Solar panels are also known as solar photovoltaic panels or solar PV systems. These are not to be confused with solar thermal systems, which use the sun to generate hot water. Photovoltaic panels sit on your roof and gather energy from the sun and generate DC (direct current) electricity.
Each panel has its own micro-inverter connected to it which converts the DC power into AC (alternating current) electricity, which can be used to power appliances in your house and can be sold back to the utility company. Before the recent invention of cost-effective micro-inverters, a single inverter was used. These had a useful lifetime less than the panels themselves, were expensive to replace and reduced the flexibility of panel configurations you could have. If you receive an estimate that doesn’t use micro-inverters, you should ask for them.
To understand how the excess electricity you generate can be sold back to the electric company, picture the electrical wires as if they were pipes and the electricity as water in those pipes. Before you install solar panels, the electricity only flows one way – from the power lines into your house and into your television, refrigerator, light bulbs and curling irons. But once you have solar panels generating electricity, it will not only go into your appliances but any excess will also flow out of your house and join the electricity generated by your utility. At these times, your electric meter will actually spin or count backwards as electricity is flowing out of your house. This is called Net Metering, whereby you are only charged for the net electricity you use. Massachusetts is a Net Metering state.
Each panel is typically 5 ft. x 3 ft., weighs around 40 lbs. and generates between 150 and 250 Watts of DC electricity per hour. For Commonwealth Rebate purposes, a 5,000 Watt (5 kW) system is optimum to minimize your cost per Watt, regardless of individual panel size. So that works out to between 20 and 33 panels.
Since your solar panels will generate more electricity the more they are in direct sunlight, they will perform best on a south facing roof if you live in Massachusetts, since the sun travels from east to west across the southern sky. However, solar panels can also be placed on eastern and western facing roofs and angled appropriately. They even have ground-mounted solar arrays. In any case, the most important factor is consistent sunlight for a large part of the day, free from significant tree shade. Whichever installer you select can do a quick shading analysis (this can be estimated without even being on site) to determine if your system will operate with at least 80% of the optimal output. If not, you won’t qualify for the Commonwealth Solar rebate and solar panels are probably not right for you.
Here’s a picture of my roof before I got solar panels (up is north). Note that it is free from shadows. Also note that I have two southerly facing roof surfaces, one facing SE and one facing SW. My solar provider put 12 panels on the SE side and put the remaining 9 panels (totalling 5 kW) on the SW side. The SE panels will generate electricity in the morning and the SW panels will generate electricity in the afternoon, with both of them generating power midday.
If after reading this, you think you’ve got the sunlight to support solar panels, then read on to learn about the Commonwealth Solar Rebate program.
If you already know all about the rebate, then choose one of the other pages from the menu on the left or claim your $500 discount now on the solar company ratings page.