FAQs — Frequently Asked Questions

Saturday, February 20th, 2010

Will having a photovoltaic solar system installed allow me to be independent of the electricity grid during blackouts?

That depends on the type of system we install. Most people are primarily looking to lower their energy costs and reduce their carbon footprints. These can be most easily achieved by installing a grid-tied system, which produces power whenever the sun is up. However, if the grid goes down (such as in an outage), the solar system will automatically shut off for safety reasons. Thus, a grid-tied system will not serve as a backup power source during power outages. For clients who live in areas that have frequent and long-duration power outages, or who need to ensure they have constant AC power for medical reasons, we would recommend a grid-tied solution with battery and/or generator backup. This is a more complex and costly solution that also requires regular maintenance of the battery bank. Thus, it usually doesn’t make economic sense for most people who only experience infrequent and short-duration power outages. Either way, we’re able to design and install the solution each client desires to meet their individual needs.

What if the roof on my (commercial or residential) building doesn’t face south? I’ve heard that can be a problem?

Great question. Of course in the northern hemisphere the solar path in the sky is sloped to the south, so a south-facing roof is ideal for installation of a solar system. However, we have equipment that helps us determine the degree of deviation from true south, so we can calculate the impact in terms of reduction in solar energy striking solar modules mounted on the target rooftop. Surprisingly, a rooftop that’s 30- or even 45-degrees off angle from true south can still be outfitted with solar modules that perform very well, as long as shading isn’t an issue.

What do you mean “Shading”? We have trees in the yard – will they be a problem?

They might be. Once again, we have equipment that allows us to measure the overall impact of shading effect across the target section of your rooftop, whether that shading comes from trees, other buildings, or portions of your own building (such as a chimney). Shading is one of two factors than can have the most serious impact on energy production from your solar array. Thus, we naturally seek to determine almost immediately (during our first site visit) what shading issues may be present. Not all shading is a problem. The shading we’re most concerned about is that which occurs between 9:30am and 3:30pm, as these are the “peak sun hours” for us here in Colorado., meaning this is when we have the most opportunity to capture “insolation” or solar radiation so we can convert it into electrical energy.

You said shading was one of two potentially problematic factors. What is the other one?

The other one is temperature. High temperature, to be specific, which is the mortal enemy of photovoltaic solar modules. The good news for us in Colorado is, that (compared with most of the “sun belt”, because we’re at altitude), we have a cooler climate. For example, Phoenix Arizona is probably the ideal spot to be in the U.S. if we want to maximize our peak sun hours. Compared with Phoenix, we have between 1.0 and 1.5 fewer peak sun hours. However, working in our favor are our 310 sunny days a year — and our altitude. At 5,280 feet (or more) above sea level, the sun’s energy doesn’t need to penetrate through as much atmosphere to reach solar modules in Colorado. Thus, the intensity of insolation here is greater than in most of the U.S. Further, our elevation means cooler temperatures as mentioned above. This is a key advantage, especially if the installer takes care to ensure that modules are installed with sufficient space between them and the rooftop to allow for convection cooling (e.g. air to circulate between the hot rooftop and the modules). The reason for this is due to the fact that the silicon wafers in solar modules are very temperature sensitive and are all rated in their specifications with a temperature coefficient. This coefficient indicates the amount of reduction in electrical energy production that will occur for each degree of increase in cell temperature.

For example, take a Canadian Solar 200-Watt module with a temperature coefficient on power output of 0.45% per degree Centigrade. With a theoretical 3,000 watt solar array comprised of 15 of these panels, for each degree (C) of increase in temperature, we’d see a 13.5-watt decrease in output power. so, for a modest temperature increase of 20 degrees Centigrade, we’d see 270 watts in lost power. That may not seem like much, but rooftops are frequently 50 degrees hotter than ambient temperature — this is heat that’s easily transferred to solar modules, with corresponding decrease in performance. Due to our cooler climate we typically see better overall performance from our solar modules than is common at lower altitudes…and that’s a good thing! And of course our design and installation expertise also helps to optimize production output from the solar arrays we install for our clients.

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