I finally had a chance to sit down and go through my solar numbers for 2014 and they look pretty good! Over the course of the year I generated a sizable surplus of power, about 35% more than I used.
Read MoreSolar Performance - December 2014
Despite being the lowest producing month of the year my numbers for December 2014 turned out to be really good compared to the installer's estimate. In fact, the DC production was 47% more than the estimate of 43 kWh at nearly 72 kWh. AC production was lower (63 kWh) due to DC-to-AC conversion losses. As expected my solar production wasn't enough to meet my usage needs for any day this month, though overall about 34% of my use was provided by the solar panels on my roof.
Read MoreAerial View & System Summary
At long last I finally found an aerial view of my roof taken after my solar panels were installed, courtesy of nearmap.com. It's fun to see how the panels are actually laid out, though the resolution here isn't high enough to see the tilt of the roof underneath. This imagery is from September 5, 2014.
Read MoreWinter Solstice: Solar Power vs. Day Length
Now that I've got a year of data under my belt I thought it would be interesting to compare my production with the length of the day. The chart below shows my daily solar production (in kWh) in blue and the length of the day (in hours) in red.
Read MoreSolar Performance - November 2014
Fall is definitely here. I only had one day this month with a surplus of power, and total production dropped under 100 kWh. On the bright side the panels still produced more than estimated, about 48% of my power use for the month.
Read MoreSolar Snow Day, Followup
Following up on the snow day post from a few days ago, here's what happened as the snow melted. Looks like it took about three to four days to get back to normal. Temperatures were in the middle to upper 30's during the day and below freezing at night.
Read MoreSolar Snow Day!
Even solar panels take the day off when it snows.
Read MoreThe Shape of Days, and a Fall Mystery
In mid-November Seattle had a series of unexpectedly clear sunny days between storm fronts that provided a great opportunity to compare my Fall solar production with sunny Summer days.
Read MoreSolar Power, One Year In
On November 21st I finished my first year of solar power with good news: I still had a surplus of power sold to Seattle City Light! Despite using just over 2500 kWh for the year I sold an extra 718 kWh. This just goes to show that solar power really does work in Seattle!
Read MoreDC to AC Conversion Efficiency
One source of loss with a solar power system is the conversion of the DC power produced by the panels to the AC power used by the electric grid. This is done by a piece of equipment called an inverter. I was curious to see how my setup compared to the spec, so I pulled data for December 2013 through October 2014.
Read MorePersonal Driving Trends
Solar Performance - October 2014
I managed to barely squeak through October with a net monthly surplus of power, just 5.68 kWh (for reference that's about a day's worth of usage). November will almost certainly be chipping away at my current annual surplus. Artisan Electric stopped by towards the end of the month to do my first annual inspection and cleaning and found that everything is right on track compared to their pre-install estimates.
Read MoreSolar Nemesis: Rain
Over the course of the day my poor solar panels weren't even able to produce half a kilowatt-hour of energy; their total for the day was just 494 Wh. In comparison, on a sunny summer's day the same system was able to produce that much power in just 11 minutes during the peak period.
Read MoreSolar Performance - September 2014
As expected given the waning days and increasing number of cloudy days production was down compared to last month's. My usage was also down a bit thanks to the cooler weather (I have yet to turn on the heat).
Read MoreAnother Bill, Another Credit
Without any solar panels I would have used 427 kWh at a cost of about $21.60, so in terms of my bill the panels saved me about $29.40. The state incentives, as usual, made up the lion's share of the financial savings, with the 773 kWh generated being worth about $417.42 in incentives compared to $39.11 in sales.
Read MoreWater Use is on the Rise
Over the last year I've done a fairly good job containing my electric and gas bills, but the water bill remains frustratingly high. In fact, it's been increasing pretty steadily.
My average daily use has been increasing every year.
Some of this increase can be attributed to the roommate I had last fall and winter (November 2013 - May 2014 bills) but the trend is up. I also have trouble figuring out where all of this water is going. The toilets are only 1.6 gpf which leaves quite a lot of water to account for every day. In the summer I use a fair amount watering the plants (the poor rain barrel only holds a couple day's worth), but that should be zeroed out in the winter. I really wish I could get a monitor like the eGauge for my water usage or at least a daily meter reading. For now, I'd better work on reducing my shower time.
Solar Shading, or, the Power of Pruning
Earlier this year I noticed that one of my panels, A2, was having a noticeable dip in power production compared to the other panels for a few hours every afternoon. A neighboring panel, A3, showed a similar problem but to a much lesser extent. The remaining panels nearby operated normally. Even though there's a tree nearby I'd originally dismissed shading as a problem since the none of the other panels were affected, but when the engineers at Tigo looked at my data they concluded that everything was operating normally and that shading must be to blame.
Panel A2 matches A1 for the first half of the day, then dives down for a few hours in the afternoon.
A few days ago I borrowed a pole pruner from a friend and was able to remove the offending branches:
Before pruning on the left, after pruning on the right.
Removing those branches seems to have fixed the problem! Just goes to show that even a few small tree limbs can significantly affect solar production. From January through August that little dip cost me a total of about 40 kWh of production. That's enough to drive a Nissan Leaf over 125 miles!
No more shading problems!
Solar Performance - August 2014
Production in August was down from July, and roughly the same as April. This makes sense given the shorter, cloudier days of late. Use was also down slightly as the cooler temperatures meant I didn't need to run the fans and air conditioning quite as much.
Solar production, grid purchase/sale, and use.
As expected, the system continued to generate a surplus of power for the month. It's on track to have a surplus on an annual basis as well! Unfortunately, panels A13 and A14 were out of commission for the first half of the month until the defective Tigo unit was replaced. Combined with the days they missed last month they are noticeably lower than the rest of the system. Panel A2 is definitely lagging due to the afternoon shading.
Percent of household energy use produced by solar.
Cumulative production by panel (DC).
Production is a bit under the installer's estimate, mainly due to the bad panels, but is still pretty much on target.
Comparison with installer's estimate.
Breaking the data out by day there were only a handful of days that the system wasn't able to generate more power than I needed. Some of these were laundry days (the dryer is a killer!) while others were just very gloomy weather.
Daily solar production, grid purchase/sale, and use.
Percent of household energy use produced by solar.
At the panel level, shading is still having a noticeable effect on panel A2, while the outages on panels A13 and A14 reduced production significantly.
Energy by panel, broken out by day. The lack of output on panel A14 (covering the dots for A13) is very apparent.
Noticeable loss of output on panels A2, A13, and A14.
This demonstrates why I wanted to make this chart: under-performing panels are easy to spot.
Hourly production shows a peak level similar to April but is shifted about an hour later in the day. I should try to find a solar elevation chart to see if this correlates.
Production by hour for the past 6 months.
The financial performance continues to be quite good, with the Renewable Energy Credit (REC) from the state bringing in the majority of the income.
REC payments are dominating the net-metering savings.
Lastly, a few more esoteric graphs.
Total production by panel direction.
Production normalized by the number of panels (8 East, 6 West).
DC to AC conversion efficiency was pretty uniform. I've noticed in the past that it drops off noticeably for lower output levels.