2009年6月3日 星期三
2009年5月11日 星期一
Beyond Fossil Fuels: Lucien Bronicki on Geothermal Energy
The chairman and chief technology officer of Ormat Technologies weighs in on the hurdles facing his industry
Editor's note: This Q&A is a part of a survey conducted by Scientific American of executives at companies engaged in developing and implementing non–fossil fuel energy technologies. Bronicki replied to the survey in a phone interview; what follows is an edited and condensed transcript of that conversation.
What technical obstacles currently most curtail the growth of geothermal energy? What are the prospects for overcoming them in the near future and the longer-term?
Geothermal can be divided in two. We have the power plants which convert the heat, in the form of steam or hot water out of the ground, and of course we have the resource itself.
Geothermal has been used for more than 100 years. Wherever you had steam coming out of the ground, you could put a steam turbine and you are in business. It is a little bit more complicated, but this is the basic idea, and the steam, after going through the turbine and the cooling tower, finds its way into the atmosphere, which means that you deplete not only the heat but also the aquifer.
So, for instance, at the Geysers, which is still the largest single geothermal field in the world, output dropped substantially in the last 40 years not because the Earth got cooler but because the aquifer was depleted.
What Ormat's contribution was to the state of the art was to extend the range of possible resources which can be used, the resources which are at lower temperatures. You still need a temperature difference, but you have extended the range by using the Organic Rankine Cycle, which is an old invention but was never really used for anything.
Also, most of our plants are air-cooled, which means that we inject everything. And therefore the sustainability of the system is extended, because you don't consume the water. Of course there are places where there is sufficient supply of cold water from rain and so on, which is called natural recharge. But in most places today water is a problem, not only for geothermal but for coal-fired plants, for nuclear plants, for any thermal regeneration.
Now, to build a power plant, our approach is to tailor-make the power plant to the resource. So it takes some engineering into do it, but I would say this is negligible. From the moment you have the permits to go on a site until you complete the plant and start it up is in the range of one year. But to explore the resource, which is done with geophysical methods similar to what is done in oil and gas, is more complex and takes longer.
We need three elements, really, to have a good resource. One is to have heat. This is relatively easy to detect. But you need two other things. You need water, which is the element that brings the heat from the depths to the surface. And you need rocks which are the edge of fractures, a fault or a permeable, so that this water can flow, so that when you drill a well the water tends to flow into the well and come out. Then, of course, you also have to reinject it back. Both need permeability or a fault. And this exploration takes time.
So, if we leave aside the site permitting, which also takes time, then exploration activities are something on the order of three years. And with the field development it may be even up to four years.
As to the technical obstacles, there is the availability of companies which deal with the geophysical approach and then the availability of drilling rigs. Until about a year ago both were very difficult to get, and we had to buy our own rigs. Short-term I would say these availabilities are not an obstacle. Nobody knows for how long, but today they are available.
Long-term, though, it is an obstacle, because most of the geologists and even the drilling personnel are older people. Young people did not come to the field. There were no programs of training, and whoever was available was grabbed by the oil industry.
So today we are working with the University of Nevada, Reno, and with M.I.T. There is a renewed interest among students in going back to geology, hydrology. But this is something that takes time. And the people have left over the years with all the sitting and waiting. So if geothermal is to grow it's important to start it now, and in the U.S. many universities are now enrolling more students in this field.
A lot of time was wasted in the U.S., because at the laboratories which are working on long-term projects and basic science, the budgets were reduced and geothermal was certainly not their priority. About three years ago the geothermal budget was cut to zero, and people left. Again, they were mostly not young people, so this was a big loss. Today there are signs that more money will go to the national laboratories and the universities.
It may be one of the problems with geothermal is that it's not so well known in spite of the fact that until about one or two years ago, geothermal was producing the same amount of kilowatt-hours as wind in the U.S., but everybody knew about wind energy. Very few people knew about geothermal energy.
As for the plants themselves, efficiencies have been improved, but we are close to the diminishing returns. Geothermal working at lower temperatures is material-intensive—we have big heat exchangers. And therefore the impact from the high material costs of the past few years impacted the cost of the power plant. But there is not much we can do from the point of view of drastically reducing it. The turbines are extremely efficient; out of what the second law of thermodynamics allows you we are getting pretty close to the limit. And therefore the big changes that will occur are improving the exploration techniques so that the time is reduced and the probability to find the right spot for drilling the well is improved.
Today I would say about one third of the wells are dry wells, low-production wells, which means that if you had better exploration accuracy, you could reduce the cost by one third. So there is a lot of gain there.
Another thing that I have to stress is that the geothermal that I have been describing is what's called hydrothermal. There was a study by M.I.T. of what is called enhanced or engineered geothermal (EGS)—this is an approach that was developed by Sandia National Laboratory. There is much more hot dry rock in the world than areas I described that have both hot rocks and also water and faults or permeability. The idea of the hot dry rock is to drill at least two wells and, again by similar techniques to oil and gas, to make fractures between the two wells so you can have a kind of heat exchanger. You pump cold water on one side, it goes through these fractures and comes up.
The estimate for the potential of hydrothermal in the U.S. is between 10,000 and 20,000 megawatts (MW), which is not negligible. It's not going to solve the problem, but it's not negligible. The potential of EGS with hot dry rock is 100,000 MW.
But there are still many challenges. Unlike conventional geothermal, you now have to find rock which you can also fracture. And you have to spend energy to pump water through it. And you have to bring the water from another area if there is no water locally. And you have to be careful not to lose water in the operation.
So these are additional energy loses for pumping, but this a big potential. It got a lot of interest, but we are unfortunately still many years away. We have a project which is partially supported by the DOE in cooperation with a number of universities and laboratories, but this is long-term. To start producing megawatt-hours this is, I would guess, 10 years away.
