Alabama Solar Association
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Education on Solar Electricity
When electricity from alternative energy is equal to or cheaper than the price of buying it from the power company
How Does a
Solar Cell Work ?
A Solar Panel / PV (Photovoltaics)
is manufactured as a
matrix of many solar cells connected together.
A solar array
is many solar panels hooked together.
Although 1 cell cannot produce much electricity, 100's in series can.
The Solar Cell
uses the fact that sunlight, traveling as photons, "excites" electrons of a charged Silicone wafer. This Silicone wafer has a + layer on one side and
a - layer on the other side.
As these electrons "flow" from one side to the other, they produce a current of electricity.
A solar system
includes many panels and Inverters.
The panels produce DC Electricity.
Inverters are needed to convert the DC to AC electricity to be used by lights & devices in buildings.
This AC electricity then passes through a Utility meter to measure the electricity put on the grid from your panels.
You get paid for that electricity by TVA.
The electricity you use in your house comes from the grid and includes your solar electricity.
Grid-tied Solar System
Your solar system consists of multiple PV Panels and Inverters. In this system, your house is still "hooked" up to the Utilities Company's main power supply. While the sun is down/low in the sky or obstructed by thick clouds, the Utilities furnishes power to your home & you pay them. During a clear day, your solar system provides power to "the grid"/Utilities Company & they pay you!
Before the DC electricity from your PV panels can be put on the grid, your Inverters convert DC to AC electricity.
You basically use the grid as a big battery.
Off-Grid Solar System
In this system, your house is not "hooked" up to the Utilities Company's main power supply ("the grid"). This is necessary in rural areas or if you want to be completely independent from Utilities. Your house is completely powered by your panels while the sun is out. It is powered by your batteries when the sun is not out. These batteries power your house at night and on very overcast days. Many overcast days in a row can run down your battery bank. There is more expense when buying batteries & they only last around 10 years. Also more panels (more juice) are needed to charge your batteries while powering your house, as well. The battery technology is not quite as advanced as that of PV panels (but it is catching up).
With Off-Grid, you are independent of the Utility Company, but must buy all the hardware (and extra PV panels) of the Grid-tied solar system PLUS batteries & Battery Controller.
The Battery Controller monitors & protects the battery from charging too fast and hurting the battery.
While the grid-tied system is almost maintenance-free (except for replacing the Inverters every 11 - 15 years), batteries require much more monitoring & maintenance.