Question

PHY 206: Renewable Energy Resources Home Work 1 Due: Friday, 22nd April, 2020 1. Explain the difference between primary and secondary energy sources. Give three examples of secondary energy sources. 2. Show that the available power from the water in the plant can be written as P = pgQH where p is the density of water [kg/m?], g is the gravitational constant (m/s?], Q is the flow rate of water [m/s] and H corresponds to the head height [m]. 3. (1) A wind turbine with 110m rotor diameter is specified with a rated power output of 3.5MW at wind speed of 15 m/s at standard air density (p) 1.225 kg/m3. Find the overall efficiency (n) of this wind turbine. (ii) Compare the efficiency calculated in part (i) to Betz limit. Why is Ocean Thermal Energy Conversion (OTEC) not feasible outside the tropics? (1) Describe how tides occur. as if you are explaining them to a 10-yearold child. (ii) Tides are very predictable, so why are the capacity factors of tidal power plant not 100%? 4. 5.

Answer 1

Question(1)

Primary energy sources are those energy sources which can be used directly, as they appear in the natural environment: e.g. coal, oil, natural gas and wood, nuclear fuels (uranium), the sun, the wind, tides, mountain lakes, the rivers (from which hydroelectric energy can be obtained) and the Earth heat that supplies geothermal energy.

On the other hand, Secondary energy sources are those energy sources which cannot be harnessed directly from nature; rather, secondary energy is energy that has already been converted.

Three examples of secondary energy sources: Battery, Fuel cells, Solar cells, Electricity

Question (2)

Power, P = Energy / time ....Equation 1

Energy

= Potential energy stored in water

= mgH

Also, mass, m

= density * volume

= ρ*V

Thus, Energy = ρ*V*gH

Substituting it in equation 1:

P = ρ*V*gH / time

= ρ*V*gH / t

= ρ*(V/t)*gH

===> P = ρ*Q*gH (Since V/t = discharge = Q)

===> P = ρgQH (ANSWER)