Where is my Wind?
Whether we are talking about wind, solar thermal, or photovoltaic projects, a proper installation is key to the success of the project and the health of the industry. Quite often we as contractors will see either minor errors in understanding of the technology or resource, system design, or placement that will negatively impact the long term productivity of a project. Most often these errors are seen with the application of wind turbines and, separately or together, with grant funded projects. Today we’ll focus on wind.
North Carolina has a terrible wind resource. There, I said it. If you are not within a mile or so of the ocean coast or up in the mountains, there is no justifiable resource. We have plenty of potential clients that come clamoring in the winter, when winds in places from Greensboro to Kinston are stronger and more consistent, but even those winds are only going to last part of the day and disappear into still doldrums come the spring and summer. Wind is variable, and we need an average annual of a certain threshold, not just a strong winter afternoon.
There is so much beautiful and undeveloped land in this state that you have to think if it made economic sense we’d see a lot more of them. The investors that put up these big GE and Vestas turbines flock to quality wind resources. Believe me, if we could put up a 1.5MW somewhere outside of Greenville and it would be productive, I’d be all for it. Unfortunately, the only place it really does make sense is in Eastern NC, but they are having real issues in this challenging economy. Some of these challenges include financing, migratory birds, zoning, and military restrictions. The mountains have similar issues and Ridge Top restrictions.
Baker Renewable Energy (BRE) has, in addition to using the historic records databases, performed extensive long term anemometer testing throughout the state. The anemometer is a tool used for measuring wind speed. Our philosophy is that if you truly do not believe the data of record, then let’s put up equipment to give you a site specific sample. Does it cost money? Yes, but far, far less than having an ornament up in your front yard for the next 25 years that will never pay for itself.
Back in 2009 BRE was contracted by the NCDOT to do a wind resource study on what the construction teams were calling “Windy Hill”. Windy Hill sits atop a minor bump along the southbound stretch of I-73/74, State Highway 220, between Black Ankle and Seagrove, NC. The DOT was in the throes of building a beautiful LEED certified rest area, up upon the hill, just below the peak. The hill above had pathways leading to it from which travelers have an overlook that allows you to see for more than 20 miles in every direction. If ever there was a location in central NC with an opportunity for good wind, this would be it, right?
We set up the anemometer in January, a cold and clear day like today, and immediately it started spinning. Knowing construction workers and tradesmen told our team and the NCDOT rep we were working with that we were wasting our time, and needed to just install a turbine.
We went back months later to retrieve our anemometer, and the data. The anemometer was truly one of the best positions we had ever dropped, with no obstacle at the hub height not just for 200 meters, but for nearly ½ mile or greater. When we processed the data we saw what we expected, but not what we wanted. We were within a rounding error of the historical wind speeds. Keep in mind if are talking about a 6mph wind, even if we were off by 20% (+/-) that still only means a 5-7mph wind give or take a little. There is no chance that our equipment is off by a 20% discrepancy. The 10-11mph average winds needed to generate power, and the consistency needed just did not exist to produce electricity consistently from the wind. Wind resource needs to be thought of like current in the ocean. You need a strong and consistent current, not just an occasional tidal flux. Long term averaging, whether speaking about wind resource or solar exposure, is the real key to successful renewable energy projects.
So what about all of those windy days? Well, when graphed out, we could see good strong winds in the mornings and the afternoons nearly all of January, but that still really only meant in the mid-teens for mph. Shouldn’t that be good enough? Well, unfortunately every night the wind died down and brought a bunch of 0’s into our averaging, and that is a key word. Average wind speed.
It does not matter if you have 2 hours every day at 24mph if you had zeroes the rest of the time. Using a popular model like the Southwest Windpower Skystream 3.7 (Yes, we are dealers, this is not meant as a plug) in conditions like that, with 24mph winds 2 hours per day and zeroes the rest of the time, we would make about 5kWhrs per day. A similar investment in a photovoltaic system nowadays would get you about 3-3.5kW and should produce conservatively 10.2kWhrs in a day. The reality at the overlook was that when it was windy the power was more like 16mph as an average, and as the power curve of these generators is exponential (ramping up) a 16mph wind has it only putting out 1kW, not the rated 2.4kW at 24mph.
Just this morning, as I was writing this piece, a potential client called from Trenton, NC. Mapping showed that what he was interested in, a Skystream 3.7 would generate less than 2,000kWhrs per year. He told us straight away he was not so sure since yesterday someone was there telling him wind would outperform solar and solar could never pay for itself. Trenton’s average wind speed is close to 6mph. This eagerness to sell, versus selling what’s correct is a strain on the industry.
We, as integrators, have to help you install what is most efficient when you use your other non-renewable resource, money. In this case, not only would solar have dramatically outperformed the wind, but the wind would not have been able to achieve the required ROI (return on investment) for the client to invest in the first place.
The real point here is the importance of citing a wind project where there is a resource for generation. Next time I will talk about the physics of wind, different wind technologies, and what to look for when considering a turbine.