The Limitations Of Renewable Power (Part 4)

Posted on Fri 08/28/2009 by




This Post was originally written in 2009. In the original Post, I used a reference to a site that had a simplified diagram which I used for explanation of this process. Since that time, that Project has folded and did not proceed to construction, and the link became invalid. Since that time, however, a much better diagram has come to the surface, and I have updated this Post to reflect that new diagram, and also used text that explains the process with respect to this new diagram…..TonyfromOz.

This process is different to Solar PV I wrote about in the post of 2 days ago. There are four or five different types of process here, but the most common ones are the Solar Power Tower, and the Solar Trough Method. The Sun’s light is focused using mirrors to a central point. At that central point. a compound is either stored or passed through pipes. The light generates a very high heat focused by the mirrors. This heat boils that compound to a molten state, and through this molten compound pipes carrying water are passed. This water is boiled to steam, and the steam then drives a conventional turbine/generator complex to produce the power. With the Solar Tower, the thousands (and thousands) of straight mirrors are mounted on Heliostats that track the path of the Sun across the sky, focusing a solid beam onto the top of a tower, where the compound is stored. The solar trough method uses specially constructed curved mirrors also mounted on those heliostats. The light is then focused onto pipes carrying the compound to a central place where that compound then creates the steam. The compound can be a form of salt, and experiments are still in train to find the best of these salts. Graphite is also used in some cases, and other compounds are also being tested. Keep in mind here also that the compound will still need ‘refueling’ over time as well, so it’s not a case of ‘set and forget’.

This process is what are being told is the way of the future. Those keen followers of renewable power are always very loud when they mention this. They tell us that this form of generating power actually can provide Base Load Power. What they have manifestly failed to do is to first check their facts before telling us that these plants can replace those coal fired power plants. They have read the carefully worded text at the sites for all these plants, and then, without a full concept of what is actually required, and then what is actually produced, they have just not even bothered to check first before telling us all that ‘the case is closed’.

This image below is of a chart indicating the power generation from a Concentrating Solar Plant which diverts the heat generated during daylight hours so that heat can be used to keep the compound in a state molten enough to make steam to drive the turbine which then drives the generator. While it may look ‘somewhat’ impressive to people who have little understanding of the process, it does require explanation to understand what this chart is attempting to explain.

The image shown here is smaller than full size. Click on the image and it will open in a new and larger window at that full size, and from there, you can navigate back and forth between the image and the following text for an explanation.

As complex as the diagram looks, it is in fact easy to understand.

The legend at the right vertical axis says Power in MW, but that is a little incorrect when referred to the ‘lines on the graph’ of the image.

The larger orange line indicates the irradiation of the Sun, and as you can see, this is only during actual daylight hours, and a little longer as it cools after Sunset.

Thee next line down indicates the heat transferred to the compound, commonly, salts that are raised to a molten state to boil water to steam to drive the turbine which drives the generator. While this looks impressive, in that it might be able to generate above that ‘nominal’ 200MW, the dark line across the graph, from around 7.30AM until around 6PM, that also that is not the actual power being generated during daylight hours.

The next line down, the dark green line indicates the amount of heat being sent to the heat storage part of the process. Move a little across the graph and that blue line there indicates the heat transfer from this storage process after the Sun has set.

The dotted crimson line averages out this heat transfer process.

The next line down is the single most important line on this graph.

This is that orange line, and this indicates the actual power being generated from this process which utilises the storage of heat to be able to keep the compound molten enough to make steam.

As you can plainly see, the actual total power that is being generated from this process amounts to just on 50MW, and of further importance is the time frame we are looking at here. That time starts at around 8AM, and then falls below that 50MW and back to Zero power at 3AM.

So, this heat diversion process will only generate 50MW, and contrary to the hype that says these plants can generate their full power for the full 24 hours of each day, they can barely manage a small amount of power output, and only achieve this for 17 hours a day.

This equates to an overall Capacity Factor of 70%.

Keep in mind that this is a theoretical maximum, because where plants like this are currently in operation, they are barely managing 60%, and that 60% equates to just under 14 and a half hours a day.

So, you will see plants of this nature in proposals stating that they have a Nameplate Capacity of 250MW and that they can produce this power 24/7/365.

The real truth is that they can actually manage only 50MW for around 15 hours at best.

Now, I want you now to take this link and go back to the image I showed you in Part 1 of this series, Jim Zim’s wonderful image of the Generator deck at Diablo Canyon Nuclear Power Plant.

If this Concentrating Solar Power was as good as those camp followers tell us, then surely we could construct one of this size to produce large numbers of electrical power. This one generator produces 1120MW of power and it does that 24/7/365 excepting for some downtime for refueling, and maintenance.

