Scientists of the University of Graz have developed a tool to make optimum use of solar energy

6.4.2015 Photovoltaics is the only form of renewable energy that is able to cover today’s global energy demand and can even do so many times over.

The diurnal cycle and the cycle of the seasons, however, mean that photovoltaics is unable to provide a constant power supply in one location. Ao.Univ.-Prof. Dr. Karl Steininger from the Institute of Economics and the Wegener Center of the University of Graz and his team have developed an analysis tool that helps to make solar power available efficiently and constantly. The paper has just been published in the renowned Proceedings of the National Academy of Sciences.

Real weather values
’We determined the real solar radiation at 270 global sites by analysing the insolation shown for these sites in the NASA data of the past twenty years and transferring them to hourly values”, Steininger says. The scientists took this data as their starting point to derive the production capacity a photovoltaics plant of a given size would have at a certain time. ’By means of our tool we are able to determine what combinations of panel surface and storage capacity make sense from an economic perspective”, the economist explains. In order to supply the minimum energy required, the plants are either dimensioned large enough to produce sufficient electricity even in overcast conditions or when insolation levels are low during winter, or the storage capacities are of such vast dimensions that seasonal and/or bad weather losses can be evened out. ’The price of the modules is currently declining more rapidly than the price of storage systems which makes larger photovoltaic surfaces often the more logical choice”, the expert says. And space is certainly not a problem. Steininger: ’It would take a mere two percent of the world’s desert areas to supply the whole world with energy at its current demand level.”

The new analytical tool also helps to combine several photovoltaic plants at different global sites in an economically efficient manner. ’If we combine sufficiently remote eastern and western sites, there will always be daytime somewhere in the grid and the excess energy can be transmitted to the places where the sun is not above the horizon.” The same is true for a combination of sites on the northern and southern hemisphere. ’In summer, Austria is able to produce four times the solar energy volume it can generate in winter”, Steininger says. Transmission costs are currently significantly lower than storage costs.

Efficient management
The tool is also very useful for energy suppliers inasmuch as it allows them to respond to current weather situations and use their own photovoltaic systems in an optimum manner. The technologies for storing the generated electrical power differ in price and efficiency. When clouds are forecast plant managers could activate additional storage for example, and thus save the costs of storage in lasting high-pressure periods.

Steininger and his team have used a theoretical concept of ’isolines” from economics for this interdisciplinary application. The concept ensures a constant output level and has been demonstrated to be of practical value for economic optimization here in situations of variable conditions of solar insolation.

More information:
PNAS.org