How to set PW's in winter?

[h2ofun]

Is interesting reading how folks solar systems pretty much tank in the winter. Mine went from like 80kwh to at best with no rain to 20 kwh.

Is also interesting when folks talk about either how many PW's one should have or how many they have, most seem to have gas for their furnace which seems totally changes how one looks at PW's.

With my house now being 99.9% electric, and large, am using like 60 kwh per day, netting like 40 kwh when solar added.

So, if I think about using PW's, seem very quickly I would drain them and not be able to refill during the winter. Seems others may have this same issue, assume one has heat pumps.

So, since a key reason for me to consider pw's is during the winter if I lose power, the house keeps working quietly. My 22K generator would work also. So, how are folks setting the pw's up in the winter time to deal with high probably of now being able to totally recharge each day?

 

[jrweiss98020]

Set them to "Backup Only" so they are always charged.

If you have whole-house backup as I do, you will have to manually load-shed anything you don't want running if the power goes out. I don't know how your generator and PWs would share the load...

 

[bmah]

So, since a key reason for me to consider pw's is during the winter if I lose power, the house keeps working quietly. My 22K generator would work also. So, how are folks setting the pw's up in the winter time to deal with high probably of now being able to totally recharge each day?

I'm thinking that as with a lot of things having to do with Powerwalls and/or solar, "it depends". Where I live, our grid power is fairly reliable, and if we have outages (excluding those lovely PSPS events) they're on the order of hours, but not days. So for this scenario, I leave my 3 Powerwalls in cost-savings mode and adjust the reserves, such that the maximum charge level during the day is close to 100%. I'll usually re-evaluate that every few days. (At the moment, that means a 60% reserve level, which should be able to run our house for about a day with a little energy conservation.) Basically the main goal is to continue to get the benefits of cost-savings mode, but maximize the reserves just in case of an outage.

If I lived someplace that had unreliable power, or was prone to long outages during conditions with little solar production, I might do something different.

Bruce.

 

[jboy210]

I just set mine to Advanced-Balanced with a 25% reserve. Even with our low 8-9 kWh/day from solar this is enough to usually cover our high-cost period (4-9 PM M-F). After 9 PM and most of the rest of the day, the system draws from the grid at the low rate and any solar goes to the PowerWalls. We have gas heating, fireplaces, and stovetop.

 

[h2ofun]

I just set mine to Advanced-Balanced with a 25% reserve. Even with our low 8-9 kWh/day from solar this is enough to usually cover our high-cost period (4-9 PM M-F). After 9 PM and most of the rest of the day, the system draws from the grid at the low rate and any solar goes to the PowerWalls. We have gas heating, fireplaces, and stovetop.

That is the key it seems to how I see folks using. Most of my energy use now is my heat pumps. If I had gas heating, would be easy to figure out how to use a PW. And then add your fireplaces, ... But with my 60kwh per day use with the heat pumps, and only getting at best 20kw per day out of my 14.5 kw solar, using the PW's a lot would leave them empty in only a few days, so might as well not have them.

 

[miimura]

I always keep my system in TBC-Balanced. As the solar production drops off in the Winter, I raise the Reserve so the headroom above is about equal to a day's best possible solar production until it reaches 75%. In the Summer, I drop the Reserve down to 25%.

Summer: (June 16)

Winter: (Dec 16)

 

[h2ofun]

Set them to "Backup Only" so they are always charged.

If you have whole-house backup as I do, you will have to manually load-shed anything you don't want running if the power goes out. I don't know how your generator and PWs would share the load...

I do have whole house backup. But when the power goes out, we are smart enough to not use things as if we have normal power. This would mean having the house much colder than normal I think. Since the solar is new, and PW's if I get, guess it would a real time watching things decision.

The generator only kicks in if there is no power. So now, no PGE, the switches engage. If I had Gateways, unless they trigger, no generator. So I guess in a power outage I would just let them get used to zero, if the outage is long and then use the generator.

 

[h2ofun]

I'm thinking that as with a lot of things having to do with Powerwalls and/or solar, "it depends". Where I live, our grid power is fairly reliable, and if we have outages (excluding those lovely PSPS events) they're on the order of hours, but not days. So for this scenario, I leave my 3 Powerwalls in cost-savings mode and adjust the reserves, such that the maximum charge level during the day is close to 100%. I'll usually re-evaluate that every few days. (At the moment, that means a 60% reserve level, which should be able to run our house for about a day with a little energy conservation.) Basically the main goal is to continue to get the benefits of cost-savings mode, but maximize the reserves just in case of an outage.

If I lived someplace that had unreliable power, or was prone to long outages during conditions with little solar production, I might do something different.

Bruce.

Being in the foothills, at 1500 feet, can get hit with snow once in a while and impact power. In 1989, we had a 8 inch snow event and were without power for 4 days. Last years PGE outage worst was like what 2 or so days. A power pole hit is like 8 hours. So far this year, only once for 1 day.

So your comments to use watch things and adjust, seems like the best way.

 

[h2ofun]

I always keep my system in TBC-Balanced. As the solar production drops off in the Winter, I raise the Reserve so the headroom above is about equal to a day's best possible solar production until it reaches 75%. In the Summer, I drop the Reserve down to 25%.

