The contract between Silkeborg Forsyning and Arcon-Sunmark was signed in February 2016. In May the construction began, and at the end of December the installation was put into operation.

Source: Arcon-Sunmark

Source: Planenergi

The event with 130 attendees took place just a few days before the Swiss referendum on an accelerated nuclear energy exit, which gave the organisers an opportunity to highlight the sun’s role in Switzerland’s energy transformation. ‘As about 10 % of the heating energy in Switzerland comes from electricity, solar thermal can help with replacing nuclear power,’ said David Stickelberger from Swissolar. The strategy assured increased media attention for solar thermal, but interest dwindled soon after the 27 November referendum, when the nuclear energy exit was rejected by Swiss voters.

The political circumstances have cast doubt on the future of solar heat. Half a year ago, cantons Zurich and Zug had announced that they would not be able to finance solar thermal incentives in 2017. And the commitment to Switzerland’s energy strategy 2050 has been put on shaky ground. A vote is scheduled for 21 May 2017, in case opponents of the strategy can gather 50 000 signatures by 19 January next year. ‘As the political situation remains unclear, cantons are postponing their decisions,’ said Stickelberger. According to current planning, the Energy Strategy 2050 is thought to enter into force in 2018. Its aim is to increase the use of renewable energies, including hydropower and energy efficiency. The energy strategy will not permit the construction of new nuclear power plants, but will not limit the lifetime of the existing ones either. The strategy will also lower the CO₂ emission limits of vehicles. The most important issue will be additional solar thermal funding from canton governments to incentivise the implementation of energy efficiency measures – including solar heat – in buildings.

Right now, solar heat is coming under fire from two sides: First, there is the cantons’ responsibility for the incentive schemes. The Harmonised Incentive Model (Harmonisiertes Fördermodell, HFM) requires that they all follow the same policy. But given budget restrictions, they have been waiting for the authors of the energy strategy to set priorities before they put aside money for solar thermal incentives. Second, the cantons have to integrate nationwide building energy standards (MuKEn). This means that cantonal law is to stipulate a certain share of renewables that needs to be met when renovating existing building stock. But like the debate about incentives, this one will only be resolved if there is a clear-cut and comprehensive energy strategy in place.

But Stickelberger also pointed to two technologies which give him hope for the future of solar thermal in Switzerland. One is the combination of solar collectors with ground-sourced heat pumps. Pumps which retrieve energy from boreholes are becoming increasingly popular across the country. The city of Zurich in particular set a 2050 target of 450 GWh/year for energy production based on ground-sourced heat pumps as part of its efficiency scenario A from the 2050 energy plan. But experiences and simulations by the Swiss-based SPF – Institute of Solar Technology show that especially in areas with high borehole density, they gradually cool the ground unless an active regeneration method is used to return heat to it in summer.

‘Unglazed solar collectors are one option to regenerate boreholes,’ explained Stickelberger. Other options are PVT collectors, which typically work at low temperatures, or conventional collectors if operated intentionally at around 25 °C. The heat pump itself can also be used for regeneration and the transfer of heat from a building or the surroundings into the ground in summer. At the conference, René Naef from Swiss engineering office naef energietechnik presented the regeneration results of nine borehole locations used to heat three multi-family properties in Mettmenstetten. After one year of operation, the temperature of boreholes using regeneration was 2 K higher than the one of surrounding buildings.

The second technology is district heating. Unlike Denmark, Switzerland has not seen much interest in district heating systems. In the cities, most networks are fed with heat from waste incineration. This type of heat is available all year round at low cost and gives solar feed-in little chance to compete. However, there are also several hundred rural district heating networks, mostly supplied by biomass boilers. At the conference, Michel Haller from the SPF Rapperswil presented a study on the potential of retrofitting these networks with solar thermal technology.
One very attractive project might be the supply of wood- and solar-based heat to the district heating network of the Beznau nuclear power plant in northern Switzerland. It has so far been powered by waste heat from one of the world´s oldest nuclear power stations. Reactor unit 1 dates from 1969 and has been turned off for safety review. After several delays in getting it back onto the grid, doubts are growing whether it will ever be operational again. Unit 2 from 1971 cannot provide enough heat for the entire year, meaning additional boilers are needed. The SPF Rapperswil and the association Wood Energy Switzerland have carried out a study to explore the options available for integrating solar and biomass into the network. “The operators have shown interest in both solar and biomass heat,” said Stickelberger.

This text was written by Eva Augsten, a German freelance journalist specialising in renewable energies.

Websites of institutions and associations mentioned in this article:
Swissolar: www.swissolar.ch
SPF Rapperswil: www.spf.ch
Suissetec: https://www.suissetec.ch/
Wood Energy Switzerland: https://www.holzenergie.ch/home.html
naef energietechnik: http://www.naef-energie.ch/
Swiss Energy Strategy 2050 (in German):
https://www.uvek.admin.ch/uvek/de/home/energie/energiestrategie-2050.html

Renaud emphasised the satisfactory results in specific solar yield of between 550 and 560 kWh/m² from the plant in Balma-Gramont, near Toulouse in southern France. The solar fraction, however, dropped from almost 6 % to 4.5 % because of an increased demand in the district heating network. The solar plant demonstrated a high degree of reliability and did not cause any major problems (stagnation never occurred). Even so, it would be advantageous to improve the system and reduce the power consumption of auxiliary components, something that is still too high (about 17 kWh per MWh of generated heat).

