Time of Use Settings help

[WHC]

As a newbie with solar panel systems, I'm uncertain about time of use settings on my Sol-Ark 15K attached to a Fortress max eVault 18 kWh battery.

The objectives I have are as follows:

1) Have solar charge the battery during peak production hours. 1pm in this case.
2) Don't discharge the battery below 30%
3) The primary time for battery usage with be from about 5 pm until 9 pm. Estimating need for 12Kwh in that time period.
4) I'd like to have the battery be charged enough so that it will not fall below 40% overnight, in the event of an overnight grid outage. Am thinking that going from 70% to 40% gives me plenty of battery power (about 5.4 kWh) for the period between 9 pm and 9 am. By 9 am in the morning, I'll either have enough solar to recharge, or be able to have plenty of daylight time to attach my generator to recharge the battery.

I'm thinking that the following time of use settings will accomplish these goals, although I am certain that I'm not certain! I recognize that there are likely many other things that should probably be considered.

And a few general questions about the settings:

1) Should the Power column use a constant value, or should that be varied, as I have seen in some setups? In this case, I used 12 kW as a constant, which is 2/3 of the full battery capacity. I have no idea if that's "correct" or not.
2) Even though I've checked the "Charge" box at 1 pm and 9 pm, am thinking that if I have plenty of solar at 1 pm, it will not require, and won't take, any charge from the grid. True? I am expecting the need to charge from the grid at 9 pm to get back up the 70% level.
3) Am I correct in thinking that charging the battery from the grid at 9pm from 30% to 70% should only require about 7.2 kWh of power from the grid? (If that's so, it sure seems like a cheap way to charge the battery).

Will appreciate any input that will help me learn more about the time of use settings.

Thanks in advance!

 

[DIYrich]

Do you have net metering (able to export excess)?
Is your main panel connected to load?
Anything between grid meter and sol-ark?

 

[WHC]

Thanks for the reply!

Yes, I do have net metering, and Main panel is connected to the load. There is a separate service (200amp) (small shop) between the Grid meter and the Solark, but there is no battery or inverter connected to that panel's loads. The Sol-Ark is tied to the grid and the 200 amp service for our primary residence.

 

[DIYrich]

Do you have time of use rate differential?
Is net metering one to one (sell 1kWh now, get 1 kWh back later?

 

[WHC]

No time of use rate differential. Net metering is 1 to 1. Any excess production is sold back to grid at the wholesale rate. (At my location, retail rate is .137 per kWh, and wholesale about 0.06 per kWh),

 

[DIYrich]

With 1 to 1 net metering, and no time of use differential, then let the grid handle the daily stuff, and save your batteries for when the grid is down. No need for time of use settings.

There are inefficiencies to charging and discharging batteries. If you had time of use, or net metering differential, then cycling with batteries makes sense.

If you want to be nice and support the grid during power strains (like in Texas right now), that is nice, but will cost you money.

 

[n2aws]

No time of use rate differential. Net metering is 1 to 1. Any excess production is sold back to grid at the wholesale rate. (At my location, retail rate is .137 per kWh, and wholesale about 0.06 per kWh),

This sounds like conflicting info.

you say net metering is 1:1, but then say you sell it at 0.06/kwh, but buy it at 0.137/kwh. that doesn't sound like 1:1

Can you clarify?

 

[DIYrich]

No time of use rate differential. Net metering is 1 to 1. Any excess production is sold back to grid at the wholesale rate. (At my location, retail rate is .137 per kWh, and wholesale about 0.06 per kWh),

So you sell at .06, and buy at .137? Then you want to maximize self consumption without regard to time.

Power column is your max draw rate on batteries.
Batt column is 40% for reserve power.
Charge and sell are blank (not checked).

It will use batteries to supplement solar until the batteties draw down to 40%. It will then use the grid. You could go lower on the battery (30%) between 8am and 2pm. Or whatever end time where batteries will recharge to 40% that day.

Solar will first be used for load.
Second to charge batteries to 100%.
Last export to grid.

You never want to charge from grid. If a hurricane is expected, then change your settings to charge from grid to 100% before the event.

Ideally you would draw down to 10% by 10am, and let it recharge during the day. But that requires manual intervention for cloudy days. Too bad they don't make 1 day overrides, so when you know it will be sunny, you override to draw down to 10% that morning.
 

 

[WHC]

This sounds like conflicting info.

you say net metering is 1:1, but then say you sell it at 0.06/kwh, but buy it at 0.137/kwh. that doesn't sound like 1:1

Can you clarify?

