Under one roof



Cities may account for just 3% of the world’s landmass, yet they represent over two-thirds of our energy consumption and comprise around 72% of global CO2 emissions. By 2050, says the European Commission, more than 80% of the world’s population will reside in cities. Worldwide initiatives aim to set a new urban status quo based on renewable energy and smart infrastructure, and over the next few pages, Europe’s initiatives come into focus.

Making European cities more sustainable is an important priority for the European Commission, according to a spokesperson for the European Climate, Infrastructure and Environment Executive Agency (CINEA). Under its Horizon 2020 funding program, CINEA made more than €3.5 billion available between 2014 and 2020 for research and innovation projects dedicated to sustainable energy in urban environments.

These funds include €390 million for smart cities and communities, €360 million for solar energy projects, and €110 million for heating and cooling. Approximately €1 billion was additionally awarded to projects addressing research and innovation for grids, storage, and energy systems, covering prosumer empowerment, smart distribution grids, local energy markets, and energy system studies.

While many demonstration projects are ongoing, a new Horizon Europe program was unveiled this June that will run between 2021 and 2027, and focusing on climate-neutral smart cities in its so-called Mission area, 100 Climate-Neutral Cities by 2030 – by and for their citizens.

Several other national and European-wide programs are working on similar goals. They include the C40 Cities Climate Leadership Group – a group of 97 global cities, representing one-twelfth of the world’s population and one-quarter of the global economy – as well as the non-profit European Green Cities, and The European Sustainable Cities Platform, launched in 2016, supported by the City of Aalborg, Denmark, the Basque Country, and ICLEI Europe. A key outcome for these projects is how the results may be transferred to other cities in the future.

Sky-high potential

The building sector alone currently represents around 36% of the EU’s GHG emissions and almost half of its final energy consumption, says SolarPower Europe (SPE). “As such, the decarbonization of the building sector will be a critical driver to achieve carbon neutrality in Europe by 2050.” Given that new builds are forecast to represent just 10% to 25% of European building stock by 2050, it is essential to focus on the EU’s existing buildings.

There is enormous potential in this sector, and innovative business models are emerging. For example, under the EU’s Horizon funded Smarter Together project, which ended this July, and ran in Lyon, Munich, and Vienna, PV systems were installed on public and private housing, in addition to developing district heating and renewables for low energy districts, among other actions.

The Lyon-Confluence urban project, for instance, redeveloped a former industrial area covering 150 hectares in the city center by installing six rooftop PV systems totaling 1.2 MWp on existing, new, and eco-refurbished buildings, thus doubling its solar capacity. Most interesting is the proposed business model of self-consumption at block scale, where electricity consumers located in several buildings consume the PV electricity produced under a virtual metering program.

The Smarter Together team references Germany’s Heidelberger Energiegenossenschaft eG (HEG) – a student energy cooperative founded in 2010 – as a successful working case in point. Overall, the HEG has around 200 cooperative members who invested over €1 million in 12 PV plants totaling 700 kWp. They tested the business model with 116 tenants of the “Neue Heimat” Cooperative Family Home, situated in Nußloch near Heidelberg, with seven solar PV systems totaling 445 kWp.

The main innovation of the project, says the Smarter Together team, lies in the metering infrastructure implemented together with the local distribution network operator (DNO). This is necessary to measure the residual energy supplied from, or the excess energy injected into, the grid via a two-way meter owned by the DNO. It also measures the PV energy produced and consumed via a regular meter owned by HEG, and measures the energy consumed by those wanting to use another energy supplier via regular meters owned by the DNO, as well as virtual meters located at the grid connection point. Consumption data is subtracted from the total energy consumed by HEG.

The total investment cost for the solar PV systems, supported by HEG, was €525,000 (€1.18/Wp) and energy is purchased from HEG at a rate of €0.254/kWh plus a monthly fee of €6.95 for a period of 20 years.

