PV System Assignment and Distributions

Overview

ResStock assigns photovoltaic (PV) systems to residential dwelling units based on housing characteristic distributions. However, the data sources1 for PV systems do not include specific building characteristics. Instead, they provide:

  • The number of PV systems by county
  • A distribution of PV system sizes
  • A distribution of PV system orientations

The units with PV systems are applied to single-family detached units with a system size and orientation assigned by the input characteristics and not any electricity consumption, roof area, or roof orientation information.

Limitations and Assumptions

  1. PV systems are not sized based on individual building energy consumption. A system may be significantly over- or under-sized for a given dwelling.
  2. No checks are performed to verify if a PV system fits on the roof or if the roof is oriented correctly for the assigned PV system.
  3. Snow cover is not accounted for in PV energy estimates.
  4. Mobile homes, multi-family units, and single-family attached homes do not have PV systems in ResStock. As a result, single-family detached units may have a slightly higher-than-expected PV system saturation.
  5. Vacant units do not have PV systems.
  6. Imposed an upper bound of 14 kWDC, which contains 95% of all installations.
  7. Counties with PV system counts less than 10 are backfilled with aggregates at the State level.

ResStock PV data is best suited for:

  1. Aggregate energy estimates
  2. Baseline PV utility-level annual load and load shape estimates

When to Scrutinize the Results

  1. Distributional Analysis
    • In both baseline and upgrade scenarios, PV-equipped units may skew results or create unrealistic outliers.
  2. Units with Large Negative Net Energy Consumption
    • If a unit has an oversized PV system, it may show significantly negative net energy consumption.
    • Since ResStock does not size PV systems to match individual energy loads, this can also affect utility bill estimates, which may appear negative depending on other fuel consumption.

  1. American Community Survey unit counts and RiDER project data on PV installation that combines LBNL’s 2020 Tracking the Sun and Wood Mackenzie’s 2020 Q4 PV reports. ↩

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