Generating electricity with the power of the sun’s rays (“solar power”, “photovoltaic power”, or “PV” for short) is possible due to the photovoltaic effect. “Photo” comes from the Greek for “light”; “voltaic” refers to the production of electricity and is a variant of Italian physicist Alessandro Volta’s name.
To illustrate how solar works, let’s follow the flow of energy through a small grid-tied residential system:
The first step in the process occurs when rays of light from the sun strike the cells within PV modules (modules are commonly called “panels”). As the light energy hits the photovoltaic cells, electrons are excited and begin to flow. Multiple cells are connected in one module, and several modules are connected together to form an array, all harnessing and summing the flow of this electric power.
The current produced in the PV modules is Direct Current (DC). However, most of the lights, appliances, and other electrical equipment in our homes operate on Alternating Current (AC). Next in the chain of energy flow is a device called an inverter, which gathers the DC produced by the array and converts it to AC which can be used in the home. The inverter regulates the AC power it outputs, so it can be safely used by even sensitive electronic devices such as televisions, computers, and audio equipment.
The AC output of the inverter is connected to the home’s main service panel, where it intermingles with the AC power supplied by the local electric utility. Net Metering refers to the physical (and financial) ability of a home’s electric meter to “run in both directions”. We are accustomed to power only flowing from the utility to the loads in our house. However, with the house now acting like a mini utility producing its own electricity, there will likely be times when electricity actually flows out of the house and to the utility.
A PV array produces electricity whenever the sun shines on it. This is true from sunrise until sunset, and often times even after the sun sets! (A full moon on a clear night can actually produce small amounts of current from a PV system.) Generally speaking, an array will produce its maximum power between roughly 9:00am and 3:00pm. During those hours, with the array pushing a strong flow of DC power into the inverter, and the inverter in turn delivering a strong flow of AC to the home, it is very likely that there will be a surplus of electric power available at the house. Why? During these hours, many homes are empty, while their occupants are off to work or school. Even for those at home during the day, their need for artificial lighting (typically about 25% of a home’s electricity consumption) will be much lower.
It is at night, when the members of our hypothetical family return home, that the electricity demand from the house increases as lights, air conditioners, televisions, and other loads are turned on. At the same time, the output of the PV system is winding down as the sun sets for the day. During these hours, the house will be a demander of power from the utility, rather than a supplier. Net metering keeps track of the net inflows and outflows of electricity throughout a billing period. The customer pays for what they use, minus the production of their array which is “sold back” to the utility.
Installing a photovoltaic electric generating system at your home or business will greatly reduce your energy costs and will have environmental benefits because it produces clean, green energy right here in the USA.