There are predominantly two types of solar power generation methods used to produce 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.
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. As renewable energy becomes more prevalent, we will see more concentrating solar power plants get developed.
The four main comercially productive concentrating solar power systems are: parabolic troughs, dish / engine systems, fresnel reflectors and central receiver systems. Each of these technologies have been proven and are currently in operation around the world with more developments in solar power 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 heat generated from this process heats the fluid to high levels so that super-charged steam is created. 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 even when the sun is not available. 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.
Fresnel reflectors provide a more concentrated focus of solar energy onto centrally placed receivers. 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 power plant is relatively small at only 5MW capacity, but it paves the way for future large-scale developments.
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. Looking as though they're honoring a higher deity, thousands of mirrors called heliostats cluster around a receiver that sits on top of a tall tower. The heat that is collected by the receiver then heats molten salt as it flows through which is then used to make steam that 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.
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.
There continues to be solid progress made in ways in which renewable energy is used to replace traditional energy sources. Concentrating solar power has proven to be a renewable energy source with still more untapped potential
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