Through a research and development support of 11.9 mio. DDK, the Danish government pushes for CSHP with seasonal storage. In charge for the project is Planenergi, the most active consulting company in the business together with the plant owner, Dronningelund District Heating. The overall concept will be to use solar heating in combination with a large scale thermal storage and a heat pump. The collector area is planned to be approx. 35,000 square metres, a storage volume of 60,000 m³ and a heat pump with 3 MW effect.

The seasonal storage is planned as a pit water storage with floating lid, a well-known solution applied in the past.

The overall budget for the project is 80 mio. DDK or approx. 10.1 mio. Euros.

We keep an eye on this project at this blog.80

At the Eurosun 2008 in Lisbon, the thematic of large scale thermal storage was part of the topic range. Per Alex Sørensen from Planenergi, Denmark did provide me a copy of three papers that I refer here. Unfortunately, it seems that one cannot get the proceeding online. (This ought to be changed for any renewable energy and environmental conference, where proceedings ought to be open access and free for reading).

T. Schmidt and D. Mangold from the Steinbeis Research Institute, Stuttgart, Germany mailto:schmidt@solites.de did present a paper including three thermal storage projects, a 5,700 m3 water tank i Munich, a borehole storage 37,500 m3 volume in Crailsheim and a 4,500 m3 pit storage in Eggenstein.

F.Ochs, J. Nussbeicker-Lux at.al. presented the following abstract to their paper “Solar assisted district heating system with seasonal thermal energy storage in Eggenstein-Leopoldshafen” with the following abstract:

The solar assisted district heating system with seasonal thermal energy storage in Eggenstein-Leopoldshafen (Germany) is the first system realized with existing renovated buildings. The system consists of 1600 m² flat plate collectors and a 4500 m³ gravel-water thermal energy store (TES) for seasonal thermal storage. Experiences gained within the BMU-project “Further development of the pit heat store technology” contributed to the design of the seasonal TES. This paper focuses on the design and construction of the gravel-water store. The monitoring concept of the solar assisted district heating system with focus
on the gravel-water TES is presented.

Per Alex Sørensen, mailto:pas@planenergi.dk, from PlanEnergi, Leo Holm and Niels Aage Jensen from Marstal Fjernvarme, Denmark presented a paper “Water Storages, Solar thermal and Heat pumps in District Heatin” with the following abstract:

In 1996 Marstal Fjernvarme (Marstal District Heating) established 8.000 m2 solar collectors that covered 13% of the yearly consumption. The solar fraction in later built district heating plants goes up to 25% covering the total summer load, but several district heating companies especially natural gas fired combined heat and power plants want a higher solar fraction in order to replace expensive natural gas. Therefore new projects with solar fractions of 50% are designed and are expected to be implemented  in 2009. Design calculations show that the production price for heat from solar thermal plants with 50% solar fraction can compete with heat prices from natural gas fired CHP plants.

For the first time, a major district heating company is planing to adopt the concept of central solar heating. The company VEKS, distributing heat in the western part of the Copenhagen area is aiming at a CSHP with a solar collector size of 20,000 m2, placed along a main highway. The plant will match the current record of the Marstal plant, also placed in Denmark. The plant will deliver approx. the heat of 5-6,000 single family houses.CEO, Lars Gulev, of the “Vestegnens Kraftvarmeselskab” district heating company estimates the plant to produce 10 GWh heat to the district heating system. The goal is to get the plant into production before the International Climate Conference in Copenhagen, 2009, where the expectations are to replace the Kyoto-protocol with a more ambitious protocol.

It is expected that the application of central solar heating is a factor 4 more cost efficient compare to single family housing solar installations.

Relevant is to mention, that the company is expecting lower production prices for the solar plant compared to the traditional co-generation plants due to the facts that solar prices are reduced as conventional heating prices are increased during the later years.

“In the first place, the solar heating plant is planed due to commercial reasons. Getting reduced CO2 pollution is a environmental side effect.” says Lars Gulev.

We hope others will take this considerations up and CSHP will play a more dominant role in the future of district heating. It would be interesting to see, if surplus heat from the power production will be cooled into the see due to this investment.

You find information on VEKS’s homepage on http://www.veks.dk (in Danish), where you change to English and will be presented for general information on the district heating system of Copenhagen. The solar plant is presented at the location http://www.veks.dk/Artikler/Seneste%20nyt/Solvarme.aspx

The Danish Engineering Newspaper did present the following news about a new very large CSHP plant:

Place: Denmark, Brænderup (near Horsens), at the mainland.

Size: 8.000 m² solar collector field, sized to deliver 10% of the district heating demand.

Of the 13 million total cost, the 3.5 millioner DDK are funded by a public body, Energinet.dk, that last year did analyse solar and district heating lead to positiv economical results. This analysis pointed out that this is due to the fact that the heat- or power plant can be turned of for some periods, where the price for power is too low to produce.
The maximum effect is estimated to 6 MW heat, with an annual production of approx. 4,000 MWh heat, leading to a yearly emission reduction of 4,300 tons CO2. The plant is designed by consultant company Planenergi and Ramboll, Denmark with Arcon solar collector producer, the same companies as involved in most of the plants in Denmark.

Blogging is online. Hence online resources are rather streight forward to point at. However, Googling turns out to show a lack of knowledge within this topic: Central Solar Heating Plants (CSHP) or Large-Scale Solar Heating. As a researcher, library information are traditionally the main source for information. Therefore I tried to search in our library including more than 45,000 journal articles. The hit rate for is 22 hits that matches the full term “Central Solar Heating Plants”; “Central Solar Heating” gives 82 hits, below 10 hits unique and written after 2000, the newest from 2004, most much older.

Can we conclude that Central (large scale) Solar Heating is not relevant?

We can cerainly conclude that the topic is not “hot”. Is this because there is no research going on, is it because the research is not pulished or is not accepted for publishing? This question is keept open.

Is the topic relevant?

Positiv aspects of CSHP: From the experiences from Marstal and most other plants, one can conclude that the efficiency for large-scale systems is much highere, compared to small solar systems. The installation price is appoximatelly 60% of the installation price for small systems. The price-performance is hereby better for both price and performance. Details can be found in the Ph.D. citet earier in the blog by me. Maintenance, effieciency improvements and other aspects do also point at large installations.

Problematic aspects of CSHP: However, heat losses can be relativelly large, if one does not consider it appropriatelly. Modells to do that can be found, among others, in “Heat-load modelling for large systems”, Applied Energy, p. 371-387, 72(1), 2002. Another negative aspect of large scale solar heating comes up, when combining solar heating with co-production power plants, where the “waste” heat is applied in district heating. This is the case for the Copenhagen District Heating, where an area with up to 30 km in wide, supplied with district heating. The problem here is, that the heat exaustion by power production does make the replacement with solar problematic, as long as the overall efficiency of the power production and “waste heat” are related.

So, the question must be answered, that the topic is very relvant for any large-scale heating system. Solar cooling could be combined, improving the efficiency even more. If you are researchers and look for an important research topic, here it is. District Heating & Cooling supported by Solar Energy with and without long-term heat and cool storage. As you find in this blog, there is a lot to work with.

One ought not to forget the main distribution and consumption system for CSHP, the District Heating. Such systems can be used for both heating and cooling. This is certainly obtained by Euroheat, an organisation for the European district heating and cooling industry. They published a nice brochure on district heating and cooling, mentioning a few of the solar plants.

The solar cooling part is of high relevance, due to the fact that cooling demands are closely related to the occurence of the sun. Hence demands and solar availability match perfectly.