Solar Energy: Heat Storage

Storing heat is crucial to smooth out the fluctuations associated with the intermittent nature of solar radiation. Possible forms of energy storage include the following:

• biomass
• hydrogen generation
• electric batteries
• mechanical flywheels
• pumping water uphill
• thermal mass

Thermal Mass:

• efficiency depends upon specific heat of material and its thermal conductivity
  • Specific Heat --> measure of how much energy a substance can store (0-1)
  • Thermal conductivity --> measure of efficiency of heat transfer (i.e. getting it back when you want it)

Values for typical materials:

• Water 1.0 4.2
• Iron 0.1 320
• Glass 0.2 4.0
• Stone 0.2 3.0
• Wood (Oak) 0.6 1.4
• Brick 0.2 4.6
• Concrete 0.15 12
• Sand 0.2 2.3

Water is the clear winner followed by conrete. So thermal mass is most effectively used in the form of large tanks of water or several tons of concrete in an insulated container.

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