Central solar heating

Central solar heating is the provision of central heating and hot water from solar energy by a system in which the water is heated centrally by arrays of solar thermal collectors (central solar heating plants - CSHPs) and distributed through district heating pipe networks (or 'block heating' systems in the case of smaller installations).

For block systems, the solar collectors are typically mounted on the building roof tops. For district heating systems, the collectors may instead be installed on the ground.

Central solar heating can involve large-scale thermal storage, scaling from diurnal storage to seasonal thermal energy storage (STES). Thermal storage increase the solar fraction - the ratio between solar energy gain to the total energy demand in the system - for solar thermal systems. Ideally, the aim for applying seasonal storage is to store solar energy collected in the summer time to the winter month.

Compared to small solar heating systems (solar combisystems), central solar heating systems have better price-performance ratios due to the lower installation price, the higher thermal efficiency and less maintenance. In some countries such as Denmark large-scale solar district heating plants are financially fully competitive to other forms of heat generation.Nicolas Perez-Mora et al.: Solar district heating and cooling: A review. International Journal of Energy Research 42, 4, 2018, 1419-1441 .

Central solar systems can also be used for solar cooling in the form of district cooling. In this case, the overall efficiency is high due to the high correlation between the energy demand and the solar radiation.

Largest CSHPs Name Country Owner Solar collector size ThermalPower Annualproduction Installationyear Storagevolume Storage typeFacilities Collector manufacturer m2 MWth GWh m3 Silkeborg DK Silkeborg Fjernvarme 157,000 110 80 2016 64,000 Water tank ARCON (DK)Current data on Danish solar heat plants (click Silkeborg in South-West Denmark, then "About the plant") Vojens DK Vojens Fjernvarme 70,000 50 35 2012–2015 203,000 Insulated water pondWater tank ARCON (DK)http://xqw.dk/work/FG22/okt/Projektforslag_for_udvidelse_af_Vojens_solvarme_med_bilag.pdfCurrent data on Danish solar heat plants (click Vojens in South-West Denmark, then "About the plant") Port Augusta, South Australia Australia Sundrop Farms 51,500 36.4 2016 Aalborg CSP. Desalination for vegetables. 1.5 MW electricity Gramm DK Gram Fjernvarme 44,801 31 20.82009- 122,000Insulated water pond. 10MW electric boiler900 kW heat pump Inspirationskatalog for store varmepumpeprojekter i fjernvarmesystemet page 59. November 2014Current data on Danish solar heat plants (click Gram in South-West Denmark, then "About the plant") Gabriela Mistral, El Loa, Atacama Desert Chile CODELCO mine 43,920 27–34 52–80 2013 4,300 Water tank ARCON (DK). Supplies an electrowinning copper process DronninglundDK37,5732618 201460,000Insulated water pond ArCon (DK)Current data on Danish solar heat plants (click Dronninglund in North Denmark, then "About the plant")Zhongba, 4,700 metres altitudeTibet (China)34,65020 201915,000Water tankArCon Marstal DK Marstal Fjernvarme 33,300 24 13.4 1996–2002, 2020 2,100 3,500 70,000 Water tank Sand/water ground pit Insulated water pond with new lid Sunmark / ARCON (DK). Feeds 0.75 MW ORC turbineCurrent data on Danish solar heat plants (click Marstal in South Denmark, then "About the plant")Første danske ORC kraftvarme maskine i Marstal, August 2013RingkøbingDK30,00022.614 2010–2014ArConCurrent data on Danish solar heat plants (click Ringkøbing in West Denmark, then "About the plant") BrønderslevDK 27,000 16.6 8,000 Water tankCSP parabolic troughCSP plant combined with biomass CHP using ORC-technologyLangkazi, 4,600 metres altitudeTibet (China)22,000 201815,000Insulated water pondArCon HjallerupDK 21,432 Current data on