# Forum Home Renovation Solar Electrical Systems  Solar Air Conditioning

## FlynnGarden

Any comments from people about solar air conditioning?  am looking at a hybrid system that operates a 7KW split unit, with AC back up for when the sun don't shine.   
Systems are not cheap (Approx 7-8K) but no power bill.  Plus the area I want to cool and heat is both hot and cold due to season.  So a comfortable house factor at play too.

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## phild01

Not sure I see the point of it, if you have solar panels, the  a/c would be using that solar output, if you don't have solar panels then get a system and sell back to the grid what the a/c doesn't need, why would you have the panels exclusively for a/c!

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## FlynnGarden

I have 6KW  grid connected solar system which provides 100% feed in tarriff return (not a net rate where only excess power goes to grid). Due to contract, and inverter limit, I cannot expand size of system. 
My power costs 22c KWH.  Director solar to panels therefore will save me 22c KWH while-ever it is going; and if electricity price rises in the future, whatever that rate is too. 
My major utilities cost is actually ducted gas heating (Canberra winters); and the split system will provide some relief in that area as well as resolving a serious summer heat problem in west facing room with floor to ceiling windows.  Ceilings are vaulted so insulation improvement not viable. 
I'm trying to improve comfort of house at least ongoing and downstream cost.

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## phild01

While I can't help I still don't understand why your existing 6kW system is inadequate for the ac as wouldn't it be the major appliance to be fed through the day. What solar capacity are these solar ac systems!
I have a 6kW split and today is overcast but getting >2kW from a 4.9kW solar system which is more than ample to run it.

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## r3nov8or

> I have 6KW  grid connected solar system which provides 100% feed in tarriff return (not a net rate where only excess power goes to grid). Due to contract, and inverter limit, I cannot expand size of system. 
> ...

  What feed in rate per kW are you receiving for this arrangement? In 'normal' arrangements you get a lot more $ benefit from self-consumption than feed-in, but your relatively low 22c kWh usage tariff may be compensating...? 
Like phild01, I also can't really help with the Solar AC your are looking at, but I just feel a little blessed that we only run the cooling for a handful of days a year and the heating for maybe 40 days {both are just in the main living areas, not bedrooms). We are either a hardy lot or Geelong is an un-documented temperate climate  :Smilie:

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## FlynnGarden

Feed in is 46c KWH.  system generates about 27 KWH per day.

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## r3nov8or

> Feed in is 46c KWH.  system generates about 27 KWH per day.

  Along with the 22 kWh cost to import, that's good reason not to mess with it  :Smilie:   
Do you have room for an independantly installed set of panels and inverter to service the houses consumption? Or would that breach your agreement too?

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## FlynnGarden

I had not thought of that.  The solar air-con runs directly off the roof top panels.  No inverter required.  Company doing these is: https://solaracdc.com.au 
Seems like such a good idea.

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## r3nov8or

Have you calculated the pay back period for the Solar AC? As a single purpose system, and your low import tariff, I imagine it will be a lot longer than a system servicing the whole home's power needs

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## FlynnGarden

That is very difficult equation as so many variables in the house and usage.  Best I can come up with is that Canstarblue says in Canberra average split aircon is $405 for heating and $63 p.a. for cooling based on average annual consumption of  4200 KWH for 4-6 KW system.  My system will be 7 KW so lets say round numbers $500.  Cost of this solar hybrid system is about $3000 more than normal split.  So on that basis there is a 6 year payback.   However, the variables.....I know in my house I spend around $2000 per year for ducted gas even when it is used carefully.  If I can reduce the load on the ducted gas, that is additional saving.  Say 20%...or $400 p.a.   Payback then starts to look like 4 years.  Then there is the fact that I have no cooling in the house at all apart from pedestal fans.  I am also sceptical of the Canstarblue cooling costs; seem too low.  and in my house the room to be cooled is a large room 10m x 5m with vaulted and raked ceilings,  Floor to ceiling windows (single glaze) facing WSW...In summer it is at least 10degrees hotter than other parts of house (split-level; three floors).  I am sure my annual cooling costs would be considerably more than the Canstarblue average; I would say up to 300% at a guess.  And the room has no heating at all which in winter means I need to crank the gas up to get warmth to upper level which can get very cold.
What is attractive about this system idea is that the heating and cooling happens whenever the sun shines.  Being on longer it cools thermal mass or warms it more thoroughly...there is an upfront cost, like solar panels, but after payback it is all good (at least until systems need replacement, but that applies to any appliance).  There is however a chance to use the AC of the hybrid system at night if really required or on dark/rainy days.
I am sure a person with better number skills could be more precise than me but this is best back of envelope calculation I can do.  Feel free to be devils advocate or demolish my numbers with better maths! And for the benefit of other readers.

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## phild01

Is it that this type of setup is so variable (because of sun conditions) that the room temperature won't be constant through the day, I would not be comfortable with that. Also if considerable ac is to be used when there is no sunshine the system has limited purpose.

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## Bart1080

...be careful what your catering for from a cooling perspective...and these aren't hot days compared to other populated areas :Smilie:   _On average, the ACT experiences fewer than 10 hot days each year (maximum temperatures above 35°C). A marginally greater number of hot days occur in the north of the ACT, and there are typically no days with temperatures greater than 35°C in the alps._ 
If it needs sun to heat, then not sure how effective it will be in winter. up to ~60% of the winter months is overcast/cloudy right when you need the heat.  Probably similar performance to my flat panel solar water heaters...next to nothing in the depths of winter.  https://weatherspark.com/y/144442/Av...lia-Year-Round

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## FlynnGarden

My existing solar system averages about 28KWH all year round, and in winter on sunny days it goes gang busters, even better I think than really hot summer days.   Its possible solar PV generation may be different efficiency to solar hot water. 
Thanks for that weather spark link,  I'll study that.  I think part of the problem is that my lounge has a lot of west-facing glass and gets its own micro-climate which is much hotter than rest of house.

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## intertd6

I’d like to know which power retailer has those rates you quoted, 22c usage (buy)& 46c feed in tariffs (sell)
inter

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