The Future in Store

Feb 14, 2019

Three futures and a quick primer in energy storage for clean energy advocates

What’s missing from this picture? (Photo: Adobe)

To many people, the quintessential image of a clean energy future consists of solar panels and wind turbines on green grass. To protect the climate (and increasingly, to save money), tomorrow’s energy will consist of using solar and wind power, right? Yet, there’s one more thing that may be as essential to that clean but intermittent renewable energy future. Where are the batteries? Not just batteries, but all forms of energy storage should be in these pictures. It’s that or a lot of transmission towers.

The future is here. We need energy storage now. Last year, not only did California need energy at night, but it had too much solar power during the day and wasted a chunk of it. That energy storage future is emerging now. The good news is that every week there seems to be storage news: California just picked big batteries over gas-powered “peaker” plants — an industry first. Hawaii just asked for approval on a huge 1 gigawatts of storage plus solar project at record-setting low prices. What could the rapidly unfolding picture of our future energy eventually look like?

Three Futures and Anything In Between

Here are pictures to illustrate three possible future energy scenarios:

1) Transmission-based Example: US Transmission lines (Photo: Andrew Goton by permission)
2) Bulk Storage Example: SDG&E Escondido Substation, CA, 30MW for 4 hours — one of the largest storage facilities in the USA (Photo:Energy Storage Exchange)
3) Distributed Storage Examples: Home and Neighborhood batteries (Photos: ProudGreenHome, Delta Electronics, Inc.)

This article will examine three energy scenarios and offer a quick introductory primer on energy storage at the moment (Feb. 2019). The three energy scenarios are:

  1. Minimal Storage: Transmission-centric: wire from the source to where it’s used (even thousands of miles)
  2. Bulk Storage: Massive storage facilities (often near remote solar and wind facilities)
  3. Distributed Storage: Smaller batteries at homes, buildings and neighborhoods

The pictures of these scenarios look very different. In all likelihood, our energy future will be a mix of these as their proponents push economical, technical and political boundaries in their bid for dominance. As ever, it mostly comes down to cost — the cost to be reliable. That cost is not necessarily determined by the cheapest power to generate — it also includes where and when it’s needed. That cost should include equity, ecological and cultural impacts. With billions being invested now in energy storage, it is indeed “energizing” to many in the energy business and energy justice circles.

The Clean Energy Revolution

The renewable energy revolution is in full swing with costs plunging. Solar, wind (and some water) for power are indeed the energy stars. Renewables are cheaper than new coal and natural gas plants and have recently become cheaper than operating existing coal and nuclear plants.

The cost of solar has plummeted nearly 90% in the last 10 years (Source: Lazard 2018).

Twenty-nine states now require increasing percentages of clean energy in their power mix, a regulation known as Renewable Portfolio Standard (RPS). California passed SB100 this summer requiring 100% by 2045, which is significant as it is the 5th largest economy in the world.

29 States require increasing percentages of clean energy. (Map source: NREL, augmented)

The federal Energy Information Administration (EIA) suggests a range of renewable electrical power growth that projects in 2040 in a range from double to half that of natural gas. The International Energy Agency (IEA) projects that solar will claim two thirds of the $10 trillion dollar global investment in power by 2040. The shift to clean energy is accelerating and can’t come quick enough for climate and renewable energy advocates.

Three projections of US power mix, which the EIA suggests is largely dependent on the cost of natural gas. (EIA 2/2018)

Yet, something else is needed to make these clean but intermittent sources reliable. We may not see the whole picture yet… What is the missing element in our energy future picture?

Three Reliability Futures

Here are some details about three possible energy futures for the US with a focus on California, as a preview, to varying degrees, for other states:

Scenario 1) Minimal Storage: No Batteries / ”Just wire it.”

(Photo by NIk Daum)

Since storage had been prohibitively expensive, the traditional approach was transmission-based supply, regionally connecting strategically located massive power plants with users. Because wind and the cheapest solar resources (desert arrays) are where they are, and not where we’d like them, the industry had been going down the path of interconnecting them 1000’s of miles apart, and relying upon trans-regional “wires” (power industry speak) to continually supply everyone’s needs. For example, there was a 2013 concept to double California’s cross-border transmission grid to 50GW by 2050.

