This post originally appeared on Mapawatt Blog and is a great comparison of residential solar vs. wind.
If you're a homeowner interested in creating your own clean energy, chances are you are considering installing a solar pv array or a wind turbine. Which is the better option? Luckily Spokesman-Review did a story on Inland Power and Light in Spokane, WA and their efforts to see whic.... They installed a solar array and a wind turbine that were comparable in cost, and then sat back to see which one came out ahead.
The solar panels have produced about five times as much electricity as the wind turbine over the past 14 months. The sun’s ability to generate more electricity than the wind – even during short winter days – has surprised the utility’s engineers. The utility bought a 35-foot wind turbine and a bank of solar panels. The systems are representative of technology scaled to individual homeowner use, Damiano said. Each cost from $22,000 to $24,000 to install.The results were surprising to them because conventional thinking is that the Northwest would have more wind than it does sun:
But wind is more erratic than people realize, he said. The wind dies down, for instance, during hot weather and cold spells. Inland Power’s turbine is similar to the larger ones installed in the Columbia River Gorge. It needs a stiff breeze of around 12 miles per hour to start producing electricity. Solar panels, on the other hand, generate a certain amount of electricity even on cloudy days.This is a great example of solar vs. wind, but aside from understanding some of the basics about solar and wind power, it is really only applicable if you live in or around Spokane, WA. At Mapawatt, we like to do the analysis ourselves and help show you how to your own analysis....so here we go! (Update - 3/28/11 - I contact Richard Damiano, Inland's chief engineer, after I wrote the post and he was gracious enough to provide me with more information on their installation. If you don't want to see my analysis, skip down to the bottom to see the actual data!)
In the Inland Power pilot project, the solar panels produced about 15 percent of a typical household’s electric needs over the course of a year. The wind turbine produced less than 3 percent.But this is a very poor way at analyzing clean energy because what is a "typical household's electric needs"? One home that is 5,000 sq. feet and has a family of six who don't really try to save energy is going to use way more energy than a 2,000 sq. feet and family of three who tries to save energy. This isn't just a few percent, but could be double or even quadruple. The only fair way to present this information is to give the yearly kWh produced, and recommend that people look at their utility bills from last year and see what percentage this would make up. Or give the range that this could make up for different households, i.e. "This solar panel array would produce 50% in a smaller home that already conserves energy, but only 15% in a large home that doesn't do a good job conserving energy". I firmly believe that when reporters try and over simplify energy data it only serves to confuse the reader more, or at worst give them false information that they then base their thought process off of.
At the bottom you can see that the average wind speed in Spokane over the course of a year was 8 mph. One of the more popular wind turbines for residential use out there is the Skystream 3.7 sold by Southwest Wind Power. This turbine is rated at 2.4 kW. Even though this site says the Skystream wind turbine costs $14,000 to $18,000 to have it installed, let's just assume this is the unit Inland installed for comparison's sake. Using the graph below on the Skystream wind turbine's power output against wind speed, you can see that the Skystream produces 100 kWh per month wind the wind speed is 8 mph.
Using this information, one would deduce that this wind turbine would produce 1,200 ( 100 kWh per month * 12 months) kWh per year. This is only a quarter of what we calculated the solar panels would produce (4,856 kWh) and this is very close to the real world results that Inland is seeing where the solar panels are producing 5 times more power than the wind turbine! Of course I made many assumptions in my analysis, but I'm in the ball park and hopefully you can see how to do some of this analysis on your own.
As you can see, it is important to do your own due diligence when deciding between solar panels or wind turbines and the need to speak to many experts. Don't believe the turbine dealer who says "The wind always blows 'round here so you'll produce a ton of power!" Now you can do the analysis yourself!Keep in mind, that this study is only for residential installations. For utility scale installations, the prices change drastically as do the operating characteristics, mostly for wind due to the height of the turbine.
From a cost-benefit standpoint, erecting a wind turbine or putting in solar panels is still a reach for most homeowners, Damiano said. Those who take the plunge are making a lifestyle choice to reduce their carbon footprint, he said. Recovering the installation costs for turbines or solar panels can take years, even with the 30 percent tax subsidy available to homeowners. “It will take you a chunk of time,” Finney acknowledged. But she encourages people to think about the long-term benefits.------------------------------------
“Some people spend $25,000 on a new car,” she said. “We decided this is how we wanted to live and how we wanted to spend our money.”
One thing that most people do not take into account is the power factor of the system. Our solar panels are rated in the mid-90% range for Power Factor, this has proven out with actual peak production of slightly over 2.0 kW, exactly what I would expect given the power factor and efficiency of the panels and inverters. The wind turbine is rated in the lower 80% range for power factor. When you take this power factor and combine it with the efficiency of the inverters we see an actual peak production from the wind turbine of only slightly more than 1.0 kW at winds of 40 mph. So even though the wind turbine is nominally larger than the solar system, the efficiency of the system is much lower resulting in about half of the peak production capability of the solar. Combined with the erratic nature of wind it is easy to see why solar is outperforming wind in our area.