Solar options for home in 2022

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450 posts

Ultimate Geek
+1 received by user: 324

#3462282 17-Feb-2026 17:26

Paul1977:

fastbike:

Unless you can run a model on a reasonably fine time base then those models are pretty useless. I was able to source production data for a nearby site (then correct it for PVpeak, orientation and slope) and I had consumption data down to 5 min resolution from our own meter so could build an accurate model across 12 months showing the net import/export at each 15 minute period. Then I could plug in various tariffs and come up with an estimated savings figure.

I have since validated it with real data from the last year which showed my modelling was a bit low for gross PV output.

3 months after the PV was installed I put in battery to time shift peak consumption, so we now self supply >95% of peak consumption. The advantage is we run our house as a house, not as a power optimization appliance.

I've taken 12 months worth of power consumption down to 30min resolution. Fed that along with as many details as I could about the proposed inverter, solar panels, orientation, roof pitch, location etc into ChatGPT for it to calculate estimates.

So our consumption data is very accurate, but some assumptions will have been made about what the solar generation will look like. I think it should be reasonably close to reality.

If you are Chch based i could send you some production data

Otautahi Christchurch

mark0x01

13 posts

Geek

#3462283 17-Feb-2026 17:26

wellygary:

mark0x01:

Looks like they have all done the caculations so they get the most benefit from our solar.

Your buy rate is going to be capped by the cost of commercial solar, that is competing with you...

Meridian's Ruakaka solar farm is expected to be producing at "$97 /MWh (9.7c/unit) levelized cost of energy (real, 2025)."

https://www.meridianenergy.co.nz/public/Investors/Reports-and-presentations/Investor-presentations/2024/ruakaka-solar-announcement-March-2025.pdf

Of course this only means that the offpeak rate will then have to increase 😃

Unfortunately I've achieved being a "standard" power user. Need more high energy toys.

mark0x01

13 posts

Geek

#3462286 17-Feb-2026 17:36

Paul1977:

If you are Chch based i could send you some production data

I'd be interested since I'm just over the river in Kaiapoi.

Still pondering on taking a punt on a solar system.

HarmLessSolutions

1230 posts

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#3462290 17-Feb-2026 17:46

EgorNZ:

.....

Regarding GST, you will be paying GST on imported energy but can only collect GST on exported energy if you are GST registered, which very few households are. So most people want to compare (import price including GST) vs (export price excluding GST).

Although that is what you would expect it isn't actually the case for some providers. In the case of PowerEdge and Ecotricity GST is added to your FIT irrespective of whether your solar installation is GST registered or not. PowerEdge actually state that their 20c/kWh FIT is GST inclusive and in Ecotricity's case they add GST as the final step of their invoices so it applies to both import and export including if that final total is a credit balance.

PowerEdge advise that the GST component will be deducted from credit balances cashed out but I don't know if this is the case for Ecotricity but I guess I'll find out in due course.

https://www.harmlesssolutions.co.nz/

Paul1977

5171 posts

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#3462293 17-Feb-2026 17:54

fastbike:

If you are Chch based i could send you some production data

In Chch, so definitely interested thanks.

Twincamr2

108 posts

Master Geek
+1 received by user: 17

#3462312 17-Feb-2026 19:51

Paul1977:

Not sure your reasoning for not touching Telsa. But doing the numbers the ROI on a battery just doesn't add up for us. It looks OK when the supplier punches the figures into their ROI tools, but that doesn't paint the full picture. The figures below are based on the best rates I could find and our specific power usage patterns.

It looks like 24 Aiko 480W panels and 10kW Fronius inverter with no battery could reduce our yearly power bills by $2,500 from an install cost of around $22,000 giving an ROI of 8.8 years ($22,000/$2,500).

Change to 24 Aiko 480W panels and Powerwall 3 (13.5kW battery with built-in 10kW inverter) could reduce our yearly power bills by $3,000 from an install cost of around $33,000 giving an ROI of 11.7 years ($35,000/$3,000).

At a glance, that looks pretty good - only 3 years added to the ROI and then bigger savings. BUT we'd actually only be gaining an additional $500 saving per year for an additional $13,000 spend. So the true ROI for the battery component is actually 26 years ($13,000/$500), which would be beyond the reasonable life expectancy of the Powerwall 3. It took me a bit to get my heads around how that maths works (because looking at it one way looks great, but looking at it the other way looks terrible), but I'm pretty sure I'm correct.

The calculations would probably be similar for a non-Tesla battery,

Except after your 8.8 years break-even point for the inverter/panels, you don't stop saving money. You're still saving $3000 per year until the 11.7 year mark (and beyond, assuming the whole system doesn't go up in smoke after 11.7 years).

