In the 2019 energy code, the self-utilization credit for a residential battery system allows proposed designs with PV systems and batteries (5 kWh or larger) to subtract additional TDV from the “Efficiency” TDV of the proposed design. The self-utilization credit is capped at a fraction of the PV-related TDV of the standard design. The cap varies by climate zone and is between 7% and 14% for a single-family residence and between 2% and 9% for a multi-family building (see Table 1 in Section 2.1.5.5).
The actual credit applied to the “Efficiency” TDV of the proposed design is the lesser of the battery related TDV in the “Final” proposed design and the cap defined above. Effectively, the self-utilization credit allows the proposed “Efficiency” design to also get credit for a portion of the TDV savings that would otherwise be seen only in the “Final” design.