But building a lot more transmission capacity to move electrons thousands of miles is expensive ($5 trillion to double California’s system)and has its own issues:

Transmission has a complicated regulatory landscape in each state with interstate commerce controlled by the Federal Energy Regulatory Commission, (FERC). Transmission is politically charged. Despite heavy pressure, this summer the California legislature did not pass AB 813, the grid regionalization bill, as described by Dave Roberts.

2050 Projected Transmission Map (Source: CEC 2014)

Power has greater value the closer it is to where it is needed, that is, locally. Increasingly, resilience is highly valued, which is especially true in West Coast earthquake country. A decentralized power system is inherently more secure and less susceptible to disruption than one fully dependent on a sensitive grid.

We can’t rely upon solar and wind, locally, without a huge amount of energy storage, be it batteries and/or something else. Reliability is king. Particularly in the United States, we pay a high price for, and we expect a reliable electric utility. It was said at a recent storage conference (ESNA) that if a system wasn’t reliable, the operators of that system wouldn’t be around for very long. Without a massive investment in the transmission grid, batteries (storage of some kind) must be included. Any storage system’s reliability is critical — it’s The Reason it exists, as we use intermittent renewable power sources.

Scenario 2) Bulk Storage: Massive Storage for Massive Renewable Generation

The trend is increasingly clear that storage is going to play a big part of the future. Recently, the California PUC has decided to build three battery storage facilities and retire three peaker plants capable of 120 MW. This ushers in a new era of a battery/storage-based renewable energy economy as opposed to building more power plants for usage peaks.

The power industry tends to “Go Big”, leveraging economies of scale in the quest for the cheapest watt, wherever it may be. This scenario largely pairs massive storage with large-scale generation: huge remote desert solar facilities (owned by corporate developers) with costly transmission (currently paid by everyone) to move the power. The San Francisco Bay Area transit system, BART, estimated their remote renewable long-term solar energy contract transmission costs at $46/MWh, which is comparable to the cost of its generation.

Batteries and other some storage methods can be located closer to the customers & loads they serve. Small cell batteries like lithium-ion also have an advantage of being able to be incrementally deployed — an installation can have its capacity grow over time. Although, that approach may not take full advantage of price breaks for large purchases.

Scenario 3) Distributed Storage: Generating and Storing At or Close to Home

How much storage? What kind of storage? Where? Owned by whom? are all questions about future storage. Today, it doesn’t require a massive power plant, hundreds of miles of high voltage lines, and a distribution system to get most of the power for homes and many businesses.

Today, an array of solar panels will often supply sufficient total power. The economics are different. Small-scale rooftop solar is more expensive per watt to install, but to a homeowner, it’s often the lowest-cost-in-the-long-run option. Today in California, more than 50% of charges can stem from distribution and transmission costs rather than generation. A watt is not just a watt — where it is matters. The remote desert industrial solar watt might be cheaper to install, but the rooftop solar watt is right where it’s needed.

Current rate rules don’t recognize where a watt comes from. Transmission fees are charged on each and every watt at every meter, regardless of whether it was kept off of the transmission grid (that is within a distribution substation). This makes remote energy look cheap. Neighborhoods could be charged up to 40% less if they actually used little external power, reflecting the value of local energy. The California Senate passed SB 692 on this in 2017, but it has not gone further into law.

Current rules don’t allow a solar watt everywhere. There is no solar rooftop rights to put whatever amount of solar you want on your rooftop (and still be connected to the grid). Currently, there are tight limits (10% in PG&E territory) on how much power beyond their own needs that most customers can provide due to “interconnect” restrictions by utilities. Relaxing these rules would enable customers and neighborhoods to get paid for every watt they could produce by fully leveraging their solar rooftops. Equipped with storage, they could decrease dependency on the grid. In a shift away from the legacy monster power plant model, utilities could pay their customers for the excess power they generate, instead of remote solar farm (corporate) developers.

Today, energy storage, as well as its generation, can be small scale. Batteries and other methods have increasingly viable economics at scales that fit in homes, buildings, industrial plants and neighborhoods. There is great interest in Distributed Energy Resources (DER) as these decentralized methods of managing reliable power are called. Campuses can be largely independent of the utility grid, with their own “microgrid.” These are expensive today. Community Choice Energy (CCE) organizations have a mission to increase renewable energy rapidly and are keen to leverage DER, often implemented as community solar or energy purchase contracts with local clean energy project developers.