Being new, my understanding may be incorrect. By net metering 1 to 1, I mean that our meter shows the number of kWh Delivered by the Grid, and the number of kWh Received from my solar. We are billed based on the difference, when the Grid provides more than my solar sent to the grid. So all of this is based on the .137 rate. In other words, if the grid delivers 100 kWh to me, and they receive 80 kWh from me, then I'm billed for 20 kWh.

If, on the other hand, my monthly Solar production exceeds what is delivered by the grid, at that point, the Elec co. pays me for the excess at the rate of 0.06 kWh that they received from my solar. So, If they Deliver 100 kWh, and they receive 120 kWh from me, then I get paid at the .06 rate for the 20 I supplied to the grid.

 

[WHC]

So you sell at .06, and buy at .137? Then you want to maximize self consumption without regard to time.

Power column is your max draw rate on batteries.
Batt column is 40% for reserve power.
Charge and sell are blank (not checked).

It will use batteries to supplement solar until the batteties draw down to 40%. It will then use the grid. You could go lower on the battery (30%) between 8am and 2pm. Or whatever end time where batteries will recharge to 40% that day.

Solar will first be used for load.
Second to charge batteries to 100%.
Last export to grid.

You never want to charge from grid. If a hurricane is expected, then change your settings to charge from grid to 100% before the event.

Ideally you would draw down to 10% by 10am, and let it recharge during the day. But that requires manual intervention for cloudy days. Too bad they don't make 1 day overrides, so when you know it will be sunny, you override to draw down to 10% that morning.
 

Excellent! This makes sense to me...and I'll adjust my settings accordingly.

Very much appreciate your advice, DIYrich!

 

[n2aws]

Being new, my understanding may be incorrect. By net metering 1 to 1, I mean that our meter shows the number of kWh Delivered by the Grid, and the number of kWh Received from my solar. We are billed based on the difference, when the Grid provides more than my solar sent to the grid. So all of this is based on the .137 rate. In other words, if the grid delivers 100 kWh to me, and they receive 80 kWh from me, then I'm billed for 20 kWh.

If, on the other hand, my monthly Solar production exceeds what is delivered by the grid, at that point, the Elec co. pays me for the excess at the rate of 0.06 kWh that they received from my solar. So, If they Deliver 100 kWh, and they receive 120 kWh from me, then I get paid at the .06 rate for the 20 I supplied to the grid.

So, just for clarification, usually when we say "1:1" or "1 to 1" regarding net metering, we mean something like "You sell it to the grid at the same price you buy it". ie, you get a 1 for 1 credit for everything you sell back.

when there is a price differential for selling vs buying, then.. batteries and self consumption start making more financial sense (barring any other reason for batteries). with a differential and batteries, you'd do something like "charge batteries to full from solar, discharge them to some pre-determined level, before relying on grid" so that you pay the minimum amount you can to the utility.

There are 2 schools of thought on the "wear and tear" for the batteries, that you may want to consider.

#1) I bought the batteries, may as well use them to save as much as I can.
- The idea is, batteries may die of old age, even if you don't use them.. so, you may as well use them.

#2) I bought the batteries for backup only, and don't want to cycle them.
(An alternative to #2: I don't want to wear my batteries out by cycling them)
- The idea is, batteries will last indefinitely if left at float voltage, essentially using them as a large UPS more than anything.


I think #2 held more merit with lead acid batteries (I can tell you I've seen more than a *lot* of 30+ year old batteries in telecom, where they were kept in float for years at a time, and only cycled a few times during an event.) I don't think it's as significant in LifePo4. if you keep them cycling between 20-80%, they can last a LONG time. it's the 80-100% zone, and the 20%-0% zone that does the most wear on lifepo4. But there is some debate about this, and I'm sure someone will post that I'm wrong. Thats why I was trying to present both schools of thought. I don't honestly know which one is "right", or if either is "wrong"

 

[WHC]

Ha! I've certainly learned in the past few weeks that it's just as difficult to know what's "right"or "wrong" with respect to Solar as in just about every other aspect of life!

 

[DIYrich]

I don't honestly know which one is "right", or if either is "wrong"

For home use, lifep04 batteries will die of old age before wearing out.

Charging/discharging efficiency (loss) is a bigger issue.

