A recent Brattle study commissioned by Solar Landscape, a leading rooftop community solar and storage (CSS) company, found that both rooftop and ground-mounted community solar projects can add significant value to an electrical grid under the right conditions. Different types of CSS projects provide similar environmental benefits, and all projects offer opportunities for greater participation from individuals, small businesses, and nonprofits who otherwise may not have the resources to develop their own solar projects.

Analysis of the Incremental Value of Rooftop Community Solar + Storage in California assessed different types of CSS projects in California and identified material differences in the energy and non-energy value streams provided by these projects. Remote, ground-mounted projects benefit from single-axis tracking, which results in a higher capacity factor, output, and avoided transmission costs. However, rooftop projects in urban and suburban areas provide greater energy, capacity, and distribution value on a levelized basis. Considering all value streams, Brattle’s experts found that rooftop projects in urban/suburban areas could provide total incremental value ranging from 4.39 ¢/kWh to 9.05 ¢/kWh relative to remote, ground-mounted projects.

Differences in the value streams explored in the study include:

  • Energy Value: Urban market nodes typically have higher locational prices, meaning urban generation provides incremental energy value over the zonal average price. Differences in the solar profile (due to tracking) also affect avoided energy costs.
  • Generation Capacity: Rooftop projects located in urban, capacity-constrained load pockets can provide local resource adequacy (RA); ground-mounted projects, likely outside load pockets, can provide system RA value but not local RA.
  • Avoided T&D Infrastructure: Rooftop projects can reduce the need for infrastructure that carries power to these load centers from more distant generators. Differences in the solar profile affect the coincidence of dispatch with transmission and distribution (T&D) peak load hours.
  • Environmental Value: Differences in the solar profile affect the coincidence of dispatch with hours of high GHG emissions.
  • Losses: Rooftop solar generation avoids T&D line losses, while ground-mounted generation encounters distribution losses.

In addition to the quantitative assessment of rooftop CSS compared to ground-mounted CSS, the study authors conducted a qualitative assessment of other potential value streams where it would be difficult to accurately calculate a dollar value. They found that rooftop projects typically have greater land use benefits since they use brownfield or unused sites and have faster project timelines than ground-mounted projects.

The study’s results may be useful for policymakers, regulators, and utility program developers seeking to understand the relative value of different types of CSS projects.

The full report – authored by Principal Tom Chapman, Senior Associate Akhilesh Ramakrishnan, Senior Research Analyst Frederick Corpuz, and Research Analyst Violette Ballecer – can be found below.

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