Ive had solar for a year and now the utility company charges a demand fee... not cool.

[vwaudiguy]

I've got a 40 Jinko 410w panel with 2 Solaredge SE10000H-US grid tie inverters. I have been pleased with the system so far as it has overproduced for the year as far as KWhs and kept me paying the minimum fee of $31 for 9 months out of the year. Winter my heat pump just eats the power. Starting in April my utility company will start charging me a "Demand" fee based on the highest Kw usage in any given 15 minute period of a billing cycle.. I'm looking for a way to combat that with the system I currently have. My demand ranges from 11.5kw to 21kw. I'm thinking it may be time to add some batteries and attempt to "peak shave" a bit. I even thought about breaking some of my heavy peak, low Kwh appliances off from the main panel into a critical load panel and try to run them completely off grid. Anyone got any tips ? I use an Emporia Vue to track my usage.

 

[hwy17]

Considering the size of your demand, and the goal of the system, I think targeting the high demand appliances specifically might be a good idea. It usually isn't but you have some large ones. What are they and what is their individual peak draw?

Also, what are the demand rates? It may not pay off to do this in any configuration.

Switching the oven to propane might be easier and cheaper.

 

[Warpspeed]

Also, what are the demand rates? It may not pay off to do this in any configuration.

Switching the oven to propane might be easier and cheaper.

You need to be realistic.
Buying 30K+ worth of batteries plus a much more powerful inverter to save a few hundred dollars, may not be a good investment.

 

[seneysolar]

With that kind of power demands, id be looking for a more efficient way to heat. Sizing a pv system with battery storage for heat will be expensive and the ROI may never be realized.

What else is running with the heat pump? You must have some resistive heating strips int the unit?

Instead of battery storage, think heat storage - in the form of propane...

 

[hwy17]

id be looking for a more efficient way to heat

I'm gonna guess OP is already on heat pumps, and it's a 5000 sq ft house.

 

[Warpspeed]

And I bet its open plan too, with a massive living area and lots of glass.

 

[zanydroid]

You need to be realistic.
Buying 30K+ worth of batteries plus a much more powerful inverter to save a few hundred dollars, may not be a good investment.

This budget is not accurate.

You can get a grid compliant inverter for $7-10k pre tax credit, equipment only. 12kW AC.

I am shocked by the 21kW peak load though. OP deserves a demand charge for bursting that high…

With that kind of power demands, id be looking for a more efficient way to heat

And buffering demand charges does not require a large system. It is more a matter of programming.

 

[OzSolar]

I'm looking for a way to combat that with the system I currently have. My demand ranges from 11.5kw to 21kw. I'm thinking it may be time to add some batteries and attempt to "peak shave" a bit.

Typical heat pumps have ~10kW of strips. Sound like you've got two heat pumps.

You could interlock them them so only one runs at a time. Alternate 30 mins on one then 30 on the other but there will still come a day where it doesn't get above 0 for for more than a few hours and your house will lose ground. It won't freeze by any means but the natives will likely get restless if the house in the upper 50's.

What utility are you on? CU?

 

[Warpspeed]

It depends on the duty cycle of the 21Kw heat pump.
If it only comes on for a few minutes every hour, true, you don't need much battery to support that, just a 21Kw+ inverter.

If it runs for fifty minutes each hour fifteen hours a day, buffering is not going to work, no matter how large the battery.

 

[seneysolar]

Heat pumps are ok in mild weather but not full on winter. My folks have one here in Michigan, it has to supplement heat with multiple 1500w electric heating elements inside the ductwork. Fighting a loosing battle in temps below 32. Waste of electricity in my book.

Electricity gets really expensive when you store it in a battery

 

[zanydroid]

This budget is not accurate.

You can get a grid compliant inverter for $7-10k pre tax credit, equipment only. 12kW AC.

I am shocked by the 21kW peak load though. OP deserves a demand charge for bursting that high…

And buffering demand charges does not require a large system. It is more a matter of programming.

Ok, these answers I gave were from small house, Northern California heat loads perspective.