Summer: (June 16)
View attachment 619282

Winter: (Dec 16)
View attachment 619286

So what is the reserve set at in winter? Not sure what the reaches 75% means? Are you saying you set such that one days production of solar brings back to 100% charge?

 

[miimura]

So what is the reserve set at in winter? Not sure what the reaches 75% means? Are you saying you set such that one days production of solar brings back to 100% charge?

A sunny day this time of year is at best 5kWh for my system, frequently less, like 3 or 4 kWh. 5kWh is about 19% or 20% of my two Powerwall system, but I never raise the Reserve above 75%. I just let it do its thing and it usually gets up to about 85% or 90% before it starts discharging for Peak. In February I will probably start generating more than 7kWh/day so I will start dropping the Reserve at that point.

The whole point of this strategy is that my solar generation cannot cover my Peak usage, so keeping the Reserve high forces the system to keep bouncing off the Reserve at a high level instead of a low one while still absorbing all the solar and using it during Peak.

 

[h2ofun]

A sunny day this time of year is at best 5kWh for my system, frequently less, like 3 or 4 kWh. 5kWh is about 19% or 20% of my two Powerwall system, but I never raise the Reserve above 75%. I just let it do its thing and it usually gets up to about 85% or 90% before it starts discharging for Peak. In February I will probably start generating more than 7kWh/day so I will start dropping the Reserve at that point.

The whole point of this strategy is that my solar generation cannot cover my Peak usage, so keeping the Reserve high forces the system to keep bouncing off the Reserve at a high level instead of a low one while still absorbing all the solar and using it during Peak.

Which TOU plan are you on? IF ev2a, with the huge price increase for peak, I guess you put your main focus with the batteries to use a much from them as possible, during these times, but also balance on how much they can recharge?

 

[miimura]

Which TOU plan are you on? IF ev2a, with the huge price increase for peak, I guess you put your main focus with the batteries to use a much from them as possible, during these times, but also balance on how much they can recharge?

Yes, EV2-A. Every Wh from solar needs to offset Peak usage as much as possible because it's double the price of Off-Peak. I have even considered using a V2H like setup or another battery system charged from Off-Peak to offset the rest of my Peak usage but the payback is too long and I just suck it up and accept that I will add hundreds of dollars to my True-up during each Winter month.

 

[h2ofun]

Yes, EV2-A. Every Wh from solar needs to offset Peak usage as much as possible because it's double the price of Off-Peak. I have even considered using a V2H like setup or another battery system charged from Off-Peak to offset the rest of my Peak usage but the payback is too long and I just suck it up and accept that I will add hundreds of dollars to my True-up during each Winter month.

That is what I thought. I am going to try and stay on tou-c as long as possible, since the difference in cost between non peak and peak is not enough to worry about.

 

[getakey]

I adjust my reserve in the winter depending on the forecast. I typically set it at 65% to 75% with 3 PWs. Below 65% it would not charge to 100%

 

[h2ofun]

I adjust my reserve in the winter depending on the forecast. I typically set it at 65% to 75% with 3 PWs. Below 65% it would not charge to 100%

What is the size of your solar?

 

[getakey]

11.8 kW

 

[h2ofun]

11.8 kW

what is your inverter size? My panels are 14.5Km but the solaredge inverter is 11.4K, so anything over than gets clipped.
I may end up splitting these panels into two inverters into 2 gateways split between 5 batteries. With 2 200 amp panels, a 400 amp service, I cannot put all 5 together

 

[DHevey]

22 kW System
5 Powerwalls
Critical loads include: One Heat pump, Electric hot water heater, Electric ovens, Refridgerator, lights, TV, Cable
Self powered mode set to 25%

The critical loads average about 35 kWh per day this time of year, and at best I can produce about 52 kWh, so I go for weeks before the critical loads see the grid. Last week, we had about six days in a row of rain, cold and cloud cover, and we switched over to the grid on day four. If needed, I can probably go 7/24/365 if I properly manage the loads, but our power is pretty reliable.

 

[getakey]

My inverter is undersized because I added more panels after initial install. Only clips in summer and not all that much. Yesterday I produced ~20 kWh which is about normal for my system on sunny winter days. I had reserve at 75% and panels charged by noon.. Tiday charged by noon as well. If it is going to be sunny, I typically move reserve down to 65% but we were heading into weekend where peak period is shorter

 

[h2ofun]

22 kW System
5 Powerwalls
Critical loads include: One Heat pump, Electric hot water heater, Electric ovens, Refridgerator, lights, TV, Cable
Self powered mode set to 25%

The critical loads average about 35 kWh per day this time of year, and at best I can produce about 52 kWh, so I go for weeks before the critical loads see the grid. Last week, we had about six days in a row of rain, cold and cloud cover, and we switched over to the grid on day four. If needed, I can probably go 7/24/365 if I properly manage the loads, but our power is pretty reliable.

Killer setup!! I will wire so everything is one the 2 GW. Too much work to worry about critical vs non critical loads. I just know if no power I cannot run all 10 of my mini split heat pump heads