Open-circuit district heating nets exist only in Russia and in Central Asia. Other CIS or former USSR countries either had only closed-circuit systems (Belarus, Ukraine, Azerbaijan etc) or reconstructed open-circuit systems to closed-circuit ones (Baltic countries).

In Russia and in Central Asia 197 heat and power plants were identified and 163 of them were evaluated so far.

Roughly half of the identified heat and power plants have a closed-circuit system and were, thus, not further considered (cf. Figure 3). 38 of the open — and mix-systems are in operation in summer (cf. Figure 4) and are, therefore, in principle appropriate for solar water preheating. Since no information about the operation mode had been

Fig. 4. Number of identified heat and power plants with open (left) and mix (right) — circuit systems by

operation conditions

In this investigation only large heat and power plants with a possible potential for several thousand square meters of uncovered collector were identified and evaluated. Beside these, various small heat plants exist (without power generation). Some of them have cold water flow rates of 50..100 m3/h, which corresponds about 500 and 1000 m2 of collector. For example, the 6 largest heat plants out of 58 operating in Bishkek have a total potential of approx. 3000 m2 of uncovered collector.

Furthermore, large closed-circle district heating nets could benefit from solar preheating due to their water losses. E. g. the closed-circle in Moscow runs approximately 3 million m3 of water. Hourly water losses of 0.1 % of the net capacity correspond to 3000 m3/h in required feeding water, possibly offering an opportunity for solar preheating.

Estimation of annual heat gains is based on the local climate data as well as on the thermal performance of the uncovered collectors. For Bishkek, three sources of meteorological data are available [3]: the program “Meteonorm”, a local weather station “Frunze”, and measurements since 2004 on a pilot solar thermal system in Bishkek [2]. A commercial water preheating system will be working in the frost-free period, in Bishkek from May to September (5 months). Based on

simulation calculations with the program TRNSYS[3] with conservative climate data energy, solar heat gains of about 1000 kWh/m2a can be expected. The technical and economical potential for the heat and power plant TEZ in Bishkek is approx. 32 MWth (45000 m2 of uncovered collectors), which is more than two times larger than the currently largest solar thermal heat plant in the

world[4].

A promising option is thereby the recognition of the solar thermal plant as a so-called CDM project in the framework of the Kyoto protocol, which can lead to additional financial gains by the generation and selling of emission certificates. An average emission factor for TEZ Bishkek equals 0.282 t CO2/MWhth when calculated with the specific emission factors of the Intergovernmental Panel on Climate Change (IPCC) and fuel mix of the TEZ Bishkek. This corresponds to an annual emission reduction of 0.31 t CO2 per m2 collector area[5]. An economic calculation of an uncovered collector located in Bishkek was carried out with following assumptions:

• investment (system costs)[6] = 44 € per m2 of uncovered collectors

• solar energy gains = 1 MWh/m2a

• interest rate = 13 %/a

• maintenance = 1 % of system costs

• certificate price (CER) = 6 €/t CO2

• system size = 45000 m2 (corresponds to 2 million € investment)

• operation time =14 a

• fossil price increase rate = 2 %/a

For fuel prices in 2007 (e. g. gas 0.98 ct/kWh) a solar heat price of 0.5 ct/kWh and a payback period of 9 years are calculated. Thus, the heat price for solar thermal heat generation lies significantly below the price for fossil fuels. Without recognition as a CDM project a solar heat price of 0.7 ct/kWh and a payback period of 12 years are expected. If the uncovered collector loop and the district heating net must be separated with a heat exchanger, the solar heat price will rise by another 0.1 ct/kWh.

Furthermore, an economic study[7] for different locations in the CIS was carried out (cf. Figure 6). Energy gains are based on simulation calculations using climate data of the program Meteonorm 5.1. Here, the simulation period is Mai to September instead of the frost-free period to have better comparability between the different sites. The water inlet temperature was set to 12°C for all locations. Some locations, however, were also simulated with the water inlet temperature of 15 and 20°C. The specific flow rate of uncovered collectors in the simulations is 100 l/m2h.

Fig. 6. Solar and conventional heat costs for different locations in the CIS. (15) and (20) represents the water inlet temperature of 15°C and 20°C respectively. Otherwise an inlet temperature of 12°C was assumed.

2. Conclusions

Uncovered collectors can be effectively applied to preheat water for open-circuit district heating nets in cities of the Commonwealth of Independent States. In Russia and in Central Asia in total 197 heat and power plants were identified and 163 of them were evaluated. 38 heat and power plants seem to be technically suitable for solar preheating. Solar heat costs of less than 0.01 €/kWhth can be expected for many sites of the CIS. Large solar heating systems can be recognized as a CDM project to receive additional financial gains.

Acknowledgements

The authors would like to express their gratitude to the Volkswagen Foundation, Germany and Rudolf and Ursula Lieberum Foundation, Germany for the financial support, as well as to the Power Plants Inc., Kyrgyzstan and to the Almaty Power Consolidated, Kazakhstan for the opportunity to visit their heat and power plants.

References

[1] K. Vajen, M. Kramer, R. Orths, E. K. Boronbaev (1999): Solar Absorber System for Preheating Feeding Water for District Heating Nets, Proc. ISES Solar World Congress 1999

[2] E. Frank, K. Vajen, A. Obozov, V. Borodin (2006): Preheating for a District Heating Net with a Multicomponent Solar Thermal System, Proc. EuroSun 2006, Glasgow

[3] R. Botpaev, A. Obozov, C. Budig, J. Orozaliev, K. Vajen (2008), Comparison of meteorological data from different sources for Bishkek, Kyrgyzstan, Proceedings EuroSun, Lisbon

[4] E. Frank (2007): Modellierung und Auslegungsoptimierung unabgedeckter Solarkollektoren fur die Vorerwarmung offener Fernwarmenetze, Dissertation, Universitat Kassel