Overview Renewable Energy Technologies

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					Overview Renewable Energy Technologies  Solar Energy

 Solar Thermal Energy
 Solar Electricity  Wind Energy

 Hydro Energy
 Biomass  Wave and Tidal Power

 Geothermal


Source: Brunner, ISTS Graz


Solar Energy
The sun is a fusion reactor emitting 70-80 MW/m2 at 6000ºC from its corona.

The solar radiation intensity is almost constant outside earths atmosphere.
Currently used solar constant: 1367 W/m2 (± 3.3%)

The Sun and the Earth

The extraterrestial irradiance of ~1.35kW/m2 is reduced down to <1kW/m2 before it hits the earths surface.

The Global irradiance received at the surface is a combination of: • Direct irradiance (Beam irradiance) • Diffuse irradiance • Reflected irradiance

On a sunny day with an apparently clear sky the global irradiance is
Figure: W.Streicher

Irradiation Potential
The earth receives >10 000 times our energy need. Swedens land area receives ~1 000 times its energy need.

Irradiation Potential
The yearly average irradiation on a horizontal surface in Europe.

Irradiation on a horizontal plane [kWh/m2/a]

kWh/m2/a Pori 918 Hamburg 964 Graz 1154 Sevilla 1715

% 100 105 126 187

Figure: European Comission PVGIS,

Irradiation Potential
The yearly average irradiation on an optimally tilted surface in Europe.

Irradiation on an optimally tilted plane [kWh/m2/a]

kWh/m2/a Pori 1129 Hamburg 1104 Graz 1321 Sevilla 1947

% 100 98 117 172

Figure: European Comission PVGIS,

Irradiation Indonesia

Irradiation on an optimally tilted plane.

Data: European Comission PVGIS,


Monthly irradiation [kWh/m2]


The uneven yearly distribution of irradiation presents a problem in the Nordic Countries: The energy demand is highest when available irradiation is lowest.



100 Pori Hamburg Graz Sevilla


For solar fractions > ~25% we need seasonal storage of energy from summer to winter
(space heating+DHW systems)





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Irradiation Potential
OK... so Swedens land area receives ~1 000 times its energy need... Nice, but is it possible to harvest this potential in practice?

The total roof area in Sweden is about 250 000 000 m2
A good single family house solar thermal system can harvest 250 kWh/m2/a Bigger solar thermal systems can harvest around 350 kWh/m2/a

If we assume 300 kWh/m2/a on the average...
300 kWh/m2/a x 250 000 000 m2 = 75 TWh/a

The energy need for heating in Sweden is about 120 TWh/a.

So, with current solar thermal technology about 63% of this could be produced by covering all roof area in Sweden with collectors.

Of course this is not possible in practice for many reasons... Surveys report <10TWh/a as realistic potential for solar thermal.

Radiation on a Sloped Surface

Total irradiance on a tilted plane: Available measured radiation data usually for horizontal Total = Beam + Diffuse + Reflected

 re-calculate for tilted:

Figures: Duffie&Beckman

Collectors: Different Collector Types
There is a multitude of collector types commercially available:

Figure: Streicher.W.

The collector type is chosen according to the requirements of the application: temperature, efficiency, fluid, pressure, feasibility, etc.

Collectors: Flat Plate
Basic construction of a flat plate collector:

Flow configurations:

Figure: Streicher.W.

Figure: Streicher.W.

The absorber:

Figure: Sunstrip AB

Collectors: Flat Plate
And how it looks like in practise...

Collectors: Evacuated Tube
Basic construction of an EVT collector:

Figure: Streicher.W.

Fluid circulating in U-pipe

Figure: Duffie&Beckman

Collectors: Efficiencies
Optical - Heat loss - Quadr.correction The efficiency of a collector:
(simplified approach)

Obtained from collector tests