Load-shedding with the battery bank - worth it?

RandomJoeRandomJoe Solar Expert Posts: 472 ✭✭✭
Argh... The electric company has dangled a carrot in front of me that is *almost* tempting, but I just don't know that it's worthwhile... I'd like to see what others think!

I have a small "off-grid" solar system in place - 1KW in panels, 48V 220AH battery bank, Outback inverter and other hardware. I currently have a few outlets placed around the house wired back to a subpanel for the Outback inverter. I've never really finished the dedicated circuits, because the remainder need to be in really difficult-to-reach places like outside walls. I've toyed with the idea of simply disconnecting a few of the existing house circuits from the "grid" breaker panel, wiring them to the "off-grid" subpanel, and just doing it that way. Grabs a few more items than I had planned on running off-grid, but that just means in a real long-term outage I'll have to be sure to unplug unnecessary items.

Now the electric company has installed smart meters in my neighborhood (very cool - I can see my usage down to every 15 minutes online - so far they don't charge for that!) and now they are pushing their "variable peak pricing" plan. Basically time-of-use, where the on-peak price varies depending on demand. The off-peak price drops to less than half the normal price (4.5 c/kwh vs 8.4 c/kwh) and even on-peak could be 4.5c (if low usage) or 8.4c ("normal" usage) only going above that for "high" or "critical". No idea yet how often they hit those other peaks.

My thought was, I could go ahead and wire up the house as planned, then use the solar/battery system to run the house from 2P-7P then (if needed) bulk-charge the bank that evening and let the solar finish the charge the next morning. The system can't run the AC, of course, but that shouldn't be necessary. The house can coast 5 hours without a problem, I'd just set it to not run at all during that time.

Of course, this does add a little inefficiency - 1kWh out of the battery would require a bit more in - but during June-Oct it's generally plenty sunny here so the bulk (if not all) of my usage would be directly from the solar panels.

Sounds great as far as that goes, but on looking back at last summer (I was home a lot more, and it was MISERABLY HOT so high usage for me) if I shifted EVERY kWh I used from standard price to off-peak I save all of $151! Nothing to sniff at, but then I start wondering if I really want to set up this deal where I'm effectively dependent on the RE system (I have to change rate plans) - if I have to replace any major components, that savings is going to take forever to pay back!

So does that sound like something you would bother doing? Anything I might not have considered?


  • BB.BB. Super Moderators, Administrators Posts: 30,759 admin
    Re: Load-shedding with the battery bank - worth it?

    You already have to solar system... So your sunk costs are already there. Otherwise, for somebody new--I would guess (without solar panels), that ~$0.45 per kWH just to do load shifting (very rough costs).

    In California, they have installed those meters. And, the original plan was for "peak" pricing for ~2 weeks a year maximum was going to be in the $0.50 to $0.65 per kWH (i.e., almost forced load shedding for anyone that uses a fair amount of power) for daytime emergency peak power (24 hour notice).

    For your needs--You already have the equipment--so why not.

    For people that don't have the equipment and are not ready to setup (and pay for) and emergency battery backed system--I don't think they will save money. But, if they have power failures, they will probably be pretty happy to have such a system (if they don't go with backup genset).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Load-shedding with the battery bank - worth it?

    i'm confused as to what the new meter and tou plan has to do with what you already power with solar off grid. this was already saving money for you whether you used it during the day or later as it is in the batteries regardless. only thing is now that you may want items that are usually run during the day on other utility circuits to maybe be on here with the solar circuits as well to save on the increased daytime costs. i can't determine your outlet availability or the capacity to add more items or switch appliances on the same circuits like instead of some night time lights you may want the microwave oven on it instead. basically switching daytime wattage to solar for the savings. you may want to branch out with enphase gt inverters and dedicated pvs to aid you in the daytime quest as this is more automatic and just keep the present off grid setup as is. wish i could tell you what is better in your circumstance.
  • RandomJoeRandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: Load-shedding with the battery bank - worth it?

    I probably didn't explain myself well, my debate wasn't really anything concrete, mostly concern for whether the potential risk is worth the (relatively small) financial reward. I will probably be rearranging the circuits anyway, I had thought about that already and was leaning toward it.

    Changing to TOU is where my primary concern was. As I looked at it more, my normal non-ac loads during the day don't amount to a whole lot so even if I did run grid power during critical rates it isn't going to break the bank. I think my imagination had me suffering an inverter breakdown, then seeing the bill skyrocket since I was running grid during the peak time!

    Probably mostly thanks to my work with commercial HVAC systems. They can get into some serious financial trouble if they don't do things right during peak demand. But that's primarily due to their peak-demand charge, which doesn't (yet?!) apply to residential TOU. For them, whatever highest kW draw they have during a 15-minute window *anywhere in a given month* sets that month's peak-demand charge. Starting a large piece of equipment during peak times is a big no-no! They make sure to have everything running they think they'll need, and if it isn't enough too bad...

    Anyway, as I said, even if I do use grid power during peak the reduction in cost for the other 19 hours of the day should more than make up for it and I'd still save a little money.

    As for going grid-tie with additional equipment, it's an idea but my roof space is limited and I already want to increase the size of my off-grid system! :) As Icarus says, the loads always grow over time... :D
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