Getting hot outside - system sizing question

[WorldwideDave]

I want to add air conditioning to my house. I want it to run off solar. It can be a dc to dc or an AC powered unit. It can be a heat pump or other inverter as well - most efficient, but I'm flexible on efficiency vs price. Example: Mini-splits can be bought for $500, or they can cost $2300 depending on brand, etc. I'm more on the budget side, I'm letting you know that now.

Assuming I run the a/c unit let's say for 10 hours a day, and I know it is going to cycle, and it must be a 120V unit because I can't do 240V, and the house is in southern california, I need to know the following:

Battery size - how many kWh or amp hours does the battery or battery bank need to be if there was NO sun for just one day?

Example: I have a 200 amp hour battery rated at 2560 Watt Hours (I think). THat's roughly 12v times 200 amps = 2400 watt hours, but voltage is typically higher when at full charge.

I believe that most mini-split, portable, or window-mount 120V a/c units use 13 amps or so and have a surge to start. Therefore, I am also looking for the right inverter size for such a setup.

Once I know that, I'll want to know panels needed and a recommended solar charge controller.

But until then, any or help or guidance on battery sizing would be great.

I thank you in advance for your responses.

 

[BentleyJ]

First thing is to size the A/C, then take the electrical specs from the name plate and design a suitable off-grid system based on run hours per day and extra battery capacity for poor solar days due to clouds and rain, if that's applicable to your climate zone.

Note: 12V was mentioned, realistically you should be looking at a 48V inverter and batteries for a high consumption appliance like A/C.

 

[Mattb4]

Arcon load is going to be a harder thing to figure because it will depend a lot on temperature, size of space to be conditioned and also the insulation of the space. For instance I just put in a couple of higher efficient window type (mounted through wall) 8000btu LG units. They are rated at 660w (660/120=5.5a). If they were running continuously that would mean that I would need to supply them that 660w all the time. Now take a 12vDC nom. battery. without loss it would need to supply 55 amps for that 660w. In real world that is likely to be 60 amps. So for every hour you want to run a LG unit like mine it would require 60ah from your battery. That is why run time as the Arcon cycles on and off would determine your real loading needs.

Your inverter must be sized to not only run the Arcon but it must start it. Depending on the Aircon that can be 2-5 times running wattage. So for my LG that would be perhaps as much as 20 amps at 120vAc or 2400w.

As BentleyJ mentioned a battery with higher voltage such as 24-48vDC will make it more practical.

 

[wpns]

Depends if you need/want the solar power for anything else, and what your other loads are. Batteries get expensive, and if _all_ you want solar for is HVAC, then look at the EG4 mini-splits, which will run on solar or grid power. [https://signaturesolar.com/eg4-9k-m...29-5-plug-n-cool-do-it-yourself-installation/ runs on 120V, the others are 240.]

A couple of random thoughts:

You definitely want inverter-style HVAC units, there are a lot of mini-splits with high SEER, though you'll have to do your own cost/benefit calculation. They also don't have a start-up surge.
You don't need as much cooling on days when the sun doesn't shine, so this may balance out your need for batteries.
Running on solar power during the day and grid power at night will save you a lot of money over buying batteries.
Grid-powered AC Splits are a _lot_ less expensive than the EG4 solar-powered ones.
See Will's videos for solar powered AC and mini-split installation, you can save a ton of money by buying the vacuum pump and gauge set over units with precharged linesets.
Personally I don't care for the solar-powered splits, I'd rather put the solar panels into my ESS and use the power for all my loads, but that's me, and I have batteries and many other loads and such.

My Mitsubishi splits run about 200 watts when idling (I use the dry function, as it's much more comfortable than trying to make things cool), but that's me in my environment with my small rooms in a concrete house. IF you have the same situation (Narrator: "He does not."] then you need 200*24 = 4.8 KWHR of battery per unit to run 24 hours, plus efficiency losses and margin, etc.

What does your power cost per KWHR?

