How Solar Works
How a Solar Panel Makes Electricity
Solar PV cells are made from photoelectric materials that release electrons when exposed to light. These released electrons can be captured and used as electric current.
Most solar PV cells today are made from thin wafers of silicon, which produces a strong photoelectric effect. Silicon is the second most abundant element in the Earth’s crust and the key ingredient in semiconductor chips for computers, cell phones and other microelectronics.1
A basic silicon PV cell has two layers. While both layers produce the photoelectric effect, each is treated with a different chemical element (in a process called doping) to produce a positive charge in one layer and a negative charge in the other. The two layers can then be stacked together to form an electrical circuit.
When light strikes a solar PV cell, electrons are knocked loose from the atoms in the cell material. Electrical conductors attached to the positive and negative sides of the cell capture the resulting electric current so it can be used to perform useful work.
A solar panel, or PV module, has several solar PV cells wired together. Solar panels are designed to supply electricity at a certain voltage, usually 12 volts.
Electrical power is measured in watts. A solar panel with a nameplate output of 320 watts and 60 PV cells will produce 320 watts ÷ 60 = 5.33 watts of power from each PV cell when the sunlight intensity is 1,000 watts per square meter and the air temperature is 25°C (77°F).2
A solar panel’s power output varies with the amount of sunlight available. But a solar panel’s efficiency—the percentage of available solar energy converted into electricity—is highest in cold air temperatures. Solar panels perform best on cold, sunny days in late winter and early spring. On the other hand, even though higher air temperatures reduce solar panel operating efficiency during the summer months, overall summer electricity production is still excellent because so much solar energy is available.
What an Inverter Does
Solar panels produce direct-current (dc) electricity. Your lights, appliances and consumer electronics use alternating current (ac) electricity.
To change the electricy produced by the solar panels into a form that can be used in you home, dc electric current from the solar panels is sent through a device called an inverter, which changes the dc current into ac current. The inverter also monitors the electricity flowing into your home from the utility company, and it adjusts the frequency and voltage of the solar electricity it sends to your electric service panel to match the frequency and voltage of the utility-supplied electricity.
Sizing Your Solar Power System
A solar power system with premium solar panels in Northeast Florida will produce about 1.5 kilowatt-hours (kWh) of net usable alternating current electricity per year for each kilowatt (kW) of nameplate solar panel output. “Net usable” means net kWh available to power electrical loads after accounting for system losses and inverter efficiency.
For example, a 9 kW system will produce about
9,000 Watts × 1.5 = 13,500 kWh of ac electricity annually
Your solar power system will produce more electricity in some months and less in others. The amount of electricity produced is influenced by rainfall, cloud cover, air temperature and seasonal changes in the sun’s path across the sky. Our sizing software uses 30 years of average hourly weather data, and takes all these factors into account when predicting your system’s electricity production.
Assuming enough roof area is available, we will size your solar power system with enough solar panels to offset up to 100% of your household’s actual or expected annual power consumption.3
Planning For the Future
Your household’s electricity consumption may increase in the future. For example, Many of our customers plan to purchase an electric car. If we know this when we size the system, we can add enough solar panels to provide for electric vehicle charging in the future.
Other reasons electricity consumption can increase include adding a swimming pool, adding a second refrigerator, an increase in the number of household occupants (which increases hot water use), installing landscape lighting, and increasing the number of “always on” appliances like smart TVs and other consumer electronics.
Why You Should Stay Connected to Your Utility Company
Most Florida houses have enough usable roof area to offset 70% to 100% of typical yearly household electric power consumption with solar. But this great rooftop solar potential comes with a couple of caveats.
First, solar electricity must be used as it is produced. The hours when solar electricity production is highest do not always correspond to the peak hours of household electricity demand. Most significantly, solar electricity production is highest during the middle of the day, when household occupants are often away at work and school. Residential electricity demand typically peaks during the early morning and early evening hours.
Second, overcast and rainy weather reduces or prevents solar electricity production on some days. (And remember, weather is factored into our solar electricity production estimates.)
Staying connected to your local electric utility allows you to balance out these daily and seasonal variations with utility electricity.
How Net Metering Works
Because solar electricity must be used as it is produced, any time of day mismatch between a rooftop solar power system’s electricity production and household electricity demand could cause solar some solar electricity production to be wasted. Of course, a solar power system’s excess electricity production can be stored in batteries, an option that is discussed in the next section.
A rooftop solar power system’s excess electricity production can be exported for utility bill credit by connecting the solar power system to the utility company power grid and “trading” electricity back and forth. This sort of trading program, which occurs automatically, is called net metering.
Here’s how net metering works:
- Once your solar power system is installed, the utility company will replace your conventional electric meter with a smart meter. The smart meter measures and keeps track of the back and forth flow of electricity.4 A solar power system connected to the utility power grid in this manner is called a grid-tied system.
- Whenever your solar power system produces more electricity than is needed at that instant for appliances, lights and other household uses, the excess solar electricity flows back to the power grid.5 You receive credit for this exported electricity on your monthly electric bill. If you have credit left over after offsetting 100% of your purchased electricity in any month, the unused portion of the credit is carried forward to the next month.6
- At night, during rainy daytime weather, and at any other time when your home electricity demand exceeds the amount of solar electricity being produced, you make up the difference by drawing electricity from the utility power grid.
Solar Plus Battery Storage
Batteries allow a solar power system to store excess solar electricity produced during the peak sunlight hours for use at other times. Batteries can be used for emergency backup power. Batteries can also replace net metering.
Battery storage is not necessary for a grid-tied solar power system with net metering, so long as the value of net metering credit is based upon retail electricity rates. Why spend extra money for battery storage when you can just sell your excess power back to the utility company? But for situations where the value of net metering credits is less than the retail price, battery storage makes sense.
And in addition to eliminating the need for the “power trading” of net metering, battery storage has a second benefit that attracts many Florida homeowners. If you’ve lived through a Florida hurricane, you know that emergency backup power can be a really big deal in this state.
Emergency backup power. Battery storage can provide emergency backup power during utility power outages, just like a generator. But unlike a generator, battery storage combined with a solar power system is completely silent and doesn’t need to be run periodically just to make sure it’s operating correctly and will start when needed. And gas and propane generators have one other problem.
During an extended power outage, generator owners in an area without power are all likely to run out of fuel at about the same time. Remember, this will be a time when gas and propane shortages are likely. Gas stations may be out of gas or have long lines.7 Also, propane deliveries are guaranteed to experience significant delays, with everyone needing delivery at more or less the same time. Your local propane distributor only has so many trucks and drivers, with the numbers based upon normal demand, not emergencies.
Battery storage avoids all these problems.
A solar power system with battery storage provides safety, comfort and peace of mind during and after severe weather, in addition to financial savings the rest of the year. Depending upon the battery storage capacity you choose, your batteries can provide enough emergency backup power for all of your typical power consumption, including air conditioning, or just enough for essentials: refrigerator, lighting, ceiling fans and consumer electronics.8
Safety issues. The inverters in grid-tied solar power systems have the ability to detect utility power outages and shut down instantly whenever an outage occurs. This is done to prevent solar electricity from feeding into the utility power grid, which would endanger utility company technicians working to restore power. If you have batteries for emergency backup power, your system will be wired with an automatic transfer switch, just like the wiring for an emergency backup generator.