Optimisation of Local and National Energy Systems : Development and Use of the MODEST Model

Sammanfattning: Energy may be supplied by a multitude of components. Computer simulation helps in finding a beneficial system design. The energy-system optimisation model MODEST has been developed, and it has been applied to municipal, regional, and national energy systems. The most favourable combinations of present and potential equipment and energy flows have been obtained.MODEST uses linear programming to minimise capital and operation costs. A flexible time division can reflect demand peaks and diurnal, weekly, seasonal, and long-term variations of demand, costs, capacities, etc. The optimal kinds, sizes, and occasions for investments and the best system operation are found. MODEST has been used to study energy supply and demand-side measures in 40 municipalities, three provinces, and the Swedish electricity system.The national power system was studied at the request of the governmental Energy Commission. A nuclear phase-out would cause a 30% cost increase for satisfying the useful energydemand that today is covered by electricity in Sweden. Cogeneration should replace some nuclear-power production, and power export would decrease. To achieve environmental sustainability, biofuel and wind power should complement hydroelectric power because naturalgas and condensing-power capacity expansion would enhance CO2 emissions significantly. Increased electricity costs would make consumers introduce more fuel switching from electricity to oil or biomass for heating. Industrial energy conservation and load management have robust profitability irrespective of nuclear-power, fossil-fuel, and carbon-dioxide restrictions. Obtained marginal costs for electricity supply may reflect electricity prices in a deregulated market and can be used as input to local studies.Many local electricity and district-heating utilities have assigned tasks where MODEST has been used as decision support. Introducing heat-only boilers and combined heat and power (CHP)plants can accomplish cost minimisation at low and high electricity prices, respectively. The use of oil, woodchips, etc. depends on taxes and environmental fees. A heat storage may cover demand peaks, increase the heat sink for CHP, and be charged by heat pumps that use cheap night electricity.MODEST has, thus, been applied to many different energy systems, and the most suitable installations and operations have been found.