Nur Energie works with various solar energy technologies – including CSP, CPV and PV- selecting the best matched technology for each particular project and its unique geographical and solar resource characteristics.
CONCENTRATED SOLAR POWER (CSP)
Concentrated solar power technology (“CSP”) uses mirrors to track the sun and concentrate solar rays onto a receiver that generates heat to produce steam, which is then sent to a steam turbine to generate electricity.
CSP technology is a very efficient application of solar power but it requires certain specific conditions. The location for a CSP plant must have high levels of direct sunlight (direct normal irradiance or “DNI”), dry climate conditions, relatively flat unused land and access to small amounts of water therefore limiting sites around the globe that can be used for CSP. The best areas for CSP are the desert regions of North Africa, South Africa, the Middle East, Tibet, Australia, the USA (California) and parts of Latin America (Chile).
Within CSP itself there are four main types of technology:
- CSP Tower
- Parabolic Trough
- Linear Fresnel
- Dish Stirling
CSP tower technology uses a field of flat mirrors (heliostats) that track the Sun and concentrate the Sun rays onto a boiler (the “Central Receiver”) that sits at the top of a tower. The central receiver then converts the large amount of solar energy collected from the total surface of the heliostats into heat in the form of steam and this is sent into a traditional steam turbine.
There are currently 3.95 GW of CSP projects operational in the world with 15.3 GW more in development and construction. Tower’s are increasingly becoming the leader in CSP technologies with a number of large scale projects online and even more in construction. The most well-known projects are Torresol’s 19MW ‘Gemasolar’ plant in Spain that operated 24 hours a day for 5 consecutive weeks in 2013 and BrightSource Energies 392MW Ivanpah plant in California, USA that recently came online making it the largest operational solar plant in the world. There are a number of other larger projects in construction in the Middle East, Africa and the Americas.
There are two commercially operational types of solar tower configurations:
1. Direct Steam Generation (DSG), where steam boiler is located atop of the central receiver tower and feeds steam directly to the turbine.
2. Molten Salt Receiver (MSR), where salts are heated atop of tower and stored in molten salt storage tanks. Thermal energy is stored in the salts is then used to produce steam, decoupling energy capture and energy release.
Other CSP technologies
A parabolic trough uses a parabolic reflector that concentrates Sunlight on to a collector tube with is located at the focal point of the parabolic trough. The troughs are usually aligned on a north-south axis and rotate to track the sun on a single axis. The thermal energy generated is used to heat a heat transfer fluid; thermal energy is carried to a heat exchanger where high pressure steam at ~400oC is generated.
Linear Fresnel collectors are line-focused components, using small flat mirrors to concentrate solar rays on to a tube collector to generate steam directly. Thermal energy is transferred through a heat transfer fluid to a heat exchanger to generate steam; which is then directed to a steam turbine to generate electricity.
Dish Stirling engines are point-focused distributed receivers that can achieve highest concentrating ratios. It consists of a standalone parabolic collector which concentrates solar rays to a receiver located at the focal point of the parabolic reflector. Heat transfer fluid is heated up to run a Stirling-engine for electricity generation.
Solar Photovoltaics (PV)
A photovoltaic system consists of several components that convert sunlight directly to electrical energy. Solar PV panels are made of silicon material that absorbs sunlight, the photons excite the electrons available in the silicon material and generate a flow of negatively charged electrons inducing an electric current.
Solar PV can be applied into building integrated systems or large utility scale systems.
Concentrated Photovoltaics (CPV)
CPV technology uses lenses and mirrors to concentrate large quantities of sunlight onto an area of PV cells where the sunlight is converted to electricity. By focusing solar light onto a cell means that less photovoltaic material is required, this system also makes use of high efficiency cells which are more economic because they require less space.