Science in Society Archive

Distributed Grid Energy Storage Comes of Age with Renewables

Distributed energy storage is becoming a new grid asset as ideal companion to renewables, offering demand response, flexibility, energy efficiency, stability and resilience of supply, replacing costly ‘peaking’ power plants and other conventional infrastructure requirements. Dr. Mae-Wan Ho

Renewables have rapidly moved into the mainstream energy supply in the space of 4 to 5 years since we released [1] Green Energies 100 Percent Renewables by 2050 (ISIS Report), and radical transformation of the electricity grid is taking place, with distributed energy storage a major player (see [2] Renewable Ousting Fossil Energy, SiS 60).

The US Department of Energy produced a report on grid energy storage in December 2013 [3] in recognition of its manifold importance for integrating energy from distributed renewable sources, enhancing efficiency, maintaining a robust and resilient electricity supply, ensuring high reliability and lowering cost, deferring and reducing infrastructure investments, and providing backup power as well as grid stabilization services, especially in times of emergency. The US has 24.6 GW of grid storage, representing ~ 2.3 % of its total electricity production capacity; 95 % of which is pumped storage hydroelectric, the rest being compressed air, thermal storage, various types of batteries, flywheels, electrochemical capacitors, etc. Europe and Japan have higher fractions of grid energy storage. Pursuit of green energy is motivating grid storage projects in Italy, Germany, UK, Canada, South Korea, as well as China and India; almost all involving the use of batteries of one kind or another. And the business is poised for phenomenal growth.

According to the Information Handling Services, Cambridge Energy Research Associates (IHS CERA), the energy storage business could grow from $200 million in 2012 to a $19 billion industry by 2017 [4]. The same report also forecasts that the US energy storage market will grow to 1.7 GW in 2017 and 2.5 GW by 2020, driven in part by the rapid expansion of distributed solar and supportive legislation set in place in the strongest US PV (photovoltaic) market, California [5]. The Self Generation Incentive Program incentivizes distributed energy projects and AB2514 mandates the state’s utilities procure 1.325 GW of storage by 2020. These policies create a market for storage technologies, and other States are following suite.

Batteries are the most popular energy storage option for both small distributed systems and utility-scale systems. Lithium-ion batteries are currently the dominant technology accompanying PV, with liquid metal electrolyte batteries and a new generation of flow batteries and zinc-air batteries coming on the market (see Box). Distributed solar storage is a smaller component of the overall mix of installed storage required by these mandates. In 2013, 10 MW of the 110 MW storage installed was behind the meter (on the customer’ side). It is growing in importance as residential solar installers like SolarCity is integrating storage into their offerings. And utilities themselves have made commitment to energy storage.

Box 1

Batteries for grid energy storage

Lithium-ion batteries are characterized by the transfer for lithium ions between the electrodes during the charge and discharge reactions [6]. The ions are inserted into the structure of other materials, such as lithium metal oxides or phosphates in the positive electrode (donor of lithium ions) and carbon (typically graphite) or lithium titanate in the negative electrode. The electrolyte is a lithium salt in an organic solvent. Both electrodes allow lithium ions to move in and out of their interiors. When a lithium-ion based cell is discharging the positive lithium ion moves from the negative electrode to enter the positive electrode. When the cell is charging the reverse occurs.

Lithium ion batteries are now the most mature battery technology. Battery power developer AES Southland announced a contract with Southern California utility company Edison to deliver a 400 MW lithium ion battery-based energy storage facility that will provide 100 MW of power for a total of four hours [7].  This dwarfs the 36 MWh battery built jointly by the State Grid Corporation of China and electric car manufacturer BYD, which was to be the largest in the world. But the 400 MW lithium battery installation will not come online until 2021.

