Hi all -
I'm a new member here, but I've been following energy storage for years. I recently decided to try building my own energy storage system (ESS),mostly as a learning exercise. I'm an electrical engineer, but my experience isn'tin the energy / power sector -- yet.
After some time researching, I think I've boiled my problem down.
I'm trying to find a battery charger /inverterwith the following constraints:
- 120V AC interface
- single circuit for charge and discharge
- no "protected loads"; energy flows in and out on "grid" side of inverter
- grid-tie / UL1741 behavior: if grid drops, the inverter drops
- don't care about backup during loss ofgrid
- small-ish size and cost
I think the last one is the problem. Every time I think I've found an inverter (from Outback or Magnum or MPP Solar), I find that the smallest they go is 2 kW or so, and they cost $1500-$2000. Or it's a small inverter but is only designed for solar self-consumption, and won't sell back to grid. I'm looking for something that's say $500 or so, and would be happy to find something used.
I plan to use this for simple price arbitrage, charging during low cost power and discharging during high cost power (I'm on a TOU plan). I do have a solar system (which will NOT be directly integrated with this ESS) and was planning to have the ESS charge in late morning when I've got free power from thesolarsystem but haven't loaded up the air conditioning yet. Then in late afternoon I'd have it discharge. The ESS will not be aware of the actualsolar power availability, rather I will use a dumb schedule to charge and discharge. I doubt that the inverter can be scheduled like this, so I'll probably have to come up with a controller (Arduino+serial or whatever) to command those mode changes, but that automation is farther off in the future, and not what I'm asking about here.First I'm just trying to find a small-ish inverter to build this around, and would be content with manual commanding at first (e.g. pushing buttons on it twice a day to change modes).
What I want to do here doesn't seem particularly cutting edge (no solar/MPPT needed) so I think I might even be able to use an older inverter model, purchased used, to do this. However it would need to be modern enough to go offline if the grid dropped (grid-tie behavior) and it would be nice if I could set the high and low battery voltage thresholds so that I could try different batteries.
I waslooking at a used Outback FXfor this, but at ~$900 usedthey are still too much for my little exploratoryproject. Plus I think I would need their Mate controller to manuallychange the modes, so more cost.I looked at MPP Solar and Victron lines but they all seemed overkill for one reason or another, but maybe you all can correct me.
The exactbattery specs arenot relevant right now, I think. Whatever the inverter needs, 12V or 24V, I'll build a battery pack to meet. I was planning on starting with a lead-acid battery first, and then move on to an 18650-based pack. In both cases it would be a very small system, so not a lot of wasted cost when I finish playing with the first battery pack.
And so I turn to you all. What am I missing? Can you point me to a small inverter that will do grid-tie like this?
I'm a new member here, but I've been following energy storage for years. I recently decided to try building my own energy storage system (ESS),mostly as a learning exercise. I'm an electrical engineer, but my experience isn'tin the energy / power sector -- yet.
After some time researching, I think I've boiled my problem down.
I'm trying to find a battery charger /inverterwith the following constraints:
- 120V AC interface
- single circuit for charge and discharge
- no "protected loads"; energy flows in and out on "grid" side of inverter
- grid-tie / UL1741 behavior: if grid drops, the inverter drops
- don't care about backup during loss ofgrid
- small-ish size and cost
I think the last one is the problem. Every time I think I've found an inverter (from Outback or Magnum or MPP Solar), I find that the smallest they go is 2 kW or so, and they cost $1500-$2000. Or it's a small inverter but is only designed for solar self-consumption, and won't sell back to grid. I'm looking for something that's say $500 or so, and would be happy to find something used.
I plan to use this for simple price arbitrage, charging during low cost power and discharging during high cost power (I'm on a TOU plan). I do have a solar system (which will NOT be directly integrated with this ESS) and was planning to have the ESS charge in late morning when I've got free power from thesolarsystem but haven't loaded up the air conditioning yet. Then in late afternoon I'd have it discharge. The ESS will not be aware of the actualsolar power availability, rather I will use a dumb schedule to charge and discharge. I doubt that the inverter can be scheduled like this, so I'll probably have to come up with a controller (Arduino+serial or whatever) to command those mode changes, but that automation is farther off in the future, and not what I'm asking about here.First I'm just trying to find a small-ish inverter to build this around, and would be content with manual commanding at first (e.g. pushing buttons on it twice a day to change modes).
What I want to do here doesn't seem particularly cutting edge (no solar/MPPT needed) so I think I might even be able to use an older inverter model, purchased used, to do this. However it would need to be modern enough to go offline if the grid dropped (grid-tie behavior) and it would be nice if I could set the high and low battery voltage thresholds so that I could try different batteries.
I waslooking at a used Outback FXfor this, but at ~$900 usedthey are still too much for my little exploratoryproject. Plus I think I would need their Mate controller to manuallychange the modes, so more cost.I looked at MPP Solar and Victron lines but they all seemed overkill for one reason or another, but maybe you all can correct me.
The exactbattery specs arenot relevant right now, I think. Whatever the inverter needs, 12V or 24V, I'll build a battery pack to meet. I was planning on starting with a lead-acid battery first, and then move on to an 18650-based pack. In both cases it would be a very small system, so not a lot of wasted cost when I finish playing with the first battery pack.
And so I turn to you all. What am I missing? Can you point me to a small inverter that will do grid-tie like this?