The Tesla Powerwall and Solar Panels
The Tesla Powerwall as a Rate Reducer
In broad brush strokes, if someone chose to do that and somehow pushed all of their energy use to those hours, they could save approximately 2.3 cents per kWh when compared to the traditional rates, saving approximately $20/month in the average home (using just over 900 kWh per month).
Most people could never push all their energy use to between the hours of 7 p.m. and 11 a.m., but with the Powerwall, you could store up 10 kWh during off-peak hours and use them on peak at the lower rate. So if you could limit your daytime use of energy (when many people are at work anyway) to 1/3 of your overall use (assuming 30 kWh per day), then you could fully live on "off-peak" energy rates.
(We should mention that these numbers are really for painting a general picture, and don't take into account things like lost efficiencies of storing and then using the off-peak power.)
Of course this $20 monthly savings comes at the cost of a battery that's roughly $7000 installed. So the Powerwall would have to offer more value than these savings alone. And that's where it comes in as a backup power source.
The Tesla Powerwall as a Backup Battery
We've already said that air conditioning would have to be turned off. After AC, refrigerators and lighting are the two biggest energy users in the typical home. Based on our research, we've found numbers ranging from 2 to 6 kWh of energy used each day by refrigerators, suspecting that 2-4 is accurate in most cases.
Meanwhile, according to this excellent resource, the typical American household runs about 60 lamps [bulbs] at 1.6 hours a day and at an average wattage of 47.7. (This depends on the time of year, location in the country, and more.) At these numbers, a household's lighting use draws 4.6 kWh per day. Considering a 10 kWh Tesla Powerwall as backup … ouch.
But many of our homes have not yet converted to LED. If we expect that 47.7 average watts in a home includes mostly 60 watt incandescent bulbs along with some at 25 and 40 watts, then a transition to LED lighting could reduce the average wattage from 47.7 to about 8. This then reduces a home's lighting energy use to about .8 kWh per day.
(Likewise, this speaks to the value of more efficient refrigerators and other appliances in the home.)
If you were to limit household energy use during a power outage to refrigeration, some lighting, a couple computers, and a little cooking, you might last a single day on a 10 kWh Powerwall with incandescent lighting; you might last two days if you had switched to LED lighting.
Even without a Powerwall, switching to LED lighting in the example above would save many homes $15 or more per month. Given the Powerwall investment of $7000 to save $20/month, this is a much easier investment -- at Lighting Supply prices, you could replace the 60 bulbs in an average home for $400 to $600 while getting name brand bulbs. (We recommend trusted brands for consistent colors and better quality when it comes to LED.) Those bulbs would pay for themselves in just a couple years … something Powerwall can't really say for itself.
The Skeptic's Look at Powerwall as a Backup Battery
Some skeptics of the Powerwall have also pointed out that, for $7000, you could get a pretty nice generator powered by natural gas to keep your entire home running regardless of how long the power was out. We don't know what drawbacks that may have, or the costs of maintenance, but this is another point to consider.
So these are our thoughts on the new Tesla Powerwall and one more reason why it's such a good idea to switch to LED lighting. Do you have more information on the Powerwall that should be considered here? Are you for it, against it, or just don't care? We'd love to hear your thoughts on any of what was discussed here.