Solar Recommendations for new build

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t0ny

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#318917 4-Mar-2025 21:07

Bit confused on the best way forward. I have a quote for 20 panels to be installed but not sure if:

20 x 440w panels are better vs 20 x 425w panels. Both use the same tech though the 425w panels are slightly cheaper
I have been given choice of either 6kw, 8 kw or 10 kw inverter but unclear if going large is better or undersizing them are better. This again would affect the price
I will probably have a 10Kw or a 17Kw battery. I assume going larger is the best option here

I intend to use excess power generated to heat a spa during the day and use the battery for when generation is low or none. The quote is from micromall.

timmmay

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#3350151 4-Mar-2025 21:14

I'm not an expert on solar or anywhere close to it. I have a system going in soon so I've done a bit of research. I chose the slightly cheaper, slightly lower spec panels, as for return on investment the more expensive panels didn't seem worthwhile.

Re inverter size, the panels won't produce peak power very often, maybe in the middle of the day in the middle of summer, if the angles are right. Inverters apparently work most efficiently at or near their capacity, and having an inverter smaller than the panels is normal - in Australia the panels are allowed to be up to 133% of the inverter size. For my 9.2kw of panels we're getting a 6kw inverter, 6.6 peak output. For your 8.5kw of panels I'd probably go with 6kw. If the inverter supports DC coupled batteries, which means the batteries run off DC before it hits the inverter rather than off the AC produced by the inverter, 6kw inverter should be plenty big enough.

The payback time on batteries is quite high in many cases. If you don't get many outages where you are then it may not be worth it, unless you want a battery for outages and emergencies. We decided not to get one initially, they can be added later.

With a spa pool and presumably a hot water cylinder you'll probably want a diverter. Ask your installer.

I suggest you get another quote, just for comparison. Harrisons and Lightforce are good national chains, and prices at the moment can be better than what's on their website.

There's lots of useful info in this thread.

Handle9

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#3350235 4-Mar-2025 23:18

timmmay:

The ROI on batteries is very high.

Don't you mean the ROI on batteries is very low? The simple payback period is very long

timmmay

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#3350254 5-Mar-2025 06:43

Handle9:

timmmay:

The ROI on batteries is very high.

Don't you mean the ROI on batteries is very low? The simple payback period is very long

Yeah typo, thanks. High payback time.

RobDickinson

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#3350289 5-Mar-2025 09:12

20 x 440w panels are better vs 20 x 425w panels. Both use the same tech though the 425w panels are slightly cheaper

8.8kw vs 8.5kw so not a lot in lot 300w you wont notice, look at efficiency and degradation etc also

I have been given choice of either 6kw, 8 kw or 10 kw inverter but unclear if going large is better or undersizing them are better. This again would affect the price

You wont gain anything by having a 10kw inverter and 8.8kw panels (which may sometimes exceed 9kw) but you will cap at the inverter level

Having more kw of panels than inverter clips the peak but will provide better shoulders vs equally low panels (i.e. 9kw + 8kw inverter vs 8kw of both)

You'll probably be capped at 5-6kw for export and its often hard to use up much of the excess

I will probably have a 10Kw or a 17Kw battery. I assume going larger is the best option here

Larger is better if you can use it but what kind of kw can it supply to your house, also remember in winter you'll struggle to fill it and in summer filling it will take a few hours.

billgates

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#3350344 5-Mar-2025 09:41

Which city are you located in as members maybe to recommend installers they have used in same city to get additional quotes. Get atleast 3 quotes. Ideally 5

Do whatever you want to do man.

t0ny

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#3350345 5-Mar-2025 09:45

Thanks for the replies. Looks like 6-8Kw inverter with 425w panels are the way to go. I have asked for quotes from Lightforce and Harrisons as well. Iam based in Auckland.

RobDickinson

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#3350347 5-Mar-2025 09:50

For me Lightforce had horrible 1980s double glazing sales techniques I wouldnt go near , and the old 'I'll talk to the manager' after a horrible overpriced quote etc

Harrisons seem ok in a big business way but were way too slow

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timmmay

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#3350349 5-Mar-2025 09:55

I found Lightforce quite expensive, about $4K more than the local place, and the sales guy didn't know what a diverter is. I suspect prices are falling and they hadn't updated their prices yet. Their base package prices were ok but adding anything on was expensive.

I signed a contract with a local firm before Harrisons even made it out to visit, I think being a recognizable national chain they get booked up.

t0ny

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#3350353 5-Mar-2025 10:04

Have asked for quotes from French Electrical and Pure Power so i have a good mix of larger firms and the smaller ones. Will report back once i get the quotes for anyone else who is interested.