Thread: running an AC unit on solar only

Bob,

We do not have panels yet, nor an AC unit.

Probably not obvious from my question.
Any clearer?

It is possible. I have a friend, loose term as I have known him for about 25 years. He has a rural block and runs one off of his ex Telstra batteries via an inverter. Recently he switched to an inverter air conditioner and can (I believe) run the newer air conditioner for much longer.

I also know some caravanners running small inverter units using only their solar on the roof of their caravan and two lithium batteries, which would be approximately 3,000W capacity. I know one of them has 700W on the roof of their caravan and they run their similar small house inverter type air conditioner in very sunny weather all day. Unfortunately one is currently in Western Australia; I don't know where the other one is.

Essentially I believe you would need to have some kind of storage system to smooth out the power; think clouds swiftly changing your solar input.

Mick.

Originally Posted by Optimark

Essentially I believe you would need to have some kind of storage system to smooth out the power; think clouds swiftly changing your solar input.

It depends on where you are but also there are those evenings / nights where it stays hot well after the sun goes down.

My experience after experimenting and monitoring solar production and house consumption. As always it depends, our system is a 7.5kw solar array, and our splits will not keep the temp low enough but using only them we still export to the grid. I monitor ours real time and can see it going up and down immediately as it happens on the computer. We have had a very hot day and turned on our ducted system because the splits wouldn't handle it and we bought a lot of electricity today. It depends on a few things

Thermal load on the house, is it in a valley or on a windy hill for instance.

How well the house is insulated especially the windows

What temperature is desired in the house, me I want to be to hold 21 degrees at 45 outside


If the solar system is big enough no problems, it will power any AC system but one thing a solar array won't do is power the AC when there is no sun and battery technology for solar is only just starting and has massive limitations on current delivery.

Here is a screen shot of our power use today up until 7pm

Edit, our ducted is 415V non inverter, you most probably can't even buy one today because they chew so much electricity.

Solar.png

The bits of green are exported energy to the grid. The black peaks are house consumption that we paid for from the grid. I think the first step is to work out how big the AC system needs to be for your requirements. If an AC installer told me it would not hold 21 degrees inside at 45 outside I would not buy. This is going to be a sizeable investment so it had better perform. The installer will waffle on about all sorts of stuff trying to dodge that one specific question as it is something they do not like being asked.

Just watching this
As would also be interested in solar AC

Cheers Matt

Thanks everybody.
I will come back with some more details, our wishes and current outdoor temperatures we want to "fight".

Yesterday, at the warmest, the temperature outside was well over 30C. Inside, in our warmest room, living area and kitchen included, it got up to 27C (wife was cooking). It was quite cooler in the bedrooms (no figures available), and there was no problem sleeping. This is with "special" blinds on in the living room. We leave all windows open during the night, close them all in the morning and lower the blinds. Temperature in that room, the morning of that day was a bit over 20C. 27C is quite warm but bearable for a few days a year.
My wish is to have a cooling system that would keep the temperature down during the day (when the solar system would work if not obstructed), having the sleeping quarters cool enough to sleep comfortably. 23C would be good enough. No need to have it running during the nights. At least, not at the moment, nights are cool enough.
Before moving to Woodend, we spent 3 years in North Melbourne. Summertime, it got really hot, in the bedroom and in the whole apartment. The split units helped but I hate them, too noisy and blowing cold air right in your face. Rant: Why double glazing has not been standard in Australia for many years is a mystery (we are from Europe).

Originally Posted by kungsleden

Rant: Why double glazing has not been standard in Australia for many years is a mystery (we are from Europe).

the answer is simple.

For almost all of Australia, it never gets cold enough for double glazing to make a difference. And besides, Australian houses are typically designed to "breathe" and to utilise cross flow vetillation which requires the windows to be open.

Residential air con is something that has only become a "thing" in the past 20 or so years.

Originally Posted by kungsleden

OK, did not search the forum very hard for an answer to my question.

We are wondering whether it is possible to run an AC unit directly from a solar panel system without connecting to the grid.
We are not interested in full on solar system at the moment, but running an AC system off grid during the summer would be nice.

from what I understand about electricity generation this is not doable.

some very rough considerations,
If you have three 10A plug-in split systems -- one for the living area, one in each of two bedrooms -- you need to plan on these running simultaneously, unless you want to get into some fancy load sharing electronics.
On really hot days you would likely want the air con units running through till at least 9 PM, and possibly later.
This is starting to look like a 7.5 kW household solar system with 30 to 50 kWh of battery backup.
Restricting yourself to two plug-in units is not going to change those numbers enough so they don't look like a regular household solar system.

Another consideration is that if your solar system is not grid connected, the air con units would need to be wired completely independently of the grid -- i.e. no way of turning the units on using grid power. I don't know about Victoria, but locally (Canada) the electricity providers have some fancy ways of frying solar (or generator) systems that are not properly isolated from the grid.

Lastly, if the sun is shining and your solar system is generating, the power has to go somewhere -- either as electrical load or heat.

Can you elaborate why you are not keen on a grid connected solar system?

I would suspect that you are going to require a decent sized system if you are planning to run the ac directly. The size of the unit, and cost, is going to be about the same as a standard grid connected system - if not more. If you just go grid then you can benefit at all times from your solar as you will be using your power while the ac is off.

I was looking at a pool pump that had a dedicated solar panel, and the idea was when there was enough power being generated the pump would run. Given the cost and the issues it was better and cheaper to do full house solar - perhaps similar to your ac.

The main reason we are not interested in a full solar system at the moment is that we are not home when the sun is out, except week-ends, and no more kid at home. So until the batteries get better and cheaper, we will not go solar. We do not use that much electricity, and we would prefer an off-grid system.

You are still going to need either a battery or a huge number of panels for running the ac directly anyway - especially if you are not home during the day as you will be trying to run the ac outside the peak generation time (5-6pm).

Have you worked out the power draw requirements of the ac unit(s) that you are planning to run? You can then work out how many panels you would need and then factor in the reduced efficiency of running late in the afternoon as you will not be achieving the full system generation.

If you have a system and you are not at home during the day the trick is to try and move things to utilise your generation. Things like delayed starting the dishwasher and washing machine to the middle of the day, charging things during the day. It also helps offset the fridge, freezer, items on standby etc.

The other problem with running any motorised device on solar is that once the solar output drops below the motor's requirement (a cloud goes over) you have to turn it off to save the motor from burning out. You then need extra power to restart it and on marginal days that will result in the unit not running at all.

This can be averted by even a "small" battery but you would need to do some testing and tweeking of the system to determine the battery size.

Originally Posted by kungsleden

The main reason we are not interested in a full solar system at the moment is that we are not home when the sun is out, except week-ends, and no more kid at home. So until the batteries get better and cheaper, we will not go solar. We do not use that much electricity, and we would prefer an off-grid system.

again, only rough numbers ...

two 10 amp, 2400W systems will draw about 5 kW per hour.
Say you run both systems for 3-4 hours each night -- that's around 15-20 kWh of juice. (on the electricity plan I'm on, 20 kWh costs about $4.50.)

To go off grid, your solar system would need to generate AND STORE at least 1.5 times your daily usage, with around 3 times daily usage being better.
At 3 times usage, your system would need to store around 60 kWh of power. But as it's only for the air con you might decide to shorten your running time, and accept a higher in house temperature, to stay within the capacity of a smaller battery.
A Tesla Powerwall 2 battery is rated for 13.5 kWh, so you might reliably be able to run two air con units for 2 to 3 hours each day.

Until you go completely off grid, me thinks that buying power from the grid is less expensive.