Wind and Solar Are Variable Resources, But What Does That Imply About the Need for Back-up Power?
Let me reiterate what I just wrote in a comment: The notion that incremental solar and wind plants require significant amounts of additional backup from fossil fuel plants is a myth. This is explained very nicely in the article linked above.
Thanks Craig,
A great, well written article by the AWEA. Thanks for the reference.
If the penetration of wind and solar power increases beyond a certain point, then increased back up power will be required. There is not total agreement about the numbers but at some point, unless new technology makes energy storage more practical, it will become a serious problem. We can wait until it does become a problem or we can anticipate it now and be prepared to deal with it. Otherwise we will be forever dependent on fossil fueled power systems for too much of our power requirements unless there is a break through in storage technology.
An exception is areas where considerable hydro power is available. In that situation, a reduction in wind and solar power can quickly be accommodated by ramping up the power of hydro systems. And, when wind and solar power are available, the output of hydro systems can be ramped down to conserve water.
I hope you will read every word of the article I linked above.
Thanks Craig for the link. And I did read every word, In fact I am very familiar with these words as they have been echoed often.
What these words don’t do though is provide a simple, concise and accurate engineering/scientific explanation for what on face value is a fairly simple and reasonable question asked by so many lay people and so often.
In essence what many have been asking for years is this: can intermittent energy generation technologies like wind and solar PV exist as commercially viable technologies into the future without “other” energy sources in place to mitigate their indeterminacy?
Professional and experienced renewable energy commentators and practitioners should not become agitated by this question nor become defensive. But they always seem to. Why?
They should relish the question and be able to deliver a forensic detailed professionally detached scientific based engineering response [but in simple terms] for all those interested to evaluate.
And it it those very commentators prepared to engage the community in this way that we should all support, and in particular, those willing to put their name to their commentary, unlike the unnamed authored article you referenced.
We all have names – and the ones that deserve most acclaim, whether we agree with their commentary or not, are certainly those proud enough to state their name up front.
In this day and age there is absolutely no excuse for an unnamed authored technology based article to be published. By name I mean person. There is no such concept as an “association or organisation based” authored article. You always name your own commentary Craig, so do I and Frank Eggers does also, for example.
Lawrence Coomber
Frank Eggers is quite right that beyond a certain point, intermittent renewables require back up power, however what is not obvious to your average person is that a surprisingly high proportion of electricity requirements can be met with intermittent renewables given the right circumstances.
The following are helpful factors
1. Widely distributed intermittent sources with a suitable grid interconnected ideally over continental scales.
In Europe, wind and solar power generated in Germany, the Netherlands, across Scandinavia, and all the way down to Italy are largely backed up by dispachable hydro power from Norway, and the Alps together with a significant contribution to baseload from the French Nuclear stations. Future grid upgrades will increase trading capability with the UK and Ireland, and between North Africa and Southern Europe.
2. Dispachable loads – To take the example of Denmark, >70% of homes and businesses are connected to district heating networks. This was initially set up using coal fired CHP, but more recently, Denmark is looking to use heat pumps and heat storage so that wind power during low value periods can be diverted to make and store heat which can then be distributed over several days. Heat storage is relatively inexpensive – In one case, in South Jutland, the Danes are using a 200,000 cubic meter thermal store in a converted gravel pit
http://www.ramboll.co.uk/projects/re/south-jutland-stores-the-suns-heat-in-the-worlds-largest-pit-heat-storage
(My research for my masters thesis indicated that >50% of Denmark’s electricity and heat demand could be met by wind power on an annual averaged basis with virtually no forced idling of wind plant using thew district heating plants to integrate wind power. Further expansion of wind power would then require supplementation with other strategies such as increased interconnection with a geographically broad power grid, or facilities specifically dedicated to electricity storage.)
Note :- Thermal stores can also be used to store cold for district cooling in hotter regions.
3. Some storage – electric vehicles can collectively be seen as dispachable loads across the grid, with smart charging solutions permitting flexibility as to when and how fast vehicle batteries are charged. These same vehicles may in future be able to provide occasional service as peak demand plant – each giving up perhaps 10% of its charge over a few hours so facilitating a reliable supply of power during extreme weather events such as >40 C / 100 F degree afternoons – into the early evening when solar power is fading.
Additional pumped storage is possible in many locations including closed loop pumped storage – where water is transferred between two reservoirs with the capability of daily cycling with minimal loss of water and no river outlet.
http://www.genexpower.com.au/projects/The_Kidston_Project
Also possible is sea water systems with cliff top reservoirs filled with sea water.
One of the stated advantages of renewable power systems is that they could, by generating power locally, eliminate the need for large grids. Obviously the approaches proposed by Gary Tulie would eliminate that possibility since large grids would be required by it. However, there is nothing wrong with large grids except in places where political instability would make them too risky.
