Battery charging in AC or DC coupled systems

[Grouch]

Hi all,
I read that a battery (such as from Tesla or LG) in an AC coupled system can be charged by the grid in an AC coupled system. I haven't seen an article (I only found 2) that mentions this can happen in a DC coupled system. Can the grid charge the battery in a DC coupled system? I imagine with today's multimode inverters, this can happen.

Thanks.

 

[jaggedben]

Yes, it is industry standard in any system that is designed to connect to the grid.

 

[Grouch]

Thanks!

 

[pv_n00b]

The technology is there, but the devil is in the details of the utility interconnection. Utilities are generally super worried that someone with a NEM PV interconnection and TOU rates will charge a battery from the grid during the low cost period and export energy back for NEM credit during the high cost period and make money on the exchange. Because of this, it has been very hard to get DC coupled PV+BESS systems approved for export if the BESS can charge from the grid. It's possible to get AC coupled systems approved because it's easier to meter the BESS and PV AC to make sure that the energy exported to the grid does not exceed the PV system production. This is why you don't see many DC coupled systems.

 

[retirede]

The technology is there, but the devil is in the details of the utility interconnection. Utilities are generally super worried that someone with a NEM PV interconnection and TOU rates will charge a battery from the grid during the low cost period and export energy back for NEM credit during the high cost period and make money on the exchange. Because of this, it has been very hard to get DC coupled PV+BESS systems approved for export if the BESS can charge from the grid. It's possible to get AC coupled systems approved because it's easier to meter the BESS and PV AC to make sure that the energy exported to the grid does not exceed the PV system production. This is why you don't see many DC coupled systems.

The fact that utilities are worried about this tells me that their on-peak rates are too high! Otherwise, they would welcome being supplied power when it’s needed most.

 

[petersonra]

The fact that utilities are worried about this tells me that their on-peak rates are too high! Otherwise, they would welcome being supplied power when it’s needed most.

I think it is more along the lines of they do not want to deal with hundreds of thousands or millions of tiny generation stations that they cannot depend on to have any control over. The utility does not get to tell the residential customer that he should shut off his generation during peak times because the utility has plenty of power, like he can with regular generation. I think until the utility can shut down the back feed from residential generation when the utility does not need the power like they can with all the other generators, it is problematic for the utility.

 

[gadfly56]

The fact that utilities are worried about this tells me that their on-peak rates are too high! Otherwise, they would welcome being supplied power when it’s needed most.

It is my understanding that most grid-tied PV owners are getting paid at the retail rate for electricity. To the POCO, this is the same as making $0 on the deal. They are probably paying the wholesale providers somewhere around a third the retail rate for power. You can see where small PV isn't a good bargain for the POCO.

 

[rainwater01]

Hi all,
I read that a battery (such as from Tesla or LG) in an AC coupled system can be charged by the grid in an AC coupled system. I haven't seen an article (I only found 2) that mentions this can happen in a DC coupled system. Can the grid charge the battery in a DC coupled system? I imagine with today's multimode inverters, this can happen.

Thanks.

For what it’s worth, You can charge Generac’s dc coupled system from the grid. I don’t think you can output to the grid from just the battery though.


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[pv_n00b]

The fact that utilities are worried about this tells me that their on-peak rates are too high! Otherwise, they would welcome being supplied power when it’s needed most.

TOU rates provide signals to consumers about the best time to use electricity. Electricity usage is a very peaky business, everyone tends to get home at the same time and turns on all the electrical gadgets at the same time. Making the rate higher motivates consumers to maybe set the dishwasher to run at midnight, cool the house down early and try to glide through the high rate period with less HVAC load. Things like that.

 

[ggunn]

TOU rates provide signals to consumers about the best time to use electricity. Electricity usage is a very peaky business, everyone tends to get home at the same time and turns on all the electrical gadgets at the same time. Making the rate higher motivates consumers to maybe set the dishwasher to run at midnight, cool the house down early and try to glide through the high rate period with less HVAC load. Things like that.

It seems to me that the POCO wouldn't have a problem with a customer buying energy when it is cheap, storing it in batteries, and then using it instead of grid power when energy is more expensive. What's the diff from their POV between that and running the dryer late at night?

 

[pv_n00b]

It seems to me that the POCO wouldn't have a problem with a customer buying energy when it is cheap, storing it in batteries, and then using it instead of grid power when energy is more expensive. What's the diff from their POV between that and running the dryer late at night?

They don't have a problem with that use case. Did I inadvertently say they did?

 

[petersonra]

It seems to me that the POCO wouldn't have a problem with a customer buying energy when it is cheap, storing it in batteries, and then using it instead of grid power when energy is more expensive. What's the diff from their POV between that and running the dryer late at night?

I don't think there is. There is a huge difference between that and buying energy when it is cheap and selling it back to the POCO on an involuntary basis when the price is very high.