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7.1.9.1 Results of modelling the network with micro-CHP

Micro-CHP was found, in the model, to have some beneficial impacts on the network, and one considerable detrimental impact. The negative impact that micro- CHP can have is causing voltage rise on the network. Neither Stirling engine nor fuel cell micro-CHP causes voltage levels on the network to exceed +10% of the rated voltage.

The benefits to the network are a reduction in instances of voltage dropping below the -6% limit, though from an already low baseline, a reduction in losses on the network and a reduction in power flows through the transformer. Losses on the network are reduced almost linearly as the amount of Stirling engine micro-CHP on the network is increased, by up to 29% below the baseline losses. Fuel cells reduce losses more rapidly than Stirling engines. However at higher penetrations, >60%, losses begin to rise again, and when all homes have fuel cell micro-CHP the losses are only 0.3 MWh lower than when all homes have Stirling engines. At the optimum penetration (from the perspective of reducing losses), of 60%, fuel cell micro-CHP reduces losses by 63%. In the baseline scenario, the transformer is overloaded for 26 minutes of the year. Both Stirling engines and fuel cell micro-CHP reduce this. When all homes have Stirling engines the transformer spends 9 minutes of the year overloaded, and when all homes have fuel cells it spends 2 minutes of the year overloaded.

The implications of these results are that micro-CHP has some benefit to the network through reducing losses, thereby saving energy, and through reducing power flows through the transformer which could avoid or delay needing to upgrade the transformer if network demands rise. They also imply that the network could accommodate all homes having Stirling engines without too many instances of voltage rise. The network could also accommodate 60% of homes having fuel cell micro-CHP, but any higher and there will be considerable increases to voltage rise potentially necessitating network reinforcement.

7.1.9.2 Results of modelling the network with solar PV and heat pumps Solar PV has similar impacts to micro-CHP in the model. It reduces instances of voltage drop, though only down to 20 minutes of the year, a lower reduction than

micro-CHP. It also reduces losses, until the percentage of homes with solar PV rises above 25%, at which point losses begin to rise again, becoming higher than the baseline losses once 75% or more of homes on the network have solar PV. Solar PV does not reduce the peak power flow through the transformer, and only reduces instances of overload down to 18 minutes of the year (from 26), a smaller reduction than micro-CHP.

Solar PV also has an impact on instances of voltage rise; the presence of solar PV can cause voltage levels to exceed the +10% limit, something that micro-CHP does not cause. Half the homes having solar PV causes the network to exceed the limit for a few minutes of the year, and 75% and 100% of homes having solar PV causes the network to exceed the limit for 1.6% and 5.3% of the year.

The impacts of Stirling engines alongside solar PV on the network are largely negligible. The presence of fuel cell micro-CHP alongside solar PV on the network will exacerbate the impacts of solar PV on voltage rise, while slightly reducing instances of voltage drop, and further reducing the power flows through the transformer. Though when all homes have both fuel cell micro-CHP and solar PV, instances of transformer overload will rise.

Heat pumps cause a considerable rise in electricity demand on the network. Through this they cause increases to instances of voltage drop, network losses and instances of transformer overload. Half the homes on the network having heat pumps cause instances of voltage dropping below -6% to triple compared to the baseline scenario; and they increase eightfold when all homes have heat pumps. Also when all homes have heat pumps network losses are more than doubled. The impacts heat pumps can have on the transformer are also considerable: increasing instances of overload up to fivefold when all homes have heat pumps. Once 75% or more of the homes on the network have heat pumps, the peak power flow through the transformer rises above 1.5 times its rated capacity, which may cause the transformer to fail. The impacts of heat pumps on voltage levels and the transformer could necessitate network reinforcement.

The presence of micro-CHP on the network alongside heat pumps will reduce their impacts on voltage levels, network losses and instances of transformer overload. The most considerable reduction is in power flows through the transformer. If 75% of

homes have heat pumps, and the rest have either Stirling engine or fuel cell micro- CHP, the maximum power flow through the transformer will no longer exceed 1.5 times its rated capacity. The implications of this are that the presence of micro-CHP could reduce or delay the need for network reinforcement caused by the presence of heat pumps.