Danish solar heat plants (click Hjallerup in West Denmark, then "About the plant") VildbjergDK 21,234 14.5 9.5 2014 ArConCurrent data on Danish solar heat plants (click Vildbjerg in West Denmark, then "About the plant")HelsingeDKHelsinge Fjernvarme 19,588 14 9.42012-2014 Current data on Danish solar heat plants (click Helsinge in East Denmark, then "About the plant") Hadsund DKHadsund Fjernvarme 20,513 14 11.5 2015 ARCON (DK)Current data on Danish solar heat plants (click Hadsund in West Denmark, then "About the plant") Nykøbing Sjælland DK 20,084 14 9.5 ARCON (DK)Current data on Danish solar heat plants (click Nykøbing Sjælland in East Denmark, then "About the plant") Gråsten DK 19,024 13 9.7 2012 ARCON (DK)Current data on Danish solar heat plants (click Gråsten in South Denmark, then "About the plant") Brædstrup DK Brædstrup Fjernvarme 18,612 14 8.9 2007/2012 5,000 19,000 Water tank Borehole storage, insulated by seashells ARCON (DK)Current data on Danish solar heat plants (click Brædstrup in Central Denmark, then "About the plant") Tarm DK 18,585 13.1 9 2013 ARCON (DK)Current data on Danish solar heat plants (click Tarm in West Denmark, then "About the plant") Jetsmark DK 15,183 10.6 7.6 2015 Arcon/Sunmark (DK)Current data on Danish solar heat plants (click Jetsmark in North Denmark, then "About the plant") Oksbøl DK 14,745 9.9 7.7 2010/2013 Sunmark (DK)Current data on Danish solar heat plants (click Oksbøl in West Denmark, then "About the plant") Jægerspris DK 13,405 8.6 6 2010 Sunmark (DK)Current data on Danish solar heat plants (click Jægerspris in East Denmark, then "About the plant") SydLangeland DK 12,500 7.5 7.5 2013 Sunmark (DK)Current data on Danish solar heat plants (click Langeland in South Denmark, then "About the plant") Grenaa DK 12,096 8.4 5.8 2014 Arcon (DK)Current data on Danish solar heat plants (click Grenaa in North Denmark, then "About the plant") SydFalster DK 12,094 8.5 6 2011 Arcon (DK)Current data on Danish solar heat plants (click Falster in South-East Denmark, then "About the plant") Hvidebæk DK 12,038 8.6 5.7 2013 Arcon (DK)Current data on Danish solar heat plants (click Hvidebæk in East Denmark, then "About the plant") Sæby DK Sæby Fjernvarme 11,866 8 6.3 2011 Sunmark (DK)Current data on Danish solar heat plants (click Sæby in North Denmark, then "About the plant") Toftlund DK 11,000 7.4 5.4 2013 Sunmark (DK)Current data on Danish solar heat plants (click Toftlund in South Denmark, then "About the plant") Kungälv SE Kungälv Energi AB 10,048 7.0 4.5 2000 1,000 Water tank ARCON (DK)Svebølle-Viskinge 10,000 5.3 52011/2014 Current data on Danish solar heat plants (click Svebølle-Viskinge in East Denmark, then "About the plant") Karup DK 8,063 5.4 3.7 2013 ARCON (DK)Current data on Danish solar heat plants (click Karup in North Denmark, then "About the plant") Strandby DK Strandby Varmeværk 8,000 5.6 3.6 2007 ARCON (DK)Current data on Danish solar heat plants (click Strandby in North Denmark, then "About the plant") Nykvärn SE Telge Energi AB 7,500 5.3 3.4 1985 1,500 Water tank Teknoterm (SE) ARCON (DK) Crailsheim DE 7,300 2012 37,500 Borehole Wagner, Schüco, Aquasol, Asgard Ærøskøbing DK Ærøskøping Fjernvarme 7,050 3.4 3 1998/2010 1,200 Water tank ARCON/Sunmark (DK)Current data on Danish solar heat plants (click Ærøskøping in South Denmark, then "About the plant") La Parreña mine Mexico Peñoles 6,270 4,4 660 Water tank ARCON (DK). Supplies an electrowinning process Falkenberg SE Falkenberg Energi AB 5,500 3.9 2.5 1989 1,100 Water tank Teknoterm (SE) ARCON (DK) Graz AT Energie Graz 6,000 2018 Water tank Neckarsulm DE Stadtwerke Neckarsulm 5,044 3.5 2.3 1997 25,000 Soil duct heat exchanger Sonnenkraft (DE) ARCON (DK) Ulsted DK Ulsted Fjernvarme 5,000 3.5 2.2 2006 1,000 Water tank ARCON (DK) Friederichshafen DE Technische Werke Fried. 4,250 3.0 1.9 1996 12,000 Concrete tank in ground ARCON (DK)