This distributed, local clean energy democracy model, that is, solar plus distributed storage, touts benefits beyond economics in terms of environmental and energy justice, like:

  • Minimizing environmental and heritage impact: avoids ecological and cultural (prehistoric archaeological & sacred tribal sites) losses
  • Limiting transmission Buildout: Less need to invest in expanding the transmission grid.
  • Less transmission-based energy losses
  • Maximizing jobs in the community for installation and maintenance
  • Use-based transmission Fees: Pay transmission fees only on the power that actually arrives (to your substation) from the transmission grid, saving up to 40%
  • Paying consumer/generators: Keep the money in the community

Which Energy Storage Future?

“The decrease in electricity storage costs is enabling the faster and larger penetration of renewable energy onto the electric power grid in California and elsewhere. Given that we need such a transition as fast as possible and throughout the world, this is good news for the solution to the problems of global warming, air pollution, and energy security.” — Professor Mark Z. Jacobson

Storage is valuable in all sectors of of a power system. With the price of batteries precipitously dropping and storage facilities having a rapid adoption curve, energy storage is extremely likely to be a major, critical element of our clean energy future.

Energy storage has value at all levels of power systems (Source: ISLR)

When discussing our energy future there are questions worth asking about storage:

  • Which storage technologies are winners?
  • Where is the storage located?
  • What scale are they deployed at?
  • Who owns and benefits from its use?

It is not uncommon with regard to energy storage to hear, as Bill Gross, the billionaire innovator behind the radical Energy Vault, said at the ESNA conference, “We need all of you — we need all the solutions”.

Our energy future is likely to include a mix of storage options

As much as clean power and climate activists call for energy from solar and wind (and water), in order for it to be reliably adopted and not depend upon out-of-area energy, there must be an equivalent call for its storage and justice in the conversation. Taking action to support a just transition to renewables is important, and can influence which future is revealed behind the energy reliability question marks.

Moving forward, the missing elements in our green, renewable future energy picture are still question marks, mysteries — a combination of many technical and regulatory issues — that enter into the political To-Be-Determined (TBD’s) to solve. That is our future in store.

The remainder of this article provides additional background information, should the reader be interested in diving deeper into energy storage. There are also several excellent resources and organizations listed at the end as Suggested Reading.

A Primer in Energy Storage

Energy advances and new regulations are happening rapidly. There are environmental impact concerns and energy justice questions as to who owns whatever new renewable and storage resources. The remainder of this article is a quick short course, an informational zap on energy storage: its why, what, who, when, how and costs — a synopsis for today (Feb. 2019) in 22 bite-sized topics, so you can be well grounded on the topic, even if you haven’t thought about energy storage before.

A Quick Primer in Energy Storage, Feb. 2019

1 WHO is Energy Storage?

That unseen third element of our energy future was what the industry trade show, Energy Storage North America (ESNA) in early Nov 2018, was all about. Virtually every entrepreneur, vendor, utility and operator of a transmission grid converged on Pasadena, CA to find out the latest on the emerging

Energy Storage North America Conference (ESNA)

technologies and markets of energy storage. Up from humble beginnings a few years ago with a few hundred attendees, this year about 2000 attended from 800 organization from across the world.

ESNA also served as the intersection of clean transportation (which is exploding with EV sales increasing by 80% last year), and phase outs of internal combustion cars being announced globally) and clean power, as you can tell again by the types of attendees:

Co-located with the CALSTART Annual Symposium and the SGO Microgrid Global Innovation Forum, ESNA facilitated collaboration between developers, utility executives, energy users, fleet managers, auto manufacturers and suppliers, policy makers, technology providers and stakeholders to advance the energy storage ecosystem across the power and transportation sectors. (ESNA)

The intersection includes using Electric Vehicles for Grid energy storage (Vehicle to Grid or V2G), and using storage for quick charge stations (which require a large flow of power). The conference sessions ranged from deep analytical dives into the business of utility energy storage to the latest in storage innovation. The focus was on United States, and, in particular, California, as the definitive leader in energy storage.

