Integration of decentralised renewable energies in existing fossil district heating grids
With the Austrian district heating systems with a total length of more than 3400 km and more than 13.000 GWh heat generation per year, a real potential for the adoption of renewable energy (under long cycle principles) is given.
The mains operators in the first instance think about useful waste heat resources and only then about new plants. As a result of an interview with network operators a short-term potential (until 2006) of annual 569.000 MWh for the feed in of heat from renewable energy (incl. waste heat utilisation) in the network could be realised. These are around 4.5 percent of the existing district heating utilisation.
A lot of projects are planned or carried out at the moment, the law on green electricity (Ökostromgesetz) activated an investigation impulse for biomass-cogeneration. An increase of the renewable energy part from at the moment 12% to approx. 16% can be reached. The CO2 reduction adds up to above 380.000 t per year (incl. steam-net-changeover, network in Salzburg)
The very good feed in tariffs (Ökostromgesetz 2002) caused an unbalance between electricity- and heat utilisation. The new designed plants will be operated primarily to produce electricity; the heat will be cooled down particularly in summer. The limit for the reasonable use of renewable energy in district heating networks is, because of the necessary high full load hours, the summer distribution.
A research demand for additional development and improvement of the summer utilisation (cooling with heat, change over of the warm water production to district heating etc.) is given. Economical factors of influence for middle and long term potentials for the feed in of renewable energy in existing district heating systems are above all the development of the law on green electricity (Ökostromgesetz) (above all feed in tariffs), development of the price of fossil fuels and the development of emission trading (prices for emission certificates).
The development towards feed in of renewable energy in existing district heating networks is positive effected by the minimised dependency of the crude oil price. The biomass prices are more stable at the moment and a long term calculation is possible, additionally subsidies can be achieved. An estimation of real long term potentials for the feed in of renewable energy in existing networks is difficult at the moment because a lot of factors can not be affected (oil price etc.).
A lot of technical solutions exist at the moment (above all for the CHP-sector) to feed in renewable energy in existing district heating systems - research potential is requested for many systems only in detailed questions. The main reasons for the less implementation by operators are the economical factors and the lack of distribution of heat in the summer time (economical problem for biomass cogeneration plants, which need a high processor load because of the high start investment).
The load of the plant (annual total load) is one of the most important parameters for the electricity- and heat generation with renewable energy. The advantages of plants operated with renewable energy can be seen at a long term level. Examples show that the combination of renewable energy (for the base load coverage) and fossil fuels to cover the pikes, an economical optimisation for the heat generation is possible and can afford economical advantages compared with fossil plants.
These plant combinations show the highest potential. Depending on the relationship between output and duration of the output of the district heating system and the construction of the biomass plant, 70 % of the heat energy can be covered by renewable energy. Important is the summer utilisation and summer efficiency of the mains.
AEE Intec (Werkvertragspartner)
Ö FPZ Arsenal GmbH (Werkvertragspartner)
S.O.L.I.D. GmbH (Werkvertragspartner)
Institut für Wärmetechnik TU Graz (Werkvertragspartner)