Net
MeteringWhen
installing a grid tied PV system, one that remains connected to the municipal
power supply, you become a mini power producer for the local utility, thanks to
an agreement called “net metering”. In the Florida Keys
the customer obtains the full retail electricity rate for kilowatt-hours
of PV produced electricity sent to the utility power grid. Essentially the
customer is billed for the net electricity purchased from the utility over the
entire billing period, which is the difference between the electricity used
from the power grid and the electricity generated by the PV system. The
electricity company also benefits because solar-generated power often coincides
with the “peak” periods of demand for electricity in turn reducing the amount
of the most expensive electricity that a utility would have to buy, which is
good for everyone in the community.
Basic System Operation
As sunlight hits the solar
panel's cells, direct current (DC) flows through the inverter, which converts
it to alternating current (AC). The AC power then flows directly into the
building (if there is demand), or into backup batteries if the system has them,
or to the utility. When the power is flowing back to the utility grid, the
electricity meter turns backward.
Solar Panel Components Photovoltaic cells are the core of
the solar panel. They are made up of at least two layers of semiconductor
material (usually pure silicon infused with boron and phosphorous). One layer
has a positive charge, the other a negative charge. When sunlight strikes the
solar panel, photons from the light are absorbed by the semiconductor atoms,
which then release electrons. The electrons, freed from the negative layer of
semiconductor, flow to the positive layer--thereby producing an electrical
current. Since the electric current flows in one direction (like a battery),
the electricity generated is called direct current (DC). Many individual cells
are wired together in a sealed weatherproof unit called a solar module or
panel.
Each of these solar panel types is estimated to last at least twenty-five years; some estimate that forty years is a reasonable expectation. The longevity rating of a solar panel refers to the number of years before the unit starts producing only 80 percent of its original power rating. For instance, some solar panels are warranted to produce at least 80 percent of their full-rated power after twenty-five years. Instead of stopping production completely, a solar panel will gradually produce less and less power over decades. Single-crystal solar panels are currently the most efficient type available, meaning that they produce the most power per square foot of module. The cells are fragile so they must be mounted in a rigid frame, and the solar panels usually have a polka dot or checkered pattern.