China is the world’s largest market for DH, in addition to being the largest solar thermal market – a promising combination. In 2017, the Chinese central government conducted SDH feasibility studies in more than 20 counties and cities in Tibet, where many houses lack space heating, and awarded funding for two sites.

The Chinese parabolic trough collector manufacturer Vicot Solar Technology has signed a contract with the local government to install a solar district heating system in Shenzha county. The photo, taken in November 2017, shows one-third of the field’s substructure. The entire installation will have 18,000 m² of aperture area. The parabolic collector field is being installed in Shenzha county. Ouyang Cheng, Marketing Manager at Vicot Solar Technology, said that half of the collector field had already been completed in 2017 and that the remaining 9,000 m² would be set up this year. The collector field will run on thermal oil and will be connected to a district heating system. Vicot said that it planned to install a molten salt storage tank and use electric boilers for backup.

Additionally, the Chinese-Danish joint venture Arcon-Sunmark Large-Scale Solar Systems Integration signed a contract with the local government to set up a SDH heating network in Langkazi county in Tibet. The system should provide solar district heating for 82,600 m² of floor area and meet 90 % of the yearly space heating demand in Langkazi, the town sharing its name with the county. The system, planned to be set up by November 2018, will consist of a 22,000 m² collector field, 15,000 m³ of pit storage and a 3 MW electric boiler. The sponsor of the pilot project is as well the China’s central government.

Since October 2016, a 75,000 m² parabolic trough collector field for district heat seems to have been operating in Inner Mongolia, an autonomous region in China. Ruicheng Zheng from the China Academy of Building Research said that she had heard about the system, but that all the information on it was only available online. On 28 December 2017, a news article appeared on sohu.com, one of China’s largest online media companies, stating that the system supplied a shopping centre and a development project known as ZhongCheng International City in the village of HongQing De, near Baotou. The journalist who interviewed the owners of the residential buildings and the shopping centre found customers satisfied with the solar space heating that the system provides.

70% of the heating and domestic hot water boiling in the ‘Kaysieva Gradina’ district in Varna, Bulgaria, could be provided by solar thermal energy by applying the SDH technology. To all the residents of Varna this is a huge opportunity to switch to clean heating, to end without using fossil fuels and to get rid of the fine particulate matter in the air. It is also crucial for achieving independence from the fuel imports. This is the conclusion of a recent survey performed by the Institute for Zero Energy Buildings in Sofia, Bulgaria. What’s more important is that the same number is relevant to all the medium and big cities in Bulgaria.

Solar district heating (SDH) consist of thermal solar collectors that produce heat for heating and domestic hot water throughout the year. This kind of installations are already very popular in Europe, especially in Denmark. ‘Today some 110 district heating companies in the country connecting between 200 and 15 000 consumers use solar district heating.’ said Per Alex Sorensen, one of the veterans of the technology, president of the FlexEnergi cluster, and a consultant at PlanEnergi, Denmark. SDH systems could function even more efficiently in Bulgaria, given the intense sunshine in the South-European country. The return on investment for a SDH system would be approximately 10 years, IZEB experts say. Its maintenance is easy and inexpensive.

The survey carried out by IZEB covers 69 residential apartment blocks build by prefabricated panels (‘panel blocks’) with a total built-up area of 285 000 square meters, located in the ‘Kaiysieva Gradina’ district of Varna. There is no centralized district heating network in this area. The main source of domestic heat are local electric stoves and air conditioners. In order to maximize the effect of the solar district heating system, thermal insulation should be applied to the residential buildings. ‘Our calculations show that, when these ‘panel’ apartment buildings have sufficient thermal insulation, thehousehold energy consumption will drop down to 85 kWh per square meter per year.’ said Dimitar Paskalev, an architect, founder and head of the Institute for Zero Energy Buildings.

Thermal solar collectors could be installed on all flat roofs of the ‘panel blocks’, where their location is most suitable considering the intensity of summer sunshine. Thermal collectors could also be integrated into the buildings’ facades. Also, these solar collectors could be a part of the thermal insulation of the residential buildings.

The heat output will reach 38 kWh/m²/a for the rooftop solar collectors and nearly 22 kWh/m²/a for the wall-mounted ones. Together, they will provide 60 kWh/m²/a. This means that district heating solar collectors can provide 70% of the annual heat consumption in the buildings. Heat energy could also be kept at seasonal storage systems placed udergroud, e.g. in the spaces between the buildings.

‘The typology of the multi-family residential appartment buildings built with pre-fabricated concrete panels is extremely popular in Bulgaria. Such type of buildings could be found both in big cities with large neighborhoods consisting of tens of panel blocks, and in smaller towns,’ said Dimitar Paskalev, head of IZEB.

At the moment Veolia Energy Varna, the district heating provider in the city, is evaluating the potential construction of a solar district heating system in Varna, the company announced. ‘We are exploring the possibilities for applying the SDHtechnology in Varna because we are trying to diversify the portfolio of energy sources we use – especially given the rising fuel prices we’re witnessing,’ said Lyubomir Kostov, Head of Customer Care and Development at Veolia Energy Varna.

