Sunspot Technology

About

Brief Description SUNSPOT is a solar thermal power plant with rock-bed storage, containing a unique set of patented and individually licensable Stellenbosch University technologies. The SUNSPOT cycle is appropriate and efficient for generating, storing and deploying solar power in arid regions. Several adjustments to the design can be made to suit various requirements, such as: A lower technology version for provision of peak electricity and other similar critical needs using just a steam turbine. A very high efficiency combined cycle hybridized plant to give baseload electricity. Technical Description Solar radiation is concentrated onto a central receiver heat exchanger by means of a field of heliostats - simple, robust tracking mirrors, designed for easy transport and deployment. In the SUNSPOT cycle, compressed ambient air is heated in one of our unique, highly efficient central receiver designs. The hot air thereafter flows through a turbine which drives a compressor and a generator supplying electricity to a grid or transmission system. Air leaving the turbine at approximately 500°C is ducted into a packed rock-bed thermal storage facility. After sunset, heated air from the rock bed is blown across a finned tube steam generator. Superheated steam is supplied to a steam turbine which drives a generator to supply electricity to the grid at night. The steam leaving the turbine condenses in a dry or hybrid cooling system which rejects heat to the environment. Value Proposition With suitable gas burners or combustors located upstream of the turbine, changes in electrical output due to fluctuations in solar radiation during cloudy or rainy periods lasting hours or even days may be eliminated. By burning additional fuel, turbine temperature and efficiency can be increased to maximize plant output during daily peak power demand periods. Together with a large thermal storage facility the resultant flexibility in the control of power generation that satisfies the demand pattern will essentially eliminate the need to manage sophisticated and costly national power grid or transmission system issues. By employing local natural rock (e.g. granite) a large low-cost thermal energy storage capacity is made available to act as thermal store for the hot turbine exhaust gas. Although other storage options employing e.g. molten salts are available, they tend to be relatively expensive and are usually limited to only a few hours of operation. The large rock bed is effective for the entire period from sunset to sunrise. The steam cycle also generates power during the day if some hot turbine exhaust gas is fed directly to the boiler. Most solar power generating plants will be located in relatively arid regions of the world where an adequate supply of cooling water may not be available. Dry-cooled (air) or hybrid (dry/wet) cooling systems will therefore be naturally considered. A novelty of the SUNSPOT cycle is the fact that most of its cooling (condensing steam) is required during the night when ambient air temperatures may be 10°C to 20°C lower than during the day and dry-cooling will be correspondingly more effective. If limited amounts of brackish or waste water are available, cycle efficiency can be enhanced during the hottest hours by installing a hybrid (dry/wet) cooling system. Unique Characteristics Patented intelligent heliostat array which is cost-effective, simple, easily transportable, and easily deployed in a wide variety of environments. Patented solar receivers, with combined or separate high & low pressure options. Patented rock-bed energy storage unit. Optimized plant design with dry/wet cooling. Target Market Power utility companies and large campus solar thermal developments. Innovation Status Heliostat support structure - PCT/IB2012/053687 A support structure for multiple heliostats - PCT/IB2013/059931 Central solar receiver - SA Provisional 2013/02381 Dual pressure gas receiver –SA Provisional 2013/02103 Solar power tower receiver – PCT/IB2013/053287 Packed rock-bed thermal energy storage facility - SA Provisional 2013/03068 Dephlegmator - WO2013011414