Overall, the energy is a mix of 30% PV and 70% imported energy from the grid. Any excess PV is injected into the local grid and sold via a feed-in tariff. “In this case, HEG becomes a real small-scale utility, which requires specialized expertise such as meter management and maintenance and energy billing to customers,” says the team.

District heating, cooling

Of the around 32% of global energy generation the world’s building sector uses, more than one-third goes to heating and cooling, thus making it a key urban sustainability target. Project Drawdown calculates that replacing existing standalone water- and space-heating systems with district heating and cooling could reduce carbon dioxide emissions by 6.3 to 9.9 gigatons by 2050 and save $1.6 trillion-2.4 trillion in energy costs, versus setup costs of $227 billion to $337 billion.

In Europe, the International Energy Agency (IEA) finds this sector responsible for 50% of energy consumption. And according to the EU’s Heating and Cooling Strategy, it will have the biggest energy demand by 2050.

As part of its four-year IEA SHC Task 55 – Towards the Integration of Large Solar Systems into District Heating and Cooling Networks, the agency says EU district heating consumes 600 TWh of energy annually and represents over 10% of its heat demand. Fossil fuels are currently the main source of heat production, with around 5,000 district heating grids in the EU operated by burning them at an annual cost of €18 billion and over 150 million tons of CO2 emissions.

Based on its 600 TWh figure, the IEA calculates that replacing them with a 30% share of solar in district heating plants would lead to an annual solar thermal substation energy of 180 TWh. This would trigger €75 billion in investments and an installed solar thermal collector surface of 300 million m2, up from the around 50 million m2 of solar collectors in operation today, it says.

Furthermore, PV coupled with thermal (PVT) is leading the trend towards hybrid solar heat solutions, according to the IEA’s report, Solar Heat Worldwide 2021, “experiencing growth of 9% on average from 2018 to 2020 and 8% in the dominant European market.”

In action

The leading market for solar district heating and cooling systems is Denmark (124 systems), followed by Germany (43), Sweden (22), Austria (19), China (18), and Poland (8), according to the IEA report. In 2020, due to the expiration of attractive policies for solar thermal and heat pumps in Denmark, Germany took over the mantle of district heating leader. Of the 11 large-scale systems (> 500m²) connected in Europe in 2020, seven were built in Germany (31,200m²), with four in Denmark (14,600m²).

Despite the slowdown, Denmark’s achievements benefited from favorable policies. In a 2019 paper published in Energy Conversion and Management, “Large-scale solar district heating plants in Danish smart thermal grid: Developments and recent trends,” the authors found that Denmark not only leads in terms of total installed capacity and numbers of large solar district heating plants (1.3 million m2 at the end of 2017), but it is also the first and only country with 17 commercial market-driven solar district heating plants.

The IEA adds that 113 Danish villages, towns, and cities use solar heat, with the town of Silkeborg holding the record for the world’s largest solar heat system – a 110 MW (156,694 m²) plant commissioned in December 2016 for an investment of around €33.5 million. Overall, it comprises 12,436 solar panels and reduces CO2 emissions by around 15,000 tons annually, covering the total annual heat consumption of 4,400 households. On average, it supplies approximately 20% of Silkeborg’s annual district heating demand; however, on sunny days, it has supplied as much as 100% of the heating demand, with surplus heat stored in tanks.

Going bigger

Many of the district heating and cooling systems operate on smaller scalesto make an impact in large metropolises, they must scale up. However, as the IEA points out, it is more complicated to utilize solar energy in the district heating of large cities than to feed it into a small grid, primarily because of the typically higher temperatures in larger networks.

In the Austrian state of Styria, work is underway on Big Solar Graz, “one of the most promising” projects for achievable high solar fractions, says the IEA, at 154 MW (220,000 m²). “Without the Big Solar System, a maximum of around 5% solar share would be achievable. “The feasibility carried out shows a technically reachable portion of up to 30% and an economic optimum at around 23%,” write the report’s authors. With optimization, they believe the solar PV share could be increased up to 60%. “The business case in the feasibility is that a newly established company will sell the produced solar heat of the system including an annual real price increase of 1.5% to the city’s local energy provider.”

