Reducing the Energy Carbon Content - Energy and Climate: How to Achieve a Successful Energy Transition - page 77

under vacuum are necessary, in particular to supply absorption solar air
conditioning systems [64, 65].
In the housing sector, thermal solar energy is used mainly to provide
sanitary hot water. It may also be used to cater for a certain proportion of
heating requirements. For these applications, flat sensors have efficiencies
in the region of 50%. An area of about 4m 2 of sensors is required to meet
the hot water requirements of a family of four [64].
High-temperature thermal solar energy to produce electricity, requiring
concentration sensors, is not yet profitable and its future prospects are still
a subject of debate.
Photovoltaic electricity generates high hopes, although it is not yet
directly competitive with the electricity produced in the current power
stations. Consequently, the only present applications concern isolated
sites for the supply of relatively reduced levels of power. Significant
progress has nevertheless been observed. As with wind power, incentive
policies can be set up to offset the cost of developments on a larger scale. In
particular, the possibility of exporting some of the electricity produced to
the electricity grid, at a sufficiently attractive purchase price, should
promote deployment of photovoltaic panels in the housing sector. As
mentioned in Chapter 5, integration of solar panels in the housing sector
could revolutionise the future design of buildings.
Photovoltaic cells are assembled in modules. After a significant drop,
the average cost of the productionmodules is currently tending to stagnate
or even increase slightly due to a shortage of silicon, further to a rapid
increase in demand. The cost of a system connected to the grid is about
D

5/Wp 3 . For a system equipped with battery storage, this cost is between

6/Wp and 8/Wp. The cost of the kWh produced is between 0.25 and

D D D

1.5 with storage [61].
The global installed power increased from 20MWp in 1985 to
37 500MWp in 2005 [60]. Current forecasts predict an installed power
of 66 400MWp in 2020.
The market is currently dominated (80% share) by mono- or multi-
crystalline silicon cells. We can expect further progress in the field of
photovoltaic cells, especially by reducing the thickness of the silicon layers
and by mass production. Thin layers are produced using multicrystalline
silicon deposited on various substrates (10-40

0.5 without storage and between 1 and

D D D

m layers) or amorphous

m

silicon (1 m layers).

m

3 Wp, watt of peak power. The peak power is the maximum power which can be delivered when
solar radiation is at a maximum.