time of use -ish system?

wattwatt

Member
Joined
May 21, 2018
Messages
55
I picked up a 12kW automatic transfer switch (ATS) just because it was so cheap. I figured I could put it to use asI also have a 12 kW 48V inverter and a ton of 18650's (so I could make a DIY powerwall). How can I set it up so I can charge the battery bank from the grid/utilityduring off-peak hours (8) and run off battery bank during peak hours (16)?


P.S. - This would be for a couple of circuits in my home and of course beforehand I will figure out what theirenergy & power needs (to properly build the battery)

P.P.S. - The automatic transfer switch is aGenerac RTG12EZA1

P.P.P.S. - I also have Arduinos and relays as I imagine I may need them to control the switch's switching mechanism/state at off-peak and on-peak start times...?
 

daromer

Moderator
Staff member
Joined
Oct 8, 2016
Messages
5,564
Use an Arduino or esp with time control and switch on and off the Gear. Note that the grid Price must be atleast 50% cheaper to compensate for losses when going from grid to battery and the. Battery to load.

You need to get hold of a Charger and then your basically set :)
 

wattwatt

Member
Joined
May 21, 2018
Messages
55
Use an Arduino or esp with time control and switch on and off the Gear. Note that the grid Price must be atleast 50% cheaper to compensate for losses when going from grid to battery and the. Battery to load.

You need to get hold of a Charger and then your basically set :)

Rats! 50%!!? Inverter is rated at 90% efficiency (probably really 85% since it's not a solid brand, Powerjack) and utility's off-peak and peak rates are $0.0999 and $0.1326 cents, respectively. Sounds like this project is not worth it. Guess I'll re-use these parts to make an emergency power/UPS system instead. Bummer.

Thanks for the help.
 

daromer

Moderator
Staff member
Joined
Oct 8, 2016
Messages
5,564
You have to calculate it but No nowadays not many places ha en enough difference in Price Making it worth :)
 

not2bme

Active member
Joined
Oct 16, 2017
Messages
479
Rats! 50%!!? Inverter is rated at 90% efficiency (probably really 85% since it's not a solid brand, Powerjack) and utility's off-peak and peak rates are $0.0999 and $0.1326 cents, respectively. Sounds like this project is not worth it. Guess I'll re-use these parts to make an emergency power/UPS system instead. Bummer.

Thanks for the help.

50% is reasonable because you have to factor 90% efficiency charging the battery and then 90% efficiency converting it back to AC.

Then there's the cost of the batteries and the material used to build it. So if the batteries are free then your ROI will fare much better. But not when you're only 25% off peak.

But at your off peak rate of 0.0999, let's see if my math is correct:

To charge 1kw it will cost you based on 90% efficiency
1kw = 1/0.9 (90% efficient to charge battery) = 1.111kw = 1.111 * 0.0999 = 0.109 per kwh

To put 1kw back into the grid it will cost you
1kw = 1*0.9 (90% efficiency to invert to grid) = 0.9kw so you lose 0.1kw = 0.0999*.01 = 0.00999

Combine the both 0.109-0.00999 = 0.121/kw. Not worth it if your peak is 0.1326


Some areas I've heard that some TOU have it that they actually pay you to use energy. Now that's worth doing!
 

wattwatt

Member
Joined
May 21, 2018
Messages
55
50% is reasonable because you have to factor 90% efficiency charging the battery and then 90% efficiency converting it back to AC.

Then there's the cost of the batteries and the material used to build it. So if the batteries are free then your ROI will fare much better. But not when you're only 25% off peak.

But at your off peak rate of 0.0999, let's see if my math is correct:

To charge 1kw it will cost you based on 90% efficiency
1kw = 1/0.9 (90% efficient to charge battery) = 1.111kw = 1.111 * 0.0999 = 0.109 per kwh

To put 1kw back into the grid it will cost you
1kw = 1*0.9 (90% efficiency to invert to grid) = 0.9kw so you lose 0.1kw = 0.0999*.01 = 0.00999

Combine the both 0.109-0.00999 = 0.121/kw. Not worth it if your peak is 0.1326


Some areas I've heard that some TOU have it that they actually pay you to use energy. Now that's worth doing!

THIS. IS. GOLD!!! Thank you!
 
Top