In recent years, the solar photovoltaic industry has developed rapidly. Over 300 GW of power generation capacity has been added in the past three years. Its use has been expanded from public utilities to residential solar energy systems. The power generation price can also compete with coal-fired power generation. By contrast, the same is solar energy. The family's concentrated solar thermal power (CSP) development pace is very slow, only 1.5GW is added in three years. The United States did not even install any CSP system after September 2015.
The advantage of CSP is that it can convert the stored thermal energy into electricity at night time, and then sell the electricity to the central power grid. Calculated at US$ 20 per KWh, the cost can compete with KWh’s 150 US$ lithium-ion battery. However, the CSP system requires extensive installation. Set up land, the construction cost is still more than US$1 billion, and the power supply to the central grid is also not enough, resulting in a lower profitability than solar PV, and the huge construction cost also means that the CSP can only be used for public utilities. Unlike solar photovoltaics, they can expand rapidly and stimulate industrial progress.
In order to improve the development advantages of CSP solar energy, the National Renewable Energy Laboratory (NREL) and the Colorado School of Mines (CSM) proposed radically different new designs. They reduced the size of traditional CSP plants by a factor of 1,000, which could be said to be reduced from an average of 545 MW. 0.76MW. To reduce costs, the team also adopted cheaper materials and passive heat transfer mechanisms, and additionally designed a solar power tower, including a new type of heat storage and power block.
The system name is STEALS, and the thermal energy can be saved by recovering aluminum. The cost per KWh can be reduced to 12 US dollars. The new heat flow control method is adopted. The valve is used to control heat transfer and heat transfer fluid using a thermothermophon. ).
(Source: AppliedEnergy)
STEALS uses the Stirling engine (also known as the hot air engine) to convert heat into electricity, and because of its smaller scale than conventional CSP, the heliostat light conversion efficiency can be increased from 66% to 84%. According to the team It is predicted that the system can achieve an annual efficiency of 24%, but the Stirling engine is smaller than the Rankine cycles and the heat conversion efficiency is only 30%.
The heliostats first reflect sunlight to the phase change material (PCM) at the bottom of the STEALS, and the sodium heat pipe connected to the PCM transfers the heat to the various systems. The top of the heat pipe is also connected to the evaporator of the thermosyphon. It will be sent to the Stirling engine and condense on the top of the engine, then the liquid sodium will return to the evaporator. To adjust the power output, adjusting the valve switch can control the sodium flow and the heat from the heat storage device to the power block.
The research cost analysis pointed out that STEALS can design product scale according to power demand. In the future, besides competing with solar energy, lithium-ion battery and coal-fired power plants, it can also complement wind energy and solar photovoltaic and accelerate the grid to achieve 100% green energy. Has been published in "Applied Energy".