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Comment: Re:This again? (Score 5, Insightful) 471

by Guspaz (#49596351) Attached to: New Test Supports NASA's Controversial EM Drive

More like tests keep showing that it IS working, and nobody is sure why. Either the problem is with the test, or there's something else happening that we don't understand, but either way, nobody is sure yet what's going on.

I think it's likely that the test is faulty, but they need to figure out why or how the test is faulty.

Comment: Re:2kW isn't enough power for a home (Score 1) 511

by Guspaz (#49594385) Attached to: Tesla Announces Home Battery System

The round trip power loss in the batteries is 8%. The charging efficiency isn't relevant, because solar during the day would be wasted/lost anyhow. If we assume the discharge loss is half that at 4%, then instead of getting 7 kWh per day, you're getting 6.72 kWh per day. It would still take around 6 years to pay off. Just 6.1 years instead of 5.9 years.

A far bigger impact would be loss in capacity over time.

Comment: Re:2kW isn't enough power for a home (Score 1) 511

by Guspaz (#49593919) Attached to: Tesla Announces Home Battery System

It depends on how much you pay for power. Say you pay $3000 (it'd be more after the installation costs and markup, but let's just pick that). That lets you move 7 kWh of power from off-peak (when you're not using it) to peak (when you need it). You're therefore saving 7 kWh per day that would otherwise be pulled from the grid. Say you're paying $0.20 per kWh. You would save $511 per year, so the battery pack would pay for itself after roughly 6 years. The remaining four years, it's actual savings.

Of course, the cost would be more than $3k, and who knows what your power company charges. Mine charges way less than $0.20, but I've got one of the lowest power costs in the world, so it's not really a good comparison to a place like California.

Comment: Re:Wow ... (Score 1) 263

by Guspaz (#49577569) Attached to: Crashing iPad App Grounds Dozens of American Airline Flights

They still carry a paper copy of their emergency handbook, the one with all the emergency procedures in it. The iPads failing in the air wouldn't be a safety issue so long as the radio didn't fail, since I don't think there's any information in the iPad that the controller can't talk the aircraft through.

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