On average we use from 15 - 30kWh/day. This powers
our home, charges our Chevy Volt (around 10kWh/day) and 2 home based businesses with all the computers and
relevant equipment. For reference, average US homes consume
upwards of 25 kWh/day. If we were to eliminate all the business
usage I believe we would average below 13kWh/day.
The design goal of the system is to generate some surplus power
in the summer months
and much less in the middle of
winter, averaging about 80-90% of our needs annually. Our
31 - panels produce
5.8kW of power in theory, but that ideal
performance is derated due to orientation and efficiency issues so the actual peak power is
4.5kW in the summer. As I observe the overall power over months, the
seasonal variation of available sun hours becomes quite clear
(see Lifetime Energy below).
The
chart below shows the estimated power that my solar panels
should generate based on
calculations from the
PVwatts calculator provided by the National Renewable Energy
Labs. The actual energy produced is obtained from monthly
reports provided by the Enphase Enlighten web interface
(above).
I update the graphs in the middle of each month after I
get my utility bill.
Our electrical power usage varies a lot due to variations in
our business use of energy intensive tools, lighting and
computers. Energy consumption also peaks in the
winter when we use small electric heaters to supplement our
propane and wood stoves when outside temperatures stay below
20F for weeks. When we purchased the
Chevy Volt in May
2012 our monthly usage went up by around 300kWh/month.
Chart shows power imported from utility in blue, and the net power
we used from the grid after factoring the solar power we exported
back to the utility (for full retail credit under the Net Metering
contract we have with the utility). Basically, the chart shows
how much energy we saved by using solar power, which is clearly more
in the summer months. We get about 1/3 of the solar energy in
the winter compared to the summer. About 10kWh on a sunny day
in winter compared to a peak of around 30 kWh/day in the summer.
Electric rates have been dropping lately. In 2010
we paid around $.15/kWh, in 2013 it is now around
$.13/kWh
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