Minnesota’s solar resource is average nationally – better than the northwest but not as good as the southwest.
Source: National Renewable Energy Laboratory
Within Minnesota, it varies by about 15%, with the southwest being the highest and the northeast the lowest (Note: Colors between maps are not comparable.)
Source: Minnesota Department of Commerce
Unlike wind energy, which has an exponential relationship between wind speeds and electricity production, solar’s changes over geography are much more linear and less related to local/regional topography (which affects wind speeds), so movements across distance don’t change the resource much. Of course, the resource can vary year to year as the maps indicate. But generally speaking, the solar resource availability isn’t the drama that wind energy projects incur.
In the scope of things, 15% across Minnesota isn’t that much and consumers should be more concerned with proper siting at their particular location, i.e. avoiding shading from trees or buildings. A badly located installation, no matter how good the intentions, can reduce energy production by 50% or more on the same property.
Proper siting includes avoiding as much shading at all times of the year. To maximize production annually, set the tilt of the panel to the latitude (45 degrees). To maximize summer production, tilt it further back somewhat (i.e. more flat) – it might hold snow longer in the winter however. Generally speaking 20-45 degrees is fine – often the pitch of your roof is what dictates the installation if that’s where you install it and want it to sit flat.
Remember that the sun’s angles change throughout the year. It is lower in the winter than the summer.
Source: National Renewable Energy Laboratory
Most people underestimate the shading at their site. The best way to know for sure? Have a solar pathfinder analysis done for your site – probably a good idea for siting a house as much as for installing solar energy. It’s a simple device that uses hand-traced diagrams to calculate exactly how much and when shading occurs at a site.
Source: Solar Pathfinder
In the end, your resource is only one part of the equation. New Jersey is fast becoming the nation’s solar leader, not because they have a great resource, but because they pay more for electricity and have strong policies and incentives. A location with half the solar resource but who pays twice as much for energy ends up in the same place.
It’s probably more practical to know what to estimate for energy production based on the technology rather than the resource.
Solar Electricity
Real world data is showing anywhere from 900-1100 kilowatt-hours AC (electric grid power) per kilowatt of solar panels (add up the size of the solar panels, which are rated in DC – five 200 watt panels is 1000 watts or 1 kilowatt) per year in Minnesota. Solar trackers, which actively move the panels to always face the sun, add about 20-30% more production, but obviously cost more and add moving parts to your system. This online calculator (click here) from NREL can be helpful in estimating electricity production and benefits. Set the “AC to DC derate factor” to 0.66, otherwise you’ll overestimate what is really being seen in the field (calculators assume a perfect world).
Don’t be scared off by the numbers – just throw some kilowatts on there and calculate away. The average sized system in Minnesota is about 3 kilowatts but generally speaking you are planning your system for your budget ($10,000) or your goals (50% solar offset) more than your roof space or resources.
All in all you’ll find that per kilowatt per year, your system will produce $50 (lower resource, bad siting, and/or lower prices) to $125 (best resource, no shading, tracking, higher prices) worth of electricity per year at current prices. It’s your guess what happens in the future but higher prices mean more benefits.
Solar Thermal
This is a bit harder nut to crack but this paper (click here) from the Solar Rating certification corporation provides estimates for a wide variety of solar equipment, hypothetically placed in St. Cloud, that is helping to heat your electric or gas hot water heater. Don’t worry too much if you’re from Duluth or Moorhead – close enough. Electric hot water heaters start on page 5 and natural gas on page 11.
But another factor comes into play here – your ability to store and use the heat, which makes solar thermal systems more complex to do “back-of-the-envelope” calculations. Generally speaking, offsetting electric water heating is more cost-effective than natural gas, even with the price increases recently. (If you are paying an off-peak rate of 3.5 cents/kWh electricity that’s effectively just over $10 per million btu. If you don’t have an off-peak rate, that can double. The natural gas equivalent varies by the time of year but has been $6-12 lately.) The annual dollar benefit can vary between $80 – 400.
See this guide (click here)on solar incentives for some more rough numbers on production, costs, incentives, and benefits.
Final Word
A qualified solar dealer will come do an assessment of your locations potential, which technology is right for you, and what energy efficiency things can maximize your solar investment. They may charge a site visit fee that pays for their time and prevents them from becoming a free teacher for someone who isn’t really that serious. Sometimes it can be applied to the cost of system should you move forward with a project. A list of solar dealers in Minnesota is located available (click here).
It should also be noted that generally speaking, you won’t get any deals by buying equipment at a discount off the internet and then hiring a dealer to install it. You may in fact be losing out on discounts from buying the complete package from the dealer. You want them to be a part of the whole process so there aren’t any surprises along the way.
Other Information
Homepower Magazine
Minnesota Renewable Energy Society Solar Home Tour Profiles
U.S. Department of Energy
