Domestic solar batteries ( T1 ? )

[Riverlander]

Hi. Just looking for a new electricity plan. Noticed all the rates have gone up again ( and will again after July 1st ) and the solar feed in has halved since last plan. Been looking again at a battery system but are having trouble making it worthwhile cost wise at the moment. My power usage for the last 12 months is Peak 2958.67 kWh Off Peak 444.40 kWh Shoulder 143.39 kWh and my solar feed in from a 6.6 system was 7493.09. Total cost last year was only $719.34 and with the new rates that would be about $ 1320.00 this year. I suppose a ball park cost for a battery set up would be about $15,000 / $20,000 and of course even if I could cover most of my power usage I would still have the supply cost of .98c/day.
Cheers John

[T1 Terry]

Hi John, not sure how the solar grid feed in works in SA. Does the house use what ever solar energy is available, then the excess goes to the grid? Or does it all go to the grid and then you buy it back? In NSW, it depended when you signed up as to the cents per kwh and if it all went into the grid and then you bought it back as required. Later they dropped the cents per kwh the next to nothing but the house used the solar and only the excess went to the grid. 7493.9kwh over 12 mths divided by 365 days = 20.5kwh per day feed in averaged over the yr, allowing for 80% of the yr being good solar weather and 5 hrs per day peak solar = 1460 peak hrs of solar x 6.6 = 9636kwh of potential generated solar. That leaves a balance of 2142kwh or 5.8kwh per day used by the household of your own solar .... and that doesn't sound right eh.

Total power used comes to 3546 kwh per yr or 9.73kwh per 24 hrs, that doesn't add up either, so what am I missing .... could be my maths after first coffee

We have set up off grid houses with as little as 2.8kw of solar and our biggest to date was 10kw of solar and they needed 3 x 4kw inverters because the used so much power, yet they didn't run out of power very often, young sons and their girlfriends and friends with their girl friends using the place without adult supervision was the only times they drained the battery over night with the swampy on flat out and all the doors and windows open .... 5 families there over the summer holidays doesn't manage to drain the battery, so the 10kw of solar supplies them with some to spare.....

T1 Terry

EDIT: Yeah, forgot to add in the solar the house used each day, so that brings the total use up to around 16 kwh per day, average family house is 20kwh per day so that sounds about right.

[T1 Terry]

So, you basically produce more solar per yr than you use with the system you already have.
400Ah @ 48v per 24 hrs, so 2 days supply to allow for crap weather, 800Ah @ 48v battery would be plenty enough.

Now we need to know what appliances you use at the same time, including pumps, fridge freezers and air conditions as well as kitchen appliances and tvs etc, so we can work out how big and how many inverters you need.
Next, do you have a generator? If you have a generator big enough to supply the house load, that would be enough back up to cover weeks of rain, you don't need the mains at all, so you would save that $1 per day or $365 per yr .... even at the crazy prices for fuel at the moment, that runs a generator for quite a while.

T1 Terry

[Newcastle George]

Just as a comparison, we have 6.6kW of solar, 3.6 facing east 3.0 facing west

Total Bill for 12 months - $646.64 Note: We do not have gas

Our total power purchased from grid during last 12 months - 5110kWh (2207 peak, 2903 off peak hot water) (14kWh/day paid for)
Total Solar output - 8144kWh (22.3/day)
Solar output used by us - 2026kWh (5.55/day)
Total fed to grid - 6118kWh (16.76/day)

George

[T1 Terry]

Just talking to Margaret and she tells me we installed 300Ah @ 48v but they have lived off grid since they built the house. They recently sold the house to a young couple and they did run out of battery once, but that was because they didn't know how to start the genset more than anything. They have 2 x 4 kw inverters supplying the house and that seems ample for their needs .....

T1 Terry

[Peter and Sandra]

We had a Tesla Powerwall 2 installed just before christmas 2021 under the NSW govt Empowering Homes Program which is available for solar and battery or battery only if you meet the postcode and income threshold requirements. Basically it is an interest free loan for either $10k for the battery or $15k if you need solar as well. We did have to fork out $5k for installation and what the loan didn't cover.
The battery is guaranteed to have at least 80% usable capacity remaining after ten years or it will be replaced under warranty.
Our quarterly bill varies from $260 to about $560 with a 5.4kw solar system with 12 panels facing north adn 8 facing west, depending on weather, aircon use and whether we are actually home.
We have electric off peak hot water and no gas but do have a slow combustion stove for heating in winter and two 8kw inverter split sytems which cool or heat the house as required. Firewood is usually free from a mates farm.
I did the sums and figured the repayments would be less than the quarterly bill even at its lowest point and despite the $5k "gap" payment, the ever dropping feed in tarriff and expected power cost increases figured if we only broke even it was still a reasonable deal so went ahead with the installation.
Our first bill was approximately two weeks after installation and it was $14.56 for the quarter, the second in April just gone was a $45 credit so we are doing well despite the huge lack of sun over the last few months.
We typically use 20-25% of the battery capacity overnight without using the aircons and the battery is usually charged back to 100% by the middle of the day.
We've only had one blackout since the battery went in and it was only two days after the install, we didn't even know the power had gone off until the Tesla Gateway sent me a text to say the mains had gone!
We can monitor power usage live on a phone app and all usage is logged and can be downloaded at any time. I forgot to add that the gateway prioritises the solar to meet house demand first, battery recharging second and back to the grid as a last resort. We can change the points at which it does its thing and it stops discharging at 6% which is also user adjustable. On a typical summers day we can have both aircons running and still be charging the battery if required.

[Riverlander]

The local sparkie that installed my system said today the solar powers the house first and the surplus goes into the grid and it is set up for batteries to be installed. He mentioned he has thought about batteries at his house and will come around and run through the figures on my property.
Cheers John