There are two main types of solar power generation methods used to produce electricity on a commercial scale. Photovoltaic panels, which are the large collections of the systems that you see in small scale on house roofs. Concentrating solar power (CSP) uses thermal solar power, the heat of the sun, to produce environmentally friendly energy.
It’s the way in which concentrating solar power plants produce electricity that we will concentrate on here. CSP plants are capable of producing electricity at a higher maximum capacity than a photovoltaic facility of the same size. They will play an increasingly important role in the move away from fossil-fuel sourced energy to that of renewable energy.
The four main comercially productive concentrating solar power systems are: parabolic troughs, dish / engine systems, fresnel reflectors and central receiver systems. The technology involved with each is proven and either has been or still is in operation around the world with more developments in solar power in progress to try to meet future demands.
Trough systems work by making use of mirrored troughs that are used to focus the sun’s energy onto a receiver tube that is filled with fluid. The fluids are heated to very high temperatures so that super-charged steam is generated. This steam is then directed into a conventional steam generator to produce electricity.
A trough-based CSP plant typically consists of rows of mirrored troughs placed parallel to each other along a north-south axis in what is known as a collector field. The troughs pivot as they follow the sun to ensure that it is continuously focused on the receiver tubes. Thermal storage is also used to allow electricity generation to continue either when the sun is not shining or after it has set. Technological advancements are continuing to prolong this production period in a bid to move to continuous solar electricity production.
Power plants known as Andasol 1, Andasol 2 and Andasol 3 in Spain all use the parabolic trough design, forming a combined 150MW solar power plant. The surface area of the mirrors used to form the energy collection field of Andasol 3 alone is around 500,000m2.
Dish / engine systems are stand-alone units that contain dish-shaped parabolic mirrors that concentrate the sun’s energy onto a receiver mounted above the dish. The receiver takes the energy and converts it into heat which is then converted into mechanical power, similar to a mechanical engine. Each dish / engine unit has a capacity of around 25kW of solar power and it tracks the sun to ensure optimum power.
An example of the dish / engine technology is the Stirling Energy Systems dish called the Suncatcher that will be used in fields of thousands to form a power facility capable of generating over 500MW of electricity
Fresnel relectors are similar to parabolic troughs except they are flat mirrors that focus light onto one receiver. Costs are reduced using this method because the rows are positioned more closely together, there are fewer moving parts and less receivers are required. The receiver is stationary and it is shared by several mirrors.
An example of a recently commissioned CSP plant using reflector technology is the Kimberlina CSP plant in California developed by Ausra. This 5MW CSP power plant is a demonstration of the technology that will be used in much larger scale developments in the future.
Central receiver systems are also known as power towers. Looking as though they're honoring a higher deity, thousands of mirrors called heliostats cluster around a receiver that sits atop a tall tower. As the energy is directed into the receiver it is used to super-heat nitrate salt mixtures which goes on to produce steam that runs a conventional steam generator. The molten salt can be stored for great lengths of time which means that this type of solar energy generates electricity continuously around the clock.
Solar One, Solar Two and the latest power tower, Solar Tres are all examples of central receiver systems. The Solar Tres power plant will be a 15MW facility and it follows on from the successful demonstration power plant known as Solar Two which was located in the Mojave Desert.
Opponents of solar energy cite cost as a limiting factor, but this is being overcome thanks to technological advancements. Already, concentrating solar power plants hold a huge advantage over the traditional fossil fuelled counterparts in the lower impact to the environment. In fact, one of the only impacts that concentrating solar power plants have on the environment is land use.
Solar energy continues to grow and with continued support it will eventually become one of the main sources of electricity around the world. Concentrating solar power has proven to be a renewable energy source with still more untapped potential
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