Which is hotter Arizona or Australia

Solar and wind power: electricity from hot air

London. It's a combination of solar and wind power, and the idea has electrified engineers and environmentalists for decades. The first concepts for solar chimney power plants already existed in the 1950s, now French-German technicians have taken them up and varied them. While the first designs provided for towers with a height of 1000 meters, surrounded by greenhouse-like operating rooms with an area of ​​800 soccer fields, the latest systems are significantly smaller: they are content with 160-meter-high chimneys on a floor area of ​​14 football pitches.

The principle of power plants is simple: They consist of the largest possible area closed at the top, on which hot air is generated like in a greenhouse, and the largest possible chimney through which the heated air rises and generates electricity via turbines . Such a power plant does not need any of the modern high-tech raw materials such as those used in the solar cell industry - gallium, indium and so on are finite and extremely rare on top of that. In addition, a updraft power plant still works at night because it uses the daytime residual heat given off by the ground in the cooler night air. The difference between day and night operation is smaller than with pure solar power plants, peaks only occur at a moderate rate. Both are good for the stability and predictability of a power grid.

+++ Hamburg pioneer of an innovative energy concept +++

However, an updraft power plant has a very low level of efficiency of well below one percent of the sun's energy. But it can work economically with that. It just has to be big enough: Experts assume that such a sun chimney with an installed nominal output of 100 to 200 megawatts (MW) can generate electricity cheaply enough (for comparison: the largest wind rotors have an output of around six MW).

Large projects have been proposing towers that are kilometers high over huge greenhouse areas for a long time, but in reality nobody really wants to get on board. On a small scale, the principle has already proven itself in real tests: A prototype in Manzanares (Spain) ran for years without any significant problems until a storm destroyed it in 1989. The plant had a peak output of only 0.05 MW, but still had a tower 194 meters high. It cost the equivalent of several million euros. For a power plant with a significant output, investors would have to invest hundreds of millions, without any intermediate step. Other solar power plants, especially large photovoltaic systems, can be expanded step by step, you can feel your way. The following applies to updraft power plants: "completely or not at all".

The Blue Pearl company in London is now promising a small energy miracle. She wants to trim the towers to a height of 160 meters, which is storm and earthquake-proof. The planned power plants also use the water that condenses in the cooling air at the top of the tower. On its way to the ground, it should drive turbines like a conventional hydropower plant and thus significantly increase the overall efficiency. The developers emphasize that drinking water can also be obtained from some of the condensation water. So you add hydropower to the combination of solar and wind energy. However, when asked, Blue Pearl did not reveal the specific trick of how this should work.

According to the company, construction of the first demonstration power plant with a nominal output of 90 MW is starting in Jordan these days (see picture). The Japanese are also said to have expressed interest.

Blue Pearl is planning several types of power plants in various output classes from 90 to 1000 MW. According to company boss Franz Wesselmann, the costs amount to between 300 million and 1.8 billion euros. The largest type of power plant would do about as much as a nuclear reactor, but only cost a third. It would be the first time that the promising idea of ​​an updraft power plant would actually be ready for the market. Because as long as the vision is haunted in the minds of the technicians, the story of false project promises will last - and the futile search for investors.

At the end of the 1990s, a updraft power plant was to be built in Rajasthan (India). The plans were skyrocketing and there were no donors. Around five years ago, the company Enviromission wanted to install a 200 MW system in Australia, the performance profile of which would have matched the power consumption of air conditioning systems perfectly. It was never built, the company is now looking for investors in the USA for a 400 MW power plant in the Arizona desert. The tower in Australia would have been a kilometer high, higher than the Burj Khalifa in Dubai, currently the tallest building in the world at 828 meters.

Recently there was another, vehement voice for electricity from updraft chimneys in the form of the Libyan environmental technician Muftah Elarbash. Elarbash aims very high and presents gigantic power plants with a "hundred by hundred kilometers" area in the Sahara. He belongs to the current transitional government of Libya, but investor interest has so far been zero.

At the moment it seems as if the existing solar power plant technologies are making the running, although they are ultimately more expensive on really large dimensions. Various teams around the world are researching photovoltaic cells that work with more common raw materials instead of rare raw materials. In this way, the expansion of solar energy generation can continue even when the raw materials used today are exhausted.