2 WHO: The Energy Storage Champion: Nancy Skinner

We owe much of California’s leadership in energy storage to insightful laws that have been crafted to fulfill the evolving needs of the clean, green future energy landscape. Indeed, the prime keynote speaker was State Senator Nancy Skinner, the author of many of those laws. Ms. Skinner has earned being regarded as a true champion of energy storage, renewable energy and the environment.

California Senator and Energy Storage Champion Nancy Skinner. 
(Photo: Sen. Skinner)

Skinner’s bill, AB 2514 (2010), made sure the CPUC and utilities plan and use energy storage electricity when needed. In 2011 Skinner was also involved in trying to pass an extension of the SGIP energy storage incentive program, the reason California has most of the residential-scale battery systems in the world. Signed into law this September, Skinner’s bill SB 1369adopts a definition for “Green Electrolytic Hydrogen” (e-hydrogen) as hydrogen made with excess electricity from renewable sources to qualify as clean energy storage. She was a co-author of the landmark SB 100 for 100% Clean Electricity by 2045 in California.

3 BASICS: What Watt is Storage?

For those wanting to understand the basics of energy storage, it starts with the units: watts and watt-hours.

  • Watts measure electrical power at any moment in time.
  • Watt-hours measure the total energy.
As an analogy, think of a watt as a certain amount of flow of water from a pipe. Then a watt-hour is the amount of water to keep that flow going for an hour.

A watt isn’t a lot of power, so the below chart describes the quantities involved:

While a solar system or power plant is measured by the (maximum) amount of power they can produce in kW or MW, energy storage devices or facilities must also be measured by how long they can sustain that power, expressed in kWh or MWh.

4 BASICS: Which Storage? Which Grid? Which Side of the Meter?

Other distinctions to be aware of include the following:

What do you mean by “energy storage”? It includes:

  • Pumped Hydro Storage (PHS) is the existing storage mainstay method (97% in the US), pumping water back uphill behind dams
  • Advanced storage includes all other forms of storage: mostly batteries, and also flywheels and more exotic forms of storage.

Where is the Storage? Installations are either:

  • “Behind the Meter” (BTM) systems are small to medium for residences and businesses, relying less on the utility, benefiting power consumers directly.
  • Front of the Meter” (FTM) storage facilities for utilities, grid operators and developers sized from small neighborhoods to increasingly massive replacements for power plants.

When you say “grid”, which grid do you mean?

  • Distribution Grid from substation to customers, 10’s of miles
  • Transmission Grid from suppliers to substations, 100’s of miles

Why are you storing energy? It could be for these purposes:

  • For power capacity — to supply power
  • For electrical (frequency) regulation — to maintain the quality of supplied power against disruptions

5 COSTS: How Much is that Kilowatt-hour in the Window?

Payment for electricity is mostly in terms of total energy:

  • Utility customers pay mostly based on total energy in kilowatt-hours (kWh), like 15 cents/kWh, often in tiers, other charges may apply.
  • Utilities pay in megawatt-hours (MWh), like $150/MWh.

By the way, since a MWh = 1000 kWh, $0.15 kWh = $150 MWh.

In California, the amount of power (in kW)at certain timesbecomes important with:

  • Time of Use (TOU) rates (Peak vs. non-Peak), and
  • Demand Charges, which are based on the highest amount of power (in any 15 minute window) in a month.

These can be a substantial portion of power bills, esp. for industrial and commercial customers. Costwise, a watt is not just a watt. It depends on when and with how many other watts.

6 WHICH Storage? Evaluating Storage’s Value

The basics of evaluating storage are in terms of watts, time and dollars: how much energy can you store for how long at what cost? For example X megawatt hours for Y cents per kilowatt hour for design life of Z years. This is summarized in the metric called LCOE (Levelized cost of Energy Storage): Total cost divided by the lifetime number of watt-hours in $/kWh.

Numerous factors go into the the valuation of any given energy storage. This spiderweb chart illustrates the value of Pumped Hydro Storage and other mechanical storage. Any given factor may be advantageous toward the middle or the perimeter. (Chart source)

But there are many cost and performance-related parameters to be evaluated (see chart) just for the economic analysis, including:

  • Does the it lose energy over time (Self-Discharge)?
  • How efficient is it?
  • How many times can the it be used (Cycle Life)?
  • How many years does it last (Lifespan)
  • Does it scale up well?

