Renewable Power, But Not For When It’s Needed Most (Part 1)

Posted on Mon 04/26/2010 by




It’s so easy to look at a set of statistics and make assumptions from them. Everybody does it, and different people can look at the same set of stats and come to different conclusions.

So, when I do this, I always try and give valid reasons as to why I come to the conclusions I reach.

To interpret some statistics, you need to understand the background of that area of statistics being referred to. I use the stats for electrical power from the U.S. Government’s own website, that of the Energy Information Administration (EIA) which is a huge site, and because of that, those stats in the main are not easily understood.

I use those stats to indicate just how inefficient renewable power really is. There are two sectors of renewable power currently most in favour, those being Wind Power, and Solar Power, which has two methods of generation, Solar Photovoltaic, which uses Solar Panels to generate electricity, and Concentrating Solar which uses the focused mirrors principle to generate power.

In hundreds of posts now, I have demonstrated just how these plants cannot be relied upon to supply the electrical power that is needed on a constant basis. To do this, I have effectively used those stats to prove the point, and it may seem like anything could be proved from statistics, so that is why careful explanation is needed.

The main area I will be concentrating on here will be those stats for renewable power, with a concentration on those numbers for Wind Power, and to explain them, I also need to explain the operation of the wind tower generator components that are housed in the nacelle atop that tall tower.

The image at right shows a very basic schematic diagram of the nacelle of a wind tower, where the generator and ancillary components are housed. If you click on the image it will open in a new and larger window, and you can just navigate back and forth from that page to this for the explanation.

Even as simple as this diagram is, it has all the requisite things that go to to the makeup of a typical nacelle. I’m not going to explain every part of the operation, just the relevant areas of operation.

In a case like this, sometimes it’s better to work backwards, and then build the operation after explaining why it needs to be like this.

The generator itself is where the power is actually generated. These generators, (alternators really) are ‘similar‘ in nature to the generators in your car, although in this case that is a basic generalisation, because they are much larger, more complex, and produce a quantum level greater power. They are however almost tiny when compared to a generator in a large power station. This size is dependent upon the weight the tower can support. They can produce up to 6MW depending upon the size of the generator, (and consequently, the tower) but the average is usually around 3 to 4 MW.

While the generator in your car is driven by a belt attached to the engine, in this case the generator is driven by the huge three bladed fan at the front of the unit.

The power the generator supplies has to be at the same frequency of the U.S. power supply, that being 60Hz, or 60 cycles per second. Because of that, they need to rotate at that 60 times a second, or 3600RPM, or a lesser exact multiple of that so that the frequency can be easily regulated. That speed of rotation is constant and has to be kept constant. To achieve this the generator is attached to a gearbox, as shown in the simple schematic. Calling it a gearbox is a vast oversimplification. It is in fact a Constant Speed Drive (CSD) and no matter what the speed of the fan at the front, this CSD keeps the generator rotating at that constant speed, so critical to keep the correct frequency of the power supplied from the unit.

The rotating fan at the front provides the driving force. This in turn is being driven by the prevailing wind at the time. If the wind is not blowing then the fan does not turn. The same applies if there is only a light wind. Also, because of the range of speed capability of that CSD, then it also stands to reason that there is an upper end of the driving speed when it cannot maintain that constant speed, so at higher wind velocities, the unit is shut down, and the fan also stops rotating. This is not achieved through guesswork or a manual controller, as it is all done automatically within the nacelle.

See at the right of the diagram, on the upper rear of the nacelle, there is an anemometer, a simple little rotating device that measures the wind speed. As simple as the diagram shows it to be, there is also a wind vane attached to the anemometer so the direction of the wind can be determined. This ensures that the nacelle is aligned so that the wind is blowing directly at the front of the fan, and that nacelle moves accordingly on top of the tower to face directly into the wind. This anemometer is connected to a computerised controller which does many things. When the wind speed picks up enough, to a preset speed enough for the CSD to drive the generator, it then starts up the fan at the front. At lower speeds, the pitch of the blades is varied so the blades can ‘catch’ most of the wind. As the wind picks up even further, this controller alters the pitch of the blades so that they still ‘catch’ the wind in the same manner. As the wind then increases and decreases, above and below preset levels, the blade pitch is varied so that the blades will be rotating at around the same speed throughout the range no matter what the strength of the wind may be. This is important mainly because of the length of those fan blades. As towers have become larger to accommodate the larger generators, then the fan size has also had to increase. Because of this, what needs to be taken into account now is the speed of the tips of the blades themselves, so as the wind increases, then the pitch of the blades narrows. The blades will look to be travelling at around the same speed in higher wind scenarios and around the same speed for lighter breezes.