Flow batteries are based on reduction-oxidation reactions. Two electrolytes dissolved in liquids contained within the system are separated by a membrane that lets electrons and protons (negative and positive electricity carriers) through while both liquids circulate in their own respective space (see [8] Going With the Flow Battery, SiS 62).  Most flow batteries currently in operation use vanadium. The electrolyte on the negative side contains two different ions of vanadium and the one on the positive side contains two different ions of vanadium oxide. Both are dissolved in acid. During charging, electrons are introduced to the negative side, converting V3+ ions to V2+, and removed from the positive side, converting VO4+ ions to VO25+. Hydrogen ions (protons) pass through the membrane from the positive side to the negative. When the battery is supplying energy, these processes are all reversed. The bulk of the electrolytes are held in storage tanks, and are pumped through the cell while the battery is being charged or discharged, where they interact electrically with each other and the electrodes. The battery can store a large amount of energy because it is held in the electrolytes rather than in the electrodes. The capacity is limited to the size of the tanks and not the cell. A new version using inexpensive organic electrolytes has been developed. The advantage of flow batteries is that they scale up more easily.There is considerable economy of scale, as bigger batteries only require bigger storage tanks for electrolytes.

Molten metal batteries use molten metals and a molten salt electrolyte all in liquid form when the battery is running. As the materials have different densities, they separate into three distinct layers [9]. When discharging, metal ions from the top layer, the anode, travel through the electrolyte to combine with ions from the bottom layer, the cathode. The process works in reverse during charging. The battery works at hundreds of degrees Celsius, and the heat generated from charging and discharging keeps the internal cell components in a molten state. MIT professor Donald Sadoway and his then graduate student David Bradwell designed the first proof of concept using antimony and magnesium with a salt electrolyte. In 2010, they formed a company Ambri funded by Bill Gates, Khosla Ventures and the energy company Total. To form a battery pack, 54 cells are stacked together; 16 packs (called an Ambri Core) will provide 200 kWh energy storage. Several Ambri Cores strung together into a full size unit can provide 500 kW for 4 hours. The company opened a new production facility in Malboro Massachusetts in November 2013 to make prototypes and demonstration units for installation in 2014 and intends to have a full-scale manufacturing facility in 2015.

Zinc-air batteries are powered by oxidizing zinc with oxygen from the air. During discharge, a mass of zinc particles forms a porous anode saturated with an electrolyte. Oxygen from the air reacts at the cathode and forms hydroxyl ions (OH-), which migrate into the zinc paste at the anode and form zincate (Zn(OH)42- , releasing electrons to travel to the cathode. The zincate decays into zinc oxide and water, which returns to the electrolyte, so water is not consumed. The reaction produces theoretically 1.65 V, but reduced to 1.35 to 1.4 in available cells [10]. Rechargeable zinc-air cells require zinc precipitation from the water-based electrolyte to be closely controlled, so it does not form dendrites for example. Electrically reversing the reaction at a bifunctional air cathode to liberate oxygen from discharged reactions products is difficult. But at least one company is testing grid-scale application. The zinc-air batteries from Eos Energy Storage draw oxygen from outside the casing giving them a higher capacity to volume ratio and substantially lowering costs. The company is taking part in a high-profile trial in New York City, where it will install one of its zinc-air batteries with 36 kWh storage capacity at a local Con Edison facility [11].

Eos has completely rebuilt its zinc-air battery. Potassium hydroxide is the usual electrolyte, which absorbs CO2 from the air and causes potassium carbonate build-up that slowly clogs the cells’ air pores. Eos uses a pH neutral electrolyte that does not absorb CO2. The battery also has a new horizontal architecture that relies on gravity instead of a membrane to separate the electrolyte from the air. This prevents build-up on the zinc electrode from rupturing membrane and the cell to fail. To maximize charge/discharge efficiency, the company fine-tuned the zinc-oxygen reaction with a mixture of chemicals (undisclosed), which improves charge/discharge efficiency from 60 % to 75 %. Eos claims that that these improvements mean the rechargeable batteries can achieve 10 000 cycles, or about 30 year life at the low price of $ 160/kWh.

Southern California leading

Southern California Edison (SCE) set a precedent for California and the US power industry on 5 November 2014, awarding local capacity procurement contracts for 2.221 GW of energy resources across the Los Angeles Basin [12]. For the first time in US power industry history, SCE intends to make strategic use of advanced energy storage systems, both in front of and behind the meter to meet local long-term electricity needs. It is also the first time a US electric utility evaluated a diverse range of conventional and preferred green energy resources including natural gas-fired power plants, solar PV, advanced energy storage, energy efficiency and demand response, and the first time a US utility solicited proposals from advanced energy storage solution providers to meet projected long-term electricity needs.