7 HOW BIG? Which Scale of Storage?

How big? When talking about electrical power and storage, the scale becomes critical. The needs, costs and values for a homeowner are far different than that of a utility or grid operator.

Basically, economies of scale apply for sheer cost. That is, bigger is cheaper, and when advanced storage is combined with solar PV it is competitive with fossil fuel plants and hydro storage ($200/MWh to $260/MWh) — see topic 5 for ”Costs”.

The current cost of storage at various scales (Source: Lazard 2018).

With the raw cost being one financial factor, the various approaches have different strengths and weakness, and the economics are always being discussed

8 WHERE Storage? Evaluating the Impact of Energy Facilities Scale and Location

The question of scale is also a question of the centralized vs. distributed tension between local rooftop solar and remote utility-scale solar installations.

Industrial solar installation. Photo by Tom Fisk from Pexels

Desert locations tend to be prefered by the industry since land is cheap and the sun plentiful.

However, there are environmental and cultural concerns:

“As we support and expand truly renewable energy, we must reject the harmful, unjust, and devastating mega-industrial scale solar and wind plants that are paving the desert and destroying and desecrating sacred and culturally significant sites of Indigenous peoples.”

  • Bradley Angel, Executive Director, 
    Greenaction for Health and Environmental Justice

“These landscapes remain imbued with substantial cultural, spiritual, and religious significance for the Tribes’ current members and future generations,… we urge BLM and the County to deny the proposed Project, which has the potential to transform this cultural landscape to an industrial one.”

  • Colorado River Indian Tribes Chair, Dennis Patch, regarding the massive Palen solar project near Joshua Tree National Park

9 WHERE Storage? Evaluating the Economies of Justice Scale

There are considerations beyond strict cost. With storage being essential to expanded renewable energy, storage resources are as vital and as profitable as generation resources. Who will own and profit from the gigawatt hours of our future energy storage?

As the size increases for generation and storage facilities, their costs per kWh generally go down. Often, so does the proximity to the users, which imposes additional transmission costs and power losses, and centralizes the financial benefits. The Sierra Club’s guidelines emphasize protection of sensitive and valuable areas and that generation should be “as close as possible to load centers” to avoid transmission.

There is strong interest by climate action and clean energy advocates not only to accelerate the transition to clean renewable energy, but also to make that a just transition, so that consumers and communities (esp. disadvantaged communities of color) also directly benefit from it. As energy democracy advocates such as John Ferrel of ISLR will point out, small-scale solar has provided 20% of recent new energy generation, shifting power (literally) to customers.

Stakeholders in the industry, including utilities, have fought to lock out and limit rooftop solar and its customer- and community-level benefits. Utilities have waged a regulatory rate battle against Community Choice Energy (CCE) programs, especially in California, which seek to aggressively implement renewable energy and includes “equitable access to things like rooftop solar” . Policy bills, such as SB 692 to make transmission charges based on substation use, which support local power, can be great leverage points for just transition activists.

With PG&E’s bankruptcy in the news, restructuring of utilities is being discussed. Conversion to a public utility and other ownership models have been proposed and are beyond the scope of this article. However, it’s valuable to note that these may address part of the equity/inequality justice issues. Among them, CESJ’s “Consumer or Customer Stock Ownership Plan” or “CSOP” is one that lets customers share in the governance and profitability of “natural monopolies,” like power companies.

Alternative utility ownership model (Chart: CESJ)

10WHY Storage? Will the Future Rely upon Energy Storage?

The answer is increasingly, yes. Battery costs are falling rapidly. Storage is valuable to all sectors.

The cost of batteries has dropped rapidly (Chart: Bloomberg NEF by permission)

The Federal Energy Regulatory Commission (FERC) unanimously approved Order 841 that directs operators of wholesale markets — Regional Transmission Organizations (RTOs) and Independent System Operators (ISOs) — to incorporate storage. The order “opens the floodgates for storage participation” in wholesale power markets, according to Ravi Manghani, director of energy storage at GTM Research.