Whatever the wind speed in the low/high range, then the fan rotates. Even though seeming to be a low speed, that shaft then drives the CSD which then gears up that speed of rotation to drive the generator at the requisite constant speed to produce the power, and at the correct frequency.

There are other designs from this one I have explained here, where the generator contributes different levels of power throughout the range of wind speed and rotation of the fan. The generator speed of these varies, and because of that, then extra componentry is needed to adjust the frequency to the absolute requirement of that 60Hz. These designs are more expensive, because each individual tower now needs separate frequency setting components, so that the total power from the whole series of towers that make up the plant can be supplied to the grid at that correct frequency. These plants are no more or no less efficient than the one I have described.

So then, why have I bothered to explain all this in the first place?

The Generator has a nameplate capacity of ‘X’ MW, so if it works all the time, 24/7/365 it can produce ‘Y’ KiloWattHours (KWH) of usable power for consumption. However it produces considerably less than that. This is known as the Efficiency Rate, or the rate of power delivered versus the Nameplate Capacity, and this is resolved with a simple calculation, even though that formula seems quite complex.

When the plant is proposed, the advertising might typically say that the plant can deliver that usable power at a rate between 30 and 35%. Currently, the average for Countries that have large numbers of these wind plants is around 20% across the whole Country, and as more of these towers are constructed, that 20% figure is staying fairly constant across the World.

I have consistently said that this 20% factor relates to the time that they are running, so, at that 20% annual average, then that works out to around 5 hours a day on average.

Once the operation of the nacelle is understood, then you can see that the generator produces its maximum power while ever the fan is rotating. So, those full power delivered amounts equate exactly to the time of operation.

So, when you are told with confidence that this form of power generation can take the place of coal fired power, then that is an outright lie, and there’s no softer way to say that.

Coal fired plants and nuclear power plants CAN deliver their power on that 24/7/365 basis. This is an absolute requirement, because across the whole of the U.S. nearly two thirds of every watt that is generated is required for 24 hours of EVERY day. This is what is called the Base Load, something that has been roundly discredited as being in any way important by all those ‘green’ believers out there.

So, there is no way whatsoever that a wind power plant that consistently runs at only 5 hours a day can supply the levels of power required absolutely for that 24 hours of every day. You can have millions of them covering every vacant inch of land in the Country, and they would still not be able to supply that level of power.

Some might say that the Efficiency rate is spread across the whole Country, and that some plants will be rotating while others are not. A wind plant in Texas can rotate for all its worth, but if the towers near New York are not, then that Texas plant cannot supply the needs for New York. The same applies for wind towers in windy PA. They cannot supply power for San Francisco.

So that 20% efficiency rate may apply for the whole of the Country, but if the power is required absolutely for 24 hours, then it’s no good having a wind plant that only operates at best for 5 hours a day. Some Months the plant might actually operate at around the quoted 35%, but if the average is still only 20%, then there must be some months when that average is even lower than 10%, and as is the case in Germany, there are months when the whole inventory of every wind plant does not even provide the guaranteed minimum of 6%.

This has been a long explanation I know, but it leads directly into Part 2. In that Part 2, I will show the most recent stats for all power consumption across the whole of the U.S. These stats are for the January 2010 power consumption. This was right in the middle of probably one of the worst Winters on record, and those figures provide the most damning indicator that renewable power just cannot supply power when it is needed most, and in this case they did not supply that power.

That level of extra power WAS supplied in the main by a dramatic increase in the power delivered from the Coal fired sector. The increase in demand was reflected in an increase in supply from nearly every sector.

Except for one sector that is. The renewable power sector, which in fact delivered less power, the only sector to fall.

Link to Part 2