Editor's note: This Q&A is a part of a survey conducted by Scientific American of executives at companies engaged in developing and implementing non–fossil fuel energy technologies. Bronicki replied to the survey in a phone interview; what follows is an edited and condensed transcript of that conversation.
What technical obstacles currently most curtail the growth of geothermal energy? What are the prospects for overcoming them in the near future and the longer-term?
Geothermal can be divided in two. We have the power plants which convert the heat, in the form of steam or hot water out of the ground, and of course we have the resource itself.
Geothermal has been used for more than 100 years. Wherever you had steam coming out of the ground, you could put a steam turbine and you are in business. It is a little bit more complicated, but this is the basic idea, and the steam, after going through the turbine and the cooling tower, finds its way into the atmosphere, which means that you deplete not only the heat but also the aquifer.
So, for instance, at the Geysers, which is still the largest single geothermal field in the world, output dropped substantially in the last 40 years not because the Earth got cooler but because the aquifer was depleted.
What Ormat's contribution was to the state of the art was to extend the range of possible resources which can be used, the resources which are at lower temperatures. You still need a temperature difference, but you have extended the range by using the Organic Rankine Cycle, which is an old invention but was never really used for anything.
Also, most of our plants are air-cooled, which means that we inject everything. And therefore the sustainability of the system is extended, because you don't consume the water. Of course there are places where there is sufficient supply of cold water from rain and so on, which is called natural recharge. But in most places today water is a problem, not only for geothermal but for coal-fired plants, for nuclear plants, for any thermal regeneration.
Now, to build a power plant, our approach is to tailor-make the power plant to the resource. So it takes some engineering into do it, but I would say this is negligible. From the moment you have the permits to go on a site until you complete the plant and start it up is in the range of one year. But to explore the resource, which is done with geophysical methods similar to what is done in oil and gas, is more complex and takes longer.
We need three elements, really, to have a good resource. One is to have heat. This is relatively easy to detect. But you need two other things. You need water, which is the element that brings the heat from the depths to the surface. And you need rocks which are the edge of fractures, a fault or a permeable, so that this water can flow, so that when you drill a well the water tends to flow into the well and come out. Then, of course, you also have to reinject it back. Both need permeability or a fault. And this exploration takes time.
So, if we leave aside the site permitting, which also takes time, then exploration activities are something on the order of three years. And with the field development it may be even up to four years.
As to the technical obstacles, there is the availability of companies which deal with the geophysical approach and then the availability of drilling rigs. Until about a year ago both were very difficult to get, and we had to buy our own rigs. Short-term I would say these availabilities are not an obstacle. Nobody knows for how long, but today they are available.
Long-term, though, it is an obstacle, because most of the geologists and even the drilling personnel are older people. Young people did not come to the field. There were no programs of training, and whoever was available was grabbed by the oil industry.
So today we are working with the University of Nevada, Reno, and with M.I.T. There is a renewed interest among students in going back to geology, hydrology. But this is something that takes time. And the people have left over the years with all the sitting and waiting. So if geothermal is to grow it's important to start it now, and in the U.S. many universities are now enrolling more students in this field.
A lot of time was wasted in the U.S., because at the laboratories which are working on long-term projects and basic science, the budgets were reduced and geothermal was certainly not their priority. About three years ago the geothermal budget was cut to zero, and people left. Again, they were mostly not young people, so this was a big loss. Today there are signs that more money will go to the national laboratories and the universities.
It may be one of the problems with geothermal is that it's not so well known in spite of the fact that until about one or two years ago, geothermal was producing the same amount of kilowatt-hours as wind in the U.S., but everybody knew about wind energy. Very few people knew about geothermal energy.
As for the plants themselves, efficiencies have been improved, but we are close to the diminishing returns. Geothermal working at lower temperatures is material-intensive—we have big heat exchangers. And therefore the impact from the high material costs of the past few years impacted the cost of the power plant. But there is not much we can do from the point of view of drastically reducing it. The turbines are extremely efficient; out of what the second law of thermodynamics allows you we are getting pretty close to the limit. And therefore the big changes that will occur are improving the exploration techniques so that the time is reduced and the probability to find the right spot for drilling the well is improved.
Today I would say about one third of the wells are dry wells, low-production wells, which means that if you had better exploration accuracy, you could reduce the cost by one third. So there is a lot of gain there.
Another thing that I have to stress is that the geothermal that I have been describing is what's called hydrothermal. There was a study by M.I.T. of what is called enhanced or engineered geothermal (EGS)—this is an approach that was developed by Sandia National Laboratory. There is much more hot dry rock in the world than areas I described that have both hot rocks and also water and faults or permeability. The idea of the hot dry rock is to drill at least two wells and, again by similar techniques to oil and gas, to make fractures between the two wells so you can have a kind of heat exchanger. You pump cold water on one side, it goes through these fractures and comes up.
The estimate for the potential of hydrothermal in the U.S. is between 10,000 and 20,000 megawatts (MW), which is not negligible. It's not going to solve the problem, but it's not negligible. The potential of EGS with hot dry rock is 100,000 MW.
But there are still many challenges. Unlike conventional geothermal, you now have to find rock which you can also fracture. And you have to spend energy to pump water through it. And you have to bring the water from another area if there is no water locally. And you have to be careful not to lose water in the operation.
So these are additional energy loses for pumping, but this a big potential. It got a lot of interest, but we are unfortunately still many years away. We have a project which is partially supported by the DOE in cooperation with a number of universities and laboratories, but this is long-term. To start producing megawatt-hours this is, I would guess, 10 years away.
訂閱：
意見 (Atom)
