Five technologies are enough for the energy transition

Photovoltaics, wind power, batteries, electrolysers and CO2 vacuum cleaners known as Direct Air Capture (DAC) - these are the five technologies we need for a successful energy transition, says Christian Breyer. However, the solar economist from Lappeenranta University of Technology (LUT) in Finland does not consider new hydropower plants, geothermal energy and bioenergy to be convincing solutions. Neither is green hydrogen. This is a cumbersome energy source that should merely be a building block for others, explains Breyer in ntv's "Climate Lab". The researcher sees the future of global energy supply on the world's oceans: In 30 years, floating solar power plants could generate electricity that can be converted into green ammonia, methanol or kerosene in huge offshore factories for synthetic fuels and distributed worldwide - thanks to decades-old processes and the new raw material CO2.

ntv.de: The German government is forging big hydrogen plans, dreaming of hydrogen heating systems and liquid gas terminals where green hydrogen will one day land, but it is missing from their list. Why is that?

Christian Breyer: The list only contains the equipment and devices that we use to achieve the energy transition, not a specific product. Otherwise, electricity would always come first, which is the most important for the energy transition. That's why photovoltaics and wind power are crucial, especially for Europe and North America. That is self-explanatory.

And what about hydropower?

It's important, but it's already being put to excellent use worldwide. The potential is largely exhausted.

Is there no more potential for growth?

Hydropower capacities can certainly be increased by a third to 50 percent. But are we only looking for cheap and renewable energy systems or also sustainable ones? If sustainability is important to us, we must treat rivers with care. Large rivers such as the Mekong in Asia, the Congo in Africa and to some extent the Amazon in Brazil have the greatest potential for hydropower. Technically, it would be possible to build hydropower plants there, and it might also be economically attractive, but the river ecology would almost certainly be destroyed. And in the Congo alone, we are talking about a good 500 species that only live there. That's why hydropower, where it exists, is always part of the solution, but like other sustainable energy sources, it is limited.

Why is that?

In the case of geothermal energy, we have seen for decades that projects do not materialize to the extent that we would have liked. Bioenergy has the major disadvantage that there is no space for energy crops, because we need it for animal feed, which we give to animals, which we in turn eat. Whether this is a smart idea is another question.

PV and wind occupy the top positions because they have proven themselves, work and are cheap?

Of course they are. Ultimately, the energy transition is an economic issue. There is potential for other technologies, but at a different cost level. Solar energy in particular is incredibly cheap and is now even the cheapest form of electricity in the world. Just think about it: half of the electricity capacity added worldwide in 2021 was already PV. By 2050, around 10 billion people will live on Earth and around three quarters of them will live in the sun belt, where the sun shines all year round. This is cheap energy that is available everywhere. That's why batteries are so important.

The first solar parks are now being built on water. Because there is so much space for infrastructure?

This is a wonderful technology called "floating PV", which has been implemented over the last ten years mainly on lakes, reservoirs or ponds, where the grid connection is comparatively simple. The question has always been: does it also work on the sea? More and more parts of the world are trying this, naturally in calm waters without high waves. It can be mastered. We have investigated this using the Caribbean as an example, because it is well known that space is relatively scarce on many islands for energy supply.

Or in Singapore.

This is one of the places where the most research is being carried out into floating PV. But this will probably only be an addition to the energy mix, because if you take a close look at the geographical location, there is a lot to be said for simply laying a power line to Sumatra. This huge Indonesian island is right next door. You wouldn't need that much space there to supply a small country like Singapore with electricity. If you take this vision 20 to 30 years further, huge factories for synthetic fuels in international waters would be possible: a large, floating PV power plant generates electricity and green hydrogen via electrolysis. You can't do much with that, so you convert it into ammonia, methanol or kerosene. These substances could in turn be collected by tankers at regular intervals from these offshore factories and distributed on the world markets.

The benefits of PV, wind and batteries are obvious. But why does the green hydrogen have to be converted again?

In principle, you can do a lot with hydrogen, but hydrogen is the smallest molecule in the universe and therefore difficult to handle. It readily diffuses through materials, is highly flammable and transportation is complicated. It can be handled technically, but it costs money. And at the end of the day, shipping and air transportation with electricity and batteries only work over short distances. I can easily recharge the battery on the Rhine, but not on large oceans. You need dense, chemical energy sources there. And we already know that kerosene does not have to be produced from crude oil: We need hydrogen and a carbon, usually CO2. We can then use the Fischer-Tropsch process to produce synthetic fuels such as kerosene.

Electrolyzers are needed for this process?

For the first step, when we produce green hydrogen. Then all we need is CO2, which is suddenly no longer an exhaust gas and causes emissions, but a raw material. Then we would have a solution for aviation that would not require any major changes to the current aircraft fleet. Another advantage is that, in addition to kerosene, hydrogen can also be converted into almost all the other important products we need: Methanol for the chemical industry or for shipping, or into ammonia as a fertilizer for agriculture. Hydrogen itself is mainly needed in steel production.

And where do we get the CO2 from? Is this the fifth key technology, the CO2 vacuum cleaner?

CO2 can come from all kinds of sources, but ultimately Direct Air Capture (DAC) is probably the most scalable solution. Because if we take climate change and the energy transition seriously, we will soon be curtailing gas-fired power plants, coal-fired power plants and coal-based steel production, and thus all major processes that produce large CO2 emissions. Waste incineration plants, paper mills and cement factories would remain, but these would be rather small sources in terms of volume to produce methanol for the chemical industry, kerosene for aviation and ammonia for agriculture. How do we close this coverage gap? We take the CO2 from the reservoir in which there is already too much, the atmosphere. The costs for this should be within an acceptable range.

Then all the problems are solved - in theory anyway. But aren't we already too late? Yes, a lot of solar parks are being built around the world, but there is a lack of storage capacity everywhere to be able to use solar power around the clock. And DAC has only been used on a small scale so far.

Wind power works, even if not all teething troubles have been resolved. But the only thing still being worked on there is the details. The same goes for photovoltaics. PV modules are becoming 0.5 percentage points more efficient on average every year. This trend has been going on for 20 years and will continue for many more years, while at the same time becoming ever cheaper.

Then we'll put a tick in the box for wind and PV. What about batteries?

We are seeing the turning point. In recent years, there have been problems with cobalt and nickel shortages, but lithium-ion batteries are now mainly used in electric cars and home storage systems, which are increasingly being built without cobalt and nickel. Do we have enough lithium? Opinions differ on this. In principle there is enough, the world's oceans are full of it, we just can't get it out efficiently. That is the real problem. This year, the two world market leaders also introduced sodium-ion batteries. There are no longer any material shortages with them.

Is everything in the bag for batteries too?

There is a lot to be said for that. These companies have a reputation to lose and wouldn't do it if they didn't know it would work. And the growth rates are enormous: if the production of PV modules is growing at 30 percent per year, battery production is growing at 50 to 100 percent per year.

And electrolysers?

The situation is more critical there because the market is much smaller. But we've already mastered the technology for 100 years and there are around two dozen manufacturers and suppliers from all over the world. It will be an exciting race to see who can offer the best products at the best prices in the end. I'm not worried. With DAC, the only question is scaling, because the technology also works in this case: it has been used in nuclear submarines and on space stations since the 1960s. The only thing missing is large-scale commercialization, and these manufacturers are now also well-funded by investors.

Clara Pfeffer and Christian Herrmann spoke to Christian Breyer. The interview has been abridged and edited for clarity.