How LPT Works

Thousands of mirrors track the sun in two dimensions and reflect the sunlight to a boiler that sits atop a tower. When the concentrated sunlight strikes the boiler’s pipes, it heats the water inside to 550°C – more than 1000° F – creating superheated steam at the temperature necessary to achieve the industry’s highest operating efficiencies. This high-temperature steam is then piped from the boiler to a standard turbine where electricity is generated. From here, transmission lines carry the power to homes and businesses. Nothing is wasted in this process. In order to conserve precious desert water, the steam is air-cooled and piped back into the system in a closed-loop, environmentally-friendly process.

Heliostats

The LPT 550 heliostats consist of two flat-glass mirrors, a support structure, a pylon and a tracking system. The mirrors are mounted onto the pylon and track the sun in two dimensions, reflecting the sunlight onto a boiler atop a tower.

BrightSource’s smaller, flat mirrors are more efficient, simpler to manufacture, and cost less to install than parabolic mirrors used in solar troughs. The heliostats are highly accurate and have over 35 years of longevity with practically zero maintenance with the exception of cleaning.

The ability to follow the sun in two dimensions enables the power system to track a greater percentage of the sun’s energy and achieve a much higher efficiency than other solar thermal technologies. Each heliostat, with a reflecting area of 14.4 m2, is individually installed and controlled with optimization software, resulting in greater flexibility in site configuration, and requiring much less site preparation. The pylons are placed directly into the ground, eliminating the need for concrete pads used with other solar thermal technologies and reducing the system’s environmental impact.

The average 100 megawatt BrightSource Energy solar plant will consist of 50,000 heliostats.

Control System

The aiming control system and the layout of solar fields are optimally designed to collect sunlight and send it to the receiver in a manner that maximizes steam output.

The aiming control system uses optimization software to instruct the solar field controller where each heliostat should aim to maximize solar energy collection and output. This patent pending software system accounts for the light flux intensity and distribution required on the boiler’s receiver, and various other conditions such as sun radiation, wind, air pressure and the number of heliostats available for tracking. When computing the optimal aiming policy, the aiming control system factors in the differences between heliostats with respect to their tracking accuracy, the intensity of the beam they reflect (both of these factors are dependent mainly on the distance to the receiver), the shape of the beam and other relevant aspects.

Tower and Boiler

The tower is a metal structure designed specifically to support the boiler and efficiently move high-quality steam to the power block at its base. The height of the tower enables heliostats from significant distances to accurately reflect sunlight to the receiver, providing the ability to scale a system to meet a customer’s specific energy needs.

The receiver is a traditional high-efficiency boiler positioned on top of the tower. The boiler converts the concentrated energy of the sun reflected from the heliostats into superheated steam. The boiler is supplied by conventional boiler manufacturers and complies with standard boiler design parameters, providing performance warranties and industry best practices. The boiler’s tubes are coated with a material that maximizes energy absorbance. The boiler has steam generation, superheating and reheating sections and is designed to generate superheated steam of 550 C of temperature and 160 bars of pressure.

Power Block

The LPT 550 power block system is the same used in traditional power generation facilities to convert steam to electricity. The only difference is that instead of using nuclear or fossil fuels, the LPT 550 system uses clean and abundant energy from the sun as a fuel source.

The power block consists of a conventional steam turbine generator with a reheat cycle, and auxiliary functions of heat rejection, water treatment, water disposal and grid interconnection capabilities. The integration of high-efficiency pre-existing turbine technologies provides performance warranties and enables the system to maximize thermal to electricity efficiencies. By using air, rather than water, to cool the steam, the power block uses 90 percent less water.

Today’s most efficient steam turbine generators are designed for 550 C. The LPT 550 system is designed specifically to meet this steam temperature level, thereby maximizing the solar plant’s overall efficiency.