By Dan Fink, Colorado

The new Tesla Energy Powerwall home battery storage system made quite the media splash when Elon Musk officially launched the product on April 30, 2015. The news media worldwide raved about this “game-changer” that would “let anyone in the world go off the grid” and “make the electrical utilities very afraid for their future.” Professional off-grid systems installers had to deal with phones ringing off the hook with questions from potential clients who wanted to “cut the tie to the utility” but had no idea how much energy they used each day, month and year, and even canceled system orders because “we want to wait to get a Powerwall.”

The only real game-changer here is Tesla Energy’s “Gigafactory 1” being built in the Nevada desert to mass-produce these lithium-ion batteries for electric vehicle, home and utility use. This will certainly result in lower cost in the long term, assuming mining technology worldwide can responsibly keep up with the mineral demand for manufacturing them. Though the actual battery formulation is not new, the hype certainly is.

The Two Most Important Electricity Terms

Power: The rate at which work is being done at any given instant. Measured in watts or kilowatts (kW=1,000 Watts), or in Joules per second. Or, how hard you are working at digging that irrigation ditch…

Energy: Work (power) generated or consumed over time. Measured in watt-hours or kilowatt-hours (kWh), or Joules. Or, how much of that irrigation ditch you actually got dug. If you were working hard, you got more done than if you were working lazily.

Lithium-Ion Battery Technology

Actually, lithium-ion batteries have been around for a long time. You likely already own many of them—in your cell phone, laptop, tablet and cordless tools—any small, rechargeable device. You may have also felt the wrath of the TSA when checking bags or boarding a plane with loose batteries; their rules are strict. Just ask Boeing, whose entire fleet of new 787 Dreamliner planes was grounded by the FAA for months after a spate of lithium-ion battery fires, and even Tesla Motors, who had to upgrade the protection around their car battery banks after fires caused by wrecks.

You have also likely been very disappointed with the performance over time of these batteries in your laptop; after only a year or so there isn’t much capacity left. That’s because lithium-ion batteries need a precise regime of charge rate, discharge rate, temperature and state of charge to meet their rated number of charge-discharge cycles. Your laptop computer is the absolute worst environment possible for these batteries—hot temperatures from the electronics, keeping it plugged into the charger most of the time at 100 percent state of charge, then discharging to nearly empty when you go on a trip. Larger lithium-ion battery banks use specialized Battery Management System (BMS) sensors and computers to monitor and adjust the charge, discharge and temperature of each cell.

There are actually a variety of different lithium-ion battery formulations, many of which are far less susceptible to damage and fire. All have been available for a few years, even for off-grid home and RV applications. They all still require BMS control.

Advantages and Disadvantages of
Lithium-Ion Technology

First, let’s take a look at some advantages and disadvantages of lithium-ion batteries from an offgrid home and RV perspective. On the plus side, they are light in weight for how much energy they store, which is extremely important  in an RV but not a factor for home use. They charge very efficiently and can handle high charge and discharge rates, even that elusive last 10 percent of capacity that is so inefficient to fill with other battery formulations. And they are predicted to have a long cycle life over many years, even when left partially discharged (such as in an RV that is unused over the winter). Also, these battery banks require no regular maintenance.

Their disadvantages include extremely high cost, easy to damage with mistreatment or heat, the need for a BMS computer and the fact that this technology is too new to have the decades of performance and cycle life data we have for traditional offgrid battery formulations.

The Tesla Energy Powerwall

Now let’s look at the Tesla Energy Powerwall from an off-grid, self-sufficiency perspective. The news isn’t very good for anyone off the grid, and the following are the talking points I was forced to develop to answer all those phone calls and emails after the product launch.

The Powerwall comes in two flavors, a 10 kilowatt-hour version and a 7 kilowatt-hour version. The 10 kWh (10 kilowatt-hour) Powerwall is intended only for on-grid backup use during blackouts, with no more than 50 discharge-charge cycles per year. It is unsuitable for off-grid use and is not marketed for that purpose. The 7 kWh Powerwall is intended for daily cycling, and could be suitable for off-grid use.

