Ways to Sustainably Restructure the Energy System to Go Fossil Fuel-Free

New research at Empa describes how much more work is needed for Switzerland to sustain without fossil fuels in the future.

In winter, the production of solar power drops significantly, but this is precisely when the demand for electricity is highest. How can we close this gap? (Image credit: iStock)

There are two potential solutions: storing large quantities of energy in summer and reducing requirement in winter, or producing energy in the “sunny south” or “windy north” of the world and transmitting it here. The Empa scientists look at their research as a provocative stimulus for politics and society.

There is a lot to do in order to eliminate fossil fuels across the nation. It is, however, clear that it is going to be a generation project. Empa scientists Martin Rüdisüli, Sinan Teske, and Urs Elber have currently estimated how long and sheer the road to a sustainable energy system might be; their research was reported at the end of June in the journal Energies.

The scientists opted for a traditional method and initially gathered real data on electricity consumption, heating demands, and hot water consumption in Switzerland. The data subsequently acted as the foundation for a thought experiment. The electricity demands of Switzerland are still relatively simple to calculate: The Swiss grid operator Swissgrid offers comprehensive values for every quarter of an hour on every day of the year.

Hot water and heating energy demands are becoming more complex. The Empa experts employed data from the district heating supplier REFUNA, which delivers waste heat from the Beznau nuclear power plant to a number of communities in the lower Aare Valley.

Data analysis revealed that the heat demand of the connected houses associates rather well with the external temperature — and at nights warmer than 18 C, the heat is thus used only for process water and shower water.

Electrifying Heating Systems and Cars

The scientists made different presuppositions for their thought experiment. First of all, the majority of Swiss residents act like people in the lower Aare Valley and reside in comparable buildings.

Secondly, in order to escape from natural gas and heating oil, the heating demands of all buildings will first be decreased by approximately 42% through renovation measures; later, 3/4 of the remaining heating demands in houses and apartments renovated in this manner will be achieved with electric heat pumps.

And thirdly, mobility will be electrified to the extent that around 2/3 of all private car journeys can occur electrically, which represents almost 20% of all kilometers driven. Alternatively, long-haul journeys and freight traffic are not very easy to convert, and hence they were exempted from the electrification of mobility in the research.

Nuclear power plants do not play a role in the Empa research anymore — since the phase-out of nuclear power has been determined as the referendum on the Energy Act of May 2017. Thus, the scientists estimated a strong expansion of photovoltaics; 50% of all roof surfaces in Switzerland graded as good to outstandingly suitable within the framework of the www.sonnendach.ch project are fitted with solar cells. This represents around one-third of all roof areas in Switzerland.

How Much Does the Demand for Electricity Increase?

Next, the scientists calculated the resulting electricity consumption, which is expected to increase by approximately 13.7 terawatt-hours per year because of heat pumps and electric vehicles — that is, by almost 25% in comparison with present consumption.

However, the temporal gap between electricity production and requirement was even more alarming than this considerable rise in consumption: solar cells generate the most electricity in summer but heat pumps and heated cars need an exceptionally large amount of electricity in winter. This leads to a seasonal supply gap.

This could be made up for by importing electricity from nearby countries, as is already the case currently in the event of deficiencies. However, the CO2 balance will possibly be affected consequently — electricity from Europe often extremely worsens the CO2 balance of Switzerland, which has been very carefully electrified. Electric cars and heat pumps thus benefit the climate the most if the electricity needed for them is also renewable.

What Do the Researchers Suggest?

However, Empa research also offers some important information on how to execute a low-CO2 energy system. Firstly, if the buildings are insulated using most up-to-date technology, it makes the most sense to replace oil-fired heating systems with heat pumps since a heat pump without correct insulation is considerably less efficient.

Secondly, each nuclear power plant should be replaced with around eight times the photovoltaic output. The reason is that a nuclear power plant supplies approximately 8,000 hours of electricity per year — a solar cell, by contrast, supplies just 1,000 hours of electricity. This denotes a huge number of solar panels — on all available surfaces.

Thirdly, the largest possible storage capacity for solar energy is required — both local battery storage facilities and pumped storage facilities, as well as other storage technologies, specifically (geothermal) heat storage facilities, but also technologies for converting electricity into chemical energy sources. This is due to the fact that the sun shines strong enough only a few hours a day to fill the storages. For the remaining time, the stored energy must last.

Fourthly, seasonal heat storage facilities must be developed so that the electricity demands of the heat pumps can be decreased in winter.

Fifthly, it is necessary to better match energy supply and requirement. There will be abundant solar power and heat in summer; however, in winter, renewable energy specifically will be a rare (and therefore expensive) commodity in the future.

Sixthly, and this is the positive news, electromobility does not tilt the balance. Under the suppositions made, the daily charging of electric vehicles at home, at work, or when shopping produces only comparatively low peaks in electricity demand in comparison with the electrical heat supply. However, a precondition for this is suitable networks with adequate capacity.

If additional renewable energies such as geothermal energy, wind power, more biomass, and a bit more hydropower are achieved in winter in the future, the coverage gap will reduce; however, most likely, it will not be possible to close it completely. The electrification of heat and mobility alone will thus not solve the issue.

For the sustainable conversion of our energy system to succeed, we need both short- and long-term—i.e. seasonal—energy storage technologies. That is why we should not play off energy sectors against each other, but keep all technical options open.

Martin Rüdisüli, Researcher, Empa

Sinan Teske further states, “We must learn from nature how to deal with solar energy, which is not available all year round. We could store as much as possible in summer and limit our needs in winter. Or we could look for partners in the southern hemisphere of the earth who can harvest solar energy and deliver it to Switzerland when winter is here, and vice versa.”

Source: www.empa.ch

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