Intermittency — a swear word! If only renewable energy sources like solar and wind could eliminate intermittency, then most of the world could reject a dependency on fossil fuels. Since our grid of the future relies on a larger proportion of wind and solar, it requires more storage capacity to overcome intermittency. We need to complement renewable energy with all kinds of renewable storage.
Energy storage is most useful when it is predictable, convenient, and dense, packing lots of power into a small space. Batteries play an integral role in maintaining renewable energy grid stability. Typically, renewables feed batteries that charge at night when demand is low and wind power is available. They discharge back to the grid as wind tapers, before solar begins ramping up. Then they charge throughout the sunny midday and discharge again as solar generation quickly falls off.
Renewable energy storage batteries are applied in alternative electricity generating systems like solar photovoltaic, wind, or water power systems, which allow energy to be stored when available and released to the grid when needed.
Shirley Meng, a materials scientist and engineer at the University of Chicago, told the New Yorker that the world needs “a whole suite of storage methods.” Not all methods will find a niche, but, she said, “I think we are way, way underinvested. Because we are really imagining trying to rebuild the entire grid system.”
Different Approaches to Energy Storage
Large-scale renewable energy storage has grown rapidly, with an increasing global demand for more energy from sources that reduce the planet’s contribution to greenhouse gas emissions.
Generation Integrated Energy Storage system (GIES) and non-GIES are popular topics of discussion these days.
- Non-GIES is a grid-scale energy storage comprised of electrochemical energy storage. With the ongoing global energy crisis and environmental concerns, various electrochemical energy storage devices, including alkali-metal ion batteries (lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries), proton-exchange membrane fuel cells, supercapacitors, and lithium-sulfur batteries, have been developed in the last two decades.
- For example, due to the rich chemistry of lithium, great progress has been made in this technology by developing advanced materials for both electrodes and electrolyte and innovative strategies to further improve the energy density, lifetime, and safety of the cells. However, using Lithium-ion batteries also has a human rights issue due to all-too-frequent child labor, a relevant environmental impact due to the natural resources required for assembly and the pollution it omits after disposal, and a relatively short-life due to cell degradation.
- Electrochemical capacitors, also called supercapacitors (SCs), are considered highly complementary to batteries due to their high power density, extremely long cycle life, low maintenance cost, and safe operation features. Their excellent performance makes SCs promising for portable electronics, power back-up devices, hybrid electric vehicles, and other electronic products.
- GIES is a novel and distinctive class of integrated energy systems, composed of a generator and an energy storage system, are non-electrochemical, and include thermal energy storage and compressed air energy storage.
- Data indicates that thermo-mechanical energy storage (TMES) technologies systems are such that, especially at higher discharge power ratings and longer discharge durations, they can offer promising performance (round-trip efficiencies higher than 60%) along with long lifetimes (>30 years), low specific costs (often below 100 $ kWh−1), low ecological footprints and unique sector-coupling features compared to other storage options.
- Compressed air energy storage (CAES) is a way to store energy generated at one time for use at another time. At utility scale, energy generated during periods of low energy demand (off-peak) can be released to meet higher demand (peak load) periods. In compressed air storage, air heats up strongly when being compressed from atmospheric pressure to a storage pressure of approximately 1,015 psia (70 bar). Standard multistage air compressors use inter- and after-coolers to reduce discharge temperatures to 300/350°F (149/177°C) and cavern injection air temperature reduced to 110/120°F (43/49°C).
There are 3 key parameters associated with both GIES and non-GIES:
- the storage (from primary energy form to storage energy form) efficiency
- transmission (from primary energy form to electricity) efficiency
- the throughput (to examine the overall GIES and non-GIES efficiency) efficiency
Data indicate that the economic and financial performance for GIES and non-GIES are comparable. As such, when considering energy policy, there seems to be a need for enhanced planning mechanisms for co-locating low-carbon power generation with energy storage systems. Governments need to examine the type and amount of optimal incentives for low-carbon power generation and not forestall the need for storage. This need has resulted in technology under current exploration in the areas of thermal, mechanical, electrical, chemical, and hybrid storage.
Energy Storage is Bipartisan
It’s partly because storage strengthens the whole grid that it has found broad political support in the US.
The Better Energy Storage Technology (BEST) Act – H.R.2986 / S.1602 provides direction to energy storage research, development, and demonstration efforts at the US Department of Energy (DOE). BEST in overview offers the following. It:
- authorizes $60 million annually for grid-scale RD&D projects over the fiscal year 2020 to 2024 period
- instructs DOE to carry out up to five grid-scale energy storage demonstration projects by the end of fiscal year 2023
- directs DOE to accelerate standardized testing of grid-scale energy storage systems in collaboration with one or more national laboratories
- requires DOE to develop a 10-year strategic plan for energy storage RD&D
The primary objective of the Duration Addition to electricitY Storage (DAYS) program is the development of long-duration electricity storage (LDES) systems that deliver electricity at a levelized cost of storage (LCOS) of 5 cents/kWh-cycle across the full range of storage durations (10 to approximately 100 hours). This requirement results in a target lifetime cost that decreases with increasing storage duration. The DAYS program includes two technical categories:
- daily-plus cycling: LDES systems that provide daily cycling, in addition to longer-duration, less frequent cycling
- non-daily cycling: LDES systems that do not provide daily cycling and only provide less frequent cycling
The Energy Act of 2020 revisited policy across the Department of Energy’s applied energy and fusion R&D programs, including by recommending funding increases and expanding efforts aimed at reducing carbon emissions. A number of congressional Democrats framed the act as a prelude to more aggressive steps. House Science Committee Chair Eddie Bernice Johnson (D-TX) called it a “down payment,” while Senator Chuck Schumer (D-NY), welcomed it as a climate policy win in a “difficult political environment.” He argued, though, that the legislation was inadequate against the threats of climate change.
Final Thoughts about Renewable Energy Storage
Fossil fuels don’t need storage — they’re a prehistoric energy repository. Their energy is unlocked by burning, and the source seemed endless. But we’ve learned that fossil fuels create an existential crisis that has opened up the field of renewable energy.
So many options are becoming evident in the need to complement renewable energy with renewable energy storage. Could shared energy storage work in residential communities, for example? A study has determined that cost savings and energy storage utilization improvements up to 13.82% and 38.98%, respectively, exist when using shared energy storage instead of individual energy storage.
As in many things in life, a mélange of renewable energy storage systems options will be the best bet to make renewable energy adoption pervasive.
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