(3BL Media/Justmeans) - One of the first questions I asked upon arriving in Abu Dhabi, a very modern city in a very oil-rich country, with a very progressive stance towards renewables, was, why? Besides the obvious fact that unlike some other people, they recognize the fact that their oil won't last forever, and they want to participate in energy after it runs out. But there's something else, too. They would like to see an orderly transition that allows them to steward their resource to make as much out of it as they can.

A great example of that is the Shams-1 hybrid solar power plant, which is located 120 km southwest of Abu Dhabi.

Shams is a joint venture between Masdar of the UAE, which contributed 60%, Total, of France, (20%), and Abengoa Solar of Spain (20%).

This unique plant uses a combination of concentrating solar power (CSP) and natural gas which adds a bit to the cost, but gives it some unique capabilities, including the ability to produce power anytime at all, even at night.

During ordinary operation, the parabolic mirrors, of which there are over 258,000, that cover an area of roughly 2.5 square kilometers, track the sun and focus its rays on a pipe containing an oil-based heat transfer fluid (HTF), which heats it to around 400 degrees Celsius. The heated fluid is then used to boil water, the result of which is used to drive a fairly conventional steam turbine.Natural gas can produce up to 50% of the plant's rated capacity, though under full sun, it contributes only 18% of the energy input. This is done by superheating the HTF to 530 Celsius, a point at which the turbine runs more efficiently. This combination produces 100 MW, enough to supply 20,000 homes here. The power is being supplied to the Abu Dhabi Electric Company through a 25 year power purchase agreement.

Part of the rationale behind this hybrid design is the fact that a plentiful supply of natural gas can be found nearby. Another unique factor of this plant, driven by its environment, is its use of dry, forced air cooling, where massive fans are used to cool the heat exchanger coils, similar to a car radiator. Water is quite scarce in this region and typical power plant cooling towers use massive amounts of water. Using this method to cool the steam so it can be pumped back through the system as a liquid saves 200 million gallons of precious water per year.

This illustrates the way that renewables require more consideration of local environment than conventional plants do. Another big problem they have is dust, which can seriously undercut the performance of the system. They have trucks and crews going out every night, which allows them to clean the entire complex in a week. The process does require water, which is a problem. Sounds like a great challenge for a team of enterprising problem solvers: figure out a way to effectively clean these mirrors, without liquids and without scratching them.

So far the plant has performed well, achieving 98.22% availability (uptime). It has produced 12% more energy than expected, using only 75%as much natural gas as anticipated. When asked about the use of storage, Abdulaziz Al Obaidli, the plant's Technical Support Manager, said that because 70% of the plant's load is for cooling during the midday hours, when the sun is strongest, there is little need for cooling.

In today's market, solar PV prices have come down so far, that they are now more cost effective than a CSP-type system. Still, CSP has certain advantages such as being more suitable for base load power.

In the meantime, not only has this plant provided great experience and learning about the challenges associated with the design and operation of this type of system; it has also displaced over 175,000 tons of CO2 and continues to do so every day it operates. Â

Image credit: RP Siegel