As I write, Maine’s first ownership-based community solar farm is taking shape at the edge of a field in Edgecomb. The solar farm will be a large solar photovoltaic system, mounted partly on the barn roof and partly on the foreground, and jointly owned by the members of the Edgecomb Community Solar Farm Association. Designed and installed by ReVision Energy, a Maine company, it will generate 46.9 kilowatts of power.
Solar photovoltaic panels generate power by converting incoming solar radiation (light) into electricity. They do this by means of solar cells that consist of a sandwich assembly of two wafers of crystalline silicon, one doped with phosphorus, the other with boron.
When this assembly is exposed to sunlight, the phosphorus-doped (top) layer gains a negative charge, the boron-doped one a positive charge. Thus, one side of the cell develops a surplus of electrons and the other one a shortage of them. The junction separating the two differently charged wafers prevents equalization, so in an external circuit connecting the two wafers, useful electric current is generated.
Solar panels are made up of a number of cells and a solar array is made up of a number of panels. The array of the Edgecomb solar farm will generate 660-volt direct current, converted by inverters to 120/240-volt alternating current to match the requirements of the power grid. The number of solar panels is determined on the basis of each member’s power demand. The average residential system requires a 5-kW solar array.
Those of us with a shade-free, south-facing roof can install our own solar panels, but people whose roof faces in the wrong direction, or whose roof is shaded by trees, cannot do so. A community solar farm provides an opportunity to tap into solar power for those who lack good solar access.
According to current law, up to nine members may create a jointly owned and operated solar array generating up to 660 kW of power. The size of each member’s share is determined the same way as those with a solar roof.
The idea is to generate as much of our own power as possible, feeding any excess, under a net metering contract, into the power grid for credit. We then use this credit at times we don’t generate enough power of our own, for example, on cloudy winter days.
Net metering works as long as a utility account-holder’s residence or business and his or her solar panels are located in the service territory of the same utility, such as Central Maine Power Co.
In case of a solar farm, the total output of the farm is banked with the utility and credited to each farm-member’s individual electric bill according to the member’s percentage share in the solar farm.
Currently solar electricity is a very good investment and a number of financing options are available. In addition to net metering, a federal tax credit equal to 30 percent of the installed cost of the system (prorated in case of a solar farm) is also available. We will explore these options and the science behind them in future “Energy Matters” columns.
(Energy Matters is offered under the auspices of the Midcoast Green Collaborative of which Paul Kando is a co-founder. Through informational forums, energy audits and hands on workshops, the Midcoast Green Collaborative works to promote environmental protection and economic development via energy conservation. For more information please visit the website www.midcoastgreencollaborative.org.)