In recent years, the Austrian solar industry has occasionally met for conferences at the Ernst Happel Stadium in Vienna. Now, future events at the stadium can finally be powered by solar energy after around 9,300 solar modules were installed on the roof of the venue, 20 metres above ground. The project has transformed the roof into an energy powerhouse that will supply 3,880 megawatt hours of clean solar power every year.
More electricity generated than consumed
What’s more, this power comes to more electricity than the stadium uses overall. “Not so long ago, an emission-free stadium was just a vision, but now we are on the verge of making it a reality,” says Vienna’s City Councillor for Sport, Peter Hacker. “I am impressed by how quickly and precisely the installation was completed. Sustainability and innovation are key criteria in the renovation of Vienna’s sports facilities. The Happel Stadium will generate more electricity than it consumes, making an important contribution to environmental and climate protection in our city.”
Three-dimensional model produced
The road to a photovoltaic stadium roof was not easy, not least because it is a listed building. Moreover, the realisation of the project involved precision work. Each trapezoidal sheet has its own dimensions due to the elliptical shape of the roof, require three-dimensional modelling before work could begin in earnest.
Due to the low load-bearing capacity, it was not possible to place pallets on the listed roof. As a result, the components – including modules, 80,000 trapezoidal sheet metal rails and over 5,000 optimisers – were initially stored inside the stadium. These were then gradually hoisted to a height of over 20 metres using scissor lifts, carried manually to their locations and assembled on the spot.
The time frame was also a challenge. The system had to be erected between the end of November and the beginning of March, when no events take place on the open field. Snow, low night-time temperatures combined with high humidity and several periods of strong wind caused work to be interrupted for days at a time. Due to an international match between Austria and Serbia on 20 March 2025, the installation had to be completed much faster than originally planned.
With the new photovoltaic system and geothermal energy under the renovated training pitches – 270 boreholes at a depth of 150 metres and ground collectors covering an area of 25,000 cubic metres – the foundations have now been laid for an emission-free stadium. In cooperation with Wien Energie and Wiener Netzen, wiring of the solar power system is currently being completed.
Work is scheduled to be finished in late 2025. Once commissioned, all generated electricity will be fed into the existing stadium network. The City of Vienna is also planning a network with several heat pumps and storage facilities as well as a connection to the neighbouring stadium swimming pool, allowing the stadium operator to use all surplus solar energy on site. (su/hcn)
The owner of a detached house in Meulebeke, Flanders, Belgium, has reconciled several things that don’t really go together. He wanted to save money and do something good for the environment at the same time, but he also didn’t want to do without the high level of comfort and various amenities he had previously enjoyed.
Heating element installed
These comforts are not just the well-heated parlour. The homeowner also has a jacuzzi. This hot tub in front of the house in the garden needs a lot of energy to heat up the 1,500 litres of water. Previously, this had to be supplied by the existing gas heating system. This was expensive, and not just since the rising energy costs due to the Russian invasion of Ukraine, which have also affected the Belgians.
My PV
The heat storage is heated by a heating rod, which in turn is controlled by an AC Thor.
To save money, the homeowner looked for an alternative for himself and his family of four. In the end, he opted for a solar-electric heating and hot water system. A 200 litre hot water tank is charged directly by a heating rod. This heating element is in turn controlled by an AC Thor power controller from the Austrian manufacturer My PV.
Own solar power in the hot water
This means that the homeowner can now utilise the profits from the existing photovoltaic system on the roof. This has an output of 15 kilowatts and provides enough energy to supply the partially renovated house with heat and hot water from March to October and also to heat the water in the jacuzzi to a pleasant 37 degrees Celsius. A second power controller from My PV was installed for this purpose, which is solely responsible for the heat in the jacuzzi.
Saving energy costs
This means that the building is almost completely disconnected from the natural gas tap. The fossil fuel is now only used for cooking. The previous gas boiler still takes over the peak load in winter.
This is noticeable on the energy bill. This is because the homeowner saves 350 euros a year compared to the prices in 2021, i.e. before the energy crisis, just for operating their hot water boiler. For the current electricity prices, he estimates that he actually saves €45 per month. What’s more, the homeowner doesn’t have to have a guilty conscience when he takes another hot bath. “In addition to the financial aspect, the relaxed feeling of complete comfort is worth mentioning, knowing that all the energy needed to heat the water in the house and in the hot tub comes from your own photovoltaic system,” emphasises the homeowner. (su/mfo)
My PV
No need to sacrifice comfort: The jacuzzi in the garden is now heated with solar power.
Mr Jorgensen, Denmark has been a pioneer in the heating transition for many years. How far have you already come? Where do you currently stand?
Our heating transition is closely linked to our district heating system. Two thirds of the approximately 3 million households in Denmark are supplied with district heating and we have a 75 per cent share of renewable energies in district heating. A good half of the district heating comes from certified biomass, primarily wood. We want to reduce this share to 35 per cent by 2035. We want our district heating supply in Denmark to be 100 per cent climate-neutral by 2030. We are focussing heavily on electrification and large heat pumps. We want to use more geothermal energy for district heating, more waste heat from industry, more ambient heat from sewage water, heat from data centres and more surplus solar power for daily and seasonal storage.
