There are predominantly two types of solar power generation methods used to generate electricity on a commercial scale. Photovoltaic panels uses the sunlight to directly produce electricity by using solar cells set in photovoltaic modules. Concentrating solar power (CSP) uses thermal solar power, the heat of the sun, to produce environmentally friendly energy.
We will take a look at the way in which concentrating solar power plants create electricity. 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.
Commercially, four types of concentrating solar power are in use: 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 further solar power development in progress to increase global capacity.
Parabolic troughs use mirrors to direct sunlight onto a fluid-filled receiver positioned in directly in front of each trough. The fluids are heated to very high temperatures so that super-charged steam is generated. A conventional steam generator is then used 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.
One of the largest developments to use the parabolic trough design is the Andasol project in Spain. The surface area of the mirrors used to form the energy collection field of Andasol 3 alone is around 500,000m2.
Fresnel relectors are similar to parabolic troughs except they are flat mirrors that focus light onto one receiver. This is a simpler system to the parabolic trough system with fewer moving parts and the rows can be positioned closer together. 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.
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. From there the energy is converted into mechanical power and electricity is generated similar to the way a mechanical engine runs. 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. It will be used in fields of thousands to form a power facility capable of generating over 500MW of electricity.
Central receiver systems are also known as power towers. These concentrating power systems operate through the use of thousands of mirrors called heliostats that track the sun and reflect the heat energy onto a receiver that sits at the top of a tall tower. Molten salt is heated as it passes through the receiver and this then makes steam which operates 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.
An example of a central receiver system in development is the Solar Tres power plant being built in Spain. 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.
One of the crippling problems with solar energy has been the high cost per watt of electricity, but technological advancements are bringing those costs down. 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 power 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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