however, Florida law forbids any local government or other entity from denying approval for the installation of solar energy devices. While a homeowners association can have a right, under Florida’s solar law, to make you change the specific location of a solar equipment installation, this right has no effect if such a change will reduce the economic effectiveness of the solar energy equipment.
So, for example, if your only south-facing sloped roof is on the front of your house, then you cannot be denied permission to install solar panels on the front roof. The precise reason is that all other alternatives would require a south-facing rack mounting assembly—or extra PV modules on a non-south-facing roof to offset reduced energy collection efficiency—and these alternatives would increase the solar power system’s cost.
Do I need my utility company’s permission to connect my solar system to the power meter?
Yes. Your utility will require you to enter into a written net metering agreement that specifies, among other things, equipment specifications and safety rules for wiring and equipment that will connect to the meter, and a schedule outlining how you will be credited or paid for electric power fed back to the grid from your solar power system. You will also receive either a new bi-directional meter or a second meter, for monitoring and recording the electricity your system feeds back to the grid.