Why couldn’t they construct a generator of this size with the steam turbine driving it all, if, after all, the process is the same?

Why they cannot do that is because a plant of this size utilising the concentrating solar process will NEVER even begin to rotate. They could have 10,000 square miles of mirrors all focused on the compound, and no matter what, it will never generate enough steam to make a unit of that size even begin to move, let alone a plant even a third of that size.

The size of the plant is totally dependent upon the amount of steam that can be generated. Make the unit too big, and it will never begin to move. So, trade offs are made. If the plant can produce only so much steam, then the weight of the turbine/generator complex is very carefully calculated so that it actually can turn over the turbine and thus drive the generator.

One of those trade offs is to have smaller complexes of turbine/generators, and in the case of a 250MW plant, they will have five units of 50MW each, adding up to that 250MW.

If the plant does have molten compound heat storage, then they will only have enough heat to drive one of those complexes, one 50MW turbine generator complex.

That extra addition of molten heat storage capability adds considerably to the up front cost as well, so a plant of this nature will be horrendously expensive.

I can hear those out there with rose green coloured glasses saying that technology will improve over the years, and that may be so.

However, the current theoretical best case scenario is that they can currently run with a 250/50MW plant, and perhaps in another 5 years, they may be able to have 500/100MW plants in operation with longer capability for heat storage, but the idea that they can have a compound stay molten enough for long enough to generate those huge amounts of power from Nuclear and large scale coal fired will be in the vernacular, a bridge too far, if ever.

To that end, these plants will only ever produce small amounts of electrical power, and by small I mean a maximum of say 300MW, which is still quite large, but to actually do that, you are talking monstrously huge sized plants with mirrors covering hundreds of acres, thousand upon thousands of mirrors, and still only producing power solely from the Sunlight at around 10 hours a day.

The largest one planned for the U.S. is the Abengoa Solana Plant at Gila Bend, near Phoenix in Arizona. Others are planned for California, and Texas, and note here especially that these are located in desert areas where there is consistent high levels of Sunlight, because a Plant of this nature would again be useless anywhere in the North East, and there is also no feasible way of getting usable amounts of electrical power transmitted over those vast distances.

This Plant will produce a Nameplate Capacity of 280MW, and again, they also state that the power will be augmented by a fossil fuel driven turbine when the absence of Solar power takes the steam off the boil. It is also stated at their site that they can produce power from solar means alone at an efficiency of 35%, and when that is extrapolated out to a daily basis, it amounts to only eight and a half hours a day. See how reality always seems to be so disappointing. This Plant will cost $1.1 Billion. (Update to 2011, and the revised cost for this Plant has blown out to $1.45 Billion)

So then again, as I have done with each of these renewable methods, let’s then take the same amount of money we spent on the Diablo Canyon Nuclear Power Plant and construct Concentrating Solar Plants, that amount being $5.6 Billion.

So then, we can now construct 5 of these plants.

Forget the millions of specially constructed mirrors, the factories to make those mirrors, the work force to do that. Forget the construction time, where to place these plants, how to get them connected together, the infrastructure to get the power to the grid. Forget that the plant will only have a life span of 20 to 25 years. Forget the workforce required to keep all those mirrors perfectly clean all the time. Forget all those things. Let’s just look at the electrical power produced.

Five of these plants will give you a Nameplate Capacity of 1400MW, only 63% of the nameplate Capacity of Diablo Canyon. However, even at their quoted sanguine efficiency rate of 35%, the plant will only produce 22% of the total usable output from The Nuclear plant, again for only eight and a half hours a day.

To actually produce the same nameplate capacity, you would need to build 8 of these plants, the cost now coming in at nearly $9 Billion, still only eight and a half hours worth of power.

To actually produce the same amount of usable power, we are looking at 23 of these plants, the cost coming in now at nearly $26 Billion, still only one third of the time.

On top of all this, the Nuclear plant will stay in operation three times as many years.

Keeping all that in mind, you do the math on how much this power will be sold to you as consumers of the electrical power.

If these plants were even a fraction as good as what they are made out to be, those in the industry would be lining up in droves to construct them. Where plants like this already exist in Europe, mainly in Spain, they are propped up by huge injections of Government money, well, taxpayer money really, both at the construction end and also at the power delivrey to the grid end.

No, this third of those renewable power plant methods suffers from the same thing as the others do. They have limitations, and as I have shown here, and in hundreds of earlier posts, those limitations are indeed quite considerable.

As Coal fired plants start closing down, and renewable plants start coming on line, there will only be one thing happening. The lights will start to wink out all over the place.

Only then will the real truth begin to come out.

These plants will never be able to replace coal fired power plants. NEVER.