Considering Solar for our new home

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Cogenate

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Master Geek

#319355 17-Apr-2025 10:08

Keen to get some thoughts on solar for my home. We have a great east/west facing vaulted roof and could fit 38 panels for 17kw. I have been quoted for 10.8kw and 17kw with a Powerwall 3.

Pricing = 43k for the 17kw and 36k for the 10.8kw, both with PW3.

I am thinking to just go for the full 17kw so that I don't regret it later on. Because it is east west I would be getting the 17kw split fairly even across the day meaning the PW3 with it's inverter should be able to take it. Thinking longer term with EVs and bidirectional charging the 17kw would be quite beneficial.

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#3364963 17-Apr-2025 10:21

Who did you get the quotes from?

Opinions are my own and not the views of my employer.

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Cogenate

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#3364965 17-Apr-2025 10:25

Total Solar in Auckland, got a couple of others that were more expensive and one more coming next week

Jase2985

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#3365094 17-Apr-2025 21:08

Single phase or 3 phase? what is your export limit? i suspect 5kW. How much power do you actually use?

Thats an awfully large amount of panels if it is single phase and a single battery on a 5kw export limit, unless you use a lot of power

timmmay

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#3365099 17-Apr-2025 21:38

The payback period on a battery is extremely high, given some power companies will pay you only 5% less than what you pay for power. The only reason to have a battery is in case you have regular power cuts.

That is a lot of panels. In summer middle of the day you'll have massive amounts of power, in winter much less so but you'll maybe have useful amounts. I doubt you'll be able to use it all, and you won't be able to export much of the excess, so I think you'll be wasting your money unless there's some factor you haven't mentioned. The east / west split means some of the you'll mostly be generating from one side unless the roof pitch is low.

We have 21 panels 9.2kw, 6kw inverter. 2/3 of the panels face north, 1/3 face west. On super sunny days we miss out on a bit of power, but not much, only in the middle of the day. On cloudy days they generate 0.5 - 2kw.

Cogenate

51 posts

Master Geek

#3365116 18-Apr-2025 07:41

Yeah agree it's on the overkill side for panels... But thinking down the line with bidirectional charging on EVs and selling power back to the grid at peak rates on octopus. Also not sure but I feel like buyback rates are terrible and that they can o ky get better from here if anything?

We both work from home with a baby on the way, ducted aircon, one EVso we can run all our appliances in the day. We are heavy aircon users in summer but we would still not use it all. Intention was with the battery to fill it at night @11cents and sell at peaks for 20+ cents.

timmmay

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#3365117 18-Apr-2025 07:58

You do sound like a high power user. Our ducted system has a 8kw outdoor, it sits around 1 - 1.5kw power usage most of the time that it's on, though it's 2kw when it first starts and sometimes it sits a bit below 1kw once it's been on for a while. Our hot water needs 3.3kw for 2-3 hours per day. Washing and drying will be a big user with a new baby. The electric car will soak up some. 17kw of panels is a heck of a lot.

On Meridian in Wellington I pay 21c for power and buyback rate is 19c, so selling is only about 10% less than buying. That could change in the future though, in Australia there's so much solar you basically get nothing for it. There's nowhere near as much here and I've read that they're trying to encourage people to get solar, one lines company is even paying extra for solar input for a year - Orion I think.

We got an inverter that is battery capable, so that if buyback rates fall we can add a battery later to make use of the power we generate better. Maybe that's something to consider.

Cogenate

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#3365118 18-Apr-2025 08:03

Awesome thanks, total solar didn't quote me on the 17kw solution it was another another company but I got them to quote so I had something to compare with.

I was leaning towards the 10kw with battery option. We intend on staying for over 10 years, but there is obviously risks there as you can plan but things can change.

timmmay

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#3365121 18-Apr-2025 08:26

Battery

Suggest an import factor to decide whether or not to get a battery is your buyback rate. Meridian was were easily the best for us, but there's no online pricing - you have to submit a form and wait a few days for a human to reply, and the person that replies can be quite slow. If you can get a buyback rate only 10% below your buy rate a battery is probably a waste of money. Meridian for us is we buy at 22c / kwc inc GST, buyback 19.55c inc GST.