The concept of storing solar heat for heating buildings seems quite practical in many areas. Considering the price of high efficiency condensing boilers and furnaces for home heating, and their limited life, it would not be surprising if district heating could be justified on an economic basis alone in which case the reduction in CO2 emissions is an important added benefit. Of course that would be practical only in urban areas where insolation is adequate.
If wind power were used to produce heat, the electrical portion could be eliminated since mechanical power can easily be directly converted into heat. In fact, some engine dynamometers use water brakes to do just that. It would work well provided the wind farms were not too far from where the heat is needed. However, it’s unclear how practical that would be since wind turbines designed only for producing heat could not be used to produce electricity.
Storage for cooling is another matter. In climates with cold winters, it may be practical to freeze water during the winter and use the ice for cooling during summer. A cleverly designed system could even use some sort of natural convection system to produce ice with little or no power required. In warmer climates, there would be no way around using heat pumps to produce the ice but at least considerable storage in a district system could result in adequate reliability where a loss of cooling could be tolerated at times.
There is still the problem of providing reliable power where outages would not be acceptable. Pumped storage has been used for many decades and works well, but its availability is geographically limited. It has been claimed that adequate battery storage probably could not be made available since the world’s amount of lithium and other materials necessary to manufacture the batteries is insufficient. I have not been able to evaluate that claim. It would be unfortunate if renewable systems were to depend on fossil fuels for reliability which seems likely.
There is much that I have not covered such as areas of the world where renewable systems would be impractical. In some places, solar power simply is not available at all for a few months during winter. Sometimes the wind does not blow for weeks at a time. If we rule out nuclear power we could be in serious trouble if we discover too late that renewables cannot do the job with adequate reliability. If that happens and power systems fail too often, it is likely that the public would demand quick fixes such as building more coal burning plants which is happening in Germany as Germany phases out nuclear plants.
Here is a post I found on Brave New Climate:
Edward Greisch commented on Open Thread 24.
in response to Peter Davies:
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@Gene Absolutely we should not. But we should not be removing the renewables + storage option from the table either.
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The bad news is: You have to make a choice. It is a forced choice. You can’t choose both [wind & solar] and nuclear.
Wind and solar destroy nuclear.
Wind and solar may as well be and are a fiendish plot by the fossil fuel industry to destroy nuclear power. Why? Because Generation 2 nuclear, as installed, cannot ramp up and down fast enough to match the intermittent nature of wind and solar.
So when wind and solar are installed, the power company automatically also builds a gas turbine fueled by natural gas. They have no other choice right now. Since they will have the gas turbine, they will have no use for the nuclear.
And then your electric bill multiplies itself by 4 or 5 times, to pay for all of that.
So, Peter Davies, you are forced to choose. The electric company will not try to buy imaginary batteries or batteries that might be available in 20 years. You must choose.
Here is a Wall Street Journal article about the Ivanpah concentrated solar plant in California. It, and the comments which follow, are exceedingly interesting:
http://www.wsj.com/articles/ivanpah-solar-plant-may-be-forced-to-shut-down-1458170858
Here are quotations from the article:
“A federally backed, $2.2 billion solar project in the California desert isn’t producing the electricity it is contractually required to deliver to PG&E Corp., which says the solar plant may be forced to shut down if it doesn’t receive a break Thursday from state regulators.
“The Ivanpah Solar Electric Generating System, owned by BrightSource Energy Inc., NRG Energy Inc. and Alphabet Inc.’s Google, uses more than 170,000 mirrors mounted to the ground to reflect sunlight to 450-foot-high towers topped by boilers that heat up to create steam, which in turn is used to generate electricity.
“But the unconventional solar-thermal project, financed with $1.5 billion in federal loans, has riled environmentalists by killing thousands of birds, many of which are burned to death—and has so far failed to produce the expected power.”
“More than 2,000 wild birds died at the Ivanpah plant between March and August of 2015, according to estimates that biologists hired by the plant owners filed this week and in December with the state Energy Commission.
“Roughly half of the dead birds the biologists found had feathers that were singed or burned, most likely from flying through an area of intense heat between the mirrors and the power towers, according to the reports.”
I was a subscriber to the WSJ for 20 years, but I stopped reading when I realized that they have a negative slant on anything that represents environmental responsibility.
But even a stopped clock is right twice per day. I often disagree with the WSJ but there is no publication with which I would always agree and they do make some valid points. The number of birds fried by Ivanpah presumably is determined by objective means with which there is unlikely to be any disagreement. There are some facts which cannot be tampered with.
