Solar options for home in 2022.

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#3258855 12-Jul-2024 16:57

The Temperature coefficient of Power Output - Pmax in panels is somewhere in the range of -0.24% /°C. The standard test conditions (STC) is = irradiance 1000 W/m², temperature 77°F (25°C). So for every 4 degrees less than 25°C you gain 1% performance, so at 5°C, you get an extra 5% which on a 420W panel is only 22w, but over a large string it could be hundreds of watts.

The max power for a Fronius 5.0 inverter is 7500w, with the max of one string being 6250w and the other 5170W.

Most installers will over panel systems by about 20-30% (inverter dependant) to make the most power they can over winter when the sun is lower in the sky and you generally make less power. The downside as mentioned is in summer they system will clip (limit the power) as you are limited to the output of the inverter which is capped at 5000W.

HarmLessSolutions

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#3258904 12-Jul-2024 17:08

Jase2985:

......

Most installers will over panel systems by about 20-30% (inverter dependant) to make the most power they can over winter when the sun is lower in the sky and you generally make less power. The downside as mentioned is in summer they system will clip (limit the power) as you are limited to the output of the inverter which is capped at 5000W.

Also in summer an overpanelled system will reach the inverter's maximum output level earlier and stay there for longer so the 'lost' generation is probably well below the percentage of panel 'excess', due to the day's extended peak generation duration (across all seasons).

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

paultaupo

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#3259212 13-Jul-2024 19:59

We are looking at putting solar on our new build. We have been talking with a company called Zen energy - anyone dealt with them before?

They have suggested 10kw panels with a 5kw inverter and a 7kw battery. The inverter feels undersized to me - interested to hear what others think

Also talking with harrisons who suggested a 10kw system with an 8 kw inverter and a 13kw Tesla power wall - in this case the inverter feels a better size but not sure how good the Tesla power walls are.

HarmLessSolutions

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#3259215 13-Jul-2024 20:31

@paultaupo, The Zen setup doesn't sound great as the inverter is going to limit production from 10kW of panels to only 5kW so I don't understand their reasoning there. A 7kWh battery will fully charge in no time so that's not the answer and do be sure to sussout the ROI of including batteries in your installation as they add considerable expense to the project and if your use model doesn't fit them you may never see their cost repaid. Also for both 10kW systems (if the Zen system upsizes their inverter) the next limitation you may strike is if you have single phase supply installed, and/or a single phase inverter is the export cap that your lines company stipulates, typically 5kW/phase. A reputable installer should be across these issues so if you don't get satisfactory answers from Zen or Harrisons do some more shopping around. SEANZ are a good resource for finding local PV installers/providers.

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

Jase2985

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#3259216 13-Jul-2024 21:21

HarmLessSolutions:

@paultaupo, The Zen setup doesn't sound great as the inverter is going to limit production from 10kW of panels to only 5kW so I don't understand their reasoning there.

And most inverters won't take double the input worth of panels, maybe 50%. But as mentioned, the output will be limited to 5kW,

The only thing i can think of is if the inverter can output its 5kW worth of AC and also output to the battery above that 5kW.

paultaupo

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#3259217 13-Jul-2024 21:50

HarmLessSolutions:

@paultaupo, The Zen setup doesn't sound great as the inverter is going to limit production from 10kW of panels to only 5kW so I don't understand their reasoning there. A 7kWh battery will fully charge in no time so that's not the answer and do be sure to sussout the ROI of including batteries in your installation as they add considerable expense to the project and if your use model doesn't fit them you may never see their cost repaid. Also for both 10kW systems (if the Zen system upsizes their inverter) the next limitation you may strike is if you have single phase supply installed, and/or a single phase inverter is the export cap that your lines company stipulates, typically 5kW/phase. A reputable installer should be across these issues so if you don't get satisfactory answers from Zen or Harrisons do some more shopping around. SEANZ are a good resource for finding local PV installers/providers.

thanks for that - basically what i thought so good to hear it from others. Still not sold on battery as the ROI is hard to make work but we do want some resilience as we are rural

Dilbonius

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#3259231 14-Jul-2024 09:21

paultaupo:

They have suggested 10kw panels with a 5kw inverter and a 7kw battery. The inverter feels undersized to me - interested to hear what others think

This seems dumb. We have just installed 7.1kw of panels on a 5kw inverter all facing north and I'm disappointed because it will be clipping hard. It's generating 4.9kw on a sunny winter day for a couple hours so in summer we'll be throwing a lot away. I think the installer spec'd it because our export on 1-phase is limited to 5kw but I feel it was wrong and we'd have been better of with fewer panels or a 6kw inverter. I have some buyers regret now.

Maybe 200% over paneling is fine if you have some east/west setup but in general it seems off. I'm not sure on the ROI of batteries but I hear it's more for resilience than ROI so I'd be careful.

With these things it's not a matter of opinion it's a matter of crunching the numbers. If someone can provide a year of data with a similar location and panel direction then you should be able to multