Friday, May 11, 2012

Solar thermal for base load power


The city of Athens hosted its oldest tradition of lighting the Olympic torch for the 2012 London Olympic Games on Thursday in Olympia. The torch was lit by solar power; using parabolic mirror to redirect the sun’s light in order to light the flame with purest natural light. The thermal energy of sun’s light can be powerful when focused to a point and it can reach a temperature more than 600C.The parabolic trough with reflective mirror focuses the sunlight on the tube called ‘collectors’ in which a fluid with high boiling point is circulated. The hot fluid in turn is used to convert water into steam in boiler. The hot oil transfers its heat to the water in a heat exchanger and returns back to the parabolic trough. It is a closed circuit system. The hot oil at 390C generates steam at 370C at 100 bar pressure, which is used to run a HP steam turbine. The standard steam condensing cycle generates power similar to fossil fuel fired power plant. A 50 Mw Trough plant in Israel (Negev Desert) is already in operation. The capacity of such plant can be easily expanded by adding modular parabolic troughs and collectors and the plant can be designed to meet specific power demands. This is a straight forward method to generate base load power using standard steam cycle. The efficiency of such system will be 41% maxium.However recently few companies are trying use a combined cycle. This increases the solar to heat efficiency from 50.5% to 53.6%.This nominal 50Mw power plant generates a total peak power of 57.10Mw using a solar collection area of 310,028m2 with annual solar to electrical efficiency at 16.3% using a water cooled condenser in the steam cycle. The cost of energy works out to $0.23 to $ 0.25 /kwhrs. By using a central solar collection tower (Heliostat) and bottoming with Rankin/kalina cycle ,it is estimated that the total installed cost can be reduced by 10%.The system can be configured from 2Mw up to 100Mw using both trough and tower system. The system can be installed in any remote, arid locations using air condensers, where cooling water is a problem. The estimated annual specific energy cost is less than 6 cents/kwhrs, comparable to low cost fossil energy but with zero pollution and with zero carbon emission. Solar thermal is a potential clean energy of the future for many countries around the world with yearlong sunshine with good intensisty.The solar thermal energy can also be used in many process industries where thermal heating is required. Solar salt pans can use solar thermal energy very efficiently to reduce their production cycle. The concentrated brine can be used as a circulation fluid in solar collectors and also be used to generate power using low heat technologies like Kalina cycle, because concentrated salt brine can store thermal heat. Gemasolar power in Spain is a base load power station supplying power for 25,000 homes 24x7 using molten salt (60% KNO3+40% NaNO3) as a thermal storage medium instead of batteries. Nine plants were built in 1980 in Mojave Desert with a combined capacity of 354 Mws. Other examples of solar base load power plants are Blythe solar with capacity of 968Mw at Riverside County, California and Ivanpah power station with capacity of 370 Mw capacities in US,both under construction. Large scale solar base load plants are no longer a theory but a commercial reality. Direct solar lighting is also being introduced using fiber optics. The sun light is collected at a central point and directed through fiber optics to various rooms inside the building supplying direct sun light. This saves not only electricity but also provides natural light to work places because human body requires certain amount of UV light exposure. Solar energy is here to stay and offer various clean energy solutions in the future.