 

[DIYrich]

Being new, my understanding may be incorrect. By net metering 1 to 1, I mean that our meter shows the number of kWh Delivered by the Grid, and the number of kWh Received from my solar. We are billed based on the difference, when the Grid provides more than my solar sent to the grid. So all of this is based on the .137 rate. In other words, if the grid delivers 100 kWh to me, and they receive 80 kWh from me, then I'm billed for 20 kWh.

If, on the other hand, my monthly Solar production exceeds what is delivered by the grid, at that point, the Elec co. pays me for the excess at the rate of 0.06 kWh that they received from my solar. So, If they Deliver 100 kWh, and they receive 120 kWh from me, then I get paid at the .06 rate for the 20 I supplied to the grid.

So net metering on a daily basis, but differential on a monthly basis. In that case, treat it like net metering 1-1, and don't exercise your batteries. Minimize charging/discharging losses.

Basically they give you the benefit of excess summer production at the wholesale rate, and charge you for winter consumption at the retail rate.

Utility is providing free time shifting during the day/month, but charging you for seasonal time shifting.

 

[WHC]

So you sell at .06, and buy at .137? Then you want to maximize self consumption without regard to time.

Power column is your max draw rate on batteries.
Batt column is 40% for reserve power.
Charge and sell are blank (not checked).

It will use batteries to supplement solar until the batteties draw down to 40%. It will then use the grid. You could go lower on the battery (30%) between 8am and 2pm. Or whatever end time where batteries will recharge to 40% that day.

Solar will first be used for load.
Second to charge batteries to 100%.
Last export to grid.

You never want to charge from grid. If a hurricane is expected, then change your settings to charge from grid to 100% before the event.

Ideally you would draw down to 10% by 10am, and let it recharge during the day. But that requires manual intervention for cloudy days. Too bad they don't make 1 day overrides, so when you know it will be sunny, you override to draw down to 10% that morning.
 

A clarification, please. "Power is the Max draw rate on the batteries" - Would that be 70% of the 18.5 kWh for the eVault Max... or 12.95? And, if I drop to 40% at perhaps 10 pm, what level will will the grid recharge to, before using the 40% parameter again? (I think my question indicates a misunderstanding about ths point...won't be the first time!) Thanks again for your advise!

 

[DIYrich]

A clarification, please. "Power is the Max draw rate on the batteries" - Would that be 70% of the 18.5 kWh for the eVault Max... or 12.95? And, if I drop to 40% at perhaps 10 pm, what level will will the grid recharge to, before using the 40% parameter again? (I think my question indicates a misunderstanding about ths point...won't be the first time!) Thanks again for your advise!

I don't know the max draw rate of the evault max. If it is an 18.5kWh battery, then 14,000 watt max should be ok.

With no "charge" boxes checked, it will not charge batteries from grid. Only from solar. No reason to charge from grid unless you want to charge to 100% for an anticipated event.

The 40% sets a limit on battery usage when connected to the grid.

Since you have 1-1 net metering during the month, you don't need the time of use settings. Don't waste energy cycling your batteries.

Note: you could use time of use settings to cycle your batteries once a week between 80-100% to keep the bms calibrated.

 

[WHC]

I don't know the max draw rate of the evault max. If it is an 18.5kWh battery, then 14,000 watt max should be ok.

With no "charge" boxes checked, it will not charge batteries from grid. Only from solar. No reason to charge from grid unless you want to charge to 100% for an anticipated event.

The 40% sets a limit on battery usage when connected to the grid.

So, if I hit 40%, at say 10 pm, then the grid takes over until I once again have solar, which will then start the recharge process. And solar will try to recharge the batteries to 100%. Correct? Thanks for your guidance.

 

[DIYrich]

So, if I hit 40%, at say 10 pm, then the grid takes over until I once again have solar, which will then start the recharge process. And solar will try to recharge the batteries to 100%. Correct? Thanks for your guidance.

Yes.

 

[WHC]

Hmmm....

Last night, battery discharged to 40%, and then grid took over. Of course, no solar activity.

It's about 9:30 am. Good solar, but all going to load and grid. None is being used to charge battery.

Here are the settings I input yesterday afternoon:

...and here's the current activity:


Are other settings necessary? Do I need to change the 40% to 100% at, maybe, 9:00 and 1:00 time periods? And leave the "Charge" block unchecked? If I do that, will it send all solar to the battery, and have the grid take over the load?

Thanks again for the help!

 

[WHC]

Yes.

Should I have the "Limited Power to Load" or "limited Power to Home" checked? The "Grid Sell" box is checked also.

In the "Other" tab, I have ensured that "Battery First" is checked.