On average I use from 15 - 30kWh/day. This powers
my home, charges my Chevy Volt (around 10kWh/day) and home based
relevant equipment. For reference, average US homes consume
upwards of 25 kWh/day. If we were to eliminate all the business
usage I believe I 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 my needs annually. The 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).
chart below shows the estimated power that my solar panels
should generate based on
calculations (see bottom of page) from the
PVwatts calculator provided by the National Renewable Energy
Labs. The calculations factor in weather data from the
nearest reporting weather station to account for seasonal
overcast. The actual energy produced is obtained from
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.
Enphase have released a study showing that their microinverters
out perform PVWatts calculations by up to 8%. They
looked at regular string inverters and found that they
underperformed PVWatts numbers by up to 8%. So this
validates my decision to invest in Enphase inverters.
My electrical power usage varies a lot due to variations in
my business use of energy intensive tools, lighting and
computers. Energy consumption also peaks in the
winter when I use small electric heaters to supplement the
propane and wood stoves when outside temperatures stay below
20F for weeks. When I purchased the
Chevy Volt in May
2012 my monthly usage went up by around 3-400kWh/month.
The chart above shows
power imported from utility in red,
solar energy generated in yellow
net power in green. Basically, the chart shows how much energy I
saved by using solar power, which is clearly more in the summer
months. At my latitude in Maine USA (44 degrees) we get about 1/3
of the solar energy in the winter compared to the summer.
My Chevy Volt uses 3-400kWh/ month year round, and the house about
the same - but both have seasonal variations that increase in
In the chart below, blue
shows energy imported, yellow
solar energy produced and
green is the net amount I'm billed for.
As you can see it goes negative in the summer as I
accumulate credit that gets used up in the Fall.
Here is the chart generated by the PV Watts