Off grid system to run HVAC only, doable?

[hertfordnc]

I checked out the HotSpot 4812 48 volt direct current variable speed compressor Air condition unit.
It looks like the heat pump I'm installing. I'm kinda thinking the inverter heat pumps are using DC to run the motor at variable speeds and that the HotSpot is doing that without the AC conversion - just a hunch

[hertfordnc]

> with a grid tied Air conditioning system you will pay around 1 dollar per Ton hour of cooling capacity, with an off grid system 1 Ton will cost 4 to 10 dollars

Huh? Sounds like you're saying solar never pays for itself? When you say $1/ton what is that based on?

A typical central AC unit (non heat pump) is SEER 10-12. The ductless system I'm installing is SEER 22

The load is 15 amps (3000 watts) peak and 600 watts average.

> Most people forget that the humidity and heat can get high even if the sun isn't shining.

I live at latitude 30 on the coast, I think understand humidity pretty well. (didn't mean to sound snarky)

So the first question is, how much battery do I need to deliver 600 watts for 24 hours and how much solar do I need to replenish that battery on a clear day in summer?

I understand it may be a ridiculous number but that is the starting point for figuring out what problems need to be solved.

I'm thinking that if it works on a hot clear sunny day it will work on days when there is less sun and less heat (they do go together somewhat)

[SunEagle]

Most people forget that the humidity and heat can get high even if the sun isn't shining. The best way to cool off when it is really humid is to use an AC system.

Relying on the sun to run an AC system will leave you hot and sweaty.

[ButchDeal]

Thanks. But I still want to understand what it would take for this vision to work, even if the answer is stupidly expensive and unrealistic.

By building the system around Air Conditioning only, then my demand would tend to align with the available sunlight, right?

no the demand will align with A/C usage, till it over runs the available light/battery and your system turns off, or starts the generator.

[Logan5]

with a grid tied Air conditioning system you will pay around 1 dollar per Ton hour of cooling capacity, with an off grid system 1 Ton will cost 4 to 10 dollars forever. with grid tie there is even a chance that price will go down when new electric rates are implemented, Off grid price is more likely to go up with the cost of lead and labor. If you are serious about Air conditioning with solar battery power, Look at the HotSpot 4812 48 volt direct current variable speed compressor Air condition unit.. It is designed to run off grid on much less power than a 220 volt native AC that requires an inverter.

[hertfordnc]

Thanks. But I still want to understand what it would take for this vision to work, even if the answer is stupidly expensive and unrealistic.

By building the system around Air Conditioning only, then my demand would tend to align with the available sunlight, right?

[ButchDeal]

First, you don't have 10 hours of good sun in a day in NC.
With Off grid you have to plan for peaks in consumption and valleys in generation.
Your batteries would need to be able to handle the difference.
The best option would be to use a bimodal system such as those from outback. Yes I know you said you didn't want to be grid tied but you can configure the outback systems to NOT feed into the grid. It would just pull extra power from the grid when needed. This would allow you to size the system more reasonably. You could cover both A/C units but during an outage turn one off.
This would be the closest to a system that might save you money. A truly off grid system would not save any money.

[hertfordnc]

I live in North Carolina. We turn on the AC in April and we might still be running it on Thanksgiving Day.

I'm renovating a small house and installing two minisplit heat pumps (five or six zones)

I want to power one of the heat pumps with solar- off grid.

So here's the math as I understand it;

The heat pump draws about 15 amps at 220VAC at full power. Most of the time it will not be drawing that much and I am thinking the 24 hour average will be closer to 3 amps

I'm thinking a refurbished forklift battery for about $1200 and a 24V / 220VAC inverter.

This is the only system I'm interested in. Air conditioning is the one thing that is really hard to reduce the cost on. you can hang your clothes to dry, install LED lights, and heat your house with wood but if you live in the South you will have air conditioning.

I do not trust my state utility commission down the road to not change the rules or add fees so I have no interest in any sort of grid tie system

I'm having trouble with the math. Starting with what solar output actually means? The system I describe above would consume about 15KW / day so in my small brain, 1500 watts of solar times 10 hours of good sun should do the trick, right?

But when I ask solar vendors about that I get different answers.


The vision could be adjusted to accommodate reality. I could just run a small heat pump and only cover one room The main idea is to have a portion of the HAVAC on a stand-alone renewable system,

Look forward to feedback


thanks

dave