ROI on a DIY Powerwall - non existant?

petee_c

New Member
I came across this forum on my search for info on choosing/building a LiFePO4 battery for a kayak trolling motor build. The info here is awesome.

Then part of me was wondering about building a DIY Powerwall to use at home. I was trying to think of something to use it for, I wondered about moving my 75 gallon planted aquarium to an off grid scenario with charging from a solar setup

Between the lights, pumps and heaters for my aquarium, I estimate I would need about 2Kwh of energy per day. Which would mean I would need to use a 250Ah 12V battery or thereabouts to make it work.

As I was piecing stuff together on paper and in my head, I quickly came to the realization, that I would never see a ROI for this little project. At 2Kwh per day, my aquarium uses about $0.27/day of electricity from the grid. Say somewhere around $100/yr.

Price estimates in Cdn$$
280Ah LiFePO4 with shipping from China $550
400W solar panels , charger from China $500
BMS, inverter, cabling $250...

Total about $1300 if lucky, and I will need a way to augment the charging with grid power. I'm near Waterloo, ON, and I don't have very good southern exposure on my roof. 43.5N latitude

13 yrs before Return on Investment, and by then my battery probably has a 50/50 chance of being dead...
 

David in nh

Solar Enthusiast
Return on Investment well that would be nice, but at this size think of more of a hobby , do you worry about ROI on the fish , tank and heaters ?

running off your power wall when the grid is down , now i find that priceless :)
 

petee_c

New Member
Return on Investment well that would be nice, but at this size think of more of a hobby , do you worry about ROI on the fish , tank and heaters ?

running off your power wall when the grid is down , now i find that priceless :)
True...

our grid hasn't been down for years, cause I bought a 3KW portable gas generator about 7 yrs ago for $300USD. 1 blackout since then, and it was probably less than 6hrs long....
 

curiouscarbon

Solar Addict
Part of the Return is the joy it brings you⭐️

That said, part of the return is the autonomy. It’s probably possible to reduce the cost further with component selection.
 

David in nh

Solar Enthusiast
True...

our grid hasn't been down for years, cause I bought a 3KW portable gas generator about 7 yrs ago for $300USD. 1 blackout since then, and it was probably less than 6hrs long....
yup thats how it goes have not started the gen in 4 years , find my self looking at storms to see if there will be a power outage , so i can use my battery back up :) oh look it snowing out :)
 

petee_c

New Member
yup thats how it goes have not started the gen in 4 years , find my self looking at storms to see if there will be a power outage , so i can use my battery back up :) oh look it snowing out :)

why wouldn't you move it to a circuit in your house that you could use it on daily? or is that not easy to do?
 

Q-Dog

Solar Enthusiast
I bought a small inverter generator just to not have to throw out everything in my refrigerator after an overnight power outage. Then I starting experimenting with what else it could run. That lead to not wanting to drag out the generator and not deal with running extension cords all over the house. And then built a battery backup to handle overnight outages until I decide to drag out the generator. Now I am looking at solar panels to keep the battery topped off. It is a bit of a hobby right now, I guess. And it's been fun to research and figure this stuff out (but not as much fun to run new circuits through the attic).

I can't say it is that much different from my car hobby. There is certainly no monetary return on investment, but I sure do enjoy working on them ... most of the time.
 

David in nh

Solar Enthusiast
why wouldn't you move it to a circuit in your house that you could use it on daily? or is that not easy to do?
at this point mine is strictly a battery back up ,with no solar , but if i added solar all i would have to do if flick the breaker off and it would switch over to the furnace automatically

 
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