How to power a load of 25kwh off battery only?

[Patel]

Hi everyone,
I am new here. I have a few questions maybe someone can help me answer.

My peak loads which I want to be able to run are 20-25kw, and average loads around 5kw, We recently turned on the heater, and we learned that when the house is very cold, and the heater turns on for the first time. It consumes a peak kwh of 15.9. We want to factor in other things too, so let's say we want to have a peak load of 25kw.

The equipment I currently have, but not set up yet:

Sol-Ark 15k Hybrid Inverter
(2) 15kwh bigbattery kong elite

My question is, the bigbattery have a continuous discharge rate of 175 amps, at 48v that means it can run loads up to 8400 watts.

We want the entire home to run from solar + battery only.

If we run the bigbattery in parallel, would this increase the continuous discharge rate to 16800 watts?

I would be very grateful for someone to give me some tips here or any comments. I have attached a energy usage from the grid which we are currently using now. The spike was from the heater turning on for the first time when the home was 40 degrees.

If anyone here offers consulting services to do a materials list of what I need, I would like to do that.

 

[BentleyJ]

Not sure where the 25kW peak load comes from, the screen shot doesn't show any where near that amount of continuous usage. Perhaps that value is calculated based on the rating plates from various appliances? In any case, with a single 15K inverter its not possible to supply that much power so you either have to practice load control either manual or automatic or install a second inverter.

The heater, is it a heat pump with an auxiliary electric heat element? An easy way to reduce compressor start up surge is by installing a soft starter.

Sol-Ark 15K can supply a maximum of 12kW continuous from battery alone so the maximum current draw (including 10% for inefficiency) would be approx. 275A. With 2 Big Batteries connected in parallel they will carry the load since its only 137.5A for each one which is below the specification stated above.

Without a more detailed accounting of the loads you wish to operate, its difficult to give additional comments.

 

[Supervstech]

Your title states 25kWh, your post states a demand from 5 to 25kW… two very distinctly different figures.

Please give examples of what instant draw demands are, and what duration the demands operate for.
Or better yet, post power company calculated usage reports.

Because to get 25kWh from a battery only needs a battery with over 25kWh of storage…

But to get a battery to power a daily average of 5 to 25 kW demand could take anywhere from 145kWh (5kW x 24hours plus 25kW) and up…

 

[Patel]

@BentleyJ and @Supervstech Thank you both for the responses.

To clarify,
This is a new manufactured home and we are currently testing grid usage prior to finishing the purchases for the build.

When the heater started, when the house was very cold, the heater was using maximum of 15.9 kwh. After the home got to the desired temperature, it was averaging about 4kwh.
Granted, there are no additional appliances currently running besides the refrigerator. So the way I calculated peak usage was estimating how much a water heater, stove, well water pump, and a computer running 24/7 would use. I anticipate if these are running simultaneously, the peak load should be about 20-25kw. Considering just the 3-ton heater was pulling 15.9kw in a hour to warm up a cold house. We don't have water yet, so I can't turn on the water heater to determine how much power it will pull.

I've attached another screenshot when the room was heated to 60 degrees, and continuously running. We were pulling about 2-3kw of power. So on average, I think the typical load would be around 5-6kw because there will be some additional appliances and computers which we intend to run on the farm.

Right now, i'm leaning towards running 2 solark 15k inverters, to power everything at peak loads. Because just running that AC in heat mode was pulling more than 1 solark 15k could handle. Even though the average continuous load would probably be less than 12kw.

But I am unable to determine if the batteries would be able to power this type of load. I'm curious if you have any suggestions.

Very much a newbie here, and trying to figure this stuff out, so any tips or advice is very much appreciated.

 

[BentleyJ]

If I'm understanding this correctly each bar on the chart represents an hour so 15.9kWh translates to an average draw of 15.9kW over that time period. Seems like the 3 ton heat pump has a 10 or 11kW aux electric heating element. Then add in the stove/oven, well pump and water heater that's a lot of power. Realistically even with 2 Sol-Arks practicing some kind of load control is going to be required. Its is also very highly recommended to add soft starters to the heat pump compressor and well pump or use a VFD well pump if possible.

Battery capacity is going to be the weak spot in the system. At the very least you will need 2 more batteries for a total of 30kWh of storage. Even with 30kWh that's only a little over an hour run time if you were operating the heat pump and water heater simultaneously starting at 40 degrees.

 

[Patel]

Definitely taking your advice on the soft starters. Thanks

Right now, I have 2 15kwh bigbattery kong elites. I plan on buying 2 more.

On the batteries, I plan on getting the BigBattery Parallel Box to parralel all 4 batteries together.

For these batteries, the continuous discharge rate is 175 amps. If we run 4 in parallel, and using the BB350 connector from the parallel box, theoretically, the max load that batteries can supply is 350amps x 48v = 16.8kw?

 

[BentleyJ]

With proper sized wiring and bus bars the batteries can supply 350A continuous which translates to 45min before they are depleted to 90% DoD.

 

[Warpspeed]

Yes indeed.
Maximum discharge rate is just that, no battery can sustain the maximum discharge for very long.
Also you need to consider there may be several days in a row with little or negligible solar to charge with.
And lastly, if you are going to flog the batteries really hard, their useful life will be very short....

 

[missingegg]

Definitely taking your advice on the soft starters. Thanks

Right now, I have 2 15kwh bigbattery kong elites. I plan on buying 2 more.

On the batteries, I plan on getting the BigBattery Parallel Box to parralel all 4 batteries together.

For these batteries, the continuous discharge rate is 175 amps. If we run 4 in parallel, and using the BB350 connector from the parallel box, theoretically, the max load that batteries can supply is 350amps x 48v = 16.8kw?

Looking at the specs on the Bigbattery site, the kong elite can be run with up to 8 in parallel. It's a little unclear from your comments so far what the peak draw is that you expect, as the kwh numbers you're mentioning are power consumed over time, and not power draw at a given moment. But I agree with other comments that it's a bad idea to plan to make normal use of the peak current, as the battery is only rated to deliver that for 6 seconds. At total of 4 kong elites in parallel are rated for continuous delivery of 30 kw, which would meet your needs. But as others have said, not for very long. I'd suggest you probably need the maximum config of 8 batteries in parallel if you really have that amount of energy demand.

I'd suggest two things:

1) Either buy or borrow a clamp-on current meter, and measure the instantaneous power draw at peak times, to evaluate what your actual needs are. You may also be able to pay an electrician to come and make these measurements. Also go find the name plates of the major appliances drawing power, and see what they're rated to draw.
2) 25 kw peak load is more power than many houses are provisioned with, even when tied into the grid. It's not out of the realm of possibility that you actually need that much power. But it's very surprising that a heater was drawing ~16 kw for an hour. If the heater in the house is actually that inefficient, I'd consider looking into replacing it with an efficient heat pump, as that may be more economical than scaling up your solar and battery to support such a high load. I note that the first picture you attached has a graph scale that implied the peak draw was a bit under 9 kwh across the 12 o'clock hour, and I'm unsure how to reconcile the graph with the label text that says 15.9 kwh. Unless that's a cumulative number for the day so far, which would seem to match the 11 am and 12 pm bars being added together?

 

[Quattrohead]

A pair of those inverters plus 6 of the batteries sound like they may run your house, I would start with that.
No mention of solar panels....going to need at least 10kw worth I would say.
Emergency heat strips in a heat pump are going to kill you, disconnect them.

 

[brandnewb]

When the heater started, when the house was very cold, the heater was using maximum of 15.9 kwh. After the home got to the desired temperature, it was averaging about 4kwh.

My 2 cents;

1) you are one cool dude. I am in awe
2) you seem to benefit from more thought on the insulation levels of your yet ot be purchaced house.

For example I have a heatpump that draws 1.3KW when it is in full operation heating 412m2 of a free standing house.

Anything more would suggest a loss of some kind

 

[Doggydogworld]

@BentleyJ and @Supervstech
This is a new manufactured home and we are currently testing grid usage prior to finishing the purchases for the build.

It's very smart to test before spending more.

We want the entire home to run from solar + battery only.

May I ask why? Is this a prepper farm? Purely an attempt to save money (or protect against inflation)? Would you consider grid backup or do you want to give your local utility the middle finger no matter how much it costs? Are you willing to slash consumption 80-90% during long cloudy stretches? How about 50%, or 20%?

The answers will drive your buying decisions. A solution that lets you consume normally during long, cloudy cold spells can cost 10-20x as much as a system that provides 95-98% of your electricity but relies on grid or generator backup.

When the heater started, when the house was very cold, the heater was using maximum of 15.9 kwh. After the home got to the desired temperature, it was averaging about 4kwh.

It helps to keep kW and kWh separate. Both are important. Residential users typically pay by the kWh, but commercial customers usually pay one amount per kWh plus an additional amount for peak kW. It costs a lot more to service a customer who draws 720 kW for one hour each month and 0 kW the other 719 hours than to service one who uses a steady 1 kW for all 720 hours, even though both use 720 kWh for the month.

Your system must handle both peak power (kW) and total consumption (kWh).

Your heater averaged 15.9 kW of power for one hour. But peak kW may have been much higher. Aircon/heat pumps, refrigerators, well pumps, pool pumps, etc. are notorious for needing 2-5x as much power to start their motors as to keep them turning. Did your heat pump draw 50 kW for ten seconds during startup? I doubt it, but you can't tell from hour-by-hour data.

There are ways to deal with startup surges. Trial and error can get expensive.

So the way I calculated peak usage was estimating how much a water heater, stove, well water pump, and a computer running 24/7 would use. I anticipate if these are running simultaneously, the peak load should be about 20-25kw. Considering just the 3-ton heater was pulling 15.9kw in a hour to warm up a cold house.

That's OK for a rough guess, but you really need to measure those startup surge for devices with large motors.

FWIW, I agree with those who say your heat pump probably used heat strips while warming the cold house. Those are real power-suckers. Turn them off and it will take a lot longer to heat the house from 40F to 60+. That's probably not a big deal. But systems also use heat strips to maintain temperature when it's very cold outside. If you need continuous 10 kW heat strip power to maintain temperature during a week-long cold, cloudy stretch that's 10 kW * 168 hours = 1680 kWh. Plus another few hundred kWh for the heat pump compressor, plus your well pump and other household loads. Maybe buy a 3000 kWh Tesla Megapack for $1++ million:



Or use grid power during exceptional weather events. Or buy a generator. Or use a gas/propane/etc. furnace. Or a wood-burning stove (start chopping). Or go to a motel for a week. Lots of options! Just do the math ahead of time so you don't get caught unprepared.