Solar electric or photovoltaic (PV) modules produce electricity from the sun’s light energy. You may have used solar cells many times without knowing it. Common applications include wrist watches and calculators, but solar cells can also be used to power household appliances, communications and water pumping equipment.
A photovoltaic system powering your home or business may be a “stand-alone” system (not connected to the utility grid), or “grid-connected”.
Question: How does the sun make electricity?
When sunlight hits a photovoltaic (PV) panel it passes through several layers of silicon which turn sunlight into electricity.
- When sunlight strikes the silicon layers, electrons move into the top layer.
- The electrons in the top layer flow into a wire, creating an electrical current.
- This electrical current, or electricity, is used to power an appliance.
- Once the electrons have passed through the appliance they flow to the bottom layer of silicon.
A stand-alone, or “off-grid” photovoltaic system will have the following principle components: photovoltaic modules that produce electricity; an inverter that converts direct current (DC) electricity to alternating current (AC) electricity (unless DC energy is directly used); batteries to store energy for use when more energy is needed than is being produced; wiring, disconnects, and other supporting components. A backup power generator is also generally built into the system.
Stand-alone photovoltaic systems are appropriate in remote locations, where utility power is not available or is cost-prohibitive to access. As a rule of thumb, stand-alone systems are more cost-effective when located more than ¼ mile from utility lines. At the present time, no rebates are available for stand-alone photovoltaic systems. Although this guide will be helpful for stand-alone systems, it is generally directed toward those wishing to “inter-tie” with the grid. Please contact RCEA for further information regarding stand-alone systems.
Question: What are the advantages of using photovoltaic energy?
- On-site green power production—no emissions.
- Longevity—modules generally guaranteed for 20-30 years.
- Low maintenance—long periods between regular maintenance.
- Quiet and Reliable—solid-state electronics; no moving parts
- Modular—easy to move and expand.
- Free and dependable energy.
- Independent—no future price increases.
- If you have batteries, your system could provide an uninterruptible power supply during utility power outages.
A grid-connected photovoltaic system will have the following principle components: photovoltaic modules that produce electricity; a specialized inverter which converts DC electricity to AC electricity; utility interconnection equipment; wiring, disconnects, and other supporting components. A grid-connected system may also include batteries to supply power in the event of a utility power outage. One benefit of grid-connected systems is that the utility “grid” serves as the storage “battery,” providing power when more electricity is needed than is being provided by the PV system. When used, batteries represent a significant part of a system’s costs and are not eligible for rebates.
“Net Metering” is the process by whichelectric consumers are credited for electrical power generated at their location at the same rate that the utility charges.
How It Works
With Net Metering, the PV system will have an electric meter that is capable
of spinning backward or is able to calculate both the electricity used
and produced. If the system generates more electricity than is consumed,
the meter spins backwards, diverting the excess electricity to the grid
for later use. If the system produces more energy than is consumed during
a billing cycle, then the customer will be credited. On an annual basis
a customer can furnish some or all of their electricity, but the utility
is not required to pay for or credit any excess electricity beyond a customer’s
bill. A minimal monthly service fee (currently $5-6/mo) will be charged.
An important benefit of ‘Net Metering” is that it allows the
PV system owner to use the grid as the energy storage system without needing
a battery backup system. This saves the customer the added expense of
installing a battery system, decreases maintenance requirements, and improves
the payback period on the system. (Systems without batteries will not
provide backup power during outages.)
When grid-connected systems are installed, regular utility electric meters are often replaced with “Time-of-Use” meters, which track electric usage by time of day. “Peak electricity”, from 12- 6 pm, is more expensive per kWh than “off peak” electricity. Because PV systems produce more electricity during “peak hours”, TOU meters allow maximum benefit from net metering, especially for people who use little electricity during daytime hours. TOU metering can have a significant positive impact on the economics of a PV system.
