Grid tied with AC coupled small battery and power dump? Exists?

[markofjohnson]

I'm a very happy grid tied SolarEdge customer in California, with a 5kW peak system that does give me a year of energy. I initially didn't want battery backup because of the cost - batteries sized to match 5kW peak doubles the price of the system. But now we face scheduled power cuts during the summer, all that sun and not a drop of power due to the grid tied design.

It sure would be great if I could have a small AC coupled battery combined with some kind of power dump that would be cheaper than a full sized battery and would let me use daytime power if there is a power cut. I've not found anything like that. I understand that if a battery backup is too small capacity for the solar array then it can't safely charge because if there is too much power the system will over-volt and damage batteries and/or the array. Is there any solution that couples a smaller cheaper battery with a power dump, so under sized batteries can charge safely, and can activate the array during the day in the case of a grid power outage.

I suspect I'm missing something that explains why I can't find something like this: ?
- systems with power dumps exist, but they cost a lot anyway, might as well have full capacity battery;
- power dumps exist, but they don't work well with fluctuating residential load;
- power dumps exist, but the trade offs are too hard to understand for residential customers so there's no market there.
- Something else?

Heck, with home AC and an electric car that sure would provide quite a power dump. As I have an electric car I already own the most expensive part of the battery system. Grrr, are there any custom solutions to use my car for this? (Chevy Volt.)

Thanks for your comments.

[scrambler]

With a hybrid inverter there is no need for power dump, as the inverter will regulate power not to exceed what the battery and the house can use.

In any case, you would need to either have a critical load panel with a transfer switch, or a whole house backup behind a transfer switch, as it is mandatory and imperative that no power can flow back to the grid during an outage, as that could electrocute workers on the line. So the inverter must be isolated from the grid when the grid goes down.

The battery system that works with regular inverters is the Powerwall, as it comes with its own gateway / transfer switch system.
A single Powerwall installed by Tesla is around $12k (depends on your exact house configuration)

[solardreamer]

I'm a very happy grid tied SolarEdge customer in California, with a 5kW peak system that does give me a year of energy. I initially didn't want battery backup because of the cost - batteries sized to match 5kW peak doubles the price of the system. But now we face scheduled power cuts during the summer, all that sun and not a drop of power due to the grid tied design.

It sure would be great if I could have a small AC coupled battery combined with some kind of power dump that would be cheaper than a full sized battery and would let me use daytime power if there is a power cut. I've not found anything like that. I understand that if a battery backup is too small capacity for the solar array then it can't safely charge because if there is too much power the system will over-volt and damage batteries and/or the array. Is there any solution that couples a smaller cheaper battery with a power dump, so under sized batteries can charge safely, and can activate the array during the day in the case of a grid power outage.

I suspect I'm missing something that explains why I can't find something like this: ?
- systems with power dumps exist, but they cost a lot anyway, might as well have full capacity battery;
- power dumps exist, but they don't work well with fluctuating residential load;
- power dumps exist, but the trade offs are too hard to understand for residential customers so there's no market there.
- Something else?

Heck, with home AC and an electric car that sure would provide quite a power dump. As I have an electric car I already own the most expensive part of the battery system. Grrr, are there any custom solutions to use my car for this? (Chevy Volt.)

Thanks for your comments.

No sure what would be acceptable cost for you. If you want batteries then you'll need an inverter anyway to make use of the batteries. The cost difference between off-grid inverter and hybrid inverter is not that big relative to the battery cost so it makes more sense to get hybrid inverter then it will either modulate or shutoff your grid tied inverters when the batteries are full. If you want batteries then hybrid inverter is really the way to go.

For me, I want similar functions you mentioned but ideally without batteries as it's not financially justifiable for occasional outages. It would be great if I can use my grid-tied inverters whenever it's available to augment generators during short term outages. Just for reference, if my solar company offered such add-on I think I would be willing to pay up to 20% more for it. Home battery systems are more like 100%+ add-on cost.