Advanced storage is exploding: The 6 gigawatts (GW) installed globally in 2017 is expected to grow to 40 GW installed in 2022. That’s over 600% growth in five years. That’s an exciting economic opportunity, especially now that California is pumping billions of dollars into it. Here are the state goals currently:

  • California: 1.825GW by 2020 (AB 2514 in 2013, + AB 2868 ).
  • NY: 1.5 GW by 2025, and up to 3 GW by 2030.
  • NJ: 600 MW by 2021 and 2 GW by 2030.
  • Massachusetts: 200 MWh. (voluntary).
  • Oregon: 5 MWh by 2020.
  • Arizona: 3 GW by 2030 proposed.

As well, Colorado, Illinois, Indiana, Minnesota, Missouri, New Mexico, Ohio and Vermont have begun proceedings on energy storage policies.

11 WHO: California Storage Leadership

As it became apparent that storage is critical to renewable power, it became a focus for insightful clean power legislators. As a result, California is clearly the world leader in energy storage, pumping billions into utility-scale projects: half of all US large-scale storage (per the EIA). CA alone has over 700 MW of storage in operation.

CAISO (California’s grid operator) took the lion’s share of new storage capacity in 2016 and 2017 (EIA chart)

Pennsylvania-New Jersey-Virginia grid operator, PJM, had the lead in storage for frequency regulation needs — large power, but for shorter minutes. The Australian battery that Tesla recently built in 3 months is primarily for power regulation: it can output a lot of power: 100MW, but with 129 MWh of energy storage — it can do that for only a little over an hour.

California leads in small-scale storage, with 90 percent of the small-scale energy storage in the US, due to its SGIP incentive program.

12 WHEN Storage? 26 Years to Clean the Power Mix

California’s SB100 requires a 100% renewable power mix by 2045. The large Natural Gas and unspecified components (grey) are to be replaced by non-carbon sources by 2045 in CA, Storage becomes increasingly vital as the renewable energy share increases.

The mix of power in California including imported power (EIA) .

13 WHEN Storage? The (Daily) Duck Curve

We also need to know about the duck curve. Electrical power demand has a daily curve generally ramping up to the evening when folks are home and turn on the lights. Solar power also has a daily curve following the sun. Put those together and you get

The “duck curve” showing the difference between energy demand throughout the day and energy production from energy demand throughout the day and energy production from mostly from solar (EIA).

Notice the ramp up in the evening — that’s actually quite a large increase in generation need. Those few hours see California’s grid carrying 10 gigawatts more — that’s like adding half of Australia. It’s a real flip from too much solar power to none. 458 GWh were curtailed in California in 2018. One scenario shows 2020 may have 25% too much solar, which without storage would have to be wasted, “curtailed”.

The problem is worldwide. In China, 7.7% of the electricity generated by wind turbines is curtailed, as is 2.9% of electricity from solar panels. It just approved its largest battery: $174 million for a 720 MWh, 2.8GWh lithium-ion grid storage battery.

14 WHEN Storage? Short-term vs Longer-term

The when of storage includes how long the storage is needed. To address the duck curve, there is a relatively short-term need of about 4–6 hour’s difference between the solar peak and the demand peak as folks go home and turn things on. This is why peak time has shifted later from noon-4pm to 3pm to 8pm and will shift even later to 4–9pm, from the high air conditioning-driven demand during the middle of hot summer days — peaking solar productions has eliminated power shortages then. The shortage is now in the evenings.

Some forms of storage, like flywheels and thermal storage, are lossy (they self-discharge). They may have enough energy left over for four hours of storage to work well for duck curve needs , but they lose enough of their energy over time such that they aren’t economical for longer-term storage needs.

Some forms will store their energy indefinitely, including batteries (mostly, some degrade over time), and gravity-based approaches. The capacity for longer storage is always a benefit, but storing large amounts of power for longer periods of time means there is less time,and fewer cycles to export the power and get paid, so the economics are correspondingly tougher.

15 HOW: Types of Storage: The Storage Solutions

Here are all the types of power storage:


  • Pumped Hydro storage (PSH) — pumping water backwards into dams
  • Compressed Air Energy Storage (CAES) -pumping air into a cavern
  • Flywheels — generally tire-sized and high-speed, mostly for power regulation
  • Gravity storage: Rail, crane and hydraulic lift of massive weights

Electrochemical (batteries):

  • Lithium-ion Batteries — the familiar battery champ
  • Lead Acid Batteries — old-style, like in your (gasoline) car. Yes, still used for storage
  • Flow Batteries — emerging tech: typically storage-container-sized grid-scale batteries
  • Other emerging tech: Molten Sodium, Nickel, all sorts of “chemistries”.