Source: Jan Erik Nielsen, PlanEnergi, DK.

There is a plant in Rise (DK) with a new collector producer, Marstal VVS (DK), a plant in Ry (DK), one of the oldest in Europe, a plant in Hamburg and a number of plants below 3,000 m2. The island of Ærø in Denmark has three of the major CSHP: Marstal, Ærøskøping, and Rise.

History of central solar heating plants

The history of CSHP given here is mainly a Nordic-European perspective on the topic.

Sweden has played a major role in the development of large-scale solar heating. According to (Dalenbäck, J-O., 1993), the first steps were taken in the early seventies in Linköping, Sweden, followed by a mature revision in 1983 in Lyckebo, Sweden. Inspired by this work, Finland developed its first plant in Kerava, and the Netherlands built a first plant in Groningen. These plants are reported under the International Energy Agency by (Dalenbäck, J-O., 1990). Note that these plants did already combine CSHPs with large-scale thermal storage.

The first large-scale solar collector fields were made on-site in Torvalle, Sweden, 1982, 2000 m2 and Malung, Sweden, 640 m2. Prefabricated collector arrays were introduced in Nykvarn, Sweden, 4000 m2 in 1985. There was from the beginning a strong international perspective and cooperation within this research field, through investigation with the European Communities (Dalenbäck, J-O., 1995) and the International Energy Agency (Dalenbäck, J-O., 1990). Denmark did enter this research area parallel to the Swedish activities with a plant in Vester Nebel in 1987, one plant in Saltum in 1988 and one in Ry in 1989, taking over the know-how for prefabricated solar collectors of large size by the Swedish company Teknoterm by the dominating company ARCON, Denmark. In the later 1990s Germany and Switzerland were active among others with plants in Stuttgart and Chemnitz.

Due to cheap land prices, in the Nordic countries new collector arrays are ground-mounted (concrete foundations or pile-driven steel) in suitable areas (low-yield agricultural, industry etc.). Countries with high ground prices tend to place solar collectors on building roofs, following the 'block plant' variant of CSHPs. In Northern Europe, 20% solar heat of annual heating requirement is the economic optimum in a district heating plant when using above-ground storage tanks. If pond storage is used, the solar contribution can reach 50%.Wittrup, Sanne. "Dansk solteknologi mod nye verdensrekorder" Ingeniøren, 23 October 2015. Accessed: 16 July 2016.

By 1999 40 CSHPs were in operation in Europe generating about 30 MW of thermal power .

Related systems Central solar heating is a sub-class of 'large-scale solar heating' systems - a term applied to systems with solar collector areas greater than 500 m2.

Aquifers, boreholes and artificial ponds (costing €30/m3) are used as heat storage (up to 90% efficient) in some central solar heating plants, which later extract the heat (similar to ground storage) via a large heat pump to supply district heating. Some of these are listed in the table above.

In Alberta, Canada the Drake Landing Solar Community has achieved a world record 97% annual solar fraction for heating needs, using solar-thermal panels on the garage roofs and thermal storage in a borehole cluster.Wong B., Thornton J. (2013). Integrating Solar & Heat Pumps . Renewable Heat Workshop. (Powerpoint)Natural Resources Canada, 2012. Canadian Solar Community Sets New World Record for Energy Efficiency and Innovation . 5 Oct. 2012.Drake Landing

Central solar heating

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