From Rhubarb to Grid Power and Beyond: Storing the Sun


Solar storage solutions of all sizes appear around the country. Storage, the holy grail of widespread solar deployment, is poised to become big.

Now that solar power is spreading rapidly, storage has become the holy grail. Good storage options — which for now still tend to be large and expensive — will be crucial for widespread solar deployment.

Storage is such a hot topic that we came across not one, not two, but three great solar storage news items today.


The rhubarb battery


What could be more American than apple pie? Rhubarb is a close second, and one we’re already enjoying in California, where spring and its first “pie plant” arrive early.


But there’s much more to rhubarb than tasty desserts. The plant also contains a feature that could be important in the development of flow batteries. And flow batteries could be key to solving the solar energy storage problem.


A research team at Harvard is working on a flow battery that’s become known as the rhubarb battery. It replaces the usual expensive metals in batteries with organic molecules called quinones — which it turns out are abundant in rhubarb.


Flow batteries have these advantages in addition to avoiding expensive metals:


  • They store energy outside the battery container in storage tanks full of fluids.

  • They can potentially be any size, which also means they offer a cheaper way to store large amounts of energy.

  • The quinones don’t get used up: instead, the molecules can flow back through the battery, adding solar energy, and the battery is recharged.


The Harvard team is still perfecting their battery, and for now they’re getting the quinones from crude oil. But who knows — someday you might have a small rhubarb-powered battery connected to your solar panels.

A solar city

The City of Lancaster has become famous in solar circles for mandating that new homes come with solar. But to really make solar work, it needs good storage, too.

So the city is taking steps to move forward in the storage area, too. It has partnered with Green Charge Networks to install an intelligent energy storage system and an electric vehicle (EV) charging station at the Lancaster Museum of Art & History (MOAH). Funded by a California Energy Commission (CEC) grant, the system will be installed by private partner Green Charge Networks at no cost to the city. The project is expected to save about $3,200 annually.

“The City of Lancaster continues to seek new and innovative ways to foster the use of renewable energy, protect the environment, and create cost savings for our taxpayers in the process,” said Mayor R. Rex Parris. “Energy storage is the cutting edge of renewable energy technology and it will propel our city toward becoming America’s first truly Net Zero City. We are proud to partner with Green Charge Networks to implement this technology in our community.”

The energy storage system will be the first installed in the area. The EV charging station, which features rapid charging capability, will be available for use by the public.

“We’re honored to partner with the City of Lancaster to help the city continue utilizing power more efficiently. Since solar-generated power is now required in new homes in the City of Lancaster, the next evolution will come from intelligent energy storage and power efficiency, which will help offset demand charges,” said Steve Kelley, Senior Vice President of Sales at Green Charge Networks.

Green Charge Networks is also partnering with some large national chains like Walgreens and 7-Eleven, as well as other cities. This could be the start of something big.

Large-scale storage

On a larger scale, Renewable Energy Systems Americas Inc. (RES Americas), a solar and wind power developer, today unveiled its energy storage system for PJM, the largest grid operator in North America.

The project consists of two containers with batteries weighing approximately 20 tons each, as well as a third container that converts the DC output to AC power for the grid.

RES Americas conceived, developed, and constructed the energy storage system, which it will own and operate. Located in Sunbury, Ohio, just outside of Columbus, the system uses a lithium battery that will provide frequency regulation to PJM. And frequency regulation, while certainly important, is just one of the services that energy storage can provide to the grid.

“Leveraging our renewable energy, transmission and distribution construction experience, we are uniquely placed to excel in energy storage, whether as an IPP, or as an EPC for a utility owner. We are excited to be one of the leaders using this new technology, ensuring that RES continues to be innovative and create value for our customers,” said Andy Oliver, Senior Vice President, Energy Storage and Technology, RES Americas.

RES Americas anticipates delivering the company’s second 4MW system in June 2014 in Ontario, Canada, for the grid operator IESO. The company is currently marketing additional fully developed frequency regulation projects for PJM.

Beyond the grid

While all these storage solutions still involve the grid, the next logical step is to break free of the grid altogether. Morgan Stanley has been making waves with its suggestion that we’re near a tipping point for a large number of homeowners and businesses to eschew the grid.

The Tesla gigawatt battery manufacturing facility could play a big role. And as we’ve seen, there are a number of new technologies in the works.

Whatever technology domintates in the end, there’s more than technology driving this potential outcome. As more utilities fight for control over solar power generation and make it hard for homes and businesses to go solar, we may see more incentive for grid defection.