FEEt – Bestehende fossile oder teilfossile Fernwärmenetze – Einbindung von dezentraler Energie aus Erneuerbaren Energieträgern – Chancen und Hemmnisse

The net operators in the first instance primarily consider useful waste heat resources and only secondly 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.

Several projects are presently being planned or carried, the law on green electricity (Ökostromgesetz) activated an investigation impulse for biomass-cogeneration. Presently can an increase of the renewable energy part from 12% to approx. 16% be reached. The CO2 reduction adds up to more than 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 renewable energy sources to the existing district heating systems are above all the development of the law on green electricity (Ökostromgesetz) (above all feed in tariffs), of the price of fossil fuels and the of emission trading (prices for emission certificates).

The development towards renewable energy sources in existing district heating networks is positive effected by the minimised dependency of the crude oil price. The biomass prices are presently more stable and a long term calculation is possible, further can subsidies be achieved. An estimation of real long term potentials for renewable energy sources to existing networks is presently difficult since a lot of factors can not be affected (oil price etc.).

There are many technical solutions (above all for the CHP-sector) to feed in renewable energy in existing district heating systems – research potential is at the most requested only in detailed issues. 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 net.