Solar thermal energy Eng. Elamir Ahmed

Definition of solar thermal energy  Solar thermal energy is a renewable energy source.  Solar thermal uses technology to harness infrared energy from sunlight to capture and store heat. This stored heat is released later to warm water and air, or on an even larger scale, to generate steam which in turn powers a turbine.

Types of solar thermal system  Active solar thermal system: Uses a pump, fan, or other powered device.  Passive solar thermal system: Does not use a pump or fan - relies on natural forces “Gravity & density”.  Indirect solar thermal system: A heat exchanger is used to transfer heat. Example: transfer heat from the circulating fluid to the city water.  Direct solar thermal system: Does not use a heat exchanger, direct heat transfer. Example: City or potable water is circulated from the tank to the collector and back.

Solar collectors  Dark Surface with High Absorptance Gathers Full Spectrum of Solar Radiation.  Glass and/or Selective Surface Used to Minimize Conduction and Re-radiation Losses.  Efficiency Dependant on Collector Design and Working Temperature.

Types of solar collectors  Collector type  temperature range (1) Flat-plate ºC ( ºF) (2) Evacuated tube ºC ( ºF) (3) Concentrating parabolic ºC ( ºF)

Flat plate collectors  Flat-plate collector is an insulated metal box with a glass or plastic cover (called the glazing) and a dark-colored absorber plate.  These collectors heat liquid or air at temperatures less than 230°F.

evacuated tube collectors  Evacuated-tube collectors are usually made of parallel rows of transparent glass tubes. Each tube contains a glass outer tube and metal absorber tube attached to a fin. The fin is covered with a coating that absorbs solar energy well, but which inhibits radiative heat loss. Air is removed, or evacuated, from the space between the two glass tubes to form a vacuum, which eliminates conductive and convective heat loss.  The collectors can achieve high temperatures (230°F to 300°F), making them more appropriate for cooling, commercial and industrial applications. However, evacuated-tube collectors are more expensive than flat-plate collectors, with cost about twice that of flat-plate collectors.

Concentrating collectors  Concentrating collectors consist of parabolic and mirrored surfaces to concentrate and get sunlight energy.  They are able to generate very high temperatures.  They demand direct sunlight and do not perform well in climates with low levels of direct sunlight.

Solar thermal application Solar water heating Solar pool heating Solar space heating Solar space cooling Solar power station Solar cooking Day-lighting

Solar water heating  One of the most cost-effective ways to include renewable technologies into a building is by incorporating solar hot water.  Most solar water heating systems for buildings have two main parts: (1) solar collector and (2) storage tank.  The most common collector used in solar hot water systems is the flat-plate collector.  Solar water heating systems can be either active or passive, but the most common are active systems.

Solar pool heating  The solar pool heating system uses the existing pool pump to circulate water through the solar collector where it is warmed by the sun.  Applicable for Indoor or Outdoor Pools  Highest Operating Efficiency

Solar space heating  A solar space-heating system can consist of passive system or active system.  Passive systems are typically less costly and less complex than active systems.  when retrofitting a building, active systems might be the only option for obtaining solar energy.

Solar space Cooling (Solar Absorption System)  Solar absorption system uses solar heat instead of electricity and compressor to drive the device.  Solar absorption systems use solar heat to separate a mixture of absorbent and refrigerant fluids. Once separated, the refrigerant is condensed and evaporated to create a cooling effect. It is then reabsorbed to repeat the cycle.  Solar space cooling systems are expensive and complicated to install and maintain.  The great advantage is reduced energy bills.

Solar absorption chiller

Solar thermal power station Power Tower Power Tower uses thousands of sun-tracking reflectors or heliostats to direct and concentrate solar radiation onto a boiler located atop a tower. The temperature in the boiler rises and the steam raised can be used to drive a turbine, which in turn drives an electric generator producing electricity.

Solar cooking  Solar cooking is a technology which has been given a lot of attention in recent years in developing countries.  The basic design is that of a box with a glass cover. The box is lined with insulation and a reflective surface is applied to concentrate the heat onto the pots. The pots can be painted black to help with heat absorption. The solar radiation raises the temperature sufficiently to boil the contents in the pots.  Cooking time is often a lot slower than conventional cooking stoves but there is no fuel cost.

Day-lighting  A simple and obvious use for solar energy is to provide light for use in buildings.  The buildings are designed in such a way that the light of the sun can be used to provide sufficient light for the activities taking place within the building.  The energy saving is significant and natural lighting is often preferred to artificial electric lighting.

Solar thermal advantages  Cost Effective: Solar thermal systems can save you up to 60% of your costs. They offer the lowest cost of renewable energy technology.  Easy installation: Solar thermal systems can easily be installed and retrofitted to most buildings.  Efficiency: Solar thermal system is the most efficient use of renewable energy; it's available when you need it, and it's a more effective solar collector - it even works in less sunny conditions.  Return on Investment: Solar thermal systems pay for themselves in as little as 5 years.  Reliability: Solar thermal systems are reliable and require little maintenance over their 25 year life.

Energy costs and energy saving (electrical energy) (solar thermal energy)

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