Figure 1 Electricity prices fluctuate mainly due to wind and solar PV – and it’s getting worse in the years to come.
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Individual buildings In case all buildings at a campus or a city are supplied with building-level heat pumps for base load and small electric boilers for peak load, the electricity consumption can only be interrupted for a few hours in case of very high electricity pric- es. Some building owners may claim that they hour by hour have bought renewable electricity and left the black electricity to the others, but that does not change the production. It is greenwashing. The flexibility provided to the electricity system to help inte- grate renewable energy is very limited if we install individu- al electric heating solutions per building. The recently seen combination of the individual heat pump solution with shared heat source “Ambient loop” (or mistakenly referred to as 5th generation district heating) has the same disadvantages in terms of flexibility as an individual heat pump. 1st generation district heating In case all buildings are connected to a 1st generation DH steam system supplied by a Combined Heat & Power (CHP) plant and steam boilers, this system can be backup in case of high electricity prices and shifted to boilers in case of low elec- tricity prices. It is, however, expensive and inefficient and has no thermal storage capacity.
The 1st generation DH systems do not add many benefits to the integration of renewable energy, seen from the electricity system. 2nd generation district heating If the steam system is converted to a 2nd generation DH hot water district heating system supplied by a natural gas boiler and a natural gas-fueled CHP in combination with a thermal storage tank, it is significantly more efficient. The thermal stor- age tank will unbundle the heat and power production. The CHP plant will replace inefficient, expensive condensing pow- er-only plants in the electricity market in case of high electric- ity prices. The CHP plant will bypass the low-pressure turbines or stop if the electricity prices are low, and the wind is on the margin. Thereby the system efficiency of heat generated by the CHP plant will be 200-300% once it is in operation. The ability to stop electricity production (in case of low electric- ity prices) and operate at full capacity (as soon as the electricity price increase) has the same impact on the electricity system as if an electric boiler or a battery was installed. Hence, from the development of 2nd generation DH, we begin to see the effect of the virtual battery.
3rd generation district heating Suppose the district heating company installs a large electric
20 HOTCOOL no.2 2023
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