Generation is not Enough As illustrated in Figure 3, the reference project where the daily demand peaks at about 4.5 MW during weekdays. The project incorporates a 2MWp rooftop PV array that offsets daytime project energy use and offers roughly a net 24% reduction in energy.
Using the grid intensity profiles from Figure 1, this level of generation translates to just about 12% reduction in project GHGI in 2020 and drops by another half to just about 6% in 2030. To reiterate, a 24% renewable energy offset will only avoid 6% of annual GHG emissions as the grid gets cleaner. To ensure that energy offsets coincide with the hours of maximum GHG intensity, there is a need for a dispatch algorithm that can simultaneously look ahead at the building demand and marginal grid emissions factors, and enables a battery bank to charge and discharge optimally to minimize or eliminate drawing from the grid during high emissions intensity hours.
ELECTRICITY (kWh)
5000
Grid to Project PV to Project
4000 3000 2000 1000 0 2500
PV GHG Avoided GHG Emissions
2020 GHG (kgCO2E )
2000 1500 1000 500 0 2500
PV GHG Avoided GHG Emissions
2030 GHG (kgCO2E )
2000 1500 1000 500 0
Typical Summer Work Week
Figure 3: Electricity demand profile for the reference project during a typical summer week showing on-site PV generation that offsets 24% of the energy use [Top] but avoids only12% of GHG Emissions in 2020 [Middle] and only 6% in 2030 [Bottom].
Decarbonizing the Built Environment
6
