saltgradient solar ponds

8/7/2019 SaltGradient Solar Ponds

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Salt-Gradient, Solar Ponds:

One Kg of salt can supply as much electricity and three times as much heatas a Kg of coal burned in a combustor.

Naturally occurring Salt Ponds, first discovered in 1902 a few meters belowLake Medive in Transylvania with temperatures reaching 84 DegreesCentigrade at the bottom.Result of varying salinity, bottom fed by bed of salt, surface washed byconstant stream of fresh water.Salinity gradient gives the lake a vertical density difference and allows totrap and store solar energy.Artificial Salt-Gradient, Solar Ponds.Thermal Energy to:

Heat Buildings.Drive Industrial Processes.Generate Electricity.Desalt Water.Power Cooling Systems.

Israel: 7,000 sq. m. Pond provides 35 KW in Summer and 15 KW in Winterwith a peak of 150 KW.

Working:

The Pond/ Lake absorbs solar radiation in the water and material at bottom.Heated water expands and becomes less dense, quickly rising to the surfaceto lose heat to the atmosphere.Salt-Gradient.More Salt : More Dense.Surface 5% by weight and relatively light.Increase salt by depth till 20% by weight.Bottom heats and expands.Cannot rise, as it is denser than the top.

Becomes non-convecting.Warm Water trapped below.Lower waters can reach boiling point and over, recorded at 107 Degreescentigrade.

Three Zones:


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Surface Zone: Wind, evaporation and surface cooling in evenings, createssurface zone: 1/10 to m deep.

Non-Convecting Zone: 1 to 1 m in depth.Bottom Storage Zone: 1 to 2 m or as little as or as much as several meters.

The deeper the zone the more the heat.Lowest zone traps heat for long periods.Damping daily or even seasonal changes.Can be tapped for energy at night as well as day.Even during long periods of cloud cover or even ice cover.Depends upon location, water clarity and ambient temperature.Solar Pond can trap 10 to 20 % Solar energy.Each sq. m = to 2 gigajoules of thermal energy per year.(about 1 million BTU)

Flat Plate Collector of 1 m square is twice as efficient but 10 times morecost.

Evaporation and mixing of salt water increases salinity of the surface,destroying the gradient.Feed saline water to the bottom and less saline to the surface.Heated water is used to extract from hot brine through Heat Exchanger.Thermo Electric DevicesOrganic Rankine Cycle Engine (Turbine powered by evaporating organicfuel).

Factors to Determine Effectiveness:

1. Availability of Lo-Cost land, salt and water.2. Favorable climate conditions: Sunny days and high temperatures.3. Favorable ground conditions, soil impervious to heat and water,

lack of moving groundwater, no nearby drinking water.4. Low price compared to other energy sources.


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Fresh

Evaporation PondSolar Gradient Pond

SALINA:Salt flat, marsh or lake dry or saline water.Low-salt water fed through submerged diffuser.Mixing technique called Redistribution.

100 sq m heat for single family home in developed countries.50 to 100 families village.Heat for converting as much Bio mass to alcohol/ methane

1/1000 th as much as forest for fuel cooking.

Brine of Oil Wells and Geo Thermal Units can be used.US = $35/ sq m for 2000 sq m pond (1978)$ 73/ sq. m. for 1000 sq. m. in 1981.For Therma;l Energy = competitive.Electricity competitive for off grid and remote locations.Outlet for extracting brine has to be carefully sited to avoid cold spots.Dollars per sq. m. Conservative BestThermal Energy 28 7Electricity (base load) 20 12

PerformanceMegajoules per sq. m./ year

Average site Superior SiteThermal Energy: 900 1700Electricity (base load) 55 110Energy Cost (20% annual charge to amortize cost): $/ gigajoule

Conservative Best caseThermal Energy:

Average: 6.22 1.56Superior: 3.29 0.82

Electricity:Average: 26.00 16.00Superior: 13.00 8.00

saltgradient solar ponds

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