House air conditioning on stand alone power
- Thread starter Aussie
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I hope the moderators don't object to me posting the specs of a product. It's not an endorsement or advertisement, just the system that I'm using.
Mines the 2nd one from the left 12K Btu, 115 volt.
Aussie
New Member
Hi tictag. It would be nice to have it in the evening. If the house was cool during the day it might not be too bad at night but we do get hot nights in summer. I am really checking my options as I didn't think I could have it at all.
The weak link here is the inverter. It will handle an easy 12Kbtu inverter minisplit. It will likely handle a 24Kbtu model.
so you should have no issues with the cooling. You should generate about 21KWh from solar, and your battery should handle a bit more ar around 24KWh at 50%DOD... what chemistry are your batteries? 2V makes me think SLA, but confirming would be good.
Aussie
New Member
A real concern is putting to many amps into my batterys and having them dry out and having a short life. They cost me $15000.
Aussie
New Member
The batterys are VRLA Tubular gel
Aussie
New Member
Thanks for the specs NMNeil.
Let us know how you get on
So your A/C is rated at 960W (according to here). Trouble is we don't know how often the compressor will actually be running in order to maintain the set temperature ... let's assume worst case i.e. on permanently during the day, and see where it takes us.
Normally I would say that you you'd also need to size your array for Winter, but assuming your A/C is your principle load, this obviously won't be used as much during Winter.
OK, let's move onto power.
Powering a 960W load from a 48V battery would draw around 20A (+losses), well within the capabilities of your battery bank and would not require any unusual or expensive cabling/connectors.
A/C units can surge up to 3x their rating, or 2,880W, but your 3,800W inverter should have no problem supporting this.
OK, nothing to see here, let's look a little more closely at your PV array(s).
80W and 200W panels only play nicely together at 400W i.e. 2 x 200W = 400W = 5 x 80W, so you have two options:
More analysis and planning is required but at this stage, looks to me like you're golden! Really not sure why you've been told that this is not possible.
Maybe I'm missing something?
- Energy consumption per day = 11,520Wh (960W x 12 hours = 11,520Wh).
- Energy storage = 24,600Wh at the recommended 50% DoD for lead-acid (48V x 1,025AH * 50% = 24,600Wh)
- ... therefore, you have just over 2 days' autonomy baked in to the system
- Energy generation per day = 17,600Wh (3,520W x 5 hours 'good sun' = 17,600Wh ... ballpark)
Normally I would say that you you'd also need to size your array for Winter, but assuming your A/C is your principle load, this obviously won't be used as much during Winter.
OK, let's move onto power.
Powering a 960W load from a 48V battery would draw around 20A (+losses), well within the capabilities of your battery bank and would not require any unusual or expensive cabling/connectors.
A/C units can surge up to 3x their rating, or 2,880W, but your 3,800W inverter should have no problem supporting this.
OK, nothing to see here, let's look a little more closely at your PV array(s).
80W and 200W panels only play nicely together at 400W i.e. 2 x 200W = 400W = 5 x 80W, so you have two options:
- Have two separate arrays with two separate SCCs OR
- Have one array, one SCC but connect them together in groups of 2S 200W + 5S 80W
More analysis and planning is required but at this stage, looks to me like you're golden! Really not sure why you've been told that this is not possible.
Maybe I'm missing something?
Aussie
New Member
Hi Tictag. My solar panels are hooked up like this Six sets of 4 x 80 watt panels and two sets of 4 x 200 watt panels into a PL60 regulater . 12 volt panels x 4 to give me my 48 volts for my system which is then inverted to 240 volts AC which powers my house.
Basicly I was told I would be charging my batterys at too high a rate and the liquid (?) would vent out and the batterys would dry out . There fore giving me a very shot life span of the batterys
Basicly I was told I would be charging my batterys at too high a rate and the liquid (?) would vent out and the batterys would dry out . There fore giving me a very shot life span of the batterys
Aussie
New Member
We get plenty of sun and on the occasions when the sun isn't shinning we won't need the air con. I want it mostly for cool.
