Designing a system to minimize peak hour grid charges and also provide grid independence

[klieber]

We recently bought a new house and are looking to install solar. I'm planning to DIY most of it, and am studying diligently. I can't figure out if what I want is possible, however, largely because I don't know the right terms to search for. I've already done a power audit and we're looking to install a 12kW PV system and a 30kWh battery backup. (Currently looking at EG4 components, but not finalized) What I'd like:

• PV + battery backup that will give us the ability to run off grid if we ever needed to, but would be grid tied otherwise.
• Uses battery for surge usage during peak hours (4-7 for us)
• Uses grid for surge usage during off peak hours
• Uses super off peak hours to charge the battery if needed (this is a nice to have, not a must have)

Our utility company has a time-of-service rate with a demand charge that is very inexpensive for off peak power (~$0.05 per kWh), but they nail you for power usage during peak hours. So, my thinking is, with the right system, I should never see any grid usage at all during peak hours.

I did search and found this thread, which asks the same question, but he didn't get a clear answer.

So: Is this type of setup common and, if so, what is it called?

Also, for bonus points, will the EG4 18KPV hybrid inverter + EG4 batteries specifically work for this setup.

Thank you!

 

[Ampster]

I have demand charges and in my case the demand charges are figured on the peak kW used at any time of any day during the billing period and are a different monthly rate in addition to the kWh charges for usage.
In my case I can offset the kWh usage by solar generation of the same amount but would need a lot of battery power to offset the demand charges.

 

[klieber]

Our demand charge is only based on peak usage during peak hours. Off-peak isn't counted at all.

We use ~3-4kWh of peak power during our 3-hour peak window on average. That will go up a bit in July/August when it gets hotter, but with a 30kWh battery bank, it should be more than sufficient to offset that usage with plenty to spare.

 

[klieber]

I think I may have answered my own question. The proper term appears to be "grid peak-shaving" or "load shedding" and yes, the EG4 18KPV appears to support it.

 

[Ampster]

The proper term appears to be "grid peak-shaving" or "load shedding"

Yes that is much easier to accomplish with a reasonable sized battery pack.

 

[Rusty959]

All of what you're asking for I believe can be accomplished by the 18kpv, all of the major modes have time associated with them so you can set when you want it to run each mode.

Additionally something you may not have considered is you can do an AC charge at specific times so you could also set it to charge your 30kWh battery bank during your super off peak time so you have a usable system to power your loads during on-peak even before you have solar ready.

 

[DIYrich]

You need Time of Use settings to charge during off-peak. EG4 18k should have that.

For the Sol-Ark, "grid peak shaving" is a 24/7 setting, so you may not want to use that (don't want to peak shave while you are charging). If EG4 has TOU grid peak shaving, that would be great.
Not sure how to TOU peak shave on the Sol-Ark. If you want no grid usage during peak hours, that doable with TOU. Mixing grid/battery with grid first under TOU is the problem.

 

[Ampster]

Not sure how to TOU peak shave on the Sol-Ark.

I find on the SolArk, that I can be charging the battery at the same time the loads are being served and some extra is going to grid export. That is on sunny days. Today with overcast my batteries charged by Noon and my 3 kW solar production is covering the 400 Watts of loads and sending the rest to the grid. In half an hour my 4PM TOU setting takes over and batteries will cover all the loads as solar starts diminishing.

 

[DIYrich]

I find on the SolArk, that I can be charging the battery at the same time the loads are being served and some extra is going to grid export. That is on sunny days. Today with overcast my batteries charged by Noon and my 3 kW solar production is covering the 400 Watts of loads and sending the rest to the grid. In half an hour my 4PM TOU setting takes over and batteries will cover all the loads as solar starts diminishing.

That is typical. Here is the scenario: how to use batteries to limit grid draw to something like 2kW? So order would be:
PV -> Grid to 2kW -> Battery -> Grid (if battery isn't enough).

 

[Ampster]

So order would be:
PV -> Grid to 2kW -> Battery -> Grid (if battery isn't enough).

That is the one detail I am not sure I clearly understand. the 2kW number has a different meaning in terms of what it limits depending on whether the Charge box or Sell box is checked. In my case, I have Charge box checked until 1 PM and Sell is checked from 9AM until 9PM even though I only have solar production until about 6PM.

 

[DIYrich]

That is the one detail I am not sure I clearly understand. the 2kW number has a different meaning in terms of what it limits depending on whether the Charge box or Sell box is checked. In my case, I have Charge box checked until 1 PM and Sell is checked from 9AM until 9PM even though I only have solar production until about 6PM.

No way to specify the 2kW number with Sol-ark under TOU. You can do it under grid support, but then it is 24/7.

 

[Rusty959]

EG4 18kpv does have times for grid peak shaving. I've got some odd things going on with the settings, but it's a new product so I'm sure some firmware updates will clean it up.



One thing it doesn't have though is sell during only certain periods. You can set maximum or force a discharge in a certain amount at specified times though.

 

[Ampster]

No way to specify the 2kW number with Sol-ark under TOU.

The number I am referring to is the one in the column to the left of the check boxes on this screen. It is titled, "Power(W)". I have heard explanations that depending on which box is checked, that may be a limit of some sort. But I have not been able to correlate it to charging or selling limits?

 

[DIYrich]

The number I am referring to is the one in the column to the left of the check boxes on this screen. It is titled, "Power(W)". I have heard explanations that depending on which box is checked, that may be a limit of some sort. But I have not been able to correlate it to charging or selling limits?

The number is how much power can come from the battery.

 

[Ampster]

The number is how much power can come from the battery.

Thanks, that makes sense. My situation has never needed those limits and that is why I never saw them in action. My big loads such as oven, electric dryer and EV chargers are all outside the the SolArk so I just manage those loads by using them off peak and/or when solar is producing lots of kWs.