 

[chrisski]

IMO, there's no easy way to get an answer to that question. Too many variables with air conditioning with the SEER rating and insulation.

Best is to ask a neighbor with Air Conditioning to see how much more power they pulled. Not cost, but extra kWh. Look at the SEER of their system, the size of there system, the size air conditioned, and compare that to the size of your area.

I made it so I could run a single 15 k BTU on my fifth wheel RV off solar. Basically had to fill the roof up, and put about as many panels on the ground to get the power. Perhaps 200 sq feet had A/C and once the AC turned on, it was on the whole time, non-stop. Above 90, it could not keep up. An RV has poor insulation and an insulated house would do much better.

The energy it took me was 1650 watts from the battery to power the 1470 watt air conditioner. That would be a 40 kWh battery bank. A Tesla powerwall was around 13 kWh of battery power. You would need just over three, so four of those to power a single 15 k BTU unit for 24 hours.

Using a mini-split on your house would be more efficient, but the hot AZ climate where I am would still pull around 20 kWh. After you build a battery bank and install everything you need for inverter etc, you will have ended up being able to pay for electricity for the air conditoner for several years.

 

[Q-Dog]

You may be a candidate for a solar air conditioner like the EG4 or the AirSpool or the Hot Spot energy unit. Plug enoughsolar panels directly into the unit and it will run as long as the sun is out. No inverter or batteries needed. There is also an AC connection so you can plug it into the grid to run it when there is no sun if you want to.

 

[SparkyJJO]

Another vote for the EG4 hybrid aircon. Just seems like it would fit in much better, no battery to mess with for this, uses grid only when solar isn't enough, and grid power is bound to be cheaper than buying batteries.

 

[WorldwideDave]

Just read the manual for the EG4. Very nicely written:

https://eg4electronics.com/backend/wp-content/uploads/2023/09/EG4-AC-DC-Plug-N-Cool-Solar-AC-Manual-12K-24K.pdf

it is for the hybrid model, which is at:

EG4 Hybrid Solar Mini-Split Air Conditioner Heat Pump AC/DC | 12000 BTU | SEER2 22 | Plug-N-Cool Do-It-Yourself Installation

Signature Solar provides solar panels, off-grid solar systems, grid-tie, and hybrid systems. Quality solar inverters, bifacial solar panels, complete solar kits, solar batteries. Featuring brands such as EG4 Electronics with their solar battery, LifePower4 and EG4 LLifePower4 and EG4 LL

signaturesolar.com

however it is 1300 USD plus shipping.
I also read the reviews - sounds like some have had to call out an A/C tech to test and charge the lines anyways at $250 USD or so.
Seems like a good unit, however, I see this as a $500 unit with a $200 inverter and some other magic built in?
I would need to also buy a solar cutoff switch (need to anyway) and it looks like a lot more panels (which I expected).
That being said, I also think that getting a bigger battery, my own inverter, panels that can be used for anything not just this device and a cheaper $500 unit that I then connect to my own inverter + batteries may be a better investment, even with having to pay an HVAC guy $250 to charge the lineset and get it all dialed in.
Just not sure.

As for the questions above about my insulation...it is a house built in the 1940s. Their is a garage below the living spaces. The roof in the garage are not insulated, so neither is my floor above it. The roof is basically tounge-and-groove wood with tar paper above it and the large sheets of shingles. No 2x4s with insulation in them. Very innefficient, like the RV reference above. Size is about 550 sq ft - not 100% certain. The side facing the sun (south) is much hotter than the bedroom and bathroom on the north. There is also a lot more windows on the east side (early sun) and the south side (sun most of the day). I have shades, tinted glass, argon filled windows, and blackout shades for days like yesterday when it hit 80 outside. Inside it got to about 88 degrees. I do not like when it is hotter inside than outside in the summer. Winter I'm okay with that.
So I need to move air and blast A/C to try to keep it cooler.
I could spend 2,000 insulating the roof (or more) but then would need to add drywall, recessed lighting and more which I cannot do for a variety of reasons.
I can add a window AC, a portable AC or a mini-split, that I would mount to a piece of wood in an open windowsill and run the lineset outside onto the deck where there is an A/C outlet already, and could put an extension cord on and connect to the ac unit. Dedicated 20 amp circuit FYI with own breaker.

