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Renewable heat
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Renewable heating sources

The different seasons and day and night times lead to variations in the heat and light available and present a challenge to their direct use to provide energy. However, this energy can be stored in various ways – directly as heat in the ground, lakes and rivers providing the heat source for heat pump systems or indirectly by the conversion of light into biomass as with plants and photosynthesis; this biomass is in turn burnt to produce heat or steam to drive electric generators.

Conversion

There are three conversion systems that produce heat

  • Absorption of sunlight to produce hot water – solar water heating
  • Concentrating the low-grade heat present in the ground, air or water – heat pumps
  • Burning biomass like wood or wood pellets – biomass

All of these systems can be incorporated into the home and can produce part or all of the heating requirements. The choice of system will depend upon the type of dwelling, its orientation and its location.

The overall conversion efficiency of any heating system will depend upon the uplift temperature as well as the amount of annual solar radiation. The larger the difference between the inlet and outlet water temperatures or the smaller the radiation intensity, the lower will be the efficiency

It will always be cost effective to reduce the heat demand before considering installing any new heating system. This will ensure that the smallest heating system possible can be installed, which will have a lower initial cost as well as a lower running cost.

Whilst on a sunny day, solar radiation can be directly received, on a cloudy day less radiation is received because it is scattered by the water droplets on the clouds. Typical values are shown in the Figure below.

Renewable heating sources



 

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