What’s your assessment of the potential of solar systems on the roof for the future energy supply?

Ute Mareck: In the SUN-AREA pilot project scientists from the Osnabrück University of Applied Technologies have calculated that, in Germany, the energy demand of all private households can be met to the tune of 100 per cent by solar power from the roof. To this end all suitable surfaces would have to be used – that is about 20 per cent of all roof surfaces. In the USA, 25 per cent of the roof surfaces of all residential homes and 60 per cent of all commercial roof surfaces would be available to house solar systems. This was indicated by the 2009 “Energy Self-Reliant States” study. So the potential is huge – we just have to use it.

Harald Tebbe: The roof is an inexhaustible resource. As with all other resources, the name of the game is to exploit them correctly. On the one hand, there are still innumerable house owners in Germany with excellently suited roofs, and we should help them to discover this hidden treasure. To this end many cities have just started to establish “roof registers”. This will enable citizens to quickly and easily check the suitability of their roofs on the Internet. On the other hand, the potential is sure to grow over the next few years: Improved systems and declining costs for solar modules will permit the use of surfaces that, from today’s viewpoint, are unsuitable or can be used only to a limited extent due to an East-West orientation or extensive shadows.

Holger Neuhaus: We should work on our “roof potential”; we should go for as large a basis of energy providers as possible. Then, by the way, we will not need any large-scale projects in the Sahara, either. After all, our vision is not just of a clean energy supply. The supply should also be independent, safe and fair. Solar power from the desert would be accompanied by exactly the same problems as we have been experiencing with oil and gas for decades: political dependencies and sophisticated long-distance supply lines. What is more, there is an inherent danger in these projects that – if at all – again only certain elite groups would benefit in the countries of origin.

What is your personal view of a full power supply with renewable energies? Will it be possible one day?

Ralf Lüdemann: The question of fully supplying society with renewable energies in the future is not a matter of “if” but of “when” and “how”. The Federal Association of Renewable Energies forecasts for 2020 that, in Germany alone, renewable energies will have a 47 per cent share of electricity consumption, and 7 per cent of it will, from today’s viewpoint, be accounted for by photovoltaic technology. This can of course only be an intermediate target on the way towards full supply, and that, however, is bound to come.

Ute Mareck: It is the right mix that counts. Whenever the sun is not shining, wind, water and biomass will be available. All renewable energy sources have their advantages and disadvantages. The solution lies in skilfully combining them. If we manage this, the energy demand in Germany can be covered to 100 per cent and for 24 hours a day with renewable energies. The pilot project “Regenerative Co-Generation Powerplant” by the Fraunhofer Institute for Wind Energy and Energy Systems Engineering (IWES) in Kassel has shown that this is possible. SolarWorld is also involved in this project. The co-generation power plant links and controls solar, wind, biomass and hydropower stations dotted around the whole of Germany. It is every bit as reliable and efficient as a conventional large-scale power station. The joint control of small and decentralized generating facilities makes it possible to provide energy reliably and in precise response to the demand.

Harald Tebbe: I would like to add one important aspect: The less we consume the less we have to generate. A full supply of renewable energies will become all the more likely the more we significantly increase the efficiency of our energy use as a whole. This, incidentally, also applies to energy consumption in the manufacture of our products – and we are also working on that.

Holger Neuhaus: Solar modules will come down in price because we consistently increase the degree of efficiency while at the same time reducing process complexity, and use considerably less raw material by significantly improving the yield. There will come a time when the silicon in a module costs less than the glass of a module. At this stage it becomes clear that low efficiency approaches like thin film technologies are pointless.

Ute Mareck: I assume that, in the coming ten years, the degree of efficiency of solar cells will increase much more rapidly than it has done so far: by about five per cent, i.e. 0.5 per cent per annum. Institutes, plant and material manufacturers worldwide have been working on photovoltaic products with increased intensity in recent years. Many of them contribute their experience from other industries such as microelectronics into the process. This gives development a major boost. An increase of the degree of efficiency is also conceivable through the hybridization of solar thermal and photovoltaic technology. Here we are only at the beginning. And let me again emphasize quite generally: People who do not use solar energy at all have a zero per cent degree of efficiency on their roof tiles, or even a negative effect in hot countries, because energy is needed to cool down overheated buildings – possibly even using fossil energy sources.

Holger Neuhaus: We are also further improving the lifespan of our products. In principle, our wish is for a product lifespan equivalent to that of the stone of a house. That is the beauty of photovoltaic technology: Nothing rotates and nothing lets off steam, and where there is no rotation and no steam, there is no damage either. To this end the factors limiting a warranty to 25 years today must be eliminated. We are working on that and I can say with absolute conviction that it is possible.

Ralf Lüdemann: Well, you see, we focus on the quality of our products: efficiency, long life, safety. This is also why we attach so much importance to subjecting all our products and all the materials they are made of to continuous quality checks during the production process and before launching innovations.

»We create solutions for almost every roof.« (Harald Tebbe)

Harald Tebbe: The storage technologies must improve in the next few years so that households can provide their own solar power and finally become energy suppliers. In cooperation with partners, we will develop complete packages including a battery: This will store the surplus energy yields of the solar plant, buffer the energy at low load times and feed it back at peak load times.

Ute Mareck: We face the dual challenge of cutting costs and at the same time securing and further increasing the recognized high quality of our products. The customer’s view is becoming more and more important in this process. Let me just emphasize one aspect: design. For example, not everyone likes blue modules on his or her roof. At this point, we should diversify our offer. In the future, SolarWorld will therefore also have black modules in its portfolio. In this way we reach broader customer groups and increase the scope of clean solar power technology.

Harald Tebbe: Quite right. In the future we will be guided even more than in the past by customer needs, and the products and their quality will play a major role in this context. We want to offer our customers an optimum “overall package”. This includes the safety of the investment, the certainty of permanent service, and protection against risks, if any.

Ralf Lüdemann: If we want to serve the mass market we will obviously have to offer our customers diversity. However, the name of the game here is not to produce boutique-type niche products for the most outlandish tastes. Our strategy is clear: We rely on a high-quality, universally applicable product without any frills. Our systems are simple, straightforward and easy-to-understand solutions. They have not been made excessively complex by being overloaded with added components. Rather, they are “allrounders” prepared in such a way that they can be combined with enhanced functionalities. We call this the “added-value option”. In the future, this will increasingly include solar thermal and buffer solutions as well as – quite significantly – the integration of smart grids.

Harald Tebbe: Generating added value for plant owners, installers and the trade is the central task of our PV systems teams: Our solutions should become ever simpler, better and more reliable. We offer solutions according to the modular construction principle: In our Sunkits^® solar kits we can combine standardized modules with an inverter, an assembly system, battery, modern control technology and other accessories. These elements are individually tailored to the customer’s needs and building situation. We create solutions for almost every roof.