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| Left pointing arrow shows the meter is running backwards! |
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Net Metering
To account for the banking of the excess electricity on the
grid, our house uses net metering.
During the day our meter runs backward and at night it runs
forward. In the summer our total daily
meter reading steadily goes backward as we generate excess electricity. During the winter it goes the other way as we
use more electricity than we generate.
The power company reads the meter once per year, and send us a bill for
the year. So far that bill has been $0 as
we generate a small net excess each year.
Net metering requires no change to your electric meter – just an
accounting change at the power company.
We do get a small bill as we pay a minimal charge of $5.44 each month
for the privilege of being connected to the grid. This is more than fair considering the huge advantage
of being able to “bank” your excess electrons on the grid.
Break Even Point
Everyone wants to know how cost effective the solar system is and
when it (or if) will pay off.
So far my system has generated a total of 36,000 kWh (36 MW)
of electricity in 4 years of operation.
According to SDG&E’s website, the cost of electricity in San Diego is
$0.154/kWh. Thus we have generated $5544
worth of electricity or $1386/yr. So the
system will pay for itself in $19,000/($1386/yr) = 13.7 years. After this point for the rest of the system’s
estimated 25-year lifetime, the system saves me money. So over 25 year lifetime of the system, I
roughly double my investment. There are a lot of caveats to this calculation so
it has to be taken with a grain of salt.
First of all it doesn’t take into account a rise in the cost of
electricity. I think we can safely
assume it will go up – the question is how much will it go up. On the other hand, as the system ages it will
produce less electricity as the cells slowly break down. If cost is really an issue for you, consider
getting a system that generates about half of your electricity need over the
year but will generate plenty on a hot, sunny day. If you change over to time-of-day metering
you will be saving yourself from having to buy the more expensive summer
afternoon electricity and instead using only the cheaper cool night electricity
rates. Currently many people are paying
$0.30/kWh to run their air conditioner.
This would make the system pay for itself in half the time and have half
the capital outlay.
The Feel Good Factor
In spite of the economic advantages of the system, the main
benefit I derive from the system is the feel good factor. This really surprised me. Even if the system wasn’t going to break
even, I would do it again in a heartbeat.
First of all it is really cool.
The techie in me loves having the system – it is definitely among my
favorite possessions. I love to watch
the meter run backwards and watching the power displays on the Sunny Boys. The pioneer in me loves the fact that I am
energy self-sufficient. The greenie in
me loves the fact that I am reducing the carbon emission footprint of my
household. The good citizen in me is
content that I am helping out with the peak power problem and reducing the
possibility of a rolling blackout. You
might say that is a lot of money to feel good, but how many people do you know
who spent the same amount of money to buy a Lexus or Mercedes instead of a more
cost-effective Civic, just to feel good and impress the neighbors? That car will just last a few years and has
no redeeming benefits to society.
Advantage to the Power Grid
Obviously, the power company makes money by selling
electricity. So if everyone converted to
a rooftop solar system, there wouldn’t be any demand for their power. I doubt that will ever happen as most people
aren’t going to make the investment for many reasons – but a big one is that
you have to live in the same spot for many years (or move your solar system
with you) to realize the benefit of your investment monetarily. However, the biggest problem for power
companies is the fact that electricity use is not evenly distributed – the
largest demand is on hot summer days when all the air conditioners kick in, and
of course this is when the solar systems are producing the most. Power companies have to have enough capacity
to meet the peak demand which is wasteful the rest of the year. Each solar system on the grid reduces the
peak demand. In California there is an initiative to convert
a million homes to solar to reduce the peak demand and avert the possibility of
rolling blackouts that occurred in 2000 and 2005.
Maintenance
We don’t do anything to maintain the system. Being up on the roof, the panels don’t get
dirty and every once in a while some helpful rain washes the dirt off for us. I did once go up and wipe the modules with a
duster and got an increase of about 0.5% for my trouble. So now I just monitor the numbers on the
inverters. This all paid off this winter
when I noticed the right inverter was putting out half of the left inverter
when normally they are within a few percent of each other. We called Carlson Solar out and they quickly
found the problem was some water that had leaked into a module’s wiring and
produced a short. This was quickly
remedied (for free under warranty) and the modules are back up and
running. The problem had no real effect
on our total generation as it happened in winter and was fixed in a few days.
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