POWER magazine has been in print for about 128 years catering to the global power generation industry. They
covered the earliest advances of steam power plants in the 1800s and addressed energy supply issues during World Wars I and II. We were the first to report on the birth of nuclear power, and today we report on modern advanced power technologies, including wind, solar, tidal, and ultrasupercritical generation.
I came upon this article entitled “Energy Storage Enables Just-in-time Generation” by Dr. Robert Peltier. (An apt name for someone involved in power, don’t you think? Do you know the Peltier effect?) Dr. Peltier is the chief editor of POWER and a mechanical engineering faculty member at Arizona State University.
The article is based on the methods used to store electrical energy. This is especially important for renewable energy sources, such as wind and solar, which are unsteady. Wind is highly erratic, at times dying out completely and in certain seasons, reaching speeds beyond the safe limits of wind turbines requiring the turbines to be “parked”. Solar only works on clear sunny days. In addition, the price of gas, diesel or coal fluctuate and electric providers may find it useful to store energy when costs are low. It may be economical for nuclear or hydroelectric power plants to store energy during off-peak hours
For those wanting a primer on energy storage methods, please refer to this Wikipedia article.
Dr. Peltier’s article lists seven methods:
- Hydrolyze water to H2+O2, React H2 with CO2 to form methane (natural gas) and store CH4. Efficiency claimed >60%.
- Hydrolyze water and react H2 with CO2 through Fischer-Tropsh process to form liquid hydrocarbon fuel such as gasoline and diesel. Claimed Efficiency >60%
- Mechanical means: store electricity as compressed air. 3000 psig.
- Mechanical means: distributed compressed air. Efficiency 90%. Lowest starting costs.
- Electricity as thermal energy: Low temperature method, create ice for refrigeration. Can be used for district cooling.
- Electricity as thermal energy: high temperature using heat pump. Claimed efficiency 72% to 80%.
- Underground pumped storage utilizing pressured gas vs. gravity. Simple concept. Raise a weight using compressed air. Claimed efficiency 75% to 80%.
Not withstanding the fact that all of the above methods have huge losses in energy conversion, they also have very high starting costs, running in the range of US$100s of millions, except for No. 4, distributed compressed air storage. This has huge potential in my opinion. “Small” air tanks about the size you see on tanker trucks can be mounted below each wind turbine or even in neighborhoods in urban or suburban areas easily and safely.
One may ask for methods No. 1 and 2, why not store hydrogen? There are many methods of hydrogen storage, including underground hydrogen storage systems but those are rare. But stopping at hydrogen+oxygen may be much more efficient as well as useful for a number of industries (hydrogen and oxygen bottling, oxygen for medical and industrial use, etc.) and upcoming technologies such as vehicles that run on hydrogen internal combustion engines and hydrogen fuel cells. I see a tremendous opportunity for wind energy-to-hydrogen conversion.
There is a plan to establish off-shore wind farms along the Eastern coast of the US, as seen from this Popular Science article earlier this year. Imagine if hydrolysis plants were established along side the wind turbines (on floating decks or sea-floor mounted rigs) and the hydrogen and oxygen could then be piped to on-shore plants or bottled directly at the off-shore location.
Hydrail (company link) proposes to use a conceptual train motor that runs on hydrogen either with the help of internal combustion engines or fuel cells. Hydrail station could be another beneficiary of hydrogen+oxygen derived by water hydrolysis powered by wind or off-peak nuclear, as this article suggests.
One may also ask, why not just store electricity in batteries. Well, that is also being tried as explained in this C-Net article. But batteries are limited to a few MWhrs and are very expensive and have environmental side-effects also.
Another example of solar-to-heat-to-electricity conversion was implemented in Spain. This project was financed jointly by the Spanish government and by Masdar/Mubadala, a company owned by the Emirate of Abu Dhabi in the United Arab Emirates. Here is a link to a new article.
In this project, solar heat is concentrated using thousands of parabolic mirrors to heat a mass of salt placed in a centrally located solar-tower up to 400 deg. C. The molten-salt can then be used to produce steam and drive turbines 24 hours a day. Once again, this kind of projects require very large areas of land as well as 100s of millions of US$ of spending.