The Full Picture

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the average long-term radiation available. If a site is

found, time series are needed for the power plant tech-

nical design phase. For larger project developments,

hourly resolved time series of up to ten years are neces-

sary, for smaller projects monthly mean values are

sufficient. GEOSS satellites provide such long-term time

series over a large geographical area.

Services for plant management

– A service line for plant

management is needed once a solar energy system is

built. Automatic fault detection and performance control

allow reliable alarm issuing and assure the validity of the

investment, while a performance check for smaller plants

gives first estimates of performance and failures. Through

comparison between the effective energy production and

the corresponding solar energy at the array plane, the

proper functioning of the solar power plant can be moni-

tored in defined time intervals. Hourly values are used

for error analysis, comparing typical patterns of energy

loss and the profile of the actual failure.

Services for utilities

– Both energy supply and demand

require information on the solar resource. The schedul-

ing of large power plants and overall grid management

necessitates precise knowledge of the expected load.

Beside temperature, irradiance has a major environ-

mental influence of up to ten per cent on electricity

demand. For this reason solar irradiance needs to be

forecasted as well load. On the supply side, electric

power transmission systems collect power from conven-

ments. Basic information for solar energy users includes the amount

of incoming solar radiation measured at ground level. Global, diffuse

and direct irradiance are needed for the different technical systems.

Spectral distribution of irradiance will be required in the future, for

example, in the use of spectrally more sensitive thin film photo-

voltaic (PV) technologies.

Earth observation allows the provision of surface solar irradiance

services specifically adapted to users’ needs in the solar energy sector.

In particular, the temporal and spatial resolution of geostationary

satellites in the GOES and the METEOSAT series are essential for

this application.

An important function of meteorological geostationary satellites

is detecting cloud fields and monitoring their evolution in time over

extended regions of the world. Clouds are the main modulator of

daily and hourly solar irradiance, thus radiance measurements from

space represent a unique data source for geographically continuous

assessments of the solar resource at the earth’s surface.

In addition to cloud information, detailed knowledge about atmos-

pheric substances like aerosol particles, water vapour, trace gases

and air molecules involved in the scattering and absorption of

sunlight is a further necessity. Such information is taken from clima-

tologies, atmospheric modelling and atmospheric satellite

measurements.

Space-based services

Services for investment decision

– Site assessment allows the investor

to find the best site for a planned power plant and to optimise the

financial yield. Site analysis and optimisation is based on maps of

Irradiance image

Image showing annual sum of direct normal irradiance for 2004

Source: DLR

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