How do you intend to decarbonise the heat supply to those buildings that are not yet connected to the district heating supply?
We currently have around 400,000 households that are still supplied with gas, which we want to move away from. To this end, our government adopted a strategic plan “Denmark can do more – two” in summer 2022. The aim is to switch to 100 per cent biogas by 2030 and to phase out the gas supply for buildings completely by 2035. The solution will then be either heat pumps or connection to the district heating supply, roughly half in each case. To this end, the Danish government has introduced accelerated heat planning, which builds on our many years of experience with mandatory municipal heat planning, which has been in place in Denmark since 1979 and is a key instrument for achieving our climate targets.
What does accelerated municipal heat planning involve?
In 2022, all Danish municipalities had to write digitally to all homeowners who still heat with gas within six months and inform them whether they will receive a district heating connection by 2028. If not, the affected homeowners will have to opt for other fossil-free solutions. All municipal utilities are currently drawing up implementation plans, in which they are calculating and specifying exactly when district heating connections will be available in the relevant areas.
Compared to Germany, this is very ambitious and strict. Aren’t there also heated debates in Denmark about a supposed state policy of prohibition at the expense of market freedoms and the “little people”?
Actually, no. We have a phenomenon here that we call “politisk forlig”, i.e. broad, consensus-orientated agreements that are supported by all parties. For example, our climate law is supported by 9 out of 10 parties, across all political camps. There has been broad support in Denmark for a policy away from fossil fuels and towards a renewable heat supply since the first oil crisis in 1973. This also includes a targeted increase in the price of gas, oil and coal by means of an energy and CO2 tax. Heating houses with gas is now the most expensive option and district heating is significantly cheaper.
How much does district heating currently cost in Denmark?
Currently, the average cost of district heating for a standard house with an annual consumption of 18.1 megawatt hours is just under 2,000 euros per year. Transparency is also important to us here. The 400 or so companies in Denmark that produce and sell district heating have to send their prices to the Danish Utility Regulatory Authority twice a year. The Inspectorate then publishes the prices on the Internet. The companies are also legally obliged to offer district heating not only as climate-neutrally as possible, but also as cost-efficiently as possible and to distribute or reinvest profits to customers. In addition, many district heating companies are organised as cooperatives and citizens have a stake in them or they are owned by municipal utilities.
So is there no cross-financing of other municipal services of general interest via income from the district heating supply?
No, cross-financing is not permitted and no profits may be generated from the district heating supply. The Kommunale Bank, in which all Danish cities and municipalities are involved, plays an important role in long-term municipal investments in the expansion of climate-neutral heat supply. It offers corporate loans on favourable terms. In addition, the municipality is the central authority for heat planning in Denmark and must approve all projects. Overall, the district heating supply in Denmark is much more heavily regulated than in Germany.
How do you pass on your experience in the field of heat planning and the expansion of municipal heat supply to your German neighbours?
On many levels. We work closely with the Federal Ministry of Economics, associations and municipal utilities as well as with federal states such as Hesse, North Rhine-Westphalia and Baden-Württemberg and with individual local authorities, either through consultation or in workshops. For example, Baden-Württemberg used our technology catalogue as a guide when introducing municipal heat planning and we cooperated in the creation of a heat planning guide and municipal heat registers.
MAN Energy Solutions
Site of a giant seawater heat pump in Esbjerg/Denmark, which feeds heat into the local grid.
We are taking a lot from Germany to Denmark to improve our heat transition. Our cooperation is a two-way street of knowledge transfer across the border. For example, funding programmes, competence centre for heat transition, technologies such as geothermal energy and waste heat.
How important is a solid data basis for municipal heat planning?
This is hugely important. But local authorities should take a pragmatic approach here. The heating plans don’t have to be 100 per cent complete before you start. Municipal heat planning is a process. Further political decisions are incorporated here and plans can be further concretised over time. Further digitalisation and standardisation of the heat plans are also crucial. It is also extremely important that the local authority brings together the major local stakeholders such as industrial companies, hospitals, data centres and schools, as well as the electricity and gas network operators, in order to identify heat usage potential and agree on plans.
What other “levers” do you think are important in the transformation of the heat supply? What are your “lessons learnt” here?
In addition to transparency, investment security and suitable framework conditions for local authorities, diversification is important when switching to a climate-neutral district heating supply. In Denmark, we have so far focussed heavily on biomass. The inclusion of more energy sources, electrification and sector coupling also increases the security of supply and resilience of the overall energy system. That is why we are now in the process of greatly expanding photovoltaics in Denmark. Large-scale solar thermal plants are also an important component of our heating transition, where we have an installed capacity of 1.2 gigawatts. Seasonal storage systems can be used to store solar heat, solar and wind power for times when the sun is not shining and the wind is not blowing. This is cheaper than battery storage and creates added value for the entire energy system.
Thank you for the interview!
The interview was conducted by Hans-Christoph Neidlein
