Christian Bauer, Ecosystems Scientist, Switzerland

“Hydropower is the most ecological form of energy”

Christian Bauer deals with life cycle assessments and the sustainability of the energy supply and mobility. Since completing his studies in ecosystem sciences in Graz, Austria, he has worked in the Laboratory for Energy Systems Analysis at the Paul Scherrer Institute in Aargau and is today responsible for their life cycle assessment activities. He played a central role from the outset in what has since become today's leading life cycle assessment database (

“The subject of life cycle assessments of energy sources will continue to grow in importance. Increasingly more people are asking themselves: Is solar energy as environmentally friendly as it’s reported to be? Is nuclear energy as bad as people say? What about hydropower? Or are there totally different solutions for the future of energy? There are a lot of half-truths being spread in heated discussions.
Of course, accepting different energy sources is an important factor when it comes to spreading them. But it's safe to assume that this will change when a certain energy source would suddenly have to cover mass consumption. How would the population react, for example, if convoys of trucks drove into forests to get wood to produce energy? All energy sources have the potential to pose an ethical-moral conflict, and when they have to deliver large amounts of energy, political arguments also play a role. But these are not the basis of our scientific research at the Paul Scherrer Institute (PSI).
Every form of energy has its strengths and weaknesses in a life cycle assessment. Sustainability plays a central role in our analysis. We have to keep in mind that there is an economically, ecological and societal sustainability. I’m interested in ecological sustainability. The best form of energy meets all three sustainability criteria. When it comes to the environmental field, which we analyse at the institute, we focus on air pollution, heavy metals, water pollution, over-fertilisation and land use.
In Switzerland, hydropower is the ideal energy source in the long term, but it can also weaken local biodiversity through land loss when a reservoir is constructed or through hydropeaking when draining water. Only 10 grams of carbon dioxide are consumed for every one kilowatt hour of energy produced by hydropower in Austria or Switzerland. Putting aside the risk of accidents and the problem of disposal, nuclear power would be as environmentally friendly because it only consumes 20 grams of carbon dioxide for one kilowatt hour of energy. This comes mostly from uranium mining and uranium enrichment. The carbon dioxide numbers for hydropower power and nuclear power also include constructing the power plants, but the infrastructure is almost negligible given the massive amounts of energy produced. This is more important in photovoltaics where manufacturing plays a larger role in comparison to the amounts of energy produced. This converts to around 60 grams of CO2 per kilowatt hour. A key element with photovoltaics is also where and under what conditions the solar cells were manufactured. If the energy used comes from hydropower, the calculations are very different than if coal power was used. Many photovoltaic systems are imported from China, where coal is the predominant source of electricity. Chinese manufacturers are not, however, particularly transparent when it comes to declaring the energy source, and so for our calculations we use the local average electricity mix as the basis. Despite the above-mentioned performance indicators, solar energy is far more ecological than any form of fossil energy. Wind power and geothermal energy produce around 20 to 30 grams of CO2 per kilowatt hour. Geothermal energy is an environmentally friendly form of energy, but drilling has caused earthquakes, leading to an acceptance problem. With wind energy, a large part of the constructed materials can be recycled at the end of their lifetime. It's not particularly complex, making it economically appealing. But when wind farms are built on land, they require a relatively large area that could otherwise be used for agriculture, for instance. As a result, only sparsely populated areas can be used for large wind farms. This would also apply to photovoltaic facilities if we don’t restrict them to rooftops.
A gas power plant produces 400 grams of CO2 per kilowatt hour, but it’s still far more ‘ecological’ than a coal-fired power plant because the latter also gives rise to even larger amounts of fine particulate matter, nitrogen oxide, sulphur dioxide and other pollutants. The commercial viability of biomass is difficult to achieve because it requires pollutant filters, which are relatively expensive for smaller facilities. Generating electricity from wood is currently unprofitable. Biomass is only profitable if the waste or residual material from agriculture is used. For example, manure or food waste produce methane when fermented. This doesn’t solve larger energy problems, but it does at least make a small contribution to the energy mix.
Even when the sun and wind produce more electricity than they do today, photovoltaic facilities and wind farms produce electricity irregularly. As there is no functioning energy supply without storage, we are also looking into storage batteries and networks at the Institute. Smart grids, i.e. intelligent electricity networks that adapt production to consumption in real-time, can also help better integrate renewable electricity. Lithium-ion batteries and other types are worth considering as storage, but also pumped storage power plants. Then there is power-to-gas technology, in which electricity is generated out of hydrogen and methane, as well as compressed air storage. These technologies are already suitable today for mass production, but they are not yet commercially viable. I don't dare predict whether this will be the case in five or ten years time.”
ittlerweile mehr als zehn Jahren mit Ökobilanzen und der Nachhaltigkeit der Energieversorgung und der Mobilität. Seit seinem Studium der Ökosystem-Wissenschaften in Graz (Österreich) ist er im Labor für Energiesystem-Analysen am Paul Scherrer Institut (PSI) im Aargau tätig und heute verantwortlich für die dortigen Aktivitäten in Sachen Ökobilanzen. Von Anfang an trug er dabei in zentraler Rolle zur heute weltweit führenden Ökobilanz-Datenbank »ecoinvent« bei.


View on the reservoir "Lago di Cavagnöö" (in the background) in Southern Switzerland. (Image: Raimundo Sierra, GNU Free Documentation License)


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