SCE awarded more than 5 times the 50 MW of energy storage capacity it was required by state power authorities. Contracts to deploy 260.6 MW of advanced energy storage capacity were awarded to AES (100 MW) (see Box), Stem (85 MW), Advanced Microgrid Solutions (50 MW), and Ice Energy Holdings (25.6 MW).

In addition to helping to meet the energy storage capacity targets set out in California’s historic AB2514 energy storage mandate, SCE’s contract awards make a strong statement about the advantages and benefits it sees in deploying energy storage capacity both on its own and the customer sides of the grid. One of the key reasons is the need to provide firm, dispatchable local capacity in places where you can’t site a huge generator, explained Advanced Microgrid Soutions’s Chief Commercial Office Katherine Ryzhaya.

“Demand response, energy efficiency, and energy storage are becoming part of contingency plans for closures of existing fossil fuel and nuclear power plants,” said Cedric Christensen, Strategen Consulting director of market development. “The benefits of running a highly ‘dispatchable’ resource on both sides of the electric meter are currently being tested throughout the country.

Years of empirical research and investigation has revealed that intelligent, distributed energy storage systems can enable grid operators and utilities to strengthen and enhance the reliability and resiliency of the power grid more efficiently and cost effectively than conventional grid assets, California Energy Storage Association (CESA) co-founder and Executive Director Janice Lin pointed out. It can be used instead of a ‘peaker’ typically natural gas-fired power plant, or as a frequency regulator, or voltage support. Moreover, they are modular and easy to install down to the house level. They can be put anywhere, avoiding the costs of having to upgrade or build new transmission lines and other supporting infrastructure.

Focus on microgrids for distributed energy generation, storage, and consumption

The rise of energy storage comes with an accompanying focus on microgrids that can function during power outages or can feed the grid when connected [13].

By early December, investments for fourth quarter of 2013 in energy storage had already exceeded all of third quarter with 15 venture stage financing rounds in the US. Lux Research estimates that the market for pairing energy storage with solar will grow to $2 billion from 2013 to 2018. Japan will lead with 381 MW storage paired with solar. In Europe, Germany is developing about 94 MW of solar-linked storage during the same period. The US will have about 75 MW.

Connecticut awarded $18 million in 2013 to 9 microgrid projects, encompassing battery storage, fuel cells, solar or combined heat and power. It plans to offer an addition $15 million in 2014 for microgrid projects selected in a competitive bidding process.

Germany’s Energiewende – all renewables and no nuclear

Germany is revolutionizing its energy system including its electricity grid. The transition, known as the Energiewende (energy transformation), will enable a rapid reduction in coal-fired power generation while nuclear power is also being phased out [14].

The growth in renewable energy between 2010 and 2013 more than made up for the post-Fukushima nuclear closures, adding output exceeding 8 large nuclear reactors in just 3 years, and leading to an overall reduction in power generation from fossil fuels. The increase in coal-fired generation was entirely due to coal replacing gas as a result of the failure of the European Emissions Trading System.

In 2013, windpower capacities of more than 32 GW was installed and more than 35 GW solar power is already installed in Germany. Electricity produced by renewables in Germany was 146.2 TWh in 2013, more than any other single energy source in the German energy mix such as coal or nuclear. The Energiewende has wide and strong social and political support, and has many economic benefits including job creation, stimulation of local economies and energy self-sufficiency (see Box 2).

Today more than 2 million PV systems are on the rooftops of German private houses, farms or small companies.

After the Fukushima disaster, more than 90 % of the German population was in favour of a nuclear phase out. Eight of Germany’s oldest and most dangerous nuclear power plants were shut down immediately and a nuclear phase-out by 2020 was decided.

By the end of 2013, renewables constitutes 25 % of Germany’s energy mix.

Box 2

Economic spinoffs of Germany’s energy transformation (15)

Job creation
About 380 000 Germans work in the renewables sector today, far more than in the conventional energy sector. Moreover, between 100 000 and 150 000 net job creation is expected in the period 2020-2030.

Cheaper electricity
In 2012, wind and solar energy drove down prices on the wholesale power market by more than 10 %.Since 2010, prices are down by 32 %.

