Monday, May 11, 2015


BloombergBusiness questions reality of Tesla backup battery claims

by Larry Geller

I was wondering how claims for Tesla’s Powerwall battery system would pencil out for potential Hawaii users. An article posted by BloombergBusiness seems to counter the bubbly exuberance exhibited by many reporters and publications.

How would either of the Tesla systems work in reality in Hawaii, given both our generally abundant sunshine, the high cost of utility power, the limited payback when HECO buys some of a homeowner’s solar-generated power, and the investment in additional equipment not mentioned by the promotion and hype for this system?

The new Bloomberg article notes that the battery system is priced competitively but that it provides very little power:

But if its sole purpose is to provide backup power to a home, the juice it offers is but a sip. The model puts out just 2 kilowatts of continuous power, which could be pretty much maxed out by a single vacuum cleaner, hair drier, microwave oven or a clothes iron. The battery isn’t powerful enough to operate a pair of space heaters; an entire home facing a winter power outage would need much more. In sunnier climes, meanwhile, it provides just enough energy to run one or two small window A/C units.

[BloombergBusiness, Tesla's New Battery Doesn't Work That Well With Solar, 5/6/2015]

To use the battery, an inverter is necessary. If running those two small windo A/C units for a short time is not satisfactory, more batteries must be added to the system. So putting the Tesla system to work will cost a pretty penny. Even in Hawaii, how will the economics work out?

Probably someone in the solar power industry here would be able to fill out the numbers on a spreadsheet.

That would make interesting reading, especially for those fed up enough with HECO to be willing to pay (almost) anything to get the utility off their backs.

The spreadsheet should take into account the possibility of consecutive days without sunshine, as can and has happened even here. When that hurricane or tropical storm heads our way, will the “backup” system poop out even before the storm arrives?

At the same time we need to think about public safety, which means a growing portion of the community in the dark for several days with no power is not a safe or sustainable situation.

This all feels like we’re at the cusp of the long-awaited moment when some homeowners can begin to thumb their noses at paying triple the national average for electricity. If not this Tesla battery, then something, soon, may pull that trick off.


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