Adding a second battery to make it 24 volt is on my radar, but not in budget yet. Wanted to see how far I could get with what I have, and plan next purchases.

Electricity is stupid expensive. It is .78 in the summer from 4 PM - 9 PM.

 

[Mattb4]

Yeah that is a high electrical rate. I would suggest painting your walls that face the sun a reflective white. If you ever redo the roof it also should be a light color. Your window shades should reflect sun because dark colors will get them pretty hot inside. Good ventilation that allows you to exhaust heat overnight should help some.

 

[chrisski]

That being said, I also think that getting a bigger battery, my own inverter, panels that can be used for anything not just this device and a cheaper $500 unit that I then connect to my own inverter + batteries may be a better investment, even with having to pay an HVAC guy $250 to charge the lineset and get it all dialed in.

I have thought about the EG4 air conditioner, but not willing to be the first on my block to try it.

Waiting to see reviews about how well it holds up in DC only mode, especially at the point where it barely has enough power to run and can cycle on and off frequently, like clouds passing over or morning and evening. If I did get this, I would still want an AC and battery unit to prevent tis cycling on and off

 

[WorldwideDave]

Seems like the product has been out for a while. What I can tell you is that I have 8 mini-splits (none like this) in various properties that cost around $600 USD each. I can't say that they have been trouble-free on A/C grid electricity. But when they work they work good.

 

[robby]

I have thought about the EG4 air conditioner, but not willing to be the first on my block to try it.

Waiting to see reviews about how well it holds up in DC only mode, especially at the point where it barely has enough power to run and can cycle on and off frequently, like clouds passing over or morning and evening. If I did get this, I would still want an AC and battery unit to prevent tis cycling on and off

I don't know about the EG4 but I have seen the high end Deye units running and they basically balance the power from the Grid with that of the PV. If the PV drops due to a cloud it pulls any extra energy from the Grid. My installer buddy said something about it also having a mode where it will throttle down the compressor to match the PV if the PV drops. Instead of using the Grid.

He has installed dozens of these AC systems and I asked him what he thought and his flat out opinion was that they are great for small offices or stores that operate 9am-5pm but for home installations he advice's just putting in a All in One Inverter system that can be upgraded over time with more PV and Batteries to run a whole home. He uses Pioneer AC units but has now started to see his customers buying these even cheaper Glacer 12K BTU ($510 Amazon) and DELLA ($650). It seems like Amazon has been stocking up on low priced AC systems for this Summer. I have seen the Della and it's not a bad unit, it cools well and uses less power than my Panasonic.
The Solar side of me likes the fact the Della can be controlled over the Internet. It fits in nicely as a dump load option.

 

[WorldwideDave]

what is a 'dump load option' - meaning that you have a lot of solar coming in, not enough battery to store, so dump load by running the A/C so the solar charge controller doesn't overheat/catch fire or something? Thanks. Beginners corner Dave

 

[1201]

@WorldwideDave
Are the walls of your garage insulated? I'm not understanding the need to insulate the ceiling if there is living space above it.

Are you able to get a grid tie agreement?

 

[wpns]

what is a 'dump load option' - meaning that you have a lot of solar coming in, not enough battery to store, so dump load by running the A/C so the solar charge controller doesn't overheat/catch fire or something? Thanks. Beginners corner Dave

Yes, except nothing will catch fire if you don't 'dump' your excess power, the solar input will just be scaled back and you'll 'waste' the potential energy.

 

[WorldwideDave]

@WorldwideDave
Are the walls of your garage insulated? I'm not understanding the need to insulate the ceiling if there is living space above it.

Are you able to get a grid tie agreement?

No