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Solar power and heat The challenges with harnessing solar energy are:
The way forward for grand geothermal utilization can only be achieved in combination with district heating networks. By applying district heating networks the plant capacity utilization can be maintained very high throughout the year, which results in low investment costs per energy unit. In combination with solar and wind energy the geothermal energy can cover the base load demand. The geothermal energy can also be used to fulfill peak load demand to some extent, if the well is rested in periods of high availability of energy from heat and wind. Biomass Biomass is without doubt one of the key energy sources in the future energy mix. However, many processes rely on fossil fuel based materials and once fossil fuels have been phased out, these processes will look towards substitutes and most likely the substituting materials will be found in the biomass. Additionally it is expected that the transportation industry will look heavily towards biomass for alternatives to fossil fuels. The challenges with biomass are: • Origin of biomass is in rural areas, potentially far from the energy demand. • Transportation of biomass in grand scale is challenging. • It is valuable resource for various processes. It is expected that many current power plants will be changed from fossil fuels to biomass plants. During power generation and fuel conversion processes heat will always be a by-product. It would only be natural to utilize the heat for heating purposes through district heating networks. Surplus heat from the industry By looking into studies made on the availability of surplus heat from industry it can be seen that surplus heat is available throughout Europe [2]. By utilizing the industry surplus heat, which is seldom used today, huge amount of fossil fuels can be replaced. The main issues with utilizing surplus heat from industry is that it can be of low temperature, which would require lifting the temperature using heat pumps. Free cooling Commercial buildings have cooling demand more or less throughout the year. For long periods of time this cooling could be achieved by utilizing free cooling from the sea, lakes or rivers. The district cooling network is then used to transport the cold from the cooling source to the buildings. This can significantly reduce the power consumption for cooling purposes. Once the district cooling network has been established, it can be used in combination with electrical chillers and thermal storages during the summer months to decouple the cooling generation and cooling demand and hence reduce the strain on the power grid during peak load periods. Heat storages Heat storages are a simple mean to decouple supply and demand. By applying heat storages the energy can be generated when it is most economical, and saved for later times.
• Solar panels need space with certain incline and facing in the direction. In urban areas this would generally mean rooftops of buildings. If solar heat is applied, the roof may need structural enhancements. • Solar energy is intermittent, both during the day and seasonal. • During winter the solar yield is low. The best utilization of solar energy can be achieved if the harnessed energy is fed in to either power or heat grids. The main issue with solar energy is that it is only accessible when the sun is shining. This implies that it cannot fulfill the whole power or heating demand throughout the year. However if the solar energy is used as alternative energy sources it provides the cleanest energy that can be achieved. Wind energy The challenges with harnessing wind energy are: • The wind is intermittent. • Large power fluctuations can be experienced within short period of time. • It is not applicable in urban areas. The best utilization of wind energy is through connection to a power grid. In countries like Denmark where high wind power concentration has been achieved there can be periods of strong winds were the power generation can become higher than the demand. In case of excess wind, and hence power generation, either some wind mills need to be stopped or the excess power needs to be used. The best way to use the excess generated power would be to heat or cool water using heat pumps and feed the hot/cold water to a district energy system. In case of low heating/cooling demand the heat or cold can be stored in large water storages for later usage. Geothermal energy In general, geothermal energy is a stable and secure renewable energy source. The challenges with utilizing geothermal energy are: • Initial investment is high. • Suitable locations can be remote. • In most locations the geothermal energy is of low temperature nature. Almost independently on locations geothermal energy can be found with sufficiently high temperature for fulfilling space heating demands, a great case can be found in Paris where a total capacity installed is 270 MWth. In case of low temperature sources heat pumps can be used to lift the temperature to suitable levels, as is done in Sønderborg, Denmark. However, the above mentioned challenges have resulted in that utilizing geothermal energy on a grand scale is not main stream, even though geothermal energy could achieve tremendous reduction in fossil fuels usage.
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