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Solar thermal

Heating and cooling with renewable energy

The energy  devoted to heating purposes makes up 57 % of Germany's overall final energy consumption.

Some 40 % of final energy  consumption in Germany is used  to heat  buildings. In the mid- to long-term goal is to have solar heating (active and  passive) cover nearly all heating demand (space  heating and  hot  water)  in new buildings  and  a large part  of demand in existing buildings. Another  field of application that  is becoming more  important is the provision  of process  heat  at high  temperatures.

Heat from solar thermal collectors

Solar heat can be collected in various ways as a source of energy:

•   Solar thermal collectors  can heat  up service water  and  drinking  water,  be used  for space heating, and  high-temperature process  heat
•   Passive solar energy  can be used  in architecture

Research and  development requirements

•   R&D into more  efficient and  more  cost- effective large collector  fields in the low temperature range, especially for the heating of buildings
•   Development of improved long-term storage as an important component in a more  intensive  collector  utilisation  strategy
•   Material research for alternative, ecologically friendly absorbers with good heat  conducti- vity, anti-corrosive properties, and  temperature  resistance
•   Development of new heat  carrier media modified for absorbers
•   Development of highly efficient collectors, including concentrating systems  for industrial and  commercial process  heat  (also in conjunction with combined heat  and power) as well as desalination of sea water
•   Development of model-based networked control systems and remote monitoring processes
•   Development of switchable absorption surfaces on building  envelopes
•   Development and  implementation  of parameters for the logging of the solar energy  yields of various systems

Heat from biomass

The sun’s energy  stored  in the form of biomass can be converted directly into heat. The thermal conversion technology used  for this is combustion. This technology has already reached an advanced level. Heat from biomass
is also produced in combined heat  and  power plants.

The potential of biomass  energy  for heat production in Germany is at least 10 % of current energy  consumption. The German government's ambitious targets for the use of biomass  as a source  of energy  require  new concepts that  will provide  for competitive generation costs along  with improved energy payback  and  ecological  impacts.

Research and  development requirements

More research needs  to be directed towards affordable, low-emission and  low-corrosion combustion technologies in the field of conventional (combustion) heat  generators for the use of solid biomass. Furthermore, innovative energy  conversion systems  must  be researched and  developed so that  residual  heat can be better utilized in cogeneration units fired by biomass  for heating and  cooling.

Cooling  with solar heat

Heat can be used  in combination with sorption technologies to drive thermodynamic circulation processes that  produce high-quality heating or cooling  (thermochemical heat pump).

Here, a distinction is made between adsorptive systems  that  work with solids (such as silica gel and  water)  and systems  that  work with fluids (such as lithium bromide and  water).

Typical temperatures for single-stage systems range from 60°C to 120°C.  They are therefore ideal for operation with solar heat, district heat, waste  heat  from cogeneration units,  or fuel cells. Because cooling  is mainly needed in the summer when  there  is generally  an excess of solar energy  and  waste  heat  available,  these environmentally friendly sorption technologies (no CFCs) are ideal for air-conditioning and refrigeration.

Another  advantage of these  cooling  systems  is that  in most  cases they can be set to a second operational mode to function as heating systems  as well. At the same  time,  sorption systems  also offer capabilities for the efficient long-term storage of thermal energy  – a major advantage of the widespread use of solar energy systems.

The technical feasibility of solar-operated systems has been demonstrated successfully in many  projects  in recent years. Today there  are already  market segments in which  it makes economic sense to use these  systems.  Investiga- tions reveal a large number of approaches to improvement, which  if implemented would enable additional markets  to be opened up to their use.

Research and  development requirements

•   Material research in the field of absorbance
•   For the development of small thermal cooling  systems  (compact, efficient heat exchangers, internal  heat  recovery)
•   Development of electric/thermal hybrid systems
•   Research into system  technology for system concepts, design, controls, maintenance, and  equipment management

Heating and  cooling  with geothermal energy

The use of geothermal energy  for heating purposes and  the use of water  saturated rock formations below  ground for cold water  storage in connection with seasonal  air-conditioning
and  cooling  is already  established on a commercial basis. Particularly, heating by means of geothermal energy  is presently experiencing a period  of considerable growth in Germany. Shallow geothermics is used  for heating and/or cooling  in connection with vertical heat exchangers and  heat  pumps. But the enormous technical potential of geothermal energy sources is still far from being  fully exploited in Germany.

Research and  development requirements

The main  R&D task consists  of providing this technology dependably and  predictably. For geothermal energy  to become economically competitive, the efficiency of geothermal systems  has to be be increased which  is indicated by seasonal  performance factor (SPF) that  describes  the ratio of useful energy  output (heat  generated) to the energy  input  (electri- city), averaged over an entire  heating season.

Depending on the heat  source  SPF of 3 to more than  4 are attained for ambient air and  water (in vertical heat  exchangers), respectively. Larger supply systems  should  be improved by a cost effective seasonal  storage of heat  or cold below  ground. Additionally,  deep heat  sources have to be exploited more  economically. Research can be divided  into two main categories:

1.   Shallow geothermics
•   An optimization of systems  above  ground will profit from an improved knowledge of the geological and  geothermal situation below  ground.
•   Higher energy  efficiency additionally requires  a program for SPF increase  to > 5. The competitiveness of absorption heat pumps needs  to be improved.
•   The integration of underground heat  and cold reservoirs in local energy  supply systems  must  be developed.

2.   Deep geothermics
•   Exploration  technologies have to be devel- oped to increase  the accuracy  of expensive drillings and  to enable forecasts  on the behaviour of the subsurface during long- term  operation.
•   Geothermal technology development requires  the systematic continuation of research aiming  at the exploration and exploitation of productive sources  at low costs and  lower risk so that  various locations with different  geological settings can be used as energy  sources.







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