Mercedes Joins Tesla in Selling Whole-House Battery Power

Mercedes-Benz is now offering a home version of its electric vehicle batteries. The home energy storage system will hold up to 20 kilowatt-hours of electricity, enough to keep the average home in power at least until the sun comes up next day. This is an alternative to installing a home generator, as long as you’re confident a power outage doesn’t last more than a day.

Tesla already does it with Powerwall in the US. Nissan has teamed with Eaton to offer xStorage Home, primarily overseas. Each uses its expertise in assembling EV battery systems to provide modules for the home.

How it works

The Mercedes-Benz Energy Storage Home will be offered in a collaboration through Vivint Solar, a US company that has installed more than 100,000 solar systems. It will be the first time for Vivint offering an energy storage system.

Energy Storage Home will be offered as a stackable modular system of lithium-ion batteries ranging from 2.5 kWh up through 20 kWh, in 2.5 kWh increments. Modules are stacked, up to four per master module. The photo above shows a single unit, 10-kWh system. They can be stand- or wall-mounted, weighing 82, 152, 223, or 293 pounds for the floorstanding unit, and 77, 148, 218, or 289 pounds for the wall-mount.

About 90 percent of the specified capacity is usable, meaning 2.3 kWh for the 2.5-kWh system, 9.2 kWh for the 10-kWh system, or 18 kWh for the 20-kWh system. The expected residual capacity after 10 years is cited as greater than 80 percent. While publicity photos show a garage location, the suggested ambient temperature is 43 to 111 degrees F (6 to 44 degrees C). Price is about $ 5,000 for a 2.5-kWh system, installed, through $ 13,000 for a 20-kWh system, Vivint says.

“As Mercedes-Benz electrifies its vehicle fleet, solar plus storage is essential to enable those vehicles to be powered by clean energy,” said Boris von Bormann, CEO of Mercedes-Benz Energy Americas.

20-kilowatt-hour whole-house generator

MB Energy Storage vs. Tesla Powerwall

The current Tesla system, Powerwall 2.0, is a 269-pound module 6.1 inches deep. Tesla says it stores 13.5 kWh. Price for the module is $ 5,500 plus an estimated $ 1,000 for installation. Up to nine units can be joined for extended power storage.

Like MB Energy Storage, the Powerwall units are designed for time-shifting solar power, making it available after sundown. In states with time-of-day pricing, they also can replace power draw in the home during high-demand periods, such as summer afternoons and winter evenings.

Tesla has a separate line of Powerpacks for industrial or utility company use. They store 210 kWh per unit.

Nissan also provides battery storage systems, xStorage Home, offered in conjunction with Eaton. Their sales effort is primarily outside the US.

Automakers are working on solar-plus-battery features, such as the ability to us an EV battery to power the house for the better part of a day. Already solar can be passed through to the car for charging at a cost of 0 cents per kilowatt hour (13 is the US average from power companies) when the sun is shining.

20-kilowatt-hour whole-house generator runs about $ 10,000 installed.

Batteries vs. generators

While the primary application of Vivint / Mercedes-Benz Energy Storage Home and Tesla Powerwall is to time-shift solar power to nighttime and peak demand periods, they are also home backup systems, putting them in competition with generators.

The average home in the US uses 30 kilowatt-hours of power a day, equal to drawing 1,250 watts around the clock, basically equal to one 15-amp circuit (loaded at 75 percent capacity, as suggested). If power goes out and you keep using all your refrigerators, TVs, lamps, etcetera, you’d exhaust the 20-kWh hour Mercedes-Benz Energy Storage Home in about 18 hours, the 13.5-kWh Tesla Powerwall in half a day. Even if you scale back by turning off lights, and not using a hair dryer or toaster oven, you won’t last more than two days. That’s where generators come in.

A 20-kilowatt generator from Generac (the biggest player), Briggs & Stratton, Cummins, GE, or Kohler would power most any home smaller than a McMansion for days on end. It’s the device you want if you have extended power failures. The second worst hurricane in the US, Hurricane Sandy in 2012, left parts of the Atlantic coast without power for several days (the luckiest people) to as much as two weeks. For a storm like that, you really want a generator.

A whole-house generator costs about $ 10,000 installed in an existing home. The majority cost is installation and permits. A 7-kilowatt generator able to power a furnace, refrigerator, lighting, and other essentials would be about two-thirds the cost. (It generally won’t power whole-house air conditioners or electric stoves.) It keeps on running as long as it has access to natural gas or propane, since most storms don’t affect natural gas distribution. But: The cost of energy is about three times as much as the energy that comes from the power company.

If you’re shopping generators, make sure you’re comparing apples to apples. In this case, beyond the kilowatt rating, make sure whether you’re being quoted for an automatic transfer switch (switching from power-company power to generator power) and whether it has load-shedding, meaning if necessary it will drop off the air conditioner if you turn on the electric stove.

You can also buy portable (barely) gasoline-powered generators. The biggest, 7 kilowatts, cost $ 1,000-$ 1,500, and burn through 12-20 gallons a day. The industry standard, Honda, goes for $ 4,000 (and, no, Honda doesn’t sell permanent-mount standby units, not yet at least). You really should keep 5-10 gallons of gas at home (in the garage or outdoor shed), treat it with fuel stabilizer such as Stabil to extend its life, and even then buy new gas every three months (pour the old fuel into your car). Most people won’t do that.

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