The “on-site gen” tab accounts for the renewable energy generated on site by PV, wind, micro CHP, or other energy saving technologies. The renewable energy associated with biomass, solar water heating, heat recovery from ventilation, or the ambient energy from heat pumps, are accounted for elsewhere in the DEAP calculation.
The electricity generated by PV, wind, or micro CHP, is split to account for the electricity used on site and electricity exported to the grid. The electricity used on site is allocated the Primary Energy Factor (PEF) of grid electricity, while the proportion exported to the grid is allocated a PEF of 1.
For the purposes of calculating the amount of renewable electricity that is used on site, a consideration has been made to account for some non-EPBD electrical loads (i.e. white goods, cooking, etc), therefore reducing the amount of renewable electricity being exported to the grid at the lower PEF of 1.
Where multiple on-site generation sources are present, the sum of uncorrected self-use from all sources could in some months exceed total electricity demand. A correction factor is therefore calculated for each month as:
correction factor = min (Dm / (EPV,self,m + Ewind,self,m), 1)
This factor is applied to the self-use of each source, with export adjusted correspondingly, so that total self-use across all sources does not exceed Dm in any month.
Photovoltaics. A PV panel produces electricity as a result of interaction of sunlight with semi-conductor materials in the PV cells. Photovoltaic technology converts sunlight directly into electricity. It works during daylight hours, but more electricity is produced when the sunshine is more intense (a sunny day) and is striking the PV modules directly. Unlike solar systems for heating water, PV technology does not produce heat.
Wind Energy. A wind turbine converts wind energy into electricity using the aerodynamic force from the rotor blades. When wind flows across the blade, the physics involved force the rotor to spin. The rotor is connected to a generator, either directly (if it’s a direct drive turbine) or through a gearbox that speed up the rotation and allow for a physically smaller generator.
Micro CHP. Micro-cogeneration from combined heat and power (CHP) plant provides both heat and electricity. It is assumed to be heat-led, meaning that it is allowed to operate only when there is a demand for space heating or hot water. The domestic application of micro-cogeneration is treated in conjunction with a conventional domestic heating system, such as a boiler or heat pump. It is also assumed that it is connected to the public electricity supply in such a way that surplus generated electricity is exported. For both group heating systems and individual dwellings, the fraction of heat from CHP (main space heating demand plus main water heating demand from CHP) needs to be determined for entry into DEAP.
While micro CHP is not treated as a source of renewable energy, it does generate electricity that can be consumed on site and exported to the grid, so it must be deducted from the total energy required for the building. Any carbon emissions associated with the generation of the energy will also be included in the assessment.