running an AC unit on solar only

[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.

[kungsleden]

Bob,

We do not have panels yet, nor an AC unit.
:U
Probably not obvious from my question.
Any clearer? :D

[Optimark]

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.

[BobL]

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.

[Chris Parks]

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.

447358

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.

[Simplicity]

Just watching this
As would also be interested in solar AC

Cheers Matt

[kungsleden]

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

[kungsleden]

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).

[ian]

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.

[ian]

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.

[Sir Stinkalot]

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.

[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.

[Sir Stinkalot]

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.

[Bohdan]

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.

[ian]

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.

[Chris Parks]

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.

Ian, Australian houses are for energy purposes leaky tents. We may not need better insulation for cold weather but we do for hot weather.

[Chris Parks]

If you look at my energy use diagram you can see how much two splits, one is a 7.5kw unit uses up until the ducted was turned on at about 11:00am. As I write this we are producing 4.98, exporting 2kw and using the rest to run the house which includes both splits. There is no guesswork or calculations required as this is live monitoring. The two splits won't keep up if the temp goes north of the high twenties and the experts told me they would and when I questioned them I was basically told that the new inverters had changed things, yeah, right. I doubt they would keep the house temp under 30 degrees on days like we have just had. This house is fully insulated in all walls and ceilings and we have installed heavy rubber backed curtains to insulate the windows and anyone who has been in the house will tell you that the area we live in is not big by any means. With the ducted running it was 21 inside when it was 39 in my workshop yesterday. It might chew power but it works really well. We installed the splits to overcome another problem not to save power and that story is too long to tell here.

[kungsleden]

Thank you for all the info.
Good. I will save some money for the time being and just buy a fan for the living room.
Our house is ducted for heating. The heating unit is 10 or more y.o. It is a good unit, but noisy.
The AC would have been a ducted unit, not splits.
We'll see when we decide to change the heating unit, maybe go with a heating/AC combo.

As far as I remember, summertime, houses in the hot parts of Europe (Southern France, Italy, Spain...) are much more livable than houses here.

[ian]

Ian, Australian houses are for energy purposes leaky tents. We may not need better insulation for cold weather but we do for hot weather.funny

our "planning betters" think that natural ventilation, especially cross flow ventilation is the way to go.
https://www.planning.nsw.gov.au/-/media/Files/DPE/Guidelines/apartment-design-guide-part-4-designing-the-building-2015-07.ashx?la=en
"The area of unobstructed window openings should be equal to at least 5% of the floor area served.
"Doors and openable windows maximise natural ventilation opportunities by using the following design solutions:


[*=1]adjustable windows with large effective openable areas.
[*=1]a variety of window types that provide safety and flexibility such as awnings and louvres
[*=1]windows which the occupants can reconfigure to funnel breezes into the apartment such as vertical louvres, casement windows and externally opening doors."


so even with double glazing, we're expected to keep the windows open most of the day.



knowing who some of the "planning betters" are, I think very few of them live west of Bondi Junction.

[Chris Parks]

Our life has changed in the last few decades with regards to heating and cooling because before that it was a very expensive exercise to install AC in a family home but just like solar panels the cost has plummeted and a lot of the previous thinking is not valid. I saw an episode of This Old House showing air exchangers for sealed houses to admit air in the winter but I bet hardly anyone in Oz would know what it was if it bit them.

[ian]

Chris
I don't want to appear to disagree with you.
Almost 30 years ago, what was then Prospect Electricity, was subsidising the purchase of home air conditioners on the basis that it increased electricity consumption -- which is a good thing if you're an electricity retailer. And of course, homes in Western Sydney are prime candidates for air conditioning.

More I was referencing current doctrine from the NSW bureaucracy that reinforces your "leaky tent" analogy.

[Chris Parks]

Chris
I don't want to appear to disagree with you.
Almost 30 years ago, what was then Prospect Electricity, was subsidising the purchase of home air conditioners on the basis that it increased electricity consumption -- which is a good thing if you're an electricity retailer. And of course, homes in Western Sydney are prime candidates for air conditioning.

More I was referencing current doctrine from the NSW bureaucracy that reinforces your "leaky tent" analogy.


Agreed, it can be hard to say stuff in writing but I was agreeing with you about the out of date ideas that the govt still hold onto when things have changed. Energy usage can't be changed while we live in the same style of house we always have done.

[ian]

Agreed, it can be hard to say stuff in writing but I was agreeing with you about the out of date ideas that the govt still hold onto when things have changed. Energy usage can't be changed while we live in the same style of house we always have done.
it gets worse.
Those "out of date ideas" were published less than 10 years ago (perhaps as few as 7) as representing the "desired future" for apartment design to obviate the need for air conditioning and thus represent "cutting edge" sustainability.

I remember seeing them when they were first published -- given where I was working at the time it may have been a prepublication draft I was given to review.
I remember at the time thinking that the people behind the "guidelines" were off the planet -- hence the comment that they must all live east of Bondi Junction.

I think it's less a matter of being out of date, more one of ignorance.

As a former work acquaintance put it -- "The [Sydney] Fish Markets is as far west as I want to go even on holidays. I'm sure that the people living in the Western [Sydney] Suburbs are nice people, I just don't want to go there."

[damian]

There is only one proper way to answer your question, calculate your needs then work backwards to discover what is required.

You have given us temperature ranges and some other scope of use data. Unfortunately while that indicates what is required it doesn't give the whole picture. You would probably need to log temps in and outside over a period of time and decide just how many hours and how many degrees and the volume of the rooms to calculate air con requirements.

21 in 40 degrees requires either tremendously efficient insulation, like a cool room, or a massively overspec'd system. I achieved this in my little teardrop camper and it was glorious, but it was the van park's power a tiny volume and massive styrofoam insulation.

