Adoption of distributed renewable energy resources such as rooftop solar or community wind and solar can have implications for energy equity. Subsidies can disproportionately benefit those who already have the capital to invest in distributed renewable energy resources while passing on some operational costs to those not benefiting from the increasing share of renewable energy. A number of policy solutions have been proposed to address these equity concerns. However, existing energy and policy infrastructure may already be exacerbating inequitable adoption.

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Now, in a study published in Nature Energy, Anna Brockway, Jennifer Conde and Duncan Callaway show that constraints on how much distributed energy resources (DERs) can be hosted by the grid in specific areas limit access to renewable energy in different ways for different communities and economic classes, making it even more difficult to overcome inequity in renewable energy adoption1.

The adoption of solar photovoltaic (PV) systems, which can contribute to reducing household electricity bills, could be limited by the hosting capacity of the grid. Hosting capacity is the amount of DERs that can be integrated into a distribution system without upgrades. Hosting capacity is calculated for various performance indices such as voltage and frequency variations, thermal overload, power quality and protection problems2. Each metric has its own hosting capacity limit.

The researchers have taken advantage of the open data provided by the State of California’s Integration Capacity Analysis (ICA) maps. In essence, the ICA is a model of the distribution grid, which includes the physical infrastructure itself, the type and performance of load on the grid, and existing generation as well as the load management measures on the grid (for example, demand response) to support the hosting capacity analysis.

Brockway and colleagues match hosting capacity data from the ICA to census data on demographics and economics at the block level. They then estimate the amount of circuit capacity needed to accommodate generation and load DERs and assess the ability of households to adopt these technologies given their local circuit limits.

The paper extensively reviews the growing body of literature that documents the persistence of social disparities in customer adoption of DERs, especially onsite solar PV3. The researchers show that hosting capacity increases with year of construction, which may imply correlations between housing age and local grid infrastructure. The real novelty of the work lies in its systematic analysis of how equitably the power grid can accommodate DERs. The paper correlates customer demographics with hosting capacity and explores possible implications for inequity in access to DERs, including income, housing characteristics and education. Income variations are insufficient for explaining the stark relationships between circuit capacity and disadvantaged communities. Brockway and colleagues claim that the correlations between hosting capacity and race are the strongest among a variety of demographic indicators analysed, showing that racial disparity is built into the grid.

The paper does not go into determining the reasons for lower hosting capacity for particular communities. Rather, it documents these disparities to raise awareness among policymakers with the hope of alleviating the situation. The researchers affirm that the State of California will have to make huge investments in grid capacity to achieve this. This is a reality check for those who tend to take a naïve approach to the adoption of renewable energy resources without considering the technical difficulties involved in the massive integration of a variable, weather-dependent energy source.

The findings also have implications for energy poverty. Energy poverty is a lack of adequate, affordable, reliable, quality, safe and environmentally friendly energy services. Access to electricity is strongly interrelated with the economic and social development of a community (for example, PV adoption can reduce household electricity bills), with the most disadvantaged often having the worst power supply, which is a major detriment to their living conditions. With all grid constraints enforced, on average, over half of households served by Pacific Gas & Electric (PG&E) and Southern California Edison (SCE) (57% and 59%, respectively) lack the grid access required to adopt sufficient PV to offset their annual electricity consumption. These are typically the households already suffering from energy poverty. The hosting capacity limits thereby exacerbate existing disparities.

Although Brockway and colleagues have studied the magnitude and distribution of DER constraints on electric grids in California, the method could be expanded to identify similar geographical, racial, social and economic disparities in grid capacity in other regions. Given the dynamics of grid expansion in the USA, the existence of similar disparities in hosting capacity in other parts of the country is likely.