At the moment, photovoltaic systems generate around twelve percent of Germany’s electricity. What do you think the figure will be in the long term?
Twelve percent is just the start, because we need to become fully climate-neutral, if possible by 2035, to enable us to meet our targets under the Paris climate agreement. That will mean focusing not just on electricity but also on our entire energy requirements. For example, in the future we will need additional electricity for charging electric cars and powering heat pumps and, as a result, the demand for electricity will increase enormously. At the moment, renewable energies make up only 20 percent of our total consumption and solar power contributes just three percent to that. This is why everything will need to be scaled up in the future. I am assuming that we will meet around one third of our entire energy demand with photovoltaics in the long term.
How do you get to this figure?
You simply need to look in detail at all the sources of energy we have in Germany. There is very little potential left in hydropower, biomass is limited by the area of land that can be cultivated, and geothermal energy is too expensive. That leaves only wind and solar power. In the case of wind energy, the number of acceptable locations is small, so we need to make up the rest with photovoltaics. That is how I get to the figure of one third and it means that we need to multiply our existing capacity by ten.
How can we manage that?
First of all, it is important to say that we have huge amounts of solar energy at our disposal. If we were to cover all the arable land in Germany with solar panels, we could supply the whole of Europe with electricity. Of course, that is not an option, but with agrivoltaics we can grow food crops and generate solar energy at the same time. That is also the advantage it has over biomass, where it is very easy to get into the food vs. fuel debate. In addition, unused roofs and facades in Germany also have considerable potential, although it is relatively complex to install solar modules there. Because of the considerable shortage of skilled staff, we will not be able to expand in this area quickly enough. By comparison, an open space can be filled with solar panels much faster. So in the future our motto will be: As much roof area as possible and as much open space as necessary. In this context, “open space” can include roadsides and contaminated ground where nothing can be cultivated anyway or, of course, agrivoltaics.
One recent trend is plug-in panels for use on balconies. What do you think of them?
Obviously they will not produce huge amounts of electricity, but they do give people the feeling of doing something themselves and of contributing to the energy transition. That is why I am a big fan of these plug-in modules. Anyone with a suitable balcony should get hold of one. Whether the investment will pay off depends, of course, on the circumstances. If the balcony is facing in the wrong direction or is in shadow, it may not make sense to buy a plug-in panel. But otherwise I think systems like this could pay for themselves in ten or twelve years.
The supply of solar and wind energy fluctuates, which means that storage solutions are needed. How do you intend to resolve the storage problem?
This issue is always rolled out as the killer argument against renewable energies. It is obvious to me, as an engineer, that we need storage because of the fluctuations in electricity generation. But we will not be able to solve this problem with one huge storage facility for the whole of Germany. Instead we need a combination of different solutions. Part of this will definitely be electric vehicles. The batteries of all the electric cars registered in Germany already have a larger storage capacity than all the German pumped storage power plants put together. If there are around 15 million electric vehicles on the road by 2030, then in purely theoretical terms we could store enough power to supply the country for one night. In addition, there are already more than 200,000 stationary batteries in private houses in Germany. Another option is power-to-heat. For example, Vattenfall is building a huge heat storage facility in Berlin that will use surplus electricity to run heat pumps. It will be able to cover the district’s heating needs for several hours if there is a lack of wind and solar power.
And how can we manage longer lulls of this kind?
Power-to-gas is a possible solution which would provide a supply for several days or weeks. In the summer or during very windy periods, we could produce hydrogen from renewable electricity which could be stored in salt caverns and used for electricity generation when required. To be able to do all this at a reasonable price, we need to work on developing our electrolysis systems further and scaling up existing prototypes.
China is making massive investments in photovoltaics and wind power, but, at the same time, also building large numbers of nuclear and coal-fired power stations. Should Germany be doing the same thing?
No. The Chinese have installed twenty times more renewable capacity than nuclear. And we must always bear in mind that China is a nuclear power. This is all about nuclear weapons. The situation in France and the United Kingdom is exactly the same. The ongoing expansion of coal-fired electricity generation in China is, of course, a disaster for the climate. However, these are often projects that were started years ago and that the Chinese government is now unwilling to abandon. The expansion of renewable energy in China is taking place on such an enormous scale that the country will hopefully move away from coal sooner or later.
People often say that we can use the sun and the wind for free, but we still have very high electricity prices in Germany. When can we expect them to fall?
At the moment, it is the gas prices and the French nuclear power plants that have been shut down for inspections or repairs which are pushing electricity prices through the roof. By contrast a solar farm can supply electricity at a cost of four cents per kilowatt hour. This means that whenever the sun shines brightly, the market price of electricity falls. So if we had much more renewable energy in our electricity mix, the prices today would be much lower.
You are setting a good example. What do you have in the way of solar panels at home?
I now have three solar systems: a small one dating back to 2005 and a large one on the south-east-facing part of the roof from 2012. Two years later, I installed another system on the north-west-facing part of the roof. I do not have space for any more. My electric car functions as my storage facility where any surplus electricity is kept. As a result, I have generated 85 percent of the electricity needed for my electric car myself over the last year.