Aussie
New Member
I have been living with stand alone power for about 14 years but my technical knowledge is limited I understand I get amp hrs in and amp hrs out . My water pump uses about so many amp hrs the fridge so many etc. My batterys usually charge at less then 30 amp hrs. I usually end up with more amps in then out. Very aware of usage. As I mentioned else where They are very expensive ($15000) so I hop to get at least 15 years from them. My first set , flooded lead acid I got 12 years. They were only 8 x 6 volts x.. 750amp hrs. I might have discharged them to deeply a few times. I have greatly increased my storage capacity with my new batterys My regulater reads amp hrs in, amp hrs out, that's why I relate to amp hrs. Thanks for the help it is much appreciated.
Aussie
New Member
I have just converted Kw to btu and think I need a 6kw system which would equal 20473btu. To tell the truth I would still be happy even if all I can do is a bedroom. I have read an undersized unit is better then oversized. Any thoughts on that? I want to cool approx 55 sq meters ( I think thats 60 sq yards) (592 sq ft)
Last edited:
John Frum
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Ahhh, OK, I'm starting to understand your requirements a little more. So you already have a full home-wide solar setup, including a SCC, and you're wondering whether you can effectively add A/C cooling to it. This is very different to planning and designing a new system to power an A/C unit with components that you had already purchased, which was my initial inference.
OK, before we go any further we need to ascertain:
You're going to need to do an energy audit to determine both power and energy demands of your existing system.
Imagine 'power' to be water flowing out of a hose, it only flows at a certain rate, you can't 'suck out' any more water. Imagine 'energy' to be the water bowser connected to the hose, it can only contain so much water. For example, if you have you TV on, together with some lights, then you put on the dishwasher ... what would happen then when the A/C unit kicks in? If there is not enough 'power' available, your inverter will trip out. Similarly, say you you wash a couple of loads, the lights have been on all night so has the A/C. If there is not enough 'energy' your batteries will discharge and you inverter will trip out. Same outcome - a dark home - but for different reasons.
The easiest way to do an energy audit is to Measure.
Buy one of those smart energy meters that connect around your primary line conductor then go around turning stuff on, note the power draw (in Watts) of each device. Also, simulate a typical day and note the daily energy consumption (in Watt-Hours).
The other way, that does not require an energy meter, is to Calculate. Draw up a table like the one following:
Once we know how much power is being drawn from your inverter, and how much energy you consume each day, we can then determine whether your inverter and battery bank is sufficiently capable of adding A/C into the mix.
To answer question (2.) we need to understand the specifications of your battery and SCC.
Typically, lead-acid batteries don't like being charged above C/10 Amps, for a 1,025AH battery bank, that's 103A. Ambient temperature also has a part to play in this. Could you please provide some kind of product link or specification for your batteries? All I need to know is the manufacturer's recommended charge rate.
I am assuming your SCC is the Plasmatronics PL60 PWM 'Regulator'. Please confirm.
If so, this is only capable of charging at 60A. If the recommended charge rate of you battery is C/10 Amps (i.e. 103A) then this SCC won't even be capable of damaging your batteries!! But the problem may well materialise that it also is unable to replenish your daily consumption. For example, assuming 5 hours 'good sun', it would only be cable of replenishing 14,400Wh (60A x 5 hours x 48V = 14,400Wh) in perfect conditions. This might not be enough depending on what we find from your energy audit.
So next steps are:
OK, before we go any further we need to ascertain:
- Can your existing system even cope with powering the additional load?
- Can your battery bank be safely charged considering the additional load?
You're going to need to do an energy audit to determine both power and energy demands of your existing system.
Imagine 'power' to be water flowing out of a hose, it only flows at a certain rate, you can't 'suck out' any more water. Imagine 'energy' to be the water bowser connected to the hose, it can only contain so much water. For example, if you have you TV on, together with some lights, then you put on the dishwasher ... what would happen then when the A/C unit kicks in? If there is not enough 'power' available, your inverter will trip out. Similarly, say you you wash a couple of loads, the lights have been on all night so has the A/C. If there is not enough 'energy' your batteries will discharge and you inverter will trip out. Same outcome - a dark home - but for different reasons.
