How Do Solar PV Systems Work?

Each solar panel receives the energy from the sun as photons. The panel is able to harvest these photons and convert them into electricity. Solar panels can typically convert about 13% of the energy they receive into actual electricity. The solar panels convert the sun's energy into DC voltage.

The DC voltage output of the solar array needs to be converted into 60 Hz AC power and have its voltage either increased or decreased to 120V. This is what the inverter does. It takes the solar array's DC power and transforms it into your house and utility grid's 120V AC, 60 Hz electricity. The inverter is typically mounted close to your electric panel either on the inside or outside wall.

The 120V AC power leaving the inverter is then connected directly to a dedicated breaker in your home's main electric panel. This ties in the solar electricity to all of your house's electrical loads and to the entire utility grid. Essentially your system is always a part of the utility grid, much like a drop of water is to the sea.

During the day time, when no one is home and the sun is shining, your solar electricity will easily be able to power any items that are left on, plus there will be much excess energy that will flow back into the grid. For your solar energy to go into the grid it must flow "backwards" through your electric meter. This results in the kWh reported to the utility company to be less and less throughout the day. Essentially you are decreasing the amount of money you will have to pay to the utility company at month's end. If it is a sunny family weekend at the house with air conditioners and all other appliances running, then most likely all of your solar energy will be used and any additional power that you need will come from the utility grid. Since only a small amount will be from the utility grid, your meter will only spin forward minimally compared to what it would have if you didn't have solar. Once again, resulting in less money that you pay to your utility company.

When you think of it, the utility company is really like a big electrical savings bank from which you can deposit solar credits in the day time and withdraw them at night time. This also works for the summer and winter months, because if you continually deposit more solar kWh's than you use in the summer, they are available for usage in the winter time when you can start withdrawing them.

In Washington we are very fortunate to have additional incentive programs that reward us for the solar energy produced every year. For this to be possible, it is necessary to know exactly how much solar energy (kWh) your system produced for the year, regardless if you use it or not. This requires that an additional electric meter be installed in between the inverter and your house's electric panel, so that it can record all your solar kWh's before your house or the utility grid uses them. Regardless if you use the solar energy or if any un-used solar energy feeds backwards into the utility grid, your solar meter records every single kWh of it. Every year this meter is read by your utility company and a check is written to you for $.15 per kWh, up to a maximum of $5000 per year.

The above explanation should make it easier to understand how a solar energy system interfaces with your home or business and the utility grid. In review:

• The solar panels are connected in series somewhat like batteries to generate the final system DC voltage
• The solar array's output is routed from the roof to the inverter (normally mounted next to the electric panel)
• The inverter converts the solar array's power from a high voltage DC to a clean 120V AC.
• The 120V AC output of the inverter goes through a dedicated electric meter whose only function is to record all the solar energy kWh that are produced for the entire year.
• The 120V AC continues to flow from the solar meter to a dedicated breaker in your house's electric panel.
• This integrates your solar electricity to both your house and the utility grid.
• When your solar system is providing the exact amount of power that your house is currently using, then your electric meter will stand still.
• When your solar system is providing more power than your house or business is using, then any excess will flow backwards through the utility meter and you will be building a credit with your utility company.
• When your solar system is providing less power than your house is using, then the utility grid will provide the rest; however, your meter will be spinning forward only for the excess electricity that is required.

We hope this explanation was helpful and for any further questions please call Sunergy Systems at (206) 297-0086.