
Ask HN: Telsa Powerwall a Good Investment? - nelsonic
I&#x27;m trying to determine if investing in a couple of Tesla Powerwall units to store solar energy is a <i>wise</i> financial decision.<p>My energy cost is $0.1649&#x2F;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.<p>Based on these assumptions I calculate that: 300 days x 24 kWh x $0.1649 = $1187.28 per year so (15000&#x2F;1187.28 =) 13 Years &quot;pay back period&quot;.<p>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 ...<p>Is it <i>economical</i> to buy a Tesla Powerwall or simply pay &quot;the grid&quot; (our major energy supplier) for (renewable) power at night?<p>Are you a Powerwall owner? Have you done a similar calculation? What is the conclusion? #discuss!<p>Note: I&#x27;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 <i>purely economic</i> perspective, does it make sense to invest in a Powerwall?<p>For reference I&#x27;ve expanded on this calculation and included all the supporting research and references in: https:&#x2F;&#x2F;github.com&#x2F;dwyl&#x2F;home&#x2F;issues&#x2F;25
======
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.

------
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.

------
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.