Work is also underway in other European countries, like France, which has a subsidy scheme for large solar thermal projects – resulting in the commissioning of the country’s first big plant in December 2017 – and Latvia, where public utility Salaspils Siltums invested €4.9 million in a 15 MW solar field and 8,000 m3 storage tank in 2019.

Second skin

While a niche market, building integrated PV (BIPV) holds much potential, and innovative projects are pushing it into the mainstream. Like district heating and cooling, Denmark is leading in this field, as Peder Vejsig Pedersen shares with pv magazine. He is the director of European Green Cities, which, for over a decade, has been the secretariat of the Danish Association of Sustainable Cities and Buildings.

Under European Green Cities, Pedersen has also been working together with Urban Renewal Copenhagen to realize “Green Solar Cities,” which focuses on large-scale BIPV and solar thermal integration in Copenhagen, and Salzburg, Austria. The team works with Danish PV producer Racell, which produces combined PV and solar thermal (PVT) modules that are integrated into building elements and generate both electricity and heating and cooling.

According to Racell, its technology provides the “highest energy yield worldwide, reaching 90%” and can be manufactured in almost any color and size. It adds that while the crystalline solar cells produce current during the day, liquid in the energy absorber cools the cells and produces heat. At night, the absorber then draws energy from the air to generate cooling, like that of a geothermal pump drawing energy from the ground.

Unlike air-to-liquid heat pumps, the “liquid-to-liquid” heat pumps are said to be noiseless and contain no moving parts. “Instead, it has panels that contain solar cells and liquid channels, allowing the liquid to absorb energy from the surrounding air. This energized liquid feeds the heat pump with continuous thermal energy. The electric power that runs the heat pump is provided by the solar cells of the PVT module. The same liquid circulates between the PVT panel and the heat pump,” Racell explains.

Most recently, this technology has been coupled with ground water-based energy systems called Aquifer Thermal Energy Storage (ATES), developed by Denmark’s Enopsol. Reportedly, ATES can be utilized as seasonal storage for the solar heating coming from the PVT elements, while large heat pump systems exploit the heated groundwater during winter.

Another Danish company, Solarplan, plans to integrate 10,000 m2 of large 4-6m2 PVT modules into the sloping roofs of 1,000 existing apartments in Avedøre, south of Copenhagen as part of a Green City Project. Under the EU’s Horizon program, work is also underway on BIPV projects, such as PVSITES, which seeks to address the large market deployment of BIPV technology, and BIPVBOOST which aims to reduce the costs of multifunctional BIPV systems by 75% by 2030. A highly flexible, automated manufacturing line for crystalline silicon-based BIPV modules is said to be in the works, as is the development of specialized modules with enhanced aesthetics, building envelope solutions, and Building Information Modelling-based digital. These solutions are currently being tested in several outdoor facilities and will be implemented in four demonstration buildings including residential and commercial uses in Spain, Belgium, and Italy.

The new headquarters of Kirk Capital, a business and investment company, represents a BIPV success story. Located between the Vejle Fjord and Vejle city center in Denmark, it is the first building designed entirely by artist Olafur Eliasson. The PV glass has been integrated in the form of a circular roof, with 11 circles of different diameters. Overall, 446 opaque crystalline glass units were installed for a total capacity of 51 kWp. According to Onyx Solar, which worked on the installation, the PV skylight had a payback time of under four years, and a reduction in heating, ventilation, and air conditioning energy demands of 25%.

These featured projects are just a few of the many examples of city solar solutions planned and/or existing today. Key to all of this is the smart integration of these individual systems into each city and electrical grid, so that they operate harmoniously, like the organs in our bodies: connected, synchronized, and healthy. Supporting policies are the backbone of these initiatives and will be the subject of the next UP feature in the November edition.

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