Theoretically speaking, 11-22kW demand can be smoothed to whatever the daily consumption kWh/24 ends up being. And a 6000XP or 18kpv has the capacity to split the difference to 17kW. Hopefully that 5kW drop in demand charge helps

Can’t go beyond that in winter without adding an impractical amount of solar. Though if you have a lot of land and high demand charge, you might be able to pull it off during the day. 180-240kWh of batteries corresponding to 11kW demand is not practical for overnight offset, I can’t imagine any grid electricity that can justify that

So starting off with analyzing the theoretical maximum change in demand charges with existing appliances will be a very high value initial analysis. Could just instantly smoke some of the cost savings concepts before wasting time analyzing it further

 

[vwaudiguy]

With that kind of power demands, id be looking for a more efficient way to heat. Sizing a pv system with battery storage for heat will be expensive and the ROI may never be realized.

What else is running with the heat pump? You must have some resistive heating strips int the unit?

Instead of battery storage, think heat storage - in the form of propane...

I had never even thought about what my demand was until I got a notice from the utility company..lol.. my house is a 3200 square foot ranch with a walkout basement.. yes my Auxiliary heat when it gets too cold is 15kw of heating strips.. they have ran for only 2 days this winter so far but that was enough. I do have an electric car which I used to charge at 32 amp but now charge at 16 to help keep my demand down.. the demand rate is $3.75 per Kw so not terrible but it will turn my 9 months of $31 each into about $100 each from what I can calculate. I have a heat pump water heater that has a higher demand than my old non heat pump but it uses way fewer Kwhs for sure.

 

[hwy17]

Turn off aux heat and set the HPWH to heat pump only mode would go a long way here. You could get a williams direct vent wall furnace to use instead of the aux.

 

[vwaudiguy]

Typical heat pumps have ~10kW of strips. Sound like you've got two heat pumps.

You could interlock them them so only one runs at a time. Alternate 30 mins on one then 30 on the other but there will still come a day where it doesn't get above 0 for for more than a few hours and your house will lose ground. It won't freeze by any means but the natives will likely get restless if the house in the upper 50's.

What utility are you on? CU?

Just one 5 ton heat pump that is showing its age... I would really like to go with a ground source heat pump next..

I live in a rural area so I have an electrical cooperative.

 

[vwaudiguy]

Turn off aux heat and set the HPWH to heat pump only mode would go a long way here. You could get a williams direct vent wall furnace to use instead of the aux.

It is on heat pump only but we got down to -5*F for a couple days and the heat pump said nope..lol..

 

[zanydroid]

It would be very helpful to see your hourly graph for daily total consumption.

Way too much guessing and trying to convert from prose to graphs

 

[1201]

@vwaudiguy It seems like a hybrid with peak shave function could help out a lot. Something like an 18k pv.

From what I've learned recently you could just add it in parallel with your existing system (breaker into main panel) and then it should charge the batteries when there is excess pv- it'll sense the system exporting to grid and start charging the batteries. And it will discharge the batteries to provide up to 12kw demand reduction during those times of high peaks.

An 18kpv $5200, 28kwh of DIY batteries at around $4500, should go a long way to reducing your own demand. If you try to use your high loads while solar is producing, that will reduce peak demand as well.

Use two 18k pvs and you could theoretically reduce peak demand to near zero. How much is the demand charge?

Doing it this way instead of moving the large loads to a backup panel means you don't have to worry about surge loads or overloading the system

 

[vwaudiguy]

It would be very helpful to see your hourly graph for daily total consumption.

Way too much guessing and trying to convert from prose

Here is today and part of yesterday from emporia.. I didn't drive the electric car today so 3.8kw didn't get added in for today.

 

[zanydroid]

Hmm thanks.

That actually looks really promising for shaving it back with a storage inverter like 18kpv that has peak shaving capability (annoyingly not all do. I don’t think powerwall has that natively).

I assume all the 11-22 kW peaks are hiding out in there somewhere?

Looks like 30kWh/day so far in February?

 

[zanydroid]

An 18kpv $5200, 28kwh of DIY batteries at around $4500, should go a long way to reducing your own demand. If you try to use your high loads while solar is producing, that will reduce peak demand as well.

Note the DIY batteries may not be a good risk to take if the POCO starts policing for unsanctioned grid tie batteries. They would be detectable if run in parallel. If they only run an off grid panel then it is a lot harder (but they also may need custom programming to peak shave).

You could do one non-DIY battery and get it approved, as such, and add DIY after. Then it gets at least 10x harder for them to detect.

I’m not convinced 30 kWh is needed but having a 2x buffer on inverter size and storage size, relative to the amount of shaving to be done, is probably a healthy margin given that we don’t know how effective the programming on the peak shaving inverter is.