Financial payback calculation for a solar system

Hi we have 2 quotes both with mid range panels
Just wondering if they look okay and does it pay in the long run to have panels with a 25 year warranty? We are at Mangrove Mountain and our quarterly bill is around $500 and we have a large shed that it can go on

Quote 1 Steve Torpy Electrical

Parts Description Amount 7,652.00 plus GST $8417.20 Amount 8.2kw
Solar:Quote to supply and install 1 x New High Quality Solar PV system comprising of: 33 x Trina Honey Split Cell Mono Perc 330watt solar panels with black frames 1 x Fronius single phase Primo 8.2-1 inverter 1 x Fronius Smart Meter for export limitation to 6kw due to cable supply to transformer Full Racking system to tin roof DC Isolators to roof panels with heat shields Total price - $12449.00 plus gst STC Rebate - $5247.00 plus gst
This system should produce around 11,600kw per annum and calculated at $0.28/kw would be valued at $3254.00 in revenue per annum Warranty 11 years

Quote 2
Freedom solar and Batteries 12 year warranty

Risen RSM120-6-330M 34 = $9114.38
Goodwe M5 GW8500-MS $1967.35
Zj Berny E-DCI-Cover $29.60
Titan TT-DR-4200 18 = $593.41
E-LKT-DC-v2 21.98 E-MC-Genuine 12 =. $98.87
Installation per watt residential 11220 = $3702.50
Tin mounting per 6 modules $386.10

ABB E-ACCB-Abb1P25 $8.24
Zj Beny E-DCI-Beny 6 = $326.10
Rebate -6290.00

Any advice is very much appreciated

Hi @karins

I’ll come back to you on this, but regarding tier 1, it’s worth reading this thread:

Hi Marty Thanks for the link.
A couple of questions please. Does it pay at all to consider putting in a larger system 10KW
as we have the shed roof available to install the panels . We do not use that much power (usually under $500 a quarter )
We will be retires in 5 to 7 years and any extra income that it may produce would helpful but I’ve been told that it is so negligible not not worry about this side of things?
A 3rd quote we just received seems to have great components and customer service is somewhat higher as is product warranty. But is more expensive.
32 Trina half cell mono panels (10.56Wp) 25 year warranty
32 x Enphase IQ7+ Micro Inverter (9.44WAC) 10 year warranty
Premium Black Clenery Ezy rack
Monitoring and 12 month tech support
This comes to $12,490.00 AFTER rebates. So quite a jump from the other quotes. Do youtsee any value to the extra out lay.
Cheers Karin

Hi Karin

I will let Marty reply on the technical side and also the quote but one problem you may have with the shed is structural. Unless you have engineering drawings showing that the shed structure is built to withstand the forces that the installation will impose on the structure.

Thanks and Best Regards

Ivan Colaço


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Hi Karin

That’s a good question, and can be roughly answered with a few calculations. You’ll need to know how much you will get paid for the solar you export. You’ll find a link under “Feed-in tariffs” in this article:

You can see general calculations for solar generation in NSW here. A conservative estimate is that you’ll generate 4kWh for every kW installed per day on average (therefore 40kWh a day with a 10kW system). If you use 10kWh of that, you will export 30kWh to the grid. The question is, how much will you get paid for that. You might be able to get 15c/kWh if you’re lucky, that’s $4.50 a day, $1650 a year. You should be able to fill in the assumptions where needed there, and hopefully work out if it is a worthwhile investment or not. If would come down to the extra cost of the bigger system, and how much you’ll get for the feed-in tariff (FIT).

Just to come back to your original comment here. It looks like those calcs assume that you will consume all of the solar that you produce. As you mention, that’s unlikely because you don’t use that much. It’s better to blend what you pay for energy (assuming that’s $0.28/kWh), and what you will receive when you export ($0.??). Let’s say you consume half of your solar energy, and export the rest, you’ll want to blend your cost of solar with your FIT 50/50, so if the FIT is $0.14, then your blended value of the solar will be $0.21 = ($0.28 + $0.14 / 2). Does that make sense?

I’m not really following this quote to be honest. I don’t see any batteries. Looks pretty dear.

It’s very tough to weigh up I find. I really like the Enphase micro inverters, you will get more solar out of them. Given any extra solar you produce will only give you whatever your FIT rate is though, it may be less compelling. It would be more compelling if you were able to offset your more expensive cost of buying energy. Read this thread for more Micro inverters (Enphase ) Vs Power optimisers (SolarEdge, Tigo) - #4 by Marty.

Last thing you might want to read if you are getting a bit confused about kW & kWh: ⚡ Solar Power vs Solar Energy - kW & kWh explained.

Hope that helps!


Of Course the 3rd quotes use Enphase micro inverter is miore dear naturally

I am not looking at Panels being Tier 1 because ALL panels that are registered on CEC list
are Tier1 . Tier 1 means the mnufacturer has attain a certain Finacial standard award by Bloomberg .
Quotations as above can be more confusing because comparing apple and orange is impossible. OK for educationnal purpose I will create a table of 5 quotes different panels but te rest is the same and you can see how the prices can be big gap
Give me 2 days or so
Regards Mel of Solar Hybrid Solution