Renewable Energy Part 4 Professor Mohamed A. El-Sharkawi

Hydrokinetic Energy

Types Small hydroelectric system Barrage System Water stream System Wave System

Types of small hydro systems Reservoir-Type Diversion-Type

Reservoir-Type Small Hydro System Generator Turbine Reservoir Penstock Discharge Head (H) H is the physical head

Potential Energy in Reservoir Generator Turbine Reservoir Penstock Discharge Head PEr Weight of water in reservoir Water head For variable head N:number of hours in one year Hi: head during ni hours

Potential Energy of Water Exiting Penstock Generator Turbine Reservoir Penstock Discharge PEp-out mass of water leaving penstock Effective water head

Potential Energy of Water Exiting Penstock Generator Turbine Reservoir Penstock Discharge PEp-out Water flow in penstock : water density, 1000kg/m3

When water is blocked When water flows Theoretical Head Generator Turbine Reservoir Penstock Discharge PEp-out When water flows Pr is the pressure at the end of the penstock in N/m2. vol is the volume of water passing through the pipe (m3) When water is blocked

Effective Head Generator Turbine Reservoir Penstock Discharge PEp-out

Evaluation The amount of electric power generated by a small hydroelectric system depends on three parameters: 1) Effective head h 2) Water flow rate 3) The efficiency

System Efficiency Power at the end of penstock Pp-out Blade Power Pblade Input power to Generator Pm Output electric power Pg Hydro losses Turbine losses Generator losses Penstock losses Power at the entrance of penstock Pp-in

Example A small hydroelectric site has a reservoir with 80 meter effective head. The penstock passes water at the rate of 100 kg/s. The hydro efficiency is 95%, the turbine efficiency is 85% and the efficiency of the generator is 90%. Assume that the owner of this small hydroelectric system sells the generated energy to the local utility at $0.15/kWh. Compute his income in 1 month.

Solution

Diversion-Type Small Hydro System (Water Stream System) Generator Turbine Discharge

Water Stream System

Water Stream System

Water Stream System The technology required to convert tidal energy into electricity is very similar to the technology used in either wind energy or hydroelectric power plants For the same blade size, the tidal mills produce much more power than wind turbines Water density is 800-1000 times the air density

Water Stream System As is the sweep area of the blades of the turbine in one revolution. Assuming a water density of 1000 kg/m3

Coefficient of Performance

Example A diversion-type small hydroelectric system is installed across a small river with current speed of 5 m/s. The diameter of the swept area of the turbine is 1.2 m. Assume that the coefficient of performance is 50%, the turbine efficiency is 90%, and the efficiency of the generator is 90%. Compute the output power of the plant and the energy generated in one year. If the price of the energy is $0.05/kWh, compute the income from this small hydroelectric plant in one year

Solution

Barrage System at High Tide Shore Dam Sea Side Turbine Water Flow Lagoon Side

Barrage System at Low Tide H Water Flow

Barrage

Barrage System A is the area of the base of the lagoon H is the maximum hydraulic heads.

Barrage System PE: Potential energy of Barrage System m: the mass of water moving from the high to low head side g: the acceleration of gravity H: the average of the difference in heads between the waters on the two sides of the dam

Barrage System: Semidiurnal tide

Barrage System: Semidiurnal tide

Issues Dams can slow the flow of water, thus potentially stimulate the growth of the red tide organism. Tidal energy is expensive method. Most of the energy is generated when the current is strong around peak or the slack of the tied.

Wave Energy

Wave Energy Hinges Hydraulic Motor Pistons Generator Wave

Wave Energy

Wave Characteristics Power/m of costal line Period of wave Trough Height (h) Wavelength (l) Crest Amplitude (a) Seawater Level Wave Characteristics Power/m of costal line Period of wave

Geothermal Energy

Cross Section of Earth

Earth Temperatures Depth Temperature 40km 100-200 km 5o-20o 500o-600o Mantle Depth

Heat Pump Pump and Heat Exchangers Hot water Tank Ground Warm air to house Hot water Tank Pump and Heat Exchangers Return cool air Geo-exchanger Ground

G Heat Magma Geothermal Reservoir Steam Turbine Reservoir Cooling Tower Mist eliminator Reservoir Heat Magma

Hot Dry Rock

The first geothermal power plants in the US (The Geysers) in northern California

Types of Geothermal Power Plants Dry Steam Power Plants: Steam temperature is very high (300oC) Flash Steam Power Plants: When the reservoir temperature is above 200oC and below 300oC the reservoir fluid is drawn into an expansion tank that lowers the pressure of the fluid. This causes some of the fluid to rapidly vaporize (flash) into steam. Binary-Cycle Power Plants: At moderate-temperature (below 200oC) the energy in the reservoir water is extracted by exchanging its heat with another fluid (called binary) The binary fluid has a much lower boiling point thus it is flashed into steam

Geothermal Energy Geothermal site must have the magma close enough to the surface to heat reservoirs accessible by current drilling technology.. Underground reservoirs are often surrounded by very hard rock; hard to reach The geothermal fluid can cause water pollution due to the presence of some gases and metals in the reservoirs. Geothermal fields could also produce carbon dioxide. Processing the reservoir fluid can produce objectionable odors.

Biomass Energy

Landfills Housings are being expanded closer to landfills Landfills and the trucks are considered sight pollution and safety hazards. Landfills produce unpleasant odors. Leachate, which is the fluid resulting from water mixed with garbage contaminates underground water. Ethanol (alcohol) and Methanol can be generated in landfills increasing the fire hazards

G Water pipes Stack Furnace Storage Turbine Condenser Steam Filter Light ash To landfills Heavy ash to landfills

Biomass Burning Biomass incineration produce heavy metal and Dioxins Heavy metal is mixed with ash posing serious pollution to water. Dioxin is the most dangerous element. It is highly carcinogenic and can cause cancer and genetic defects.