Solar power calculations

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boosacnoodle

231 posts

Master Geek

#2469018 24-Apr-2020 09:09

linw:

So, with 11 yr payback, by the time you break even, it would be renewal time. Makes no sense to me.

Makes more sense in hotter climes when you need cooling when the panels are producing.

Most inverters are warranted for 10-15 years with the panels warranted for 20-25 years usually. The way that the warranty on panels works is similar to the way that batteries in consumer electronics works, i.e. not that they're written off at 20 years, but rather that at 20 years you will get 80% of the initial capacity.

logo

457 posts

Ultimate Geek

Trusted

#2469036 24-Apr-2020 09:49

kotuku4:

The price quoted seems ok. The battery is wimpy. Do you have electric water heating? If yes consider a solar diverter.

Solar probably won't work out financially, on buy back. Branz, consumer, ECCA come to the same conclusion. There is a great tool of the EECA website to calculate. https://www.energywise.govt.nz/tools/solar-tool/

I ran the numbers for my situation, and had a 10 year payback.

I have a 7 year old system, with some higher buy back rates earlier on, I now consider it paid off. Still looking at battery options and electric car, but they still seem way off to me. I'm happy that I invested in my own power company (Solar)

I've got gas (continous on demand) hot water. When I installed it I hoped that my combined gas/power bill will come down with gas being more efficient (no hot water cyclinder to keep hot all day). IRL the bills stayed about the same but everyone just takes longer showers without fear of the hot water running out.

While I like the idea of a battery it seems really weak and only get less than 50c a day saving. I can cut out a coffee and make a weeks power saving in one hit.

kotuku4

359 posts

Ultimate Geek

Lifetime subscriber

#2469054 24-Apr-2020 10:26

Solar PV is very reliable. Not to be confused with Solar hot water systems. Panels are warranted to produce 86% of rated output at 25 years, for example. But will continue to be useful power generators for decades beyond that. The inverter or micro inverters are reliable, and getting cheaper.

The panel efficiency on terms of overall wattage rating and low light generation is improving. My 2013 panels are 245 Watt, same size panel today 300 Watt or better, and cheaper.

Consider overall energy efficiency, insulation, glazing, appliances, heating, power plan and usage. 4kW is a fairly large install, if you are also using gas.

TwoSeven

1463 posts

Uber Geek

#2469176 24-Apr-2020 12:46

I think a lot of people seem to be focusing on the capex cost of a solar install, but without the consideration of all of the other things one can do to make that install more efficient.

Firstly, solar water and solar PV are two different things. If one is going to use up 28sqm of roof space putting PV in, why not add an efficient Solar water heater as well.

Looking at devices in the house, lights, fridge, water cylinder, heating, cooking, computer all have solar options.

Finally, the question I often ask, is one really interested in getting back the capex? For me, I would rather have a reduced opex so that when I retire, I’m not worried so much when its pension time and the bills turn up.

Software Engineer
(the practice of real science, engineering and management)

snnet

846 posts

Ultimate Geek

Subscriber

#2469262 24-Apr-2020 13:20

TwoSeven:

I think a lot of people seem to be focusing on the capex cost of a solar install, but without the consideration of all of the other things one can do to make that install more efficient.

Firstly, solar water and solar PV are two different things. If one is going to use up 28sqm of roof space putting PV in, why not add an efficient Solar water heater as well.

Looking at devices in the house, lights, fridge, water cylinder, heating, cooking, computer all have solar options.

Finally, the question I often ask, is one really interested in getting back the capex? For me, I would rather have a reduced opex so that when I retire, I’m not worried so much when its pension time and the bills turn up.

Hopefully by the time you're retired the $4000 batteries are cheaper then 🤣

Jase2985

9714 posts

Uber Geek

Lifetime subscriber

#2469325 24-Apr-2020 13:40

linw:

So, with 11 yr payback, by the time you break even, it would be renewal time. Makes no sense to me.

ummm as mentioned inverters warranties are 10-15 years and panels have a warranty greater than that.

Terciops

15 posts

Geek

#2474128 30-Apr-2020 15:18

Jase2985:

linw:

So, with 11 yr payback, by the time you break even, it would be renewal time. Makes no sense to me.

ummm as mentioned inverters warranties are 10-15 years and panels have a warranty greater than that.

I am at year 11 on my PV system using the original equipment with no measurable degradation + some panel / equipment additions over time. Well past payback, but think on the ROI instead for a shorter term view.

How much will 10K return to you from a savings/investment account right now? 5/8ths of sod all after tax. Think of solar as Photon Harvesting/Farming. And it is tax free.

Typical ROI will be > 10% using modern pricing. My system cost me 3 times what it would now, but I have now generated and mostly self consumed over 60,000 kWh. The longest journey starts with the smallest step.

BTW, use a diverter if you have electric hot water, to totally max out self consumption.

My real time house graphics are here : https://www.youtube.com/user/terciops/live

Paladin's Facebook page (with a lot of techie stuff) : https://www.facebook.com/groups/1108024512629017/

PolicyGuy

738 posts

Ultimate Geek

Lifetime subscriber

#2474154 30-Apr-2020 15:53

Terciops:

How much will 10K return to you from a savings/investment account right now?

5/8ths of sod all before tax and almost nothing at all after tax. 😠

FTFY 😉

Terciops

15 posts

Geek

#2474162 30-Apr-2020 16:04

PolicyGuy:

Terciops:

How much will 10K return to you from a savings/investment account right now?

5/8ths of sod all before tax and almost nothing at all after tax. 😠

FTFY 😉

Much more accurate 😎

Amosnz

502 posts

Ultimate Geek

Lifetime subscriber

#2474171 30-Apr-2020 16:21

When we last did the calculations we worked out we'd save more using solar to charge an EV for everyday use than we would to power the house.

Yes we'd have to buy a leaf or similar as well, but we already have 2 cars so would offset that extra cost by selling one.

Speedtest

TwoSeven

1463 posts

Uber Geek

#2474218 30-Apr-2020 17:44

snnet:

Hopefully by the time you're retired the $4000 batteries are cheaper then 🤣

I think you are paying to much.

also the type of batteries one uses depends on the number of cycles one is going to put them through. For example, 3000 cycles vs 7000 cycles.

Also, there is a difference if one is using 2v or 12v batteries.

Software Engineer
(the practice of real science, engineering and management)

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