Credit: CSIRO [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
The world is going green. With each passing day, we learn of new evidence that anthropogenic causes are the leading causes of climate change and global warming. In recognizing that we as human beings are the main culprits in the destruction of mother nature, we are now diverting more of our resources to finding new and cleaner means of powering our economies. Importantly, the financial resources and manpower being invested in these kinds of research is aimed at ensuring that the renewable and sustainable energy sources we exploit can be done so economically. Otherwise, the drive to go fully sustainable will not be tenable.
One of the ways of making renewable energy sources, solar energy in particular, economical is to enhance the storage potential possible so as to even out the peaks and troughs characteristic of solar power generation. This means that by storing the excess solar energy produced during peak hours when the sun is shining the brightest, you can use the stored energy for when production dips significantly due to lack of solar radiation (at night) or there being less than stellar conditions for solar energy production (cloudy days).
While many people will consider batteries as the only way to store energy, there are many other ways of storing solar energy. One alternative to batteries is the concept of steam as energy storage. The idea itself is not new. It was invented in 1874 by Andrew Bettis Brown, a Scottish engineer. However, what is new is the way the concept is implemented. With new technology and new material, it is now possible to store solar energy using steam in a cost-effective and efficient manner, making solar energy production more lucrative and reliable.
How Steam As Energy Storage Works
Just like any other energy storage technology, steam as energy storage works by charging and discharging.
The Charge – The charging process involves filling the steam storage tank half-full with cold water. Thereafter, steam generated through solar heating is blown into the tank through perforated pipes located near the bottom of the tank. As steam rises, some of it will condense and heat the water in the tank. The remaining steam will penetrate the water and fill the empty space left at the top of the tank. At the end of the charging process, the water will have significantly risen in temperature, pressure, and water level (up to about three-quarters of the tank).
The Discharge – For discharging, steam can be drawn out of the tank to drive a steam turbine that produces electricity (or the steam can be used as is in manufacturing processes). During the discharge process, the pressure will continuously drop as more and more steam is released. However, the reduction in pressure causes the water left in the tank to boil and release more steam, thereby constantly recharging the tank with steam until the overall system does not have ample pressure and steam to produce more steam. The gradual reduction in temperature and pressure allows the energy stored to be released gradually.
A good example of this technology in use is the PS10 solar power plant in Spain near Seville. There are even newer and better versions of such system, including EnergyNest AS and Aalborg CSP A/S. An even more audacious plan to use this technology was mooted – a fireless locomotive in Sacramento back in 2009. The plan was to install thermal solar energy harvesters in portions of the Sacramento Rail Yards to collect solar energy. The energy produced by PG&E steam plant would also be used to supplement energy supply around the area. However, the vast majority of the steam was to be used to charge and recharge fireless steam locomotives that are used in the popular tourist trains.