What does Octopus give you for buy and buyback rate for OctopusFlexi Standard User plan? To give an idea of Meridian prices, they pay a little more buyback, and their flat sell rate for us is about 15% less than the Octopus off-peak rate.

I suspect a battery won't be worthwhile once you go through this process. You can easily add a battery later. You should consider when you buy whether you want a Powerwall or the brand that matches with your inverter.

Inverter

Without a battery you'd need an inverter sized for your panels. Generally inverters are undersized compared with panels - we have 9kw panels 6kw inverter. In peak summer middle of the day we'll lose a few kw of generation, but most of the time we're below 6kw output anyway.

Export Limit?

Take this one with a grain of salt as I'm not sure about it. Another thing I've read is if your solar system output is too high you might not be approved for export. I don't really know if this is true, I suggest this is something you ask your installer because it might be lines company specific. If you share the city you live in someone else might know about this.

johno1234

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#3365126 18-Apr-2025 09:08

timmmay:

You do sound like a high power user. Our ducted system has a 8kw outdoor, it sits around 1 - 1.5kw power usage most of the time that it's on, though it's 2kw when it first starts and sometimes it sits a bit below 1kw once it's been on for a while.

Yet these high powered systems have to be installed on a 30A circuit. Do they briefly draw that when they have a cold or hot house to deal with?

timmmay

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#3365142 18-Apr-2025 10:51

johno1234:

Yet these high powered systems have to be installed on a 30A circuit. Do they briefly draw that when they have a cold or hot house to deal with?

Not according to the Shelly monitoring my ducted heat pump.

plas

451 posts

Ultimate Geek

#3365253 18-Apr-2025 11:34

If your thinking about a PW3 its best to make the decision now as it includes the inverter.

I don't have a complete months data yet and still need to double check figures against a bill.

Between 3am-6am Power is free so we fully charge the PW, heat the water, warm the house for the morning etc. PW generally covers us through to the evening if the weather has been really bad, but most days it charges completely back up. Our power is bought back at wholesale which has been roughly 30c, I guess if I wanted to make a bit more $ back I could charge the PW @ 0c then on fine days dump the battery back onto the grid.

Well aware that in other months the wholesale rate will be poor, but I'm not worried about the return on the battery and the panels will pay for themselves over their lifetime.

Stu1

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#3367550 25-Apr-2025 18:52

plas:

If your thinking about a PW3 its best to make the decision now as it includes the inverter.

I don't have a complete months data yet and still need to double check figures against a bill.

Between 3am-6am Power is free so we fully charge the PW, heat the water, warm the house for the morning etc. PW generally covers us through to the evening if the weather has been really bad, but most days it charges completely back up. Our power is bought back at wholesale which has been roughly 30c, I guess if I wanted to make a bit more $ back I could charge the PW @ 0c then on fine days dump the battery back onto the grid.

Well aware that in other months the wholesale rate will be poor, but I'm not worried about the return on the battery and the panels will pay for themselves over their lifetime.

How do you get free power 3 to 6?

Stu

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#3367554 25-Apr-2025 18:56

Z Energy offered free power from 3am to 6am, from memory.

People often mistake me for an adult because of my age.

Keep calm, and carry on posting.

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DjShadow

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#3367558 25-Apr-2025 19:27

Been looking at getting Solar myself, I did find an interesting part on Wellington Electricity’s website which talks about congestion zones on the network which I’m understanding as too many people exporting power back to the grid. They included a map so maybe check your line company’s website if they mention the same

plas

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Ultimate Geek

#3369382 30-Apr-2025 23:44

Stu:

Z Energy offered free power from 3am to 6am, from memory.

Correct. https://www.z.co.nz/products-and-services/z-app/power-your-home/ev-at-home-plan

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