Optimization of solar district heating systems:: seasonal storage, heat pumps, and cogeneration

The dynamic energy, emission, and cost optimization model deeco is further developed and applied to the analysis of solar district heating systems with seasonal storage in a pilot project of the Bavarian Research Foundation. The optimum integration of condensing boilers, compression and absorption heat pumps, and cogeneration of heat and power is computed for 100 well insulated housing units with an annual total heat demand of 616 MWh. Collector areas between 1 and 2.5 m(2) per MWh heat demand and water storage volumes between 1.2 and 4.2 m(3) per m(2) collector area satisfy between 32 and 95 per cent of the total heat demand by solar thermal heat. Compared with a reference case with individual condensing boilers and electricity taken from the public grid, selected scenarios achieve (non-renewable primary) energy savings between 15 and 35% associated with cost increases between -20% and 140%; cogeneration turns out to be quite attractive from an economical point of view. With cogeneration and a solar contribution to the heat supply of 80%, emission reductions of CO2-equivalents by 33%, SO2 by 20%, and NOx by 22% can be achieved at cost increases of 120%. Fossil fuel savings of more than 40% are possible if electricity is produced from non-fossil energy sources. (C) 2000 Elsevier Science Ltd. All rights reserved.