8.8 years of $500 return for the batteries plus 2.9 years of the full $3000 apportioned to the battery gives... $13,100, Not surprisingly a rounding error away from exactly the marginal cost of the battery.

So no, 26 years break-even is not correct for the battery, it's an additional 2.9 years.

Handle9

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#3462314 17-Feb-2026 20:00

Twincamr2:

Paul1977:

Not sure your reasoning for not touching Telsa. But doing the numbers the ROI on a battery just doesn't add up for us. It looks OK when the supplier punches the figures into their ROI tools, but that doesn't paint the full picture. The figures below are based on the best rates I could find and our specific power usage patterns.

It looks like 24 Aiko 480W panels and 10kW Fronius inverter with no battery could reduce our yearly power bills by $2,500 from an install cost of around $22,000 giving an ROI of 8.8 years ($22,000/$2,500).

Change to 24 Aiko 480W panels and Powerwall 3 (13.5kW battery with built-in 10kW inverter) could reduce our yearly power bills by $3,000 from an install cost of around $33,000 giving an ROI of 11.7 years ($35,000/$3,000).

At a glance, that looks pretty good - only 3 years added to the ROI and then bigger savings. BUT we'd actually only be gaining an additional $500 saving per year for an additional $13,000 spend. So the true ROI for the battery component is actually 26 years ($13,000/$500), which would be beyond the reasonable life expectancy of the Powerwall 3. It took me a bit to get my heads around how that maths works (because looking at it one way looks great, but looking at it the other way looks terrible), but I'm pretty sure I'm correct.

The calculations would probably be similar for a non-Tesla battery,

Except after your 8.8 years break-even point for the inverter/panels, you don't stop saving money. You're still saving $3000 per year until the 11.7 year mark (and beyond, assuming the whole system doesn't go up in smoke after 11.7 years).

8.8 years of $500 return for the batteries plus 2.9 years of the full $3000 apportioned to the battery gives... $13,100, Not surprisingly a rounding error away from exactly the marginal cost of the battery.

So no, 26 years break-even is not correct for the battery, it's an additional 2.9 years.

Why would you apportion 2.9 years @$3000 of simple payback period to the battery. It's savings from the inverter and panels. The battery has not resulted in $3000 of saving, it has resulted in $500.

Also if the unit is years you are talking about simple payback period. If it's a percentage it's return on investment. When simple payback is done it's done. ROI continues for the life of the plant.

Paul1977

5171 posts

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#3462364 17-Feb-2026 20:22

Twincamr2:

Paul1977:

Not sure your reasoning for not touching Telsa. But doing the numbers the ROI on a battery just doesn't add up for us. It looks OK when the supplier punches the figures into their ROI tools, but that doesn't paint the full picture. The figures below are based on the best rates I could find and our specific power usage patterns.

It looks like 24 Aiko 480W panels and 10kW Fronius inverter with no battery could reduce our yearly power bills by $2,500 from an install cost of around $22,000 giving an ROI of 8.8 years ($22,000/$2,500).

Change to 24 Aiko 480W panels and Powerwall 3 (13.5kW battery with built-in 10kW inverter) could reduce our yearly power bills by $3,000 from an install cost of around $33,000 giving an ROI of 11.7 years ($35,000/$3,000).

At a glance, that looks pretty good - only 3 years added to the ROI and then bigger savings. BUT we'd actually only be gaining an additional $500 saving per year for an additional $13,000 spend. So the true ROI for the battery component is actually 26 years ($13,000/$500), which would be beyond the reasonable life expectancy of the Powerwall 3. It took me a bit to get my heads around how that maths works (because looking at it one way looks great, but looking at it the other way looks terrible), but I'm pretty sure I'm correct.

The calculations would probably be similar for a non-Tesla battery,

Except after your 8.8 years break-even point for the inverter/panels, you don't stop saving money. You're still saving $3000 per year until the 11.7 year mark (and beyond, assuming the whole system doesn't go up in smoke after 11.7 years).

8.8 years of $500 return for the batteries plus 2.9 years of the full $3000 apportioned to the battery gives... $13,100, Not surprisingly a rounding error away from exactly the marginal cost of the battery.

So no, 26 years break-even is not correct for the battery, it's an additional 2.9 years.

But since you hit the break even point for the panels only option after 8.8 years, that’s 2.9 years of of $2500 potential savings you aren’t getting while you are still paying off the battery.

And only $500 per year of “savings” can be apportioned to the battery, not the full $3,000 ($2500 from panels/inverter, $500 from battery)

That’s what I meant by the basic ROI calculators being misleading, because initially I thought exactly the same as you.

