Solar Photovoltaic
Submitted by admin_green on Fri, 09/11/2009 - 14:50
Here comes the sun, here comes the sun, and we say…it's all right.
You need to know the angles. That's how you get the most from your solar photovoltaic system.
Tom Krawczyk did the solar assessment for the Green Leaf Inn site on June 9, 2008 (you can e-mail Tom here). Part of his report also forms the basis for our page on solar hot water systems. Much of his report discussed the relative advantages of a roof-mounted vs. a pole-mounted system. You can see the full report here.
The solar question: roof mount or pole mount? Roofs provide large amounts of otherwise wasted space, and are usually pitched at a pretty good angle to catch the sun. Poles provide maximum energy efficiency, but put your panels in places you might have used for something else...like a garden.
As with so many of the decisions we will have to make, this boils down to weighing our desire to present guests with the most enjoyable B&B experience against our desire to create the most energy efficient environment.
Simply put: poles are more efficient. But roofs provide a LOT of space, pitched at a pretty good angle, which isn't being used for anything else. With solar voltaic systems, the more empty space you have for panels, the more electricity you can produce. The rule of thumb is 10 watts of power per square foot, or roughly 100 square feet per kW.
Pole-mounted systems can be pitched at the most efficient angles, and can track the sun across the sky for maximum efficiency. A tracking system, while adding to the cost, can increase efficiency substantially. Poles-mounted panels can also be repositioned manually. Poles can be put anywhere, but sometimes the best locations are spots you'd just as soon use for other things.
Doing the math.
Annual electric use for the house is currently in the range of 22-23,000 kW/H, which translates to an average of 64kW/H per day. The rule of thumb is to assume four hours of usable sunlight per day, so divide this daily total by four and we need a minimum of 16,000 watts of capacity for the house. This doesn't factor in peak versus base usage, mind you, so 20,000 is probably a more reliable figure. That would require two hundred 100-watt panels, or about seventy 300-watt panels. Holy smokes!
Clearly, we need to take a very careful look at our energy use, and find ways to reduce our demand. Or we're going to need a bigger garden. And we'll certainly be considering some of the new solar materials that make it easier to incorporate solar power generation directly into the materials used for new building.
