Alternative path to 100 pct renewable energy using energy storage


United StatesAs states strive for 100 percent renewable energy, energy storage will be critical in providing a more varied power supply. However, no single technology will be a panacea for all of the world’s energy storage demands.

According to a recent National Renewable Energy Laboratory (NREL) analysis titled “Optimal energy storage portfolio for high and ultrahigh carbon-free and renewable power systems,” a portfolio of storage solutions makes the most economic sense for future energy systems.

Guerra and his colleagues Joshua Eichman and Paul Denholm developed a proprietary high-resolution optimization model to analyze energy storage options across the United States. Geographic variance, among other aspects, was discovered by the researchers to have a significant impact on an energy storage portfolio. The California Independent System Operator (CAISO) grid, for example, is solar-powered, discharging seasonal storage for around 50 days to cover winter months in the model, whereas the wind-powered Midcontinent Independent System Operator (MISO) could deploy shorter-duration seasonal storage (but still much longer than most currently deployed storage technologies) with capacity ranging from 5 to 14 days.

Storage technologies suffer inherent trade-offs in terms of efficiency and capital costs for both the power and energy components, which is why various technologies are advantageous. Short-duration (intraday) storage, such as Li-ion batteries, has higher efficiency but also higher energy costs, whereas longer-duration (daily) storage, such as compressed air or pumped heat, has lower energy costs but is less efficient.

Storage portfolio for 100% renewable energy

The researchers discovered some unexpected results for ultrahigh renewable systems: As a system nears 100 percent renewable operation, a growing share of its storage portfolio would benefit from multiple-day to seasonal storage capacity. This is due to an increasing seasonal mismatch between remaining load and renewable resource supply. Shorter-duration storage, on the other hand, is more successful in smoothing the diurnal oscillations of solar on a grid like CAISO.

As we get closer to 100 percent renewable systems, another surprising technique emerges in which storage-to-storage charging becomes economically attractive. As a result, renewable curtailment begins to fall as more renewable energy may be routed to storage. These dynamics for ultrahigh renewable systems demonstrate how competing elements can have a significant impact on an ideal storage portfolio.

The effect on the energy industry

The study’s findings are critical for system operators, technology developers, power providers, and the broader industry. The main message for these organizations is that an ideal energy storage portfolio will change greatly from one region to the next and will depend on the quantity of renewables. As more cities and states set clean-energy goals, stakeholders looking 10 or 20 years ahead should be aware of the larger energy storage technology landscape and how it fits into their systems.

Now that the researchers have proven significant cost disparities in storage deployments, future work will focus on a more comprehensive evaluation of storage value.