So from what you have told us lets assume you want to cool 100 sqm of well insulated house and knock 7C off temps. Most guides suggest 140 kW per sqm but I'd go up from that, maybe 200. That sounds like a lot but bigger units aren't that much dearer and given they are all inverters these days they won't use more power than they need.

Incidentally I only ever buy panasonic. I know people who have had problems with every other brand, including daikin. I don't know anyone who has had an issue with a panasonic. The one running in my bedroom right now I installed in about 2000 and it has been saving my life every summer since. The only problem I have had was it stopped when a python climbed into it and inconsiderately died and got stuck in the fan.

So you have 20kW of units. Their duty cycle is about 1/3 and power consumption is about 2/3 to 3/4 of rated power, so they will pull about 5kW/hr. You get about 4 hours effective production out of solar across most of australia so if you are using them for 8 hours 2 days a week (80kW/h) you will need about 3kW of panels assuming perfect storage (4*4*7. It's actually 2.8). I'd probably want 4kW but whatever. From there you have to size your batteries.

Now you'd be crazy to size a solar system that way. What I'd be doing is sizing it to take the bulk of the load and adding an auto start generator. That would kick in when the load is high and the saving on the solar would pay to buy and run the genset for years and years. In fact if it was ONLY the air con I'd lose solar altogether and install a gas or diesel generator to do the whole shebang. Panels are cheap but the battery you'd need would be huge and expensive.

Incidentally solar is not eco. Most enviro stuff isn't. Enviromentalism is a religion and only coopts science when it suits them. Photo voltaic panels need more energy to make them than they ever produce. You are exporting the pollution not negating it.

Anyway hope that helps.

[BobL]

Incidentally solar is not eco. Most enviro stuff isn't. Enviromentalism is a religion and only coopts science when it suits them. Photo voltaic panels need more energy to make them than they ever produce. You are exporting the pollution not negating it.

That was only correct up to about 2010. Since then photocells are making more than they use and by 2020 all the solar electricity production on the planet will have paid back all the non-renewable electricity that photo cells have ever used in their manufacture.

See https://pubs.acs.org/doi/abs/10.1021/es3038824
and
https://phys.org/news/2016-12-solar-panels-repay-energy-debt.html

[Pete57]

As someone else mentioned some caravan owners have done it:
https://caravanersforum.com/viewtopic.php?t=79305
but caravans are smaller. Interesting info anyway.

[HUON]

Tesla firewall wont work with a stand alone system. It's designed to work into the grid.

[Bushmiller]

My understanding of the Tesla firewall battery was that it was an emergency back up system that is short term rated. The enigmatic Mr Musk just very slightly skipped over that when introducing the system. It is there to tide you over until normal supply can be restored. I don't know the details of how long it can last, but from time immemorial power stations have had a similar system in place, albeit with a different level of technology. Hospitals have an emergency back up sytem too: It's called a Diesel generator.

Regards
Paul

[Chris Parks]

My understanding of the Tesla firewall battery was that it was an emergency back up system that is short term rated. The enigmatic Mr Musk just very slightly skipped over that when introducing the system. It is there to tide you over until normal supply can be restored. I don't know the details of how long it can last, but from time immemorial power stations have had a similar system in place, albeit with a different level of technology. Hospitals have an emergency back up sytem too: It's called a Diesel generator.

Regards
Paul

A Tesla battery has fairly low limits of discharge or current draw...

Telsa's Powerwall 2, for example, has a continuous output capacity of 5kW (higher rates possible for short periods) and a storage capacity of 13.2kWh (at the beginning of its warrantied life). Tesla's Powerwall is a 'power battery', able to instantaneously release stored energy at a relatively high rate.Jun 15, 2018

So run at maximum and allowing for the fact that it cannot be discharged entirely it will power a house for about two hours.

[Bushmiller]

Chris

That is pretty much as I surmised, but thanks for supplying the detail.

Regards
Paul

[HUON]

Kungsleden, after all the problems with grid power this early into summer why on earth would you consider relying on the grid (power supply). The weird thing about all of this is that people are paying more for a failing last century power technology. I would have thought that the long term economical choice would be to invest in a stand alone system (power producing technology,batteries and inverter).Or organise your neighbours/community to create a power supply co-op.
Check out the Yackandanda website (TRY).

[Pearo]

FWIW, there is (or was) a manufacturer that did make inverter splits that would run directly from solar, no grid and no battery. They were only pretty small units though, might get away with one to cool a small bedroom. I just had a quick google, but cant find them right now.

I did look closely at the units, and the were a DC inverter, and the solar power fed straight into the unit. I cant recall what the voltage, but given they only needed half a dozen panels maybe it was realm of 120-150VDC. I would imaging they can probably take a bit more, but I guess you call always series-parallel 2 strings.

Given the number of 1kw systems you can pick up on gumtree now for a few hundred dollars, it may actually be viable if you have the space for the panels.

[Bazzam]

I run a 3.5 Fujitsu Inverter AC in my tiny house. (About the same area as a big living room). Fully off grid, I have 4.8 Kw useable per day. 1.6Kw PV.
I usually aim for about 5/8 degrees below ambient and the unit pulls about 900W when starting and drops to about 350W intermittently.
So with good sunshine I can run it and still charge my batts. Reluctant to run it after sunset unless sure I have a good sun next day.
I bought a good Honda gennie as backup, but the Charge controller/inverter wont play with it.

[DaveVman]

If anyone is still looking at this thread, there are now solar powered DC air conditioners. With either battery or hybrid to increase working hours. I have no idea how good they are. Just letting you know they exist.