Solar Roof


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This website describes the system of photovoltaic solar panels installed on the roof of my home in Wauwatosa, Wisconsin, USA. It is a 3.72 kW grid-tied system with parallel metering. (We also have a geothermal heating/cooling system.) Click on the tabs above to see the following information, or scroll down for recent news.

Recent News

2013 June 14 Sometime in early May, our solar meter rolled over 20,000 kWh of electricity generated, which corresponds to a savings of over 15 tons of CO2. Also, this latest utility bill represents five full years of data. Overall, we have generated 20,426 kWh and used 27,416 kWh, which means we make 75% of the energy we use. Geothermal optimization is nearly complete, so we expect next winter's data to be excellent.

2011 June 15 We now have three full years of data, which show we have generated 73% of our electricity overall. Consumption was much higher this winter, due to the geothermal system, which uses electricity for heating instead of gas. However, we have experimented with the geothermal changeover threshold, and so we expect this effect to be less noticeable next winter.

2011 February 08 January's production was lower than usual, because we've had a lot of snow. It usually melts off the panels by itself in a day or two (as long as the temperatures aren't too cold), but this month we had snow every two or three days between January 10th and February 2nd, so we made very little energy during that time.

2010 November 02 Sometime during the late morning, our solar meter rolled over to five digits, so we have now generated over 10,000 kWh in the nearly 29 months the system has been online! (As a species, we have a strange propensity to celebrate arbitrary numerical milestones.) This represents over 7 tons of CO2 that we prevented from being added to the atmosphere.

2010 September 08 Our home will be listed on the MREA Solar Tour again this year. Feel free to drop by on Saturday, October 2nd, to see our installation and ask questions.

2010 August 15 This summer (especially July) has been hotter and rainier than usual, which is a bad combination for solar power, because our air conditioner has been using a lot of electricity, but our solar panels can't generate much. However, we replaced our traditional air conditioner with a geothermal heating/cooling system in mid-July. It has now been online for one full utility billing cycle, and initial data indicates it will yield a significant savings on our summer electricity consumption.

2010 June 16 With the arrival of this month's utility bill, we now have 24 months of data, and the total result is 8068 kWh generated and 9074 kWh consumed, which means we have generated 89% of our electricity overall. Looking at just the last 12 months, we generated 3995 kWh and used 4295 kWh, which is 93% and represents a significant increase over the first 12 months.

2010 March 17 The arrival of the March data on the Performance page signals the end of the "dark" season, with sunny days now generating as much as 15 kWh and the overall generation for the month rising to 80% of our usage.

2010 January 21 We now have a full calendar year of data on the Performance page, showing we generated 92% of the electricity we used in 2009, despite having a cloudier-than-usual autumn. The year includes four months in which the percentage was above 100%.

2009 June 16 We have now received twelve utility bills since the solar array was installed a year ago. In the first year of operation, we generated 4073 kWh and consumed 4779 kWh, so we made 85% of the electricity we used! At the rate of 1.556 lb CO2 per kWh (see FAQ #6), this means we saved over 3 tons of CO2. We expect to have even better results in the next year, because our summer and fall production should be higher as a result of the inverter calibration performed by Magnetek field engineer Tron Melzl in November 2008.

2009 April 15 For the first time since the system was installed, we generated more energy in a one-month billing period than we consumed! That's very exciting news, and I think we can now expect that to happen for 2-3 months each spring and autumn.

2009 March 14 Feb-Mar data is now available on the Performance page. Winter is definitely over (from a solar perspective, at least)! Not only did our overall generation for the month exceed last year's Sep-Oct data, but the latest graph in the Daily Performance section shows very little shading, and it is clear that the flat-top problem is gone.

2009 February 13 We Energies posted my Jan-Feb utility bill, so I've updated the Performance page with new data. Sunlight has returned to its Oct-Nov levels, but we're still spending a lot of money on gas for heating. Also, I've posted a lot of new detailed analyses of the Daily Performance graphs at the bottom of the Performance page.

2009 January 27 I added another batch of pictures on the Performance page showing the graph of energy produced on cloudless days. It's interesting to see the sources of shade in the winter are completely different than in the summer. There's also a picture showing a summary of the whole year 2008.

2009 January 15 Our cash-back reward check from Focus on Energy finally arrived! (It wasn't the Focus people's fault--they were waiting for paperwork from the consultant who did my Home Performance Audit.) Also, our latest utility bill was just posted, so I've updated the Performance page with this month's dismal numbers. In general, the snow melts off the panels all by itself in a day or two after a snowfall, but it snows every two or three days, so the panels seem to be covered more often than not. Couple that with the facts that there are very few sunny days in a Wisconsin winter and they are pretty short days anyway, and you can see why we only generated 27% of our electricity this past month.

2009 January 5 Considering having solar panels installed on your house? Well, there's good news and bad news. The bad news is that We Energies is no longer offering its Solar Buy-Back Rate (see FAQ #3), because it has received so many applications that the program is full. The good news is that as of 2009 the $2000 cap on the federal government's tax credit has been lifted (see FAQ #2), so you can now claim the full 30% of your installation costs. In my case, I estimate the Solar Buy-Back Rate is worth about $5000 to me, but I would have gotten an extra $5000 or so if my tax credit wasn't capped, so it's pretty much a wash.

2008 December 25 Merry Christmas! The garage's solar panel is closer to the ground, so I've been able to keep it swept clear of snow. On the few sunny days we've had this month, it has stored enough power in the battery array to power a string of LED lights on my garage for about six hours each evening all month.

2008 December 21 This is the shortest day of the year. I've noticed two effects: (1) the graph on my inverter's display is much narrower than in the summer (I'll post more pictures on the Performance page soon), and (2) the sun now rises/sets far enough to the south that my dormer isn't shading the panels at all, but the neighbor's roof is!

2008 December 17 Snow has been an issue. Although we've had a couple of light snowfalls that have melted clear the next day, a nasty combination of heavy snow and freezing rain on 11/30 didn't finally melt off the panels until 12/13. I tried sweeping it off with a push broom duct-taped to some extension poles, but it was packed on too well. I don't want to try scraping with a roof rake, because I'm afraid of scratching the panels' cover glass.