  • Molten Salt — a way to store a lot of heat, typically at thermal solar facilities
  • Chilled Water / Ice — useful for facilities that have cooling needs like food storage
  • Underground thermal storage (UCES)- heating rock layers in the ground


  • Supercapacitors — bulky but quick solid-state way to store some power efficiently
  • Superconducting Magnetic Energy Storage (SMES) — Not practical yet: super-cold


  • Hydrogen — the clean fuel
  • (Methane , etc.— but it’s carbon polluting)

16 Transportation: Power Storage Needs and Benefits

(Photo: Univ. of Warwick)

Under types of storage, we should also mention the idea of using the batteries of electric vehicles, so-called vehicle-to-grid (V2G) — aka, Bi-Directional Charging, solutions. Excess power charge in a EV truck or car might have in the evening could conceivably be used (thorough advanced smart meter technology) to help power the grid, and the vehicle still be charged in the morning.

No major electric car manufacturer provides this capability, but a number of fleet owners, including the military, are testing out this nascent technology.

Storage is also called for with quick chargers for EV’s, which consume large amounts of power when in use. By charging batteries or other storage slowly, the maximum power use can be limited and avoid high Demand Charges based on that maximum power. Used batteries are also being reused for portable EV Charging carts that are not fixed to specific parking spaces.

17 Pumped Storage Hydropower (PSH): It’s a Pumped World

97% of energy storage in America (some 21 GW) is behind dams: water literally pumped uphill, stored, to be let back down when needed. This is called Pumped Storage Hydropower (PSH) or “hydrobatteries”. It’s the one existing low-cost method of storage (around $200/MW lifetime).

The past growth of Pumped Hydro Storage (Chart: IHA)
The projected growth of pumped Hydro Storage, with vast majority being built in China. (Chart: IHA)

But hydrobatteries tend to be massive and there only so many suitable dams — most of the major ones have been built. The Hoover dam is proposed. While worldwide PSH could grow by 50%, the prospects in the US are more limited (mostly using smaller dams), as shown in the below chart — most of the growth is projected in China.

18 Lithium Leads the Charge

Among “Advanced Storage” tech, lithium is the king. Of the 835 MW of advanced energy storage in the US at the beginning of 2018, over 80% is Lithium-ion battery storage, and it’s trending higher.

Over 80% of Storage is Lithium-ion battery storage, (Charts Source: EIA).

One of the concerns with lithium is the environmental, energy and cultural impacts of extracting lithium and other needed (heavy) metals, like cobalt and nickel. Efforts to reuse and recycle these metals are just beginning.

19The Other Batteries (Chemistries): Build a Better Battery, and They Will Come

There are many battery chemistries. Some are tweaks of Lithium-Ion like using foamed copper anodes. Others include magnesium, lithium-sulfur, aluminum-graphite, Bioelectrochemical batteries. Further out approaches include thin film, and solid state batteries (think transistors that store energy). Innovators are pushing the tech as fast a possible. Main factors include longevity, degradation, and environmental impact. But the big three factors are: cost, cost and cost.

Going with the Electrolytic Flow

There is plenty on interest in “flow batteries,” where, rather than the charge being chemically stored in the electrodes of the battery, it’s in the liquid between them — an ionic solution is stored outside of the cell, and can be fed into the cell in order to generate electricity. The total amount of electricity that can be generated depends on the size of the storage tanks. Typically with sulfuric acid and vanadium salt as electrolyte with electrodes are made of graphite bipolar plates. Some flow batteries are hot new tech, as in liquid metal which is self-heated by the power flow. Japan has a 15 MW/60 MWh redox flow battery system for frequency regulation.

20 Mechanical Storage: Existing and Innovations

Other approaches include “mechanical” approaches: flywheels and gravity-based systems including railways with rocks.

Flywheels have been used to store electricity for some time, though mostly for power regulation, Uninterruptible Power Systems (UPS’s) and unusual high power needs. Typical flywheels are high speed and about the size of a stack of tires, storing 10’s of kWh, requiring an array of the devices for utility-scale storage (MW’s).

Amber Kinetics is testing flywheel storage with California’s City of Alameda Municipal Power and Hawaiian Electric.