The easiest way to do an energy audit is to Measure.
Buy one of those smart energy meters that connect around your primary line conductor then go around turning stuff on, note the power draw (in Watts) of each device. Also, simulate a typical day and note the daily energy consumption (in Watt-Hours).
The other way, that does not require an energy meter, is to Calculate. Draw up a table like the one following:
| Device | Rating (W) | Time (h) | Energy (Wh) |
|---|---|---|---|
| Dishwasher | 2,300W | 1.5 hours | 3,450Wh |
| Lighting | 220W | 8 hours | 1,760Wh |
| " | " | " | " |
| TOTAL | 3,5020Wh |
Once we know how much power is being drawn from your inverter, and how much energy you consume each day, we can then determine whether your inverter and battery bank is sufficiently capable of adding A/C into the mix.
To answer question (2.) we need to understand the specifications of your battery and SCC.
Typically, lead-acid batteries don't like being charged above C/10 Amps, for a 1,025AH battery bank, that's 103A. Ambient temperature also has a part to play in this. Could you please provide some kind of product link or specification for your batteries? All I need to know is the manufacturer's recommended charge rate.
I am assuming your SCC is the Plasmatronics PL60 PWM 'Regulator'. Please confirm.
If so, this is only capable of charging at 60A. If the recommended charge rate of you battery is C/10 Amps (i.e. 103A) then this SCC won't even be capable of damaging your batteries!! But the problem may well materialise that it also is unable to replenish your daily consumption. For example, assuming 5 hours 'good sun', it would only be cable of replenishing 14,400Wh (60A x 5 hours x 48V = 14,400Wh) in perfect conditions. This might not be enough depending on what we find from your energy audit.
So next steps are:
- Provide specs for your batteries and SCC
- Carry out an energy audit
Last edited:
Aussie
New Member
tictag Thanks so much. Your help is very much appreciated. I shall do as you suggest and get back to you
Yes it is the PL 60 in your link. Mine is an older model but I imagine the same specs.
Yes it is the PL 60 in your link. Mine is an older model but I imagine the same specs.
Aussie
New Member
Just an update. Thanks for all the help you all gave me.
I ended up buying a 7.1 Kw for the living area and a 3.5 Kw for the bed room. ( Mitsubishi heavy industries inverter reverse cycle air cons )
If I run the 7.1 around 26 c on a 32 degree day, I can run it all day , no worrys. I only run one at a time of course. The 7.1 , once at temp only draws around 15 amp hours.
Never thought I could have air con with stand alone power and am rapt now that I have it. Had a few 40 c days and all was good.
Thanks again for all the help.
I ended up buying a 7.1 Kw for the living area and a 3.5 Kw for the bed room. ( Mitsubishi heavy industries inverter reverse cycle air cons )
If I run the 7.1 around 26 c on a 32 degree day, I can run it all day , no worrys. I only run one at a time of course. The 7.1 , once at temp only draws around 15 amp hours.
Never thought I could have air con with stand alone power and am rapt now that I have it. Had a few 40 c days and all was good.
Thanks again for all the help.
Just make sure you aren’t exceeding the discharge rate of those cells, and are correctly charging them at the top of charge.
Ask for details from the person that told you it couldn’t be done without shortening the lifespan of your cells.
Most people i know using those cells with heavy house loads end up ditching them after 5 years or so.
(effectively 3 times the price of LiFePO4 for half the life).
Proceed with caution - it’s your money!
Ask for details from the person that told you it couldn’t be done without shortening the lifespan of your cells.
Most people i know using those cells with heavy house loads end up ditching them after 5 years or so.
(effectively 3 times the price of LiFePO4 for half the life).
Proceed with caution - it’s your money!
Aussie
New Member
Aussie
New Member
What are these LiFePO4's? Not aware of them.
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