EDIT: To say I may be confusing terminolgies and misusing ROI when I mean “break even”, but the gist is still that for my usage I wouldn’t be financially better off long term unless the Powerwall lasted longer than 26 years.

dantheperson

226 posts

Master Geek
+1 received by user: 63

#3462371 17-Feb-2026 20:34

wellygary:

Your buy rate is going to be capped by the cost of commercial solar, that is competing with you...

Meridian's Ruakaka solar farm is expected to be producing at "$97 /MWh (9.7c/unit) levelized cost of energy (real, 2025)."

https://www.meridianenergy.co.nz/public/Investors/Reports-and-presentations/Investor-presentations/2024/ruakaka-solar-announcement-March-2025.pdf

Yes, that's another reason i jumped to meridian and locked in their 17 cent export rate for 3 years. With all the commercial solar coming online this year there could be a risk it devalues mid-day power and pushes down the retail export rates. I was happy with octopus TOU plans, but they only offer floating rates.

Paul1977

5171 posts

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+1 received by user: 2192

#3462373 17-Feb-2026 20:38

Handle9:

Twincamr2:

Except after your 8.8 years break-even point for the inverter/panels, you don't stop saving money. You're still saving $3000 per year until the 11.7 year mark (and beyond, assuming the whole system doesn't go up in smoke after 11.7 years).

8.8 years of $500 return for the batteries plus 2.9 years of the full $3000 apportioned to the battery gives... $13,100, Not surprisingly a rounding error away from exactly the marginal cost of the battery.

So no, 26 years break-even is not correct for the battery, it's an additional 2.9 years.

Why would you apportion 2.9 years @$3000 of simple payback period to the battery. It's savings from the inverter and panels. The battery has not resulted in $3000 of saving, it has resulted in $500.

Also if the unit is years you are talking about simple payback period. If it's a percentage it's return on investment. When simple payback is done it's done. ROI continues for the life of the plant.

That was my fault, I said ROI when I really meant “payback period” or “break even point”.

kangaroo13

87 posts

Master Geek
+1 received by user: 90

#3462376 17-Feb-2026 20:49

Twincamr2:

Paul1977:

...

It looks like 24 Aiko 480W panels and 10kW Fronius inverter with no battery could reduce our yearly power bills by $2,500 from an install cost of around $22,000 giving an ROI of 8.8 years ($22,000/$2,500).

Change to 24 Aiko 480W panels and Powerwall 3 (13.5kW battery with built-in 10kW inverter) could reduce our yearly power bills by $3,000 from an install cost of around $33,000 giving an ROI of 11.7 years ($35,000/$3,000).

At a glance, that looks pretty good - only 3 years added to the ROI and then bigger savings. BUT we'd actually only be gaining an additional $500 saving per year for an additional $13,000 spend. So the true ROI for the battery component is actually 26 years ($13,000/$500), which would be beyond the reasonable life expectancy of the Powerwall 3. It took me a bit to get my heads around how that maths works (because looking at it one way looks great, but looking at it the other way looks terrible), but I'm pretty sure I'm correct.

...

Except after your 8.8 years break-even point for the inverter/panels, you don't stop saving money. You're still saving $3000 per year until the 11.7 year mark (and beyond, assuming the whole system doesn't go up in smoke after 11.7 years).

8.8 years of $500 return for the batteries plus 2.9 years of the full $3000 apportioned to the battery gives... $13,100, Not surprisingly a rounding error away from exactly the marginal cost of the battery.

So no, 26 years break-even is not correct for the battery, it's an additional 2.9 years.

Per Handle9, I think the plant life needs to be considered

1) Breakeven for system without a battery is 22K/2500 = 8.8y

2) Breakeven for system with battery is 35K/3000 = 11.7y

But - what is the lifetime of the battery? Let's say it is 12 years, then after 12 years you have net result of

1) 12*2500 - 22K = 8K credit

2) 12*3000 - 35K = 1K credit and you are up for a new battery.

If it is 15 years (quite a reasonable assumption), then you are still ahead by not having invested in the battery:

1) 15.5K credit

2) 10.0K credit

The values get closer by $500 per year. It is only after 26years that the profit from both becomes equalised (both $43K credit). i.e. unless your battery lasts more than 26 years, you're always ahead financially having just invested in the inverter+panels. It's not to say that system 2 is a bad investment, as long as the battery lasts 12+ years. But system 1 is a better one.

This does ignore the time value of money (including financing costs) - which makes paying the additional $13K up front less appealing. Exacerbated by the likely ongoing trend of batteries getting cheaper.

It is hard to justify the extra spend on a battery on purely financial basis if it is only resulting in an extra $500 saving each year.

