Batteries under solar modules just like microinverters and optimizers


From pv magazine USA.

Energy storage provider Yotta Energy has designed a 1 kWh battery to be mounted under rooftop solar modules.

Ten years ago, the idea of putting a microinverter or optimizer behind a rooftop solar panel was a stretch. Today, module-level panel electronics warrant their own initialism and enjoy an 80% market share in the U.S. residential solar market.

Texan company Yotta believes batteries are headed in the same direction: To module-level micro-storage. The business is deploying a 52lb, 1 kWh lithium iron-phosphate battery on the same solar module racking gear which holds the ballast.

Yotta chief executive Omeed Badkoobeh believes safety and reliability fears are rendered moot by stable battery chemistry and the company’s solutions to thermal issues.

The CEO told pv magazine the device’s temperature-control methods are “completely solid state”.

Pilot systems

There are no active components on “the hot side”, said Badkoobeh, no moving parts, no fans, no pumps, no Peltier coolers and no power usage. On “the cold side”, the firm does use power in its phase-change heat exchange system, a technology used in space applications.

The Yotta chief sees his company’s innovation as a solution for solar-plus-storage “in the urban environment” and the Austin-based company is rolling out pilot deployments with strategic partners.

“Many solar developers get requests for storage,” said Badkoobeh, but settle for just doing solar now, out of inexperience or availability. “We see that shifting,” said the CEO. “Soon it will be automatic to deploy storage.”

Badkoobeh claims Yotta’s system “allows for the lowest installed costs for adding energy storage to any solar PV system. The ability to remotely design and conserve space opens up opportunities for more solar installers to incorporate energy storage.” The chief executive said his product enables the “ability to install just the right amount of storage and the ability to expand”.

Yotta has been backed by grants and $1.5 million of seed funding from undisclosed investors. The CEO is working on follow-on funding to keep the ten-strong company moving ahead.

Hasn’t this been done before?

Californian company SolPad in 2016 made bold claims about a yet-to-be commercialized solid-state battery designed to be installed under modules along with a microinverter. Four years on, and replete with new CEO Terry Jester, SolPad is still developing the technology and plans to come to market this year.

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Barry Cinnamon, an experienced solar and storage installer at Cinnamon Energy Systems has worked with SolPad. He told pv magazine: “I think the idea has a lot of potential. The physical constraints of finding room for batteries on the sides of houses are very challenging and getting worse with new [building] codes. So putting the batteries on the roof avoids that problem completely. Carrying up a bunch of 40lb batteries is much easier than installing a 220lb battery on the side of a house. There are also some interesting design issues with either sending DC power down from the roof (to a backup inverter) or actually doing the backup power generation on the roof with micros [microinverters].”

SolPad co-founder Christopher Estes said the Mountain View start-up “has a very sophisticated energy storage and energy analytics solution that is far superior in all aspects” – just the sort of thing a co-founder would say.

Ready to ship

Solar industry veteran Jester told pv magazine: “We have a full suite of products including load controller (for demand charge management [and] reduction), inverter (1 kW), battery storage (2 kWh), gateway, junction boxes and all the wiring needed to install a system.

“We’ve shipped our first load controllers and are excited that we are nearly through UL [Underwriter Laboratories] certification with our product suite – several components, such as the battery, junction boxes and the cables are complete – with expected shipments of the inverter storage system in Q2 of 2020. The inverter is GaN [gallium nitride] based, bi-directional and will deliver almost 10% more energy than products out there now because of low parasitic losses and high inverter performance – even in low power ranges. We can run off-grid with ease and the load controller will manage the battery state of charge [and] load shedding if off-grid for extended periods of time.”

Another Californian start-up with similar ideas, JLM Energy, offered 20-year warranties for its module-level storage – right up until it went bankrupt.

Getting through “the arc of acceptance”

Yotta boss Badkoobeh mentioned a large battery design that “took a year to site”, noting it required fire suppression systems and had to be a certain distance from the building concerned.

“Every project for energy storage is a custom-engineered process,” said Badkoobeh, because storage is complex and expensive and “people don’t want to take the technical risk”. He added: “Centralized systems require a lot more human intervention.”

John Powers, CEO of Berkeley-based software startup Extensible Energy told pv magazine: “Batteries are great. Utilities are deploying batteries on the grid. But a 20 kWh battery in a commercial building is large, complicated and requires fire suppression. The installed cost is many times the cost of the battery itself.”

Such arguments help make the case for smaller batteries but Badkoobeh said he knows he “must get through the arc of acceptance” – and used the term several times while speaking to pv magazine.


Installer Cinnamon noted: “The challenge for every company with batteries and inverters is getting the requisite UL certifications – and making sure the system works. It’s expensive and time-consuming.”

Another installer told pv magazine: “Real-world pricing to the consumer means a lot and we know nothing about where that’s going to be when [Yotta] finally starts to ship in quantity … [inverter companies] Enphase, SolarEdge, Pika/Generac … all bringing new storage [to market] and they’ll all go through a painful burn-in period. They all have their work cut out for them. I see the expanding storage space likely to be just as brutal, if not more so, than solar module manufacturing and sales.”

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