Is it worth my while getting a battery?

I don't think many inverters will allow you to discharge the battery to the grid, it's extremely inefficient because you lose around 20% of the energy you put in

Also if you aren't on a smart meter then it'll make no difference as you'll be getting deemed export

You can oversize the battery to make use of the night rate, some of the folks here have done that. For me it's taken the payback period from 10+ years down to 6 years

I've only gotten solar this year, so I guess we'll see how well it works out

You can figure out the payback for it and see if it makes sense. There's a few different ways but here's what I did (apologies in advance for the spiel, but boards f**ks up numbered lists when I use them):

First, figure out your month by month consumption for the past year or two.

Calculate your solar PV generation for each month using a tool like PV GIS

If you've a big battery then your self consumption will be close to 100%. For some margin, subtract 90% of your monthly generation from your monthly day rate consumption (not the night consumption, solar doesn't work at night 😉)

What's leftover is what you need to buy from the grid. Figure out the average daily consumption by dividing the day rate usage by the number of days. The highest value for a month is theoretically the ideal battery size for you (obviously there's a whole heap of factors affecting that, so take the value with a healthy dose of skepticism)

Use the daily consumption to decide on what size battery you are going to buy. There's probably not much point in getting a bigger battery than you need for one day, at least at first

Multiply the battery size by the number of days in a month, then subtract this number from the day rate usage for each month. Also add 120% of that number to the night rate consumption to account for losses charging the battery from the grid

Add up the new consumption for every month and that's your new annual consumption

Use that to figure out your annual bill, remember to add in the money you get from exporting electricity. Subtract that from your current bill to figure out the annual savings (remember to account for any discounts that are expiring, those folks on the 8c night rate are all crying these days)

Now go and get some quotes for the system cost. Divide that by your annual savings and that's your payback period

@the_amazing_raisin - "I don't think many inverters will allow you to discharge the battery to the grid"

I haven't heard of any inverter that actually won't allow you to do that 😁

It's exactly what I plan to do once I get a smart meter. You are right, you would have about 20% round trip losses from AC -> inverter -> battery -> inverter -> AC, but that is not all that much if FIT is nearly double what you pay for night rate. I believe this sort of peak shaving / grid stabilising is more important in the transition to fully renewable energy, than the renewable energy itself, as it is where we have the biggest shortfall. It is relatively cheap and easy to add 1GW of wind turbines to the grid. It is not easy and not cheap to add 1GWh of batteries.

I forgot to mention that would be a 5kw inverter that we're installing and that we're already on EI Smart meter plan (with 12.6c form 2-4am)

Thanks all for the tips. I learned a lot, as always and feel that I might be heading closer to the right track for peak shaving (or to reduce the payback time) , even if I maybe can't get Fit for it.

True, perhaps I should say it isn't advised to discharge the battery to the grid, unless you've a utility scale battery 😉

Personally I think the best grid balancing people can do is to shift their consumption around either through changing habits, or getting solar and batteries (or all of the above)

Then we'll stop creating that big evening peak which helps the grid be more predictable and easier to switch to renewables

Put the shovel away.