However, what may not have been factored in is the opportunity to sell excess stored energy into the spot market, or even playing the arbitrage game between buying on night rate and selling on day rate/spot market. It would work your battery a lot harder (reduce lifetime), and rather depends on market prices, not just now, but well into the future.

Twincamr2

108 posts

Master Geek
+1 received by user: 17

#3462377 17-Feb-2026 20:58

kangaroo13:

Per Handle9, I think the plant life needs to be considered

1) Breakeven for system without a battery is 22K/2500 = 8.8y

2) Breakeven for system with battery is 35K/3000 = 11.7y

But - what is the lifetime of the battery? Let's say it is 12 years, then after 12 years you have net result of

1) 12*2500 - 22K = 8K credit

2) 12*3000 - 35K = 1K credit and you are up for a new battery.

If it is 15 years (quite a reasonable assumption), then you are still ahead by not having invested in the battery:

1) 15.5K credit

2) 10.0K credit

The values get closer by $500 per year. It is only after 26years that the profit from both becomes equalised (both $43K credit). i.e. unless your battery lasts more than 26 years, you're always ahead financially having just invested in the inverter+panels. It's not to say that system 2 is a bad investment, as long as the battery lasts 12+ years. But system 1 is a better one.

This does ignore the time value of money (including financing costs) - which makes paying the additional $13K up front less appealing. Exacerbated by the likely ongoing trend of batteries getting cheaper.

It is hard to justify the extra spend on a battery on purely financial basis if it is only resulting in an extra $500 saving each year.

However, what may not have been factored in is the opportunity to sell excess stored energy into the spot market, or even playing the arbitrage game between buying on night rate and selling on day rate/spot market. It would work your battery a lot harder (reduce lifetime), and rather depends on market prices, not just now, but well into the future.

Thank you for explaining that so clearly. I understand the difference in our takes on the situation now.

Paul1977

5171 posts

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#3462378 17-Feb-2026 21:02

Twincamr2:

kangaroo13:

Per Handle9, I think the plant life needs to be considered

1) Breakeven for system without a battery is 22K/2500 = 8.8y

2) Breakeven for system with battery is 35K/3000 = 11.7y

But - what is the lifetime of the battery? Let's say it is 12 years, then after 12 years you have net result of

1) 12*2500 - 22K = 8K credit

2) 12*3000 - 35K = 1K credit and you are up for a new battery.

If it is 15 years (quite a reasonable assumption), then you are still ahead by not having invested in the battery:

1) 15.5K credit

2) 10.0K credit

The values get closer by $500 per year. It is only after 26years that the profit from both becomes equalised (both $43K credit). i.e. unless your battery lasts more than 26 years, you're always ahead financially having just invested in the inverter+panels. It's not to say that system 2 is a bad investment, as long as the battery lasts 12+ years. But system 1 is a better one.

This does ignore the time value of money (including financing costs) - which makes paying the additional $13K up front less appealing. Exacerbated by the likely ongoing trend of batteries getting cheaper.

It is hard to justify the extra spend on a battery on purely financial basis if it is only resulting in an extra $500 saving each year.

However, what may not have been factored in is the opportunity to sell excess stored energy into the spot market, or even playing the arbitrage game between buying on night rate and selling on day rate/spot market. It would work your battery a lot harder (reduce lifetime), and rather depends on market prices, not just now, but well into the future.

Thank you for explaining that so clearly. I understand the difference in our takes on the situation now.

Agreed, @kangaroo13 explained it far more clearly than I did!

richms

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#3462386 17-Feb-2026 21:51

mark0x01:

Paul1977:

If you are Chch based i could send you some production data

I'd be interested since I'm just over the river in Kaiapoi.

Still pondering on taking a punt on a solar system.

If you can put something in that is where you will not need scaffolding, and the cabling is easy then starting small is viable. Look at your usage in peak sunlight times and what you can easily delay to that like hotwater heater not coming on till 10am after your morning showers and then installing something will have a very short payback time. If you can use a banks greenwashing loan, even better. And if you want a carport and can get them to do you a solar carport install at 1%, even better.

Richard rich.ms

sen8or

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#3462474 18-Feb-2026 08:07

I assume a solar install includes setting up of your house to optimise solar energy?

For now, we use about 65% low rate / night rate energy. HWC only comes on at night, washing / dishwasher put on overnight where possible etc. The HWC is controlled by the meter (I think), but I assume that this is changed when we switch to solar for a different meter (with export). Are things like HWC programmable from the new meter / inverter?

We can readily change power use on some things (washing / dishwasher) but as we work during the day, day time use is negligible otherwise and being in Christchurch, heating is necessary usually from April / May through to July/August (not all the time but most mornings and evenings).

Thanks

Sen

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