Many assessments of energy efficiency measures and program impacts provide only annual electricity savings estimates. Energy efficiency savings, however, are not constant throughout the year and instead can vary over the course of the day and by season. Since the cost of electricity generation and delivery also varies within a day and over the year, non-hourly estimates of energy efficiency impacts fail to recognize times when both savings and system costs are high. This disconnect is particularly important for space-conditioning energy efficiency projects, which reduce heating and/or cooling demand and can provide much of their value to the grid when system costs are high.
In an open-access article recently published in Energy Efficiency, Berkeley Lab shows the importance of the time-sensitive value of energy efficiency. The study covers 18,000 residential space-conditioning projects in California and demonstrates how hourly savings profiles reveal significant additional value relative to an annual savings approach. The article shows that space conditioning measures provide additional system value with either gas turbines or battery storage as the marginal grid resource.
Space conditioning measures provide peak savings when system costs are highest
As the figure below shows, the space-conditioning measures in the projects we studied include more efficient air-conditioning, new and efficient windows, doors, and skylights, and other envelope measures, like insulation. Importantly, these measures deliver significant savings during summer peak system cost periods and are major drivers of overall project grid value (i.e., the grid costs avoided by the electricity savings).
When gas turbines are the marginal resource, nearly half of the grid value produced by savings from the projects occurs in the summer between 4 and 8 PM. Largely because of these summer evening savings, we find that the projects are 53% more valuable to the grid than a non-time-sensitive estimate would suggest. With battery storage as a marginal resource, the projects provide about a third of their annual grid value in those hours and 37% more value to the grid than a non-time-sensitive estimate would suggest.
Our results confirm that efficient space-conditioning measures can play a significant role in managing peak demand in California. We expect that time-sensitive valuations of space-conditioning measures in other jurisdictions would also reveal additional grid value.
Residential energy efficiency space-conditioning measures can support an evolving grid
Savings from the space-conditioning measures in the study extend beyond the early evening when system load and costs are highest. These late evening (8-10PM) savings provide significant value to the California grid when battery storage is the marginal resource (as our article explains in more detail). As solar production pushes back peak net load later into the evening, these savings could be increasingly valuable.
Our methods can be replicated to estimate the time-sensitive value of energy efficiency savings in other jurisdictions.
We use well-established methods (CALTRACK) and open-source tools to estimate hourly electricity savings. With access to electricity load and project data, utilities can produce similar hourly savings shapes for their programs. Combined with time-sensitive estimates of avoided costs, these results can help utilities and program implementers identify which efficiency investments are most valuable to the utility system and adjust program designs accordingly.
The full article is open-access and available to download at Energy Efficiency. A forthcoming Berkeley Lab tool will help users calculate the time-sensitive value of energy efficiency measures and programs.