I'm in NSW - curious on what you got, what subsidy/ies you were able to obtain.

I'd previously looked into this and it sounded like a package was required - PVC + battery - whereas I've already got 10kW inverter + 12kW panels, and basically just want something around that size (40kWh).

Street pricing seemed to be around the $9k installed per 10kWh, so a) your subsidy options sounds spectacular - around 60% discount? - and b) payback for me would probably be around 8 years.

But if I switch vendors (Amber I think is what one of my friends is on) I can engage in something analogous to wholesale market activity, 10m bidding / sales, rapidly decrease the projected lifetime of my battery, but potentially be $-positive even through the winter months.

But all that feels like something the power companies here in AU are going to try to try to undercut / tax.

15Kwh Lifepo4 48V 300Ah is less than $2k USD. You are overpaying a lot for installation.

You need inverters to run them, and you can't just put more battery on one inverter. The price is about 1:1 now for battery and inverter costs when I looked into it last.

You absolutely can put multiple batteries on one inverter. The limiting factor is the DC bus bar and breakers, not the inverter, which just needs to be sized to consumption.

Yes there's nothing stopping you, but economically a given kW battery installation stores about 4 hours of power.

There's 4 to 6 hours of peak renewable energy per day.

If you add more batteries, you increase power and energy at the same time and ratio: so for any practical home battery system you're cycling the cells daily, which means you your power for charging must match.

If you put more batteries on one inverter, then you're scaling a lot of other costs (BMS, bus bars and space) but you'll never actually be able to utilize that capacity - it'll sit idle most of the time because you can't get it in and out of the cells fast enough.

Are your figures, notably 4-6 hours of generation, overlooking the potential for home battery owners to buy power in during off-peak (cheaper) periods, for either their own usage, or for selling back to the grid, at other times?

I've costed it and it doesn't work out. But you can realize why without doing the calculations: unlike solar, batteries aren't surface area limited. So better capitalized producer can achieve better economies of scale and just build warehouses of the things to do exactly that. Which is what they do - and thus off peak power trends towards a tiny margin over the warranted kWh cost of a battery.

Okay, I think you're in a different part of the world to me, then - I can generate about 85kWh in a day here, mid-summer, about 34 degrees south, and that's throttled by my 10kW inverter.

I could go higher with a better inverter, but energy providers in Australia, or at least my part of it, basically drop all pretence once you go over 10kW feed-in, and the already pitiful rates they'll offer as standard asymptote towards zero.

Time of usage tariffs vary quite wildly here, but it's not uncommon to have close to 70c at peak hours, and 20c at off-peak. These fees are complicated by the daily connection charge, which is around $1.00 but varies on your location, provider, and your ToU and other schemes.

Some 'pretend to be a wholesaler' options exist here, but our wholesale pricing is bid and sold in 10m blocks, not 15m, as per your other note.

Also, we have ~6 hours a day where peak pricing is generally applied, and maybe ~9 hours where we're at off-peak pricing - so the math tends to be more compelling.

Well, I suppose our perspectives differ. My own solar installation is off-grid, so the battery pack is sized to last for 4-7 days. I don't have the luxury of tapping the grid if they tap out, and running the generator's quite expensive.

6.2kW 48V -> 230AC inverter is $300

And if you run the numbers, the battery which can deliver 6.2kW is only about 1.5kwH in capacity. This matters because while discharging slowly is fine, to gain any economic benefit you need to be able to charge at essentially full power.

If you have 100kwh of batteries and only 6kw of AC connection then it would take 3 days of typical solar charging to get them to full capacity. And any kwh sitting there that you don't charge/discharge is costing you money for grid batteries - the economics still depend on being grid interactive.

The best demand signal in my local grid for example is exactly 1 hour wide. Which means s you get 4 15 minute intervals to basically try and dump power for the best price.

I have a relative with a 30kWh battery on Amber. They spent AU$10k for it after subsidies.

They don't expect to ever pay for electricity again - instead their biggest problem with Amber is what to do when they are overproducing. They got charged $2.50 the other day when they didn't curtail production and had to dump power into the grid!

5 x SigEnergy SigenStor Bat 8.0 (8kWh/battery) + 12kW inverter (Sigenstor EC) on single phase. The SRES battery rebate (https://cer.gov.au/batteries) was ~30%. Total was a bit under $15k. I already have 16.6kW of panels on the roof from 5 years ago.

There are two providers (Globird and Ovo) I have been researching that provide 2-3 free hours of electricity per day between 11-2pm. That + solar would easily fill the batteries, so that power bill might drop even more.

You should get some quotes from battery/solar installers (no doubt you have heard of solarquotes.com.au). Prices have dropped a lot this year.

Excellent info - thank you.

Yes, I've been through solarquotes.com.au a few times but haven't looked in earnest for some time. This is encouraging information.

I know my usage can easily be 15-20kWh in a day, and I can get a week of overcast though it's not common.

The 'free' electricity offers presumably are in return for a guarantee to feed-in to them outside sunlight peak, I suppose?

I assume the power providers have come up with ToU and FiT tariffs based on a LOT of data, so we here with our spreadsheets and one or two datapoints aren't likely to come out far ahead, but it sounds like break-even within a few years is feasible.

They don't require that we feed in at any specific time, but they do price their peak rates quite high so you have to ensure you have enough storage to not consume at those times.

No doubt their models and prices will be updated once more large homes BESS are installed.

How does the cheap rates work? You get subsidised grid rates because of the batteries?

In Australia it's common to have Time of Usage (ToU) billing.

Figures depend on provider and plan, but sometimes cheap (as per parent's 6c / kWh), but during the midday to 6pm range it may be up to 60c.

So, grid rates aren't subsidised, but having a storage medium means you can arbitrage power quite easily.

The AEMO (Australian Energy Market Operator) website has some good data can see price of electricity in realish time. This is for the NEM (which is east coast states + South Australia), the west coast is on a separately managed grid with no interconnection.

https://www.aemo.com.au/energy-systems/electricity/national-...

You can also view the breakdown of where the grid is sourcing energy from (i.e. what portion of the grid is supplied from solar pv etc at any given time).

I know that some big industrial users (large factories etc) can optimize/spin up production lines etc based on the spot price. Although I'm not sure if they use the same public AEMO data there might be a dedicated api or similar involved.

That would be cool if I could afford to own a house.

A great example of what's possible when policy actually aligns with long-term sustainability goals

This is actually very regressive policy because it only rewards people who 1) own their own home and 2) can afford a significant capital investment. And under current retail rate structures it shifts the burden of maintaining the grid onto those who can't afford to make these investments and who will end up seeing there rates rise unless the cost of grid connectivity is increased.

It's also economically questionable because it's simply much cheaper to build and manage a smaller number of large batteries then thousands of home batteries.

I understand why these schemes are politically attractive; people like to own their own stuff. But there is a very real chance this increases the cost of energy here.

I'm curious how you see this potentially increasing the cost of energy? Why can't we do both large systems and small distributed systems?

I see the following benefits:

1. Stabilises the grid

2. Smooths peak demands. Check the Price and Demand graph here: https://www.aemo.com.au/energy-systems/electricity/national-...

3. Increases supply -> energy prices decrease?

4. Accelerated move away from coal generation and towards renewables.

5. Job creation (solar and storage installation)

Drawbacks:

1. Renters, lower income houses and apartment dwellers don't have access the subsidies

2. Exposure to dodgy installers and systems just like we saw with the Australia solar scheme.