There are two components to determining the value of an energy system; the price and the amount of energy produced. Recently, a family member sent me an email asking about this system:
http://www.aerotecture.com/This is my response:
I think it is important to keep your eye on the ball, however, so bear with me for a quick, first cut analysis of the system. "The ball" in this case is the quickest, most efficient transition to renewables that we can achieve. If current climate change projections are even close to accurate, time and financial resources need be maximized.
This type of system (small collection area at rooftop height) runs up against physics as, generally speaking, there simply isn't the wind that you need at that altitude. The energy contained in wind is exponentially related to the speed of the wind, a doubling of speed produces an 8X increase in power. Related to that is the drag that the wind experiences as it interfaces with the surface. That drag decreases rapidly with altitude. So while a turbine with a swept area larger than a football field and a hub height of 260 ft will produce (in a good area for wind) electricity at a lifetime average of $0.04 - $0.06 a kWh, this rooftop unit will probably only deliver electricity at about $0.50/kWh.
The big variable is summed up in the system's "capacity factor" which is a percentage of the maximum annual production capacity of the generator (all types) . At 1.5KW (max rating) x 8760 (number of hours in year) = 13,140 kilowattHOURS potentially per year. A good wind regime (NM desert for example) will produce between 30-40% of that for a 30-40% capacity factor.
A rooftop system will very rarely produce 20%, usually it is less than 10%. So say it is 15%:
13140 x 0.15 = 1,971 kilowatthours per year.
With a 20 year life span, that would equal 39,420 kWh lifetime production.
$21,000 /39,420 = $0.53 /kWh.
The national average price is about $0.09 /kWh.
Large scale wind through a public utility is usually about $0.11/kWh.
This article also gives a good summary of small wind economics:
http://www.cattlenetwork.com/Content.asp?ContentID=280257New Energy Economics: Wind - What Is Its Value?
If you have been a regular reader of this column, you are going to notice a switch. For the past six months, I have described the various economic facets of biofuel energy. Given the rapid increase in wind development across the region, I am going to shift gears for the next several months and do the same for wind energy.
Similar to biofuels, I am going to start with the very basics and proceed to discuss several economic policies that are impacting the development of the wind industry across the region. Just as with biofuels, I invite any questions and/or comments on issues that I raise.
Many people have an initial impression that the economics of wind energy is easy to evaluate. After all, all one needs to do is determine how much wind there is, put up a turbine and then sell the power back to the utility company.
Unfortunately, it is far more complicated. Technical considerations, consumer demand, utility pricing and public policy all have a large impact on wind economics. In the next couple of articles, I am going to focus on each of these topics, but let's start with wind.
Even at low wind speeds, do turbines make economical power? Is more wind always better? No is the answer to both questions. The graph illustrates the technical efficiency of a 1.65-megawatt wind turbine.
Two important points to keep in mind; First, at wind speeds below 10 mph, a wind turbine produces very little energy. We will see in future articles that even wind speeds under 15 mph are not economically viable because enough energy isn't produced to cover the high ownership (fixed) costs of erecting a wind tower.
Second, wind towers are not engineered with enough strength to capture high wind speeds. When wind speeds exceed design thresholds, internal brakes limit turbine rotation. Turbines could be designed to generate energy at higher wind speeds, but strengthening the tower and other turbine components is not economical with our present technology.
The fundamental formula for wind energy is power =1/2 pAV3.
Where p is the air density (just like any other density -- how much a given volume of wind weighs), A is the swept area of the blades (how much surface area of the turbine actually catchs wind) and V is the velocity of wind usually measured in mph. Notice that the velocity of wind is raised to the power of 3.
This is the most important factor. Most of us are aware of how quickly something rises geometrically if it is squared or raised to the power of two. The power of wind rises more quickly because it is raised by a factor of three.
Thus, wind speed is by far the most important consideration when siting a new wind turbine. In my next article, I am going to illustrate how variable wind speeds can be, even in a small geographical region.
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