Published on February 13th, 2017 | by Tina Casey0
Harvard To Trump: Our Mega Rhubarb Energy Storage Device Beats Your Coal
February 13th, 2017 by Tina Casey
A research team from Harvard University’s John A. Paulson School of Engineering and Applied Sciences has come up with a new, low cost “mega” scale energy storage system that could function effectively for ten or more years with minimal need for maintenance and repair. In commercial operation, the new battery would open up the door for more wind and solar energy in the grid, and slam the door on coal.
Aside from hastening the demise of coal for power generation, the new battery also poses a threat to the current gold standard for energy storage, lithium-ion. In addition to large arrays for grid use, the Harvard technology is easily scalable for home use, where it could store energy from rooftop solar panels.
New Energy Storage System From Harvard: #ThanksObama!
The US Department of Energy has not updated its news page since Inauguration Day, but advanced energy programs that flourished under the Obama Administration are still bearing new fruit.
The Harvard University energy storage project has been supported by the Energy Department’s Office of Electricity Delivery and Energy Reliability, and by its Advanced Research Projects Agency-Energy funding division for breakthrough technologies.
ARPA-E was launched under the Bush Administration but did not kick into gear with funding until Obama took office.
The Harvard project caught the eye of ARPA-E because it promises low cost, grid-scale energy storage.
ARPA-E began funding the Harvard energy storage research back in 2012 under its OPEN funding program. The program was “designed to catalyze transformational breakthroughs across the entire spectrum of energy technologies”
OPEN focused on “game-changing” projects that would cement America’s history of global technological leadership in energy related fields. To make the cut, applicants had to meet three main goals:
Security: Increased access to and use of domestically produced sources of energy would help reduce U.S. dependence on foreign oil and increase our nation’s energy security.
Environment: Developing new and renewable sources of energy would reduce our reliance on fossil fuels that create harmful greenhouse gas emissions and contribute to global warming.
Economy: Inexpensive sources of energy would help the millions of American consumers and small business owners who can’t afford the energy they need to live and work.
Revving Up The Next Generation Of Flow Batteries
The Harvard device is a flow battery. Loosely speaking, this type of energy storage system is based on the electrical charge that occurs when two specialized liquids flow adjacent to each other, typically separated by a thin membrane.
The liquids are stored in separate tanks until they are needed, so flow batteries are easy to maintain and can sit idle for long periods of time without losing efficiency.
On the down side, conventional flow batteries are large, clunky affairs. They rely on expensive metals and require regular maintenance in order to maintain capacity.
The Harvard project demonstrates how quickly flow battery technology has improved in recent years.
In 2014, the Harvard team reported that it had successfully replaced the metal-based liquid in flow batteries with organic molecules called quinones.
If you had to look quinones up, so did we. Here’s an explainer from a paper published in the US National Library of Medicine:
Quinones are ubiquitous in nature and constitute an important class of naturally occurring compounds found in plants, fungi and bacteria. Human exposure to quinones therefore occurs via the diet, but also clinically or via airborne pollutants.
The Harvard team was interested in quinones because they are cheap and abundant. They exist in crude oil as well as plants, for example. However, quinone exposure can provoke toxic reactions in humans, so supply chain issues are going to be one challenge for commercializing the technology.
Setting that aside, once the team began focusing on quinones, the question was which quinones would function most effectively in a flow battery. The 2014 research involved identifying the properties of more than 10,000 different quinone molecules in search of the best candidates for a flow battery.
In a win for bio-based alternatives to petroleum, the first iteration of the new flow battery used a quinone that was practically the same as a quinone from rhubarb.
More And Better Energy Storage
The 2014 report covered a flow battery that maintained efficiency over 100 charge-discharge cycles. That’s not much, so one critical task of the team was to improve the discharge rate. It looks like they did that.
The new research was just published in the journal ACS Energy Letters under the title, “A Neutral pH Aqueous Organic/Organometallic Redox Flow Battery with Extremely High Capacity Retention,” which has all the details.
For those of you on the go, the bottom line is that the Harvard team boosted the performance of their flow battery up to a loss of just one percent capacity every 1,000 cycles.
The key breakthrough was to find molecules that don’t degrade as quickly in neutral solutions. The use of a neutral solution is important from a cost control perspective, because it helps keep the cost of the membrane down:
…Most flow batteries today use expensive polymers that can withstand the aggressive chemistry inside the battery. They can account for up to one-third of the total cost of the device. With essentially salt water on both sides of the membrane, expensive polymers can be replaced by cheap hydrocarbons.
Though the primary target is grid scale energy storage, the new iteration of the Harvard flow batteries requires minimal maintenance and would be as safe for home use as any other large appliance. Here’s the rundown from Harvard:
Because we were able to dissolve the electrolytes in neutral water, this is a long-lasting battery that you could put in your basement…If it spilled on the floor, it wouldn’t eat the concrete and since the medium is noncorrosive, you can use cheaper materials to build the components of the batteries, like the tanks and pumps.
What About Lithium-Ion Batteries?
The Harvard team focused on flow batteries in order to meet a two-day energy storage standard for integrating wind and solar energy into the grid.
According to the team’s 2014 research, lithium-ion does not fit the bill:
To store 50 hours of energy from a 1-megawatt power capacity wind turbine (50 megawatt-hours), for example, a possible solution would be to buy traditional batteries with 50 megawatt-hours of energy storage, but they’d come with 50 megawatts of power capacity. Paying for 50 megawatts of power capacity when only 1 megawatt is necessary makes little economic sense.
In contrast, flow batteries offer a more stable discharge platform:
…in solid-electrode batteries, such as those commonly found in cars and mobile devices, the power conversion hardware and energy capacity are packaged together in one unit and cannot be decoupled. Consequently they can maintain peak discharge power for less than an hour before being drained, and are therefore ill suited to store intermittent renewables.
Don’t hold your breath for that, but as of 2014 Harvard’s partner in the project, Sustainable Innovations, was looking forward to building a demo model that would fit into a horse trailer.
And What About Coal?
The combined one-two punch of energy storage with renewable energy is a dire threat to the market for coal in power generation, but that’s still off in the future.
For the here and now, industry analysts widely concur that a glut of cheap natural gas has been the main driver pushing coal out of the market.
President Trump ran his campaign on a promise to bring coal jobs back to the US, but three weeks into his presidency he seems much more preoccupied with supporting his daughter’s fashion business while Republicans in Congress aim to cut coal miners out of their new ACA benefits for black lung disease.
Trump also worked hard to get longtime ExxonMobil CEO Rex Tillerson on board as US Secretary of State. With that status Tillerson is in a good position to continue his company’s business model, which in recent years has included pushing coal out of the global power generating market in favor of natural gas.
Photo (cropped): Harvard flow battery 2014 by Eliza Grinnell.