The survey was initially announced during the first in Bulgaria training for design and construction of solar district systems. It took place during the ‘Black Seaside Days of Intelligent Energy’ in June 2017 at the Technical University Varna. It was organized by the Association of Bulgarian Black-Sea Municipalities and the Black-Sea Regional Energy Management Agency together with the Institute for Zero Energy Buildings, the National Association of Municipalities in Bulgaria, the Sofena Agency, the Technical University Varna and the Black Sea Research Energy Center.

The IZEB study of the potential of solar district heating in the ‘Kaysieva gradina’ district in Varna was carried out within the SDHp2m project (Solar District Heating … from Policy to Market) funded under the EU Horizon 2020 program.

Marta Stoilova

Operators of several gas-driven combined cycle power plants, or CCPPs, have notified the German Federal Network Agency of their systems’ final shutdown. These plants are no longer economically viable, as they have been running ever fewer hours because of a high proportion of cost-effective renewable grid electricity. Their shutdown will create a shortage of supply in district heating networks providing thermal energy to German municipalities. Utility-scale solar thermal plants equipped with seasonal storage could help close the gap at heat prices of around 36 EUR/MWh, Christian Holter said. Holter is the Managing Director of Austrian turnkey system supplier S.O.L.I.D., which has carried out feasibility studies on behalf of several European cities.

Read the interview on solarthermalworld.org.

Graz is making constant efforts to increase the share of renewable energy in the city’s district heating system. So the project ‘HELIOS’ in Graz with its 2 000 m² solar plant has been put into operation in September 2017. The thermal energy is fed into the district heating grid of Graz.

‘HELIOS’ has a 2 000 m² solar field which will be expanded to 10 000 m² at its final completion. The expected capacity at the moment is about 2,5 GWh. The plant is situated on a closed residual waste disposal site. For this reason, all solar pipelines are laid aboveground in order to be prepared for underground movements. An unpressurized aboveground storage tank holding 2 500 m³ offers the possibility of absorbing thermal power peaks. A landfill gas CHP unit with a capacity of about 120 kW (electrical) and 170 kW (thermal) is also part of the project. The electrical output is used for self-sufficiency and to run a Power-to-Heat unit. The plant is operated by ‘Energie Graz’. ‘HELIOS’ has received funding from the local state of Styria (approx. 1,17 Mio. €) and from the state of Austria, ‘K.L.I.E.N.’ (approx. 0,45 Mio €).

Three installed systems and one more planned: SDH shows a few examples of operation in Italy but quite good perspectives thanks to relevant incentives and the recent inclusion in the National Energy Strategy for 2030. A workshop in Venice on 15 December 2017 will analyze the status quo and the possible developments.

Plants in operation and plans for the near future

As shown in the map below, three SDH plants are in operation at the moment in Italy. The first SDH plant has been installed in 2015 for feeding in the district heating network of Varese: 990 m² of flat plate solar collectors are used for pre-heating either the make-up water or the return line of the network. Operational results for the first year show a very good performance, with a +13 % over the expected design yield.

The second system, commissioned in 2016, has a much smaller size, with a total gross area of 63 m², and combines solar thermal with a gas-fired CHP unit for a local district heating network located in the mountain village of Sansicario, in the province of Turin. The peculiarities of this plant are the use of two different technologies, flat plate collectors and evacuated tubes, and the opportunity to test solar thermal operation at 1 600 meters above sea level.

The last example is a 200 m² solar plant connected to the district heating network of the city of Lodi in 2017. This is a case of ‘third-party access’ since the whole solar thermal production is injected into the grid and is purchased by the DH utility from the owner of the solar thermal system. Besides these installed systems, the utility Gruppo Iren has planned to install a 600 m² SDH system for its DH network in Turin by 2020.

Incentives and policies: Good perspectives

The national incentive of Conto Termico 2.0 supports energy efficiency measures and small renewable heat systems, including solar thermal plants, also for district heating applications, up to 2 500 m² gross area. The amount of the incentive, paid in five annual instalments, depends on the system size, the application and the expected collector yield. For SDH plants, this amount can range between 40 % and 60 % of the investment cost.

Furthermore, budgetary resources for this scheme are quite generous, corresponding to a yearly amount of 200 million EUR for public bodies and 700 million EUR for private subjects, and a larger portion of these resources are still available.

From a policy point of view, it is worth to mention that, thanks to a consultation comment sent by Ambiente Italia on behalf of the SDHp2m project, the National Energy Strategy, released by the Italian Government in November 2017, explicitly includes solar district heating as a viable option to ‘reduce installation and O&M costs’ and ‘particularly interesting for smart and flexible district heating network, where multiple energy sources are operating together’.

A workshop in Venice

On 15 December 2017, Ambiente Italia organized, in collaboration with the Veneto Region, a specific workshop on the use of solar thermal in combination with other renewables, especially biomass, for supplying thermal energy through small local DH grids.

More information on the event is available here.