Gravity storage is pushing something, water or a rock, up somehow, and deriving energy on the way back down. A major advantage of these of approaches is that they do not lose energy over time. One example is Heindl Energy’s design which hydraulically lifts a monster 1000’ diameter chunk of rock in the ground.

The newest major gravity/mechanical innovative player, Energy Vault, announced its system at ESNA: a 6-headed automated crane that is designed to store or discharge 5 MW of power continuously, by lifting or lowering 35 ton blocks. They already have a customer.

Energy Vault: a 6-headed automated crane that is designed to store or discharge 5 MW of power continuously, by lifting or lowering 35 ton blocks.

21 Hydrogen—The Clean Gas — Depending on Its Source

“Green hydrogen is poised to be an indispensable tool in California’s energy storage toolkit,”

  • California State Senator Nancy Skinner.

Hydrogen is really the only completely GHG-free (non-carbon) fuel. Hydrogen burning is, chemically:

H2+O2 -> Energy + H2O

This can be reversed through electrolysis, which requires a lot of electrical energy:

H2O + Energy -> H2 + O2

Electrical power into hydrogen as storage is known as Power To Gas (P2G). There is big potential, bolstered by cleanly created (“green”) hydrogen now being considered by law (SB 1369) as a form of storage. Widespread adoption would provide a solution the transportation fueling issues.

San Francisco Bay area’s AC Transit runs the largest fleet of hydrogen fuel cell buses in the US (Photo: AC Transit)

However, today most hydrogen fuel is generated by oil refineries, and is thus very GHG-dirty: 150 gCO2e/MJ, compared to 88 with bio gas source, which is growing in availability. An entire infrastructure is needed for H2 to be adopted on a large scale.

22 And Now for Something Completely Different…

There are plenty of ideas for researching other more economical and longer-lasting ways to store electrons, like:

There are literally 1000’s of new energy storage ideas and projects from white papers to garage prototypes to well-funded startups and corporate endeavours. The future is indeed bright for tech, business and policy breakthroughs that provide economical storage options in a variety of applications. The future in store is as varied as the choices we make.




Advocacy groups

Groups range from environmental/climate/consumer, to industry associations, to vendors. Here are a few:

  • Clean Coalition —a nonprofit organization to accelerate the transition to renewable energy and a modern grid has a team (PAEC) seeking to streamlining permits for energy storage projects
  • Institute for Local Self-Reliance — ISLR — Works to expand clean, dispersed energy generation and increase local ownership
  • Local Clean Energy Alliance — LCEA— Promotes the development and democratization of local renewable energy resources
  • NRDC is part of the Community Storage Initiative (CSI) which supports wide-scale implementation of energy storage technologies
  • Sierra Club: Ready for 100, Energy Storage in Texas, Energy Facility Siting Policy
  • 350 Bay Area (Clean Power, Transportation programs) Advocates for socially equitable solutions and a just transition to clean energy.
  • CalCCA Advocates for Community Choice in California
  • California Solar & Storage Association — CalSSA— promotes the widespread deployment of smart, local, clean energy technologies
  • CALSTART — Strategic Broker For The Clean Transportation Technology Industry

Regulatory and Industry Entities

Policy-wise in California the electric power (storage) players include:

  • California Energy Commission (Mission)
  • CALSeed — Early stage energy storage grants
  • EPIC Grants — Development and market adoption grants
  • California Independent System Operator (CAISO), owns and operates the California transmission system
  • California Public Utilities Commission (CPUC), regulates electrical power in California


  • Investor-Owned Utilities: In California: PG&E, SDG&E, etc.
  • Community Choice Aggregation / CCA’s — New community-based providers of power using existing distribution system. Also known as Community Choice Energy (CCE) providers
  • Governmental Utilities (Municipalities and other public utilities) See Northern Calif. Power Association

Thanks to: Laura Neish, Jack Lucero Fleck, Jeff Gould, John Farrell, Don Marsh, Courtney Scott and Rudy Wrobel.

About Rand Wrobel: Rand is an IT and energy consultant in Alameda, CA. He volunteers as a co-Founder, Board member and CIO for 350 Bay Area, and Executive Director for the nonprofit LilliWorks Foundation (for children with severe disabilities), and youth Ultimate coach. Rand has an energy storage innovation in early development.

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