THE ECHO - Ferrostaal

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ProjECtS
“Solar power will
become much cheaper”
Professor Robert Pitz-Paal, Head of Solar Research at the German Aerospace
Centre, on cost-effective solar power and power imports from Africa
Mr. Pitz-Paal, you predict a bright future for “Concentrating
Solar Power Technology”. What does that mean exactly?
Hold a magnifying glass between the sun and a sheet of paper
– you can start a fire like that. Concentrating Solar Power
Technology works similarly: solar radiation is concentrated
and, using mirror technology, such high temperatures
are generated at a focal point that the heat can be used, for
example, to drive a conventional steam turbine power
plant.
What technologies already exist for this purpose? How
do they differ from each other?
In the case of parabolic trough collectors, the concentrator
is a trough in the shape of a parabola, along the focus line
of which a pipe is heated. The new linear Fresnel systems
are closely related to these. They represent a simplified approach
– the parabolic trough is divided into slices, so to
speak, and arranged on one plane. Then we also have the socalled
tower power plants with central receivers. In this case,
mirrors are moved to follow the sun and concentrate the ra-
diation at the top of a tower equipped with a heat exchanger.
There is also a system with parabolic dishes fitted with a
radiation receiver at the focal point which passes the solar
energy directly to an interfaced engine. Collectors of this
type, however, can only generate a few tens of kilowatts.
That is not very much. Which technologies are suitable
for large-scale power plants?
Parabolic trough collectors are already relatively well established.
They have been used commercially in the USA since
the mid-80s. Early this year, the first commercial tower power
plant went into operation, a 10 megawatt plant in Seville.
All the other technologies are still in the pilot phase – we
can’t really speak of commercial use yet.
What does the economic viability of solarthermal power
plants depend on?
One essential factor is the location – the incident solar radiation
which occurs there. The more radiation, the better. The
differences are great. In Germany, solar radiation is not even
THE ECHO August 2007
half as high as in southern Spain. In the Californian desert
it is another thirty or forty per cent higher - three times as
high as in Germany in other words. That makes power generation
much cheaper. Another important factor is the size
of the solar power plant. The larger the plant, the more viable.
And then, of course, the technology is also crucial - it
has to be as inexpensive as possible while nevertheless being
efficient. If higher temperatures can be achieved at lower
cost, the viability can be increased. That is exactly the aim
of Fresnel technology.
How realistic are solar power plants in Africa? The sunshine
is very reliable there.
There have already been invitations to tender in various African
states. In Algeria, construction of the first power plant
is just starting. Morocco and Egypt will probably conclude
contracts this year. The potential in North Africa is enormous.
There are really large open spaces there, with very
high radiation combined with a rapidly growing demand
for energy. Particularly in the case of Africa, it is important
that solar technology be developed quickly and for it to
become competitive. This is due to the fact that in Africa,
unlike here, there are very few subsidies for regenerative
energy.
If we bundle solar power generation for Europe in that
region, are we not making ourselves as dependent in future
on the sunny countries of Africa as we now are on
the oil states?
No. The DLR has carried out a series of studies. The scenarios
assume that, by 2050, about 15 per cent of our energy requirements
can be covered by solar imports from Africa and that
the remainder will largely be directly generated in Europe using
our own renewable resources. Today we are still 60 per
cent dependent on imports.
But renewable resources are still relatively expensive to
produce, so there is little demand. According to dLR forecasts,
production costs for solarthermal power plants will
be halved by the year 2020. How will this be achieved?
The Scientific Advisory Board to the German Federal Government
estimates that, by the end of the century, energy requirements
will mainly be met by solarthermal power plants.
By the mass production of components, by the construction
of very large plants and by the achievement of better
efficiency by means of higher temperatures – for example
by direct steam generation using Fresnel technology – and
by the integration of large thermal energy storage units. All
of these factors are already feasible. But until we have reached
that stage, we will be dependent on subsidised markets.
do firms who invest now have to accept that they will
make losses in the initial phase?
I think not because, fortunately, there are feed-in tariffs and
other incentives. The market introduction of solar technology
has political support, the additional costs for renew-
able energies in Spain and Germany, for example, are borne
by all power consumers – an essential mechanism which
costs the individual citizen very little but which will benefit
national economies in the long term, as prices for fossil
fuels are rising.
Example of the global energy
mix in 2100
Primary energy use (exajoules per year)
1600
1400
1200
1000
800
600
400
200
0
Geothermics
Other renewables
Solar collectors
Solarthermal power plants
and photovoltaic units
Wind
Biomass (modern)
Biomass (traditional)
Hydropower
Gas
Coal
(Source: Wissenschaftlicher Beirat der Bundesregierung für globale Umweltveränderungen
– Scientific Advisory Board to the German Federal Government on Global Environmental
Change – 2003)
Oil
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