Promoting community and small business projects
By 2013, more than half of investments in renewables had been made by small investors.

To conclude

Distributed energy storage is coming of age, not just for the national grid but also for microgrids, local communities, and homes. This will accelerate the shift to renewable energies as prices drop and numerous innovations continue. Fossil fuels, especially coal and oil are also losing out in the market place [2], and do not bode well for the future. The same goes for nuclear energy, which is completely uneconomic by all accounts and cannot go ahead without enormous subsidies at the taxpayers’s expense (see [16] Nuclear Subsidies Largesse by other Names, SiS 59). It is also highly unsafe [1] as both Chernobyl and Fukushima continue to remind us (see [17] Death Camp Fukushima Chernobyl - an I-SIS special report, SiS 55; [18] Fukushima Crisis Goes Global and other articles in the series, SiS 61, and [19] Tokyo Contaminated and Not Fit for Habitation, Doctor Says, SiS 64).

Article first published 25/11/14


  1. Ho MW, Cherry B, Burcher S and Saunder PT. Green Energies, 100 % Renewables by 2050, ISIS/TWN, London/Penang, 2009,
  2. Ho MW. Renewable ousting fossil energy. Science in Society 60, 32-35, 2013.
  3. Grid Energy Storage, US Department of Energy, December 2013,
  4. The Role of Energy Storage in the PV Industry, IMS Research (now IHS CERA) report, World, 2014.
  5.  “Sitting at the tip of the iceberg: the huge potential of energy storage”, Markus Elsaesser, Renewable, 18 June 2014,
  6. Lithium-ion battery. Wikipedia, 20 November 2014,
  7. “World’s largest lithium-ion battery to be built in Southern California, dwarfs previous installations”, Joel Hruska, ExtremeTech, 20 November 2014,
  8. Saunders PT. Going with the flow battery. Science in Society 62, 48-49, 2014.
  9. “A liquid metal battery for grid storage nears production”, Martin Lamonica, IEE Spectrum, 8 November 2013,
  10. Zinc-air battery. Wikipedia, 8 September 2014,
  11. “Testing zinc air battery storage in the New York City grid”, Kent Harrington, Chenected 8 July 2014,
  12. “Energy storage emerges as an all-purpose grid asset”, Andrew Burger, Renewable, 19 November 2014,
  13. “Transmission and energy storage 2014 outlook: the macro and micro transformation of electric grids”, Elisa Wood, Renewable, 23 January 2014,
  14. “Energiewende, the energy transformation in Germany”, Background briefing for the IPCC WB3 report in Berlin, 7-11 April 2014, Greenpeace International,
  15. Oct.29, 2014 – Energiewende (Energy Shift): The remarkable renewable energy transformation in Germany: an inspiration for Alberta”, Dr. Miishka Lysack, University of Calgary,
  16. Saunders PT. Nuclear subsidies largess by other names. Science in Society 59, 2-3, 2013.
  17. Ho MW, Greaves S and Saunders PT. Death camp Fukushima Chernobyl. I-SIS Special Report, Science in Society 55, 12-42, 2012.  
  18. Ho MW. Fukushima crisis goes global. Science in Society 61, 4-9, 2014.
  19. Greaves S. Tokyo contaminated and not fit for habitation, doctor says. Science in Society 64, 50-51, 2014.

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There are 2 comments on this article so far. Add your comment above.

Michael Comment left 27th November 2014 19:07:19
Very good to read that one of the engineers' old argument against wind and solar (that is, "you can't store electricity, so weather-dependant energy production is useless") is being beaten by an engineer's old argument for nuclear power ("if it has problems, we'll fix it"). However, your article needs a fix: energy storage is not in current but energy (KWh, MWh, not KW, MW) and units in the article are inconsistent. Could you correct this? In addition, it's good to store energy but the storage overall efficiency (energy out/energy put in) is an important factor so I hope to read a rating of each technology in a next issue! Thanks

Tom Comment left 29th November 2014 04:04:33
Another key value is the lifetime cost per kilowatt hour,(not just of the storage capacity, but of the storage capacity times the number of cycles the battery can undergo) which needs to be less than the cost of alternative electricity. Flow batteries seem to be approaching parity against UK peak retail electricity costs.