Size matters: Solar radiation falls on the earth at 1366 Watts/meter² at midday in the summer. This is slightly less than the power required by a coffee maker. But we don't wish to heat a small pot of coffee, we want to heat something like 80 gallons of water to 180°F. So we will need more than one square meter. Also, the panels are not 100% efficient, but that can be the subject of another post.
It is fairly common to use two panels that are 4×10 feet in size for domestic hot water, or about 80 ft² or 7.4 m². For the location that I had chosen, this would not work because it would block some first floor windows. So I decided, instead, to use three panels that are 4×6 feet in size as shown in the image. This is 72 ft² or 6.7 m², so just a little bit less the area of the two 4×10 panels.
The location is just outside of my dining room bay window and represented a few challenges. Firstly, I didn't want the panels to block any of the dining room window for obvious reasons. That limited the height of the assembly. Secondly, these panels will need to shed snow in the winter, so the bottom should not be too close to the ground. In fact, ideally the bottom would be at least 3 feet off the ground so that snow sliding off the panels wouldn't form a pile at the base and block the panels. In the end, I decided to compromise on the snow issue. I will simply have to shovel the bottom of the panels out in the winter. In any case, it should be clear that the 4×10 panels would not work here as they would block the window.
The location is on the back of the house and has a concrete walkway right at the location where the panels need to go. The walkway is, surprisingly, not parallel with the house. So in the left side of the image you can see that the concrete pier I am planning barely touches the walkway. However, on the right side of the image, the concrete pier is almost in the middle of the walkway.
Part of the walkway will need to be removed and recast. Annoying.
The grade is sloped from the left to the right. So the piers on the left will stick out of the ground a lot less than the piers on the right. Not really a problem, but aesthetically not very pleasing. I think the concrete piers will be ugly. It would be nice to think of a way to hide them from view.
To help with the appear, I decided to center the three panels on the center of the dining room window. This leaves a little bit of space to the left, perhaps I can have some flowers planed there. The area to the right needs to be left open so that the oil-guy can reach the oil filler cap. Nice that the solar panels can hide some of the fossil fuel hardware which is stained with oil and frankly a little smelly.
The location faces almost perfectly south and has great solar coverage from morning until about 3pm for the summer. Winter coverage is going to be poor due to the location of trees and the low elevation of the installation. The panel angle will be fixed at 45 degrees which is roughly the latitude up here in the Boston suburbs. This is generally considered a good compromise between optimum summer and winter heat collection.
Next post, I will talk about the solar coverage measurements.
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