Archive for April, 2009

Green Power Sources

April 19, 2009

There are a number different possibilities for generating green power. Each has its advocates, advantages, and drawbacks. The main ones are discussed here.

Solar
Wind
Plug-in Vehicles as Energy Storage
Conventional Biofuels
Algae Biofuel
Hydrogen
Clean coal
Tidal/Wave
Geothermal
Nuclear

Solar

Photovoltaic cells convert sunlight directly into electricity. The silicon cells are very expensive and though their price is likely to come down, they are not likely to be competitive any time soon. New, novel types of cells are beginning to come onto the market and although their efficiencies are less that silicon cells, their prices are substantially lower and will likely go much lower. Theoretically, batteries could be used to store power for when the sun doesn’t shine, but, for large scale applications, batteries are now far too expensive

Photothermal power uses solar collectors to concentrate sunlight onto steam generators. This technique has the advantage that energy can be stored as heat.

Neither form of solar power can be used to supply all of our power requirements, since there will always be times when the sun doesn’t shine for extended periods. There have been some statistical arguments to show that if enough solar power installations were connected to a smart grid, enough stations would have power to take up the slack for those that didn’t. Sounds to me like the argument why sub-prime loans were a good investment.

Wind

Intermittent power. Mature technology, available now. Cannot by itself be a complete solution because it requires either a whole lot of energy storage or a backup power source (coal fired or neulear plant.) If the backup source were clean power, there’d be no need for the intermittant power. Again, long high voltage transmission lines would be needed. A whole lot of building materials would be needed to build all the wind generators – at a time when the Chinese are building one hundred new cities.

Plug-in Vehicles as Energy Storage

Not a complete answer. Even assuming that enough power is available for night time requirements, this power form would require considerably more daytime power, greatly increasing the power generation requirements. The probability that this will happen may be low, but it was like that with sub prime mortgages.

Conventional Biofuels

Production may take more CO2 from the atmosphere than it produces when burned – a very good thing. However, it needs a lot of land for production and either takes it from food production or plant life that does a better job of taking CO2 from the atmosphere or from wildlife habitat. Until now, Biofuels have been extremely counterproductive since forests and food crops have been sacrificed for their production.

Algae Biofuel

A lot of potential, especially for converting sewage into fuel. Considerable development is needed since the current price is ten times too high to be competitive. Extreme caution must be used before algae can be used on a large scale. We have to introduce them very slowly. Otherwise, there’s no way we can be sure that they won’t do really bad things to the environment. Remember Silent Spring.

Hydrogen

Very attractive as a motor fuel on the downstream end – makes only water when it burns. Upstream, it’s not so great. It needs to be separated from either water or methane. Separating it from water takes electrical energy, a lot of it, separating it from methane makes a lot of CO2. Big changes in infrastructure will be needed before it can be transported and stored effectively. An unlimited source of electricity would make it much more attractive.

Clean coal

Carbon sequestration is mostly what the clean coal advocates are talking about. This involves using chemical means to separate the carbon dioxide from air and storing it where it won’t pollute the atmosphere – typically in saline aquifers or in the gaps left by the oil in an oilfield. One interesting aspect of carbon sequestration is that it needn’t be done near the polution source. Since the CO2 spreads rapidly around the world, the sequestration equipment can be placed where the CO2 can be disposed of. No need for expensive piping. Once the CO2 producing plants have been phased out, carbon sequestrion can be used to lower the CO2 concentration in the air.

Thie technology has progressed to the point where a pilot plant is being built in Germany. The German process will use pure oxygen and specially processed coal and will be expensive.

However, coal is inherently a very dirty fuel. Coal contains every element up to uranium – a lot of them are bad for humans and the environment, especially mercury, lead, sulfer, and uranium. In fact, a coal fired plant puts out something like 8 times as much radiation as a nuclear power plant. Once pollutants get separated out, a very expensive process, they will consits of a large quantity of material that will need to be kept out of the environment forever, preferably not in holding ponds.

Tidal/Wave

In development – with some promising results. Would take time to develop and require enhancement of the power grid.

Geothermal

Hot rock geothermal can use a combination of existing technologies to build powerplants. This form of power is widely available and is being applied on a relatively small scale. Can use off-the-shelf technology without much modification. Actively developed in Europe. Construction of a pilot plant in Australia is well under way. A concentrated form of power like this makes efficient use of resources and needs the least enhancement of the power grid.

Nuclear

The dangers have been greatly reduced and are far less than many people think. It’s a concentrated form of power that uses comparatively few resources and requires minimal changes to the power grid

Emissions: Coal-fired power plants put out a lot of uranium and other radioactive materials in their smoke and cause many times more radiation pollution than nuclear plants.

Safety systems are far more reliable than at Three Mile Island or Chernobyl. They work like sprinkler systems in buildings: the sprinklers go on whenever the temperature goes up – no need for operators or control systems. If there’s a problem, it’s taken care of. In the case of a reactor, too high a temperature makes the control rods come down and shut off the system. No fuss, no strain. Once the problem’s fixed, the reactor can be started up again.

Uranium, plutonium, and existing nuclear waste can be used as fuel in fast neutron reactors,producing wastes whose radioactivity goes down to safe levels in 400 years and are far less hazardous than those from current reactors. A drawback is that this type of reactor can be used to produce weapons grade material. One such reactor is producing electricity in France. Although similar reactors have been operating in this country for many years, development of reactors specifically suited for electric power generation was stopped here a few years ago.

Weapons proliferation: Hegemony and coersion have been terribly ineffective at stopping it. When world tensions are reduced and existing stockpiles of weapons are being destroyed, the incentive to obtain nuclear weapons will lessen. The US can initiate this process by setting the example of destroying warheads and by helping other countries work together in the development of their power systems. We all have the common goal of stopping the environmental crisis and a huge incentive to meet it.

Cost: Although reactors have been expensive, their cost is coming down quickly. Reactors used to be specially designed and custom built. Extensive engineering work and feasibility studies had to be done for each one. Those costs will be greatly reduced when the new modular reactors being developed in Japan become readily available.

Conclusion: The intermittant power sources require baseline power and can never supply more than the difference between baseline and peak power. This limits their potential to 15% or less of the total power needs. Large plants for supplying base load power will always be required. At present, their are only two type of base load power plants: coal and nuclear. Smaller power plants, which can quickly adapt to changing power needs, will also be required. Since adaquate power storage at competitive cost will not be available for some time, if ever, these fast acting power sources will need to be coal-fired or geothermal. In other words, intermittant power can only be used to supplement conventional power.

The only cost-competitive base-load power plants that are now available are coal fired and nuclear. Since it’s widely agreed that coal plants should be phased out, nuclear is the only viable option.

The next post will tell how a power grid has to work and what needs to be done to get one to work that way.

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Jim Flint