There is no doubt that the Ivanpah project has negative unintended consequence vis-a-vis birds. That’s not arguable. I object to the blatant slant against renewables, etc., e.g., the constant coverage of bad news in cleantech.
For example, there are 6.5 million people employed by the solar PV industry; that’s not promises, that’s 6.5 million weekly paychecks. Try to find that covered in the WSJ.
Ivanpah appears to have a particular problem with bird deaths which is not generally shared by other types of concentrated solar power.
Parabolic trough designs it would appear have far lower impacts on birds and bats as there is not the same degree of concentration across a large volume of free air – if a bird were to fly through the beam of a parabolic trough concentrator they would experience far lower temperatures for far less time than they would experience flying through the concentrated solar flux of a solar tower – chances are they would come out the other side before suffering significant harm.
Obviously the parabolic trough type of CSP would result in fewer bird deaths. The concentrated line-shaped beam from the mirror travels only a very short distance before being absorbed by the tube whereas with the power tower design, the distance between the mirrors and the collector is a few hundred feet.
The parabolic trough type of CSP, unless there have been changes that I don’t know about, generates a lower temperature than the power tower type and therefore has a lower thermodynamic efficiency. The result is that it requires a larger land area and a larger steam turbine to generate the same power. Also, the lower temperature means that using air cooling instead of water cooling for the condensers results in a greater efficiency loss. Thus, air cooling is more practical for the power tower type than the trough type. In desert areas that is an important advantage.
The higher temperature for the power type also makes heat storage more practical.
It is likely that the power tower type of CSP will win out over the parabolic trough type because it is likely to cost less for the amount of power generated.
Frank, you are certainly right about the relative thermodynamic efficiency of power generation between the parabolic trough and power tower design, however in terms of levelised cost of electricity and land use considerations, I am not so sure.
Mirrors for the power tower type of collector will probably need more land area per area of mirror to prevent one row shading another, so the higher layout density of parabolic trough may compensate for the difference in relative efficiency – especially for the newer larger and higher temperature variants now coming into production – withthe technology having the potential to reach around 500 centigrade.
Where concentrated solar is used for thermal loads rather than power, the efficiency question will disappear for temperature requirements within the output range of the collector – e.g. steam for cooking in a food processing factory.
On cost, there is a chance that parabolic trough, or possibly linear fresnel lenses when mass produced might offer significantly lower hardware cost offsetting the efficiency reduction associated with the lower temperature – alternatively, as an interim measure, the parabolic trough technology might be hybridised with a gas burning power plant – pre-heating steam before the final gas burn – thereby achieving thermodynamic efficiency similar to a combined cycle gas turbine for the solar heat contribution.
I would need to review in more detail before commenting on air cooling though I think you may be right – parabolic trough will probably suffer a greater efficiency loss through its lower operating temperature.
Gary,
I’m not certain of the relative cost of parabolic trough vs power tower type either. However, I think that shading effects would also be a problem with the trough type too. There were changes made to the Ivanpah system for environmental reasons.
Another stated advantage of the power tower type is that less land leveling is required because the units can be mounted on uneven land. How big an advantage that is I don’t know.
The Ivanpah installation in CA, which is the power tower type, burns moderate quantities of natural gas on a daily basis although I really don’t know why. It also has some PV panels but I don’t remember where I got that information.
You can easily find images for Ivanpah; they are impressive.
I still maintain that, except under limited special circumstances, the world will have to get most of its power from nuclear reactors but that our current nuclear technology is not a good one.
Germany has about 30% renewable penetration. One would expect that to result in lower CO2 emissions, but France, which has far lower renewable penetration, emits about 10% as much CO2 as Germany. Regarding that, here is a post I found on bravenewclimate.com:
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Julian commented on Open Thread 24.
in response to Barry Brook:
From what I’ve been able to find, the German CO2 intensity was 510 g/kWh in 2013
(http://www.renewablesinternational.net/carbon-emissions-from-german-power-sector-balanced-in-2013/150/537/77625/) whereas it’s about 40 g/kWh for France (http://www.rte-france.com/en/eco2mix/eco2mix-co2-en).
Why aren’t those two figures discussed more? Because as far as I can tell, it shows that decarbonizing through renewables is not an effective strategy for Germany. Considering they’re above 30% renewable penetration already, you’d say that the CO2 intensity should already be far lower than it currently is. The curve of CO2 reductions also doesn’t seem to follow the much steeper curve of renewable penetration. So as far as my layman eye can tell, it doesn’t seem that German renewables are good at mitigating CO2, or in other words: a kWh of solar/wind seems to reduce CO2 emissions by far less than a kWh of French nuclear energy (around 10 times less).
Is that a fair conclusion to draw from those numbers?