The 7 kWh model has one big limitation—it only stores 7 kWh! The average U.S. home uses 33 kWh hours per day. All of a sudden, that $3,000 price tag for a single Powerwall looks a little more daunting when you have to buy more of them (you can stack up to nine together). Even energy-conscious owners with efficient off-grid homes still often use 3 to 4 kWh per day, and no battery lasts long when cycled to completely empty. Tesla hasn’t yet revealed how deep cycling affects their battery life.

The Powerwall has very limited maximum power output capability—only 2,000 Watts, with a short surge to 3,000. This is not even enough to run the main stovetop burner or oven on an electric range. A typical microwave oven combined with a refrigerator and TV running at the same time would max out this system. Tesla Energy has promised that they will upgrade to allow double the load, but that also means you can drain your battery twice as fast—about two hours in a typical home.

The Powerwall is not compatible with your existing renewable energy system. The battery operates at 350 to 400 volts DC, and no existing inverter, generator charger or solar charge controller will work with it. You’ll have to scrap your existing system and buy new equipment only from a Tesla Energy distributor. Tesla has promised that the system will include a DC voltage converter that will allow your existing solar array to function with the Powerwall, but even the very few Tesla distributors out there have stated they have no technical information yet about how this will be implemented.

The Tesla battery bank uses an active liquid cooling system controlled by the BMS computer, which will likely extend battery life. But it also adds another level of complexity and parts that can fail in the system.

Another important problem— you can’t buy one yet. They are sold out on pre-orders through 2016, and raised more than $800 million with this tactic.

You can, however, pre-order your new Powerwall in a variety of snappy color schemes! If this is an important factor for you off the grid, you are likely better suited to living in the big city. I inquired if they had a model that would match my off-grid color scheme of wood, antiques, mud, and dog and cat hair, but was politely told that option was not available for pre-order, though perhaps the “charcoal” option would best match my woodstove heating, campfire mentality.

Other Lithium-ion Options

If you (and especially your local renewable energy dealer and consultant) think that lithium-ion battery storage might be right for your off-grid application, I suggest that you stick with a tried-and-true option instead. The GBS battery has been a proven performer for over two years in RV applications, weighs only 54 pounds for a typical 200 amp-hour RV battery bank (compared to 250 pounds for the same size lead-acid battery bank) and includes a BMS and sensors to monitor each cell. Contact Larry Crutcher at Starlight Solar (2998 S Shari Ave., Yuma, AZ 85365; 928- 342-9103; www.starlightsolar.com) for more detailed information.

And be sure to contact Brandon and Maggie at Iron Edison (12860 W Cedar Dr. #105, Lakewood, CO 80228; 720-432-643; https://ironedison. com), they distribute a lithium-ion battery specifically designed for larger off-grid home power systems, and like the GBS it’s compatible with all existing inverters, chargers and charge controllers. It includes a BMS and metal case. They also distribute Nickel-Iron (NiFe or “Edison Cell”) battery banks, which I discussed in the March/April 2014 issue of Countryside, and I am now a proud and happy owner of a bank of these batteries from Iron Edison. I’ll be writing a detailed update on this in the next issue.

Saltwater Battery Banks

A new option worth keeping an eye on is the Aquion Energy Aqueous Ion Hybrid battery. It uses a special saltwater blend and carbon technology. The disadvantages so far are a very low maximum power output, extremely high cost, a strange charge/discharge/voltage curve that is not yet fully compatible with some renewable energy system equipment, and a short track record. The company promises big improvements in their next generation battery over the next year or two.

Hype Versus Hope?

At the end of the day, I think the Tesla Energy Powerwall has given false hope to millions of under-informed people worldwide that some new battery technology breakthrough has taken place, when the only real innovation involved is a huge investment in a factory for mass production. Other more compatible, tested, proven and available battery bank options exist.

However, for a few folks with inquiring minds and a burning desire to live off the grid, the announcement spurred them to learn more about the reality of how much energy they need and use on a daily, weekly monthly and yearly basis. And that education is how the worldwide energy storage problem will be tackled, in lockstep with technology. Both wasted energy in the wealthy world and limited access to renewable energy systems in the impoverished world are huge barriers.

The combination of education and mass production could put us on the right path—but Elon Musk, how about a lot less hype and a little more realism and education about energy storage?