Thermodynamics problem Concentrated solar power driven electricity generation is

Question

Thermodynamics problem

Concentrated solar power driven electricity generation is popular in areas where fuel sources are either absent or highly expensive. Such systems can be very large, like the 650 MW plant recently commissioned in Tamil Nadu, or much smaller village-scale units. Regardless of scale, the best one can expect from direct solar radiation is about 1300 W/m^2. Assume a 1 m^2 collector and that the units uses water as the working fluid. For safety reasons the peak pressure must be less than 5 bar (75 psia). Assume a surroundings temperature of 35 C and a mass flow rate of 0.3 g/sec. Water exists the condenser as a saturated liquid. What is the minimum condenser temperature? Assume 75% of the collected sunlight is deposited in the water while it's flowing through the boiler. If the steam exits the turbine at the minimum condenser temperature and with a quality of 100%, what is the turbine output power (in W)? What is the pump power necessary to run the system (in W)? What is the system thermal efficiency?

Explanation / Answer

SOLUTION:- m = 0.3 g/s, T1 = 35C = 308K

As mentioned in the problem 75 % of sunlight is absorbed by water equivalent to Q = 1300W for 1m2 collector.

By formula Q = m x Cp x (T2 - 35) i.e. 1300 = 0.0003 x 4187 x (T2 - 308)

i.e. T2 = 1343K = 1070C

Assuming the turbine efficiency of 90%, the power output by calculations = 155 KW (ANSWER)

System thermal efficiency = 0.75 x 0.90 = 0.675 = 67.5 % (ANSWER)

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