Renaud also presented the monitoring outcomes of the 300 m² flat plate collector SDH plant in Juvignac in southern France. Although the annual solar yield matches up with design values (about 720 kWh/m²), the solar fraction is below expectations (about 4 % instead of 5,5 %) – again, because of higher demand from power consumers. This plant did experience some stagnation because of interruptions in the DH network: One option to avoid this problem in the future would be to include a tank for storing additional solar heat.

A national survey carried out by the Regional Energy and Environment Agency of Auvergne – Rhône-Alpes (RAEE) found that 800 DHC systems were in operation countrywide, with around 15 % of the district heating demand being covered by renewable energy sources and 25 % by waste heat, at an average cost of heat of 70 EUR/MWh. The number of SDH installations was said to be three existing ones and two under construction. The SDH collector area expected to be installed by 2030 was 800 000 m², plus an increase by a factor of 5 in the use of RES in district heating (from 0,7 MTOE to 3,4).

Beyond the pilot plants and their crucial role as ‘technology showrooms’, there should also be proper policies in place to promote SDH and in many cases the best place to do this is at regional level. In the framework of Horizon 2020 project SDHp2m…from policy to market, the French region of Auvergne – Rhône-Alpes is currently drafting a strategy document to develop SDH locally in cooperation with RAEE, the National Solar Energy Institute (INES) and CEA Tech.

RAEE’s starting point was a SWOT analysis – which is short for Strengths, Weaknesses, Opportunities and Threats. The results highlighted the typical strengths of solar thermal – being a freely available resource and a no-emission ‘fuel’ – as well as its opportunities, in line with current developments in the district heating sector, such as in low-temperature systems, long-term storage, energy efficiency, etc. ‘Regarding drawbacks, we looked at the space requirements as the main weakness and at building heat regulations, which have not been yet extended to include SDH contribution,’ RAEE’s Mathieu Eberhardt said. Finally, the main threat to widespread market deployment was the competition among many different thermal energy sources: other renewables, cheap waste heat and fossil fuels, especially natural gas.

In order to develop a joint strategy, the region set up a stakeholder group by organising a kick-off meeting in May 2016. Many of the 22 people attending the meeting came from different backgrounds: associations or stakeholders from the DH and solar industry, policy makers, DH operators and planners, energy cooperatives and initiatives, urban planners and heat planning experts, financing institutions and national agencies.

The discussions during this meeting led to the identification of several stakeholder suggestions:
•    Develop common list of arguments to convince local authorities in region that SDH is relevant
•    Include solar thermal more effectively in strategic planning
•    Develop tailored communication packages to reach citizens
•    Develop or disseminate simple tools to professionals to facilitate SDH feasibility studies
•    Utilise the opportunity of case studies planned as part of SDHp2m
•    Increase awareness of technology prices (and ROI) in France compared to other solutions with low fossil fuel prices.

Eberhardt said that the stakeholder group was going to meet again in November 2016 in order to present a final version of the initial national survey on SDH and the regional action plan. Beyond that, another relevant event will take place in the region in February 2017: the SDH conference in Clermont-Ferrand. At national level, there is a district heating conference organised by French district heating association AMORCE and scheduled in Paris for 6/7 December 2016.

Riccardo Battisti

The district heating session also included a report by Samuel Knabl from Austrian research institute AEE INTEC on the monitoring results of 30 of the country’s SDH plants, which had been supported by the national subsidy scheme for large-scale systems. The majority of the 14 systems which completed the monitoring phase almost achieved their expected solar yields; only two installations deviated significantly in their results. Knabl emphasised the fact that the return temperature of the district heating grid had a significant impact on collector field efficiency, as the above chart shows: specific collector yields ranged from 240 to 520 kWh/m2a.

Promising results came in from the biomass-fired district heating plant in Mallnitz, where in summer the peak load operation hours of the oil-fired boiler as well as the operation time of the biomass boilers was significantly reduced. Another example is the suburb of Salzburg-Lehen, where a 2,048 m2 collector field heats around 38,000 m2 of floor area in flats, a youth hostel, office buildings, a hotel and 150 renovated homes. The solar fraction is 29 %, of which 12 % are directly used in the buildings and 17 % originate from indirect use by the heat pumps, which have a seasonal performance factor of 4.5.

Primary technical and performance figures based on 2015 data from three Danish large-scale SDH plants. *102 % of storage efficiency has only been possible because the system used a certain amount of heat from the previous year. BTES is short for Borehole Thermal Energy Storage; PTES is Pit Thermal Energy Storage
Source: SDH conference presentation from Solites

The presentation by Thomas Schmidt from German research institute Solites confirmed the often-quoted average annual yield of 400 to 450 kWh/m2 for large-scale collector fields in Denmark. Schmidt went through the monitoring data provided by the operators of the three SDH systems in Marstal, Dronninglund and Braedstrup (see the table above). The difference in yield (between 395 and 447 kWh/m2a) was mainly a result of older collectors still being in operation, Schmidt explained. Whereas the 37,600 m2 in Dronninglund were installed in 2014, more than half of the 33,000 m2 in Marstal had been installed before 2004, while 15,000 m2 were added in 2012. In Braedstrup, 8,000 m2 of collectors were inaugurated in 2007.

In addition, the Solites researcher analysed the relationship between heat taken from the storage tank and the tank storage capacity, which leads to the number of storage cycles. A ratio of 1 is achieved when – as in the Marstal case – a large part of the heat is fed directly into the district heating network. In Dronninglund, the mode of operation is that almost all solar energy is transferred to the grid through the seasonal storage tank, drawing more than twice the energy capacity of the pit storage over a year. System efficiency also depends on these different modes of operation because it includes the losses compared to heat utilisation by tank.

Braedstrup cannot be directly compared to the two other installations. Its pilot-phase borehole storage offers a much lower heat capacity (400 MWh) and maximum temperature (about 49 °C). Still, the monitored solar share of 23 % is higher than the 18 % that the system was expected to have. An extension of the seasonal storage is in preparation.

More information:
Gram district heating
Institute of Thermodynamics and Thermal Engineering
AEE INTEC
Steinbeis Research Institute Solites

Riccardo Battisti

180 international experts from 20 countries – also this is a record number – have met for the 4th International Solar District Heating Conference in order to benefit from the experience of this leading country. They were not only impressed by the top-class presentations and technical tours to some of the world largest solar collector plants, but could also admire a reduced-scale model of such a plant in Legoland Billund, where the Conference took place. This solar collector plant made in Lego bricks represents the plant from Braedstrup, with which the world-wide unique boom of the Danish XXL solar thermal plants began, approximately ten years ago.Large-scale solar thermal plants can compete today with all forms of fossil fuels. The sector reaches heat prices from 3 to 5 cents pro kWh, provided that the plant is large enough. And they are always getting larger: in Silkeborg in Central Denmark the new record plant is currently under construction with 156 000 m² and a nominal power of 110 Megawatt. But the world’s market leader Denmark is not the only country in which solar thermal plants in such dimensions are developing. In the Austrian city of Graz, plans are being made for a plant of even more impressive dimensions: 450 000 m² solar thermal collectors should supply the district heating network of the second largest city of the Alpine Republic to cover 20% of the heat demand.

Also political spheres have become aware of the importance of renewable district heating all around Europe. “District Heating and Cooling are now an important topic in Brussels to push renewable energies and efficiency technologies.” said Paul Voss, director of the European District Heating Association Euroheat & Power. Unlike in some earlier papers from the EU, they play an important role in the recently published Heating and Cooling Strategy until 2030. This also appears in the most recent budget planning for EU subsidy programs.

For the organizers of the 4th International Solar District Heating Conference, the Danish District Heating Association, the engineering office PlanEnergi and the German Steinbeis Research Institute Solites, the economical feasibility is currently not the main reason why the development of renewable district heating networks in Europe and the world is still so uneven. There are several well made subsidy programs at national level, in Germany, Italy, France and Austria, reports Thomas Pauschinger from Solites. Outside of Denmark, the possibility of using solar heat for district heating networks is simply still not enough known. One of the barriers is administrative obstacles like finding and getting permission for adapted locations for building large collector fields. Pauschinger: “At the local level, there are three main problems: areas, areas and areas.”

This is not the case in Denmark, where the collector fields are mostly located in agricultural areas at the city’s borders. The solar thermal networks are mostly organized in cooperatives and realized without subsidies, thanks to the high taxes on fossil fuels, among other things. In Jelling, the local operator of the plant reported that the heat price for customers has decreased as a consequence of the installation of 15 000 m² solar collectors. This is the case in several other locations in Denmark. Jelling was, together with the recently extended 44 800 m² solar thermal plant of the City of Gram, aim of a technical tour in the framework of the international congress. Gram is currently the district heating network with the highest solar fraction. More than 50% of the yearly heat demand is covered by the sun. This is enabled by a pit thermal energy storage in which 122 000 m³ water are being heated up to 90°C during the summer.

If the experts who travelled to Billund are of course interested in such constantly increasing records, they also come to exchange on technical details and share experiences from colleagues from other countries, research institutes and companies which are being discussed really openly in this circle.  The main topics are here longevity, energy efficiency and a reliable operation of such plants, said Pauschinger: „These details are the decisive factors for continuously reducing the costs of harvesting solar energy.”

The next opportunity for such a large and intensive exchange will arise in 2018 for the next edition of the conference in Austria.

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