Part 3 of our Series on Solar + Batteries

For the rest of the series on Battery Storage, also see Part 1 (Understanding the Buzz Around the Tesla PowerWall) and Part 2 (Solar + Battery Storage Applications)

Most of the recent attention being paid to residential and commercial energy storage systems has centered around Lithium Ion battery (Li-Ion or LIB) technologies, such as the technology which is used in the Tesla PowerWall. To be precise, the term “Lithium Ion Battery” actually refers to a family of battery technologies which, while they share some basic features, actually include a wide variety of different chemistries and performance, safety and life cycle characteristics.



Cutaway of Nissan LEAF showing the lithium-ion battery system. Photo courtesy: “Nissan Leaf 012” by Tennen-GasOwn work. Licensed under CC BY-SA 3.0 via Wikimedia Commons.

For those who didn’t enjoy HS chemistry, we recommend you skip the next paragraph.

Your Android or iPhone is probably powered by a Lithium Cobalt Oxide (LICoO2) battery, which is the LIB of choice for most consumer electronics because of its very high specific energy (meaning it stores a comparatively large amount of energy given its weight). On the other hand, many handheld power tools, which require more short term power (but less energy) than your cell phone may use a Lithium Manganese Oxide (LiMn2O4 or LMO) battery.  Many Electric Vehicles and Electric bicycles use a Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2 or NMC) battery which have both high power and high capacity. Tesla motors has used a Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAluO2 or NCA), which is similar to the NMC battery. While a complete review of Li-Ion battery chemistries and their applications is obviously beyond the scope of this article, the point is that while often referred to simply as “lithium ion,” the universe of LIB technologies is actually broad and varied with lots of exciting development happening on a number of competing technologies.  For the interested reader, an excellent supplemental resource about LIB technologies and applications can be found here:

As a group, Lithium Ion batteries have some significant advantages over most other contemporary battery technology which have made them virtually ubiquitous in our portable electronics (phones, tablets, laptops) and also, more recently, in electric vehicles. Most notable amongst those advantages is that compared to other technologies they tend to be have relatively high energy and power density (for definitions of these terms see part 1).

On the other hand, LIB generally still tend to be more expensive than alternative technologies, may or may not have great cycle life (as anyone with a three year old cell phone that has trouble holding a charge can attest), and in some cases can be thermally unstable (see, for example, the early Boeing Dreamliner battery fires). In portable electronics and vehicular applications, minimizing weight and volume of the battery is often the most important design characteristic (after safety, of course) and so LIB batteries have become nearly ubiquitous in those applications.  Even Toyota, who has long held onto the proven and relatively economical Nickel Metal Hydride (NiMH) batteries in their Prius vehicles, is rumored to be switching to Li-Ion for the 2016 model year.

Lithium Ion – Not the Only Battery Game in Town

In stationary power applications such as residential battery backup power or commercial demand management systems, weight and volume of the battery are relatively unimportant, and designers are far more concerned about calendar and cycle life, roundtrip charge efficiency, toxicity of the battery and, of course, cost.

In these stationary markets, other battery technologies  may well challenge Li-Ion’s dominance. A few examples of other (non LIB) battery technology that may make sense in stationary applications, and which are commercially available today include:

Firefly Energy

Firefly Energy Battery SystemThe Firefly Energy battery is a new development in conventional deep cycle Lead Acid (PbA). Lead Acid batteries, both flooded and sealed, have been the workhorse of all kinds of stationary energy storage systems around the world for decades. Typical applications include Uninterruptible Power Systems (UPS) for servers and all kinds of businesses operations, Telecom backup, and of course also off grid solar homes and marine applications. In the latter two applications one significant weakness of the PbA chemistry is how adversely battery cycle life and capacity are affected by partial state of charge cycling (cycling the battery without fully recharging it in between, as can happen when you are off grid and the solar or generator are insufficient to recharge the batteries completely each day). The Firefly Oasis battery, originally developed by Caterpillar but now manufactured by Firefly International Energy of Peoria, IL uses a proprietary microcell carbon foam technology which increases cycle life of the battery dramatically, especially in partial state of charge cycling (recharging a battery but not completely refilling it) and so may be a good fit for off grid or marine applications where traditional PbA batteries historically die premature deaths, but the use of LiIon and other advanced battery chemistries is cost prohibitive.

Ambri and Eos Energy Storage

EOS Energy StorageAt the other end of the stationary energy storage market, well financed startups like Ambri and Eos Energy Storage are pursuing exciting emerging battery technologies for the ‘grid scale’ energy storage market. These products are primarily designed to be operated by grid operators to help balance the power needs of the grid against the availability of generation (especially somewhat intermittent renewable generation like wind and solar).

Ambri is working to commercialize a grid scale Liquid Metal Battery with a molton salt electrolyte, based on research done in the lab of Prof Saddoway at MIT. Ambri’s battery promises to achieve low cost because it consists of inexpensive, earth-abundant materials and because the liquid electrolyte resists many of the failure mode inherent in solid electrolyte batteries. At the same time the folks at Eos Energy Storage in New York are working on their Zynth ™ (zinc hybrid cathode with aqueous electrolyte) battery technology which also uses inexpensive and widely available materials to achieve long-life and low life cycle cost.

The above manufacturers and many others are all working to find the perfect battery solution to a range of stationary energy storage applications that they think will provide a better value proposition that LIB. In the meantime, Tesla’s Elon Musk, among many others, is betting on economies of scale driven by the ballooning demand for advanced LIB in the EV industry to help drive down the cost of Li-Ion batteries so they can prove to be the most economical, even in applications where weight and volume are not paramount.

Tesla PowerWall

Tesla powerwall schematicThe much-heralded Tesla PowerWall is finally rolling off assembly lines and becoming available for installation. The PowerWall is a self-contained unit including batteries, a battery management system, and an inverter capable of both grid-tied and islanded operation. One or more PowerWalls may be installed to match the power and energy requirements of the site. PowerWall is an energy storage system, not a solar inverter, so it must still be installed with a standard grid-tied solar inverter and solar array to provide clean backup power.


A Local, Smart, Solar + Storage Solution

Pika Energy REBus Charger

Pika Energy, based in Westbrook, Maine, makes an innovative small wind turbine that improves upon older designs that were prone to failure over time. In the process of building this windmill system, they designed a high-voltage micro-grid system they call REbus.

For the tech junkies, REbus is a high voltage (380vDC) micro-grid system that enables a Pika wind or solar installation to enjoy long distance runs from the home site to the windmill site, using smaller wire than a lower voltage system.  The REbus system can incorporate multiple sources of electricity – such as solar PV, as well as wind – and have them all recharge a battery bank as well as communicate with the grid.  In addition to electricity, REbus allows devices to communicate intelligence with each other as well.

Pika uses REbus as the backbone for several home-scale smart energy products, centered on the Pika Energy Island inverter. The Energy Island connects to the grid, a PV array, and one or more smart batteries to provide affordable grid-tied energy and flexible backup power. Pika’s smart battery lineup includes both the maintenance-free AGM lead-acid Coral, and the lithium-ion Harbor, which utilizes Panasonic battery cells. Both batteries connect quickly and easily to the Energy Island, so adding batteries is truly plug-and-play.

We are very excited to have the opportunity to work with another leading Maine renewable energy company to integrate energy storage together with solar (and wind) for ReVision Energy customers in Maine, New Hampshire, and Massachusetts.

Tesla’s Not the Only Game in Town – other leading energy storage systems

While Tesla is attracting the lion’s share of the buzz, they are far from the only manufacturer of leading-edge battery energy storage technology. 

LG Chem has released the RESU lithium-ion battery, which couples with a grid-tied inverter from SolarEdge. The SolarEdge/LG Chem combination can provide solar powered backup as well as maximizing self-consumption through storing daytime solar generation for use at night.

Sonnenbatterie has chosen to develop a completely integrated stand alone system, including charger/inverter, battery management and the Lithium Ion battery itself, which is currently made by Sony. Sonnenbatterie’s offering, designed for and built in the German market, automatically optimizes a grid-connected home for self-consumption.  The device represents what’s possible with a smarter grid, as it has intelligence such as the ability to use excess PV generation to run washing machines and dryers when its batteries are charged up, rather than backfeeding energy to the grid.  The system has a learning algorithm so it grows smarter over time, and can do things such as postpone battery charging times until the ideal grid peak.  These kinds of features are not yet heavily used in the current US grid but are much more common in Europe.  In addition to their residential products, Sonnenbatterie is developing commercial energy storage products aimed primarily at the demand management application.

A Stored Energy Future

Tesla, Pika, SolarEdge, Fronius, LG Chem and Sonnenbatterie represent just a handful of the increasingly competitive residential and small commercial energy storage space. As we have done for years with solar electric, solar hot water and heat pump space heating technology, ReVision Energy will continue to work collaboratively with a variety of manufacturers and developers of products to help identify which are the most robust and cost effective solutions for our customer’s energy needs. We are proud to be your local, trusted renewable energy experts and if you have an energy storage application that you’d like to discuss with us, please feel free to reach out and talk to one of our solar design professionals about your goals and your application to see if one of the above products is the right fit for you.

So concludes Part 3 of our series on Battery Storage! If you missed our other installments, see Part 1 (Understanding the Buzz Around the Tesla PowerWall) and Part 2 (Solar + Battery Storage Applications)