This video is from The US Department of Energy.
Solar PV is a pollution-free way to produce your own electricity. Solar cells generate electricity whenever sunlight is present and produce the most power when the sun shines directly on the panels (mid-day).
The amount of electricity generated by a solar system depends upon its location (where in the state), shade the site is from trees or other buildings, how large the system is (how many panels), and the power output capacity of the solar panels.
Grid-Tied: Solar PV delivers electricity to a building that is already connected to the electric grid thereby replacing power the building would have needed to purchase from the utility. However, during a power outage, the solar electricity is automatically disconnected and thus solar without batteries is not a source of backup power.
Off-Grid: Solar PV generates electricity for that is stored in batteries. Solar charges up the batteries throughout the daytime and the electricity is drawn from the batteries during the daytime or overnight. Off grid PV is used to power remote homes or cabins, boats, RVs and other uses.
Rooftop Solar PV for Grid-Connected Buildings
A common standard rooftop PV module (panel) is a 60 cell panel that is comprised of 60 solar wafers strung together, covered with tempered glass and a protective back sheet, and held within a sturdy aluminum frame. The panel measures roughly 66 inches by 40 inches by 2 inches in height. Another common module size is 72 cells. Smaller size modules are also common for uses such as boats and RVs.
The number of solar panels needed to power your grid-connected building is determined by the annual electrical usage of the building in kilowatt hours (kWh) and by the amount of useable roof space that faces west, southwest, south, southeast or east.
When determining the best size solar system, it is helpful to first do as much as you can through energy efficiency to reduce the amount of electricity you need annually, and to plan for future uses such as the addition of charging an electric vehicle.
The common term used to describe a solar system’s size is KW. Systems that range in size from 1 KW to <12 KW are considered “residential” in size. (See Solar Incentives page.)
1 KW is not the same as 1 solar panel. Panels are tested at the manufacturing facility and graded according to their wattage. Today’s solar panels range in wattages from around 200 watts to 340 wattage. This number relates to their power output.
The number of panels in a system (for example, 12) multiplied by the wattage of each panel (for example, 300w) equals the solar system size (in this example, 3600 watts or 3.6 KW).
Solar PV can also be placed onto poles or ground mounts. In these instances electric wiring brings power to a nearby building and the wires must be buried underground from the solar structure to the building.
The primary components in a solar system are:
- Modules (aka panels)
- Roof racking or means of attachment to the roof, pole or ground mount
To ensure the consistency and quality of PV systems and increase consumer confidence in system performance, various groups -- such as the Institute of Electrical and Electronics Engineers (IEEE), the International Electrotechnical Commission (IEC), and the American Society for Testing and Materials (ASTM) -- are working on standards and performance criteria for PV systems.
A more recent advancement in the generation of electricity from solar cells is the use of flexible layers of semiconductor materials. Though not yet manufactured in Washington, thin film can be used as
- Rooftop or solar shingles
- Roof tiles
- Building facades
- Glazing for skylights or atria.
Thin Film produces less power at lower efficiency and currently at greater expense. Research continues to make this form of solar cell viable.
In the Solar Research section of our website, you can find out about other solar substances being researched here in WA.
Solar Panel Recycling
Efforts are being made to address the recycling of damaged and/or decommissioned solar PV panels. Here is a list of links for more information about this topic.
- The Washington State Department of Ecology website has information concerning current legislation and manufacturer guidance.
- HB 2645 concerning the photovoltaic module stewardship and takeback program which was passed in 2020, but later vetoed by Governor Inslee due to pandemic related budget cuts.
- Solar Washington addressed this topic at the 2019 Washington State Solar Summit. See the session on "Solar panel recycling & addressing the current Washington recycling legislation (Photovoltaic module stewardship and takeback program)". (Note that information from this presentation may have been updated in the interim.)