Tuesday, November 07, 2006

Solar Panels: What We Got

Great dreams can be dashed quickly by a dose of reality. When the sales representative from Sunlight Solar (John Sych) came to do an analysis of the house, he quickly pointed out the pros and cons. A great pro was that the roof was sloped at a good 45 degrees, so it was well positioned for sunlight in both the winter and summer. One con is that the roof was oriented some to the East Southeast, as opposed to directly South, so the exposure to the Sun's path wasn't ideal, but that was a minor thing. The biggest con was definitely the trees on our property and our neighbor's property.

I had been eyeing our offending trees for some time and was looking for an excuse to take them down. The solar panel was definitely going to be the excuse, but our neighbor's trees were another matter. It was pointed out that the neighbor's trees were the bigger offenders, and they would cut the afternoon sun rather significantly. Not thinking it that big of a deal, I told him that wouldn't affect my decision, but then John informed me that the rebate is contingent upon a system that doesn't have too much shade.

To get the rebate at the time that I got it (the rules have since changed slightly), the solar panel system needs to produce 75% or more of the theoretical amount for a system oriented south at the best angle and with no shading. John's guess that a system on our roof would be close to failing the test, but he'd have to take the measurements and get back to me, and sure enough, the initial design failed.

After speaking with the neighbors, they agreed to let me take one of the shading trees down, but not the worst one (it is a nice tree, I have to admit) provided I paid for the removal. Putting the federal tax credit towards that, getting the array still made sense. So, we cut the tree down along with some in my yard. John came back out and said he could get an array to pass, but it would have to be smaller in size than originally intended to get the system to pass the efficiency requirement. Done! The picture below shows the front roof in the late afternoon in early November, the shadow of the neighbor's tree is clearly present.

The original plan of covering the front and some of the back roof to max out the rebate was thereby reduced to about a third of the original desired size. Of course I could still put more up, but it would mean foregoing the rebate, and without the rebate, the economics aren't as clear cut. In the meantime, I keep eyeing that neighbor's tree. If we had thought about it before we did the renovation, I'm guessing we would have tried to put a roof up in the back that wouldn't have had the shading issues and built our expansion around a good solar roof, but that is definitely hindsight.

We ended up with a 2.58 kilowatt peak array consisting of 12 of the 215 watt Sunpower panels (www.sunpowercorp.com), and a 2 kilowatt inverter (www.pvpowered.com) that converts the DC power from the panels into AC power that is on the electric grid.

The installation was done by Sunlight Solar by early May, 2006, and it went off pretty much without a hitch. All I did was write 3 checks, namely an initial deposit, a midpoint payment, and a final one upon state inspection. They took care of the rebate, and it all went exceedingly well. Since then, the panel has worked as advertised, producing the power at the rate that they estimated it would.

In the summer, the 2.5KW array should cover 30% of the power needs (based upon the usage we had prior to our renovation), but it only gives 10-15% of our historical power usage in the winter. The smallness of these numbers speaks to the difficulty of replacing all fossil fuel plants with solar panels--it just isn't so easy. A need exists to become more efficient with the generated power to make it work autonomously, or a serious reduction in living standards would be required. One area of work in the future is to deal with this issue. A combination of more panels and better use may do it, but we'll have to see.

I'll post more on the performance of the solar panels and how much it is relative to our electricity use. Part of the problem is that we are still having work done on the house, so we haven't reached our normal usage patterns yet. This doesn't affect the amount generated, but it speaks to the expected coverage of our needs from solar alone.

An interesting question to ask is how much did our array help in reducing our dependence on oil, and specifically foreign oil. The answer is a surprisingly small. That is the subject of the next post.


Blogger Markku said...


I live in southwestern Finland at 61N. My wife and I live in a rowhouse with a total floor area of about 800-900 square feet. We have the following electrical appliances: one microwave oven, one electical oven, one electrical stove with electric ventilation over it, two refridgerators, two freezers, about 15-20 lightbulbs, a few fluorescent tubes, one television, one VCR, one DVD player, one laptop computer, one toaster, one coffeemaker, one washing machine, one dishwashing machine, one rechargeable electric toothbrush, two cell phones, one hair dryer, one stereo with two small loudspeakers, and an electric sauna (power 2kW but used less than once every two months for an hour or so at a time).

Our average power consumption per year is about 500 watts, which translates into about 4000 kWhs per year. We don't have AC because it is rarely needed in our climate. Afternoon outside temperatures tend to reach 77 degrees only in July. 86 degrees tends exceeded only on a couple of days per year.

Our building has district heating. The heat comes from a gas fired district heating plant less than a mile away.

We dry our clothes on a rack outside in the summer and inside the sauna in the winter (without heating the sauna).

Average solar radiation intensity (at ground level) during the year where I live is similar to that near the southern coast of Alaska, that is, about 3 kWh/24h/m^2. Assuming 10% efficiency at converting that into ac, the average daily power output per m^2 from solar panels on our rooftop could be 10W. Most of the 50 m^2 of panels required to theoretically meet all of our electricity needs could fit on the southern side of our roof. We'd probably have to cut down one more large tree on our yard to minimize shade. But nothing could be done about the ones lining the street on the southwestern side. But they are not a signifigant problem at least in the summer.

Electricity is relatively cheap in Finland compared to the rest of Europe: about 10 cents (euro) per kWh. As far as I know, there are no tax rebates from installing photovoltaics but I could be wrong. I don't recall experiencing the slightest disturbances in the grid for decades.

I've heard that Americans usually dry their clothes in a dryer instead of hanging it to dry on a rack or a line. Using a dryer doesn't seem to save much labor to me. Life without AC, however, must be very uncomfortable in large parts of North America in the summer.

Can your air conditioning work in reverse in the winter - as an air heat pump?

3:57 AM, November 23, 2006  
Blogger Going Green said...

Hello markku:

It is interesting to see the difference between you and us. We have 4200 square feet, a few more lightbulbs, and I'm guessing our appliances are not as efficient as yours. Our daily consumption is over 2kW, four times yours.

Our panels generate 2420 kWh per year, so if your house was at our place and the lifestyle was the same, the panels would generate half of your usage. Shading is a big issue and prevents us from installing more panels. I think the proponents of solar underestimate the problem.

The two appliances in terms of electricity use are the clothes dryer and the oven.

The dryer is rated at 5 kW and is a big power hog. I'd disagree with you about the dryer. It is much easier than the clothes line. Drying times are less, the time to put the clothes on the lines are saved, and the clothes come out softer. Still, it is a problem, and I'm trying to figure out how to lower the usage without a lifestyle reduction.

AC is definitely an issue for Americans that most Europeans worry less about. We just put in a heat pump that does heating and cooling. I'll describe that in a later post.

6:27 AM, November 26, 2006  
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