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Ask HN: Telsa Powerwall a Good Investment?

4 points by nelsonic ↗ HN
I'm trying to determine if investing in a couple of Tesla Powerwall units to store solar energy is a wise financial decision.

My energy cost is $0.1649/kWh. The installed price of the two Powerwall units is $15k. I expect fully charge and discharge the Powerwall 300 days per year (based on historical average sunshine hours per month) and use 24kWh each night.

Based on these assumptions I calculate that: 300 days x 24 kWh x $0.1649 = $1187.28 per year so (15000/1187.28 =) 13 Years "pay back period".

The Warranty on the product is 10 Years and the useful life is claimed to be 15 years. However many people claim that the performance (storage capacity) will degrade down to 70% of original capacity after 10 years so this calculation should factor that in too ...

Is it economical to buy a Tesla Powerwall or simply pay "the grid" (our major energy supplier) for (renewable) power at night?

Are you a Powerwall owner? Have you done a similar calculation? What is the conclusion? #discuss!

Note: I'm a huge fan of what Elon is doing and have much love for Tesla as a company, but I want to know from a purely economic perspective, does it make sense to invest in a Powerwall?

For reference I've expanded on this calculation and included all the supporting research and references in: https://github.com/dwyl/home/issues/25

5 comments

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cjbprime
It seems like you answered your own question? You have to pay a lot of money now for a breakeven that happens in close to fifteen years, which is close to the lifetime of the device. Which means that the value of the device to you is close to $0, but it costs you $15k. Why does that seem like it might be a good deal?
CiaranMcNulty
Comes down to whether they're willing to forfeit the potential 10-20k profit from investing that 15k wisely over 15 years, if it means they're burning less carbon
cjbprime
If your terminal goal was to see less carbon be burned, rather than to make a good financial decision, you could presumably accomplish more of that by taking the $15k (or ~$35k after investment) and using it to e.g. buy carbon offsets -- it's much cheaper and more effective to reduce emissions in the developing world than in countries like the US.
KineticTroi
You can build generic powerwalls much cheaper. Just search youtube for build your own powerwall. Also, they make much more sense if your using the packs to power assist car engines, where they can payback within a 1-2 years. Of course, this, depending on your driving habits. For solar home system, I think using a bunch of the 250 watt micro inverters with built in grid tie circuits is a more practical system. Batteries are almost an unnecessary step unless your into the whole disaster prep scene. They can sync your panels to the 60hz grid and turn your meter backwards all without anyone having to be involved. Just a much less complicated system to implement and operate.
gandalfian
Portugal is a good bit further south than the UK. Perhaps you do have much more winter sun than us. But I worry you have underestimated how much solar panels it will take to make a surplus of 24kw over you daytime winter consumption. I suspect you will need 50-100kw of panels to reliably fill a 24kw battery in the winter. Then in the summer you will have vast surplus of several hundred kw. Perhaps you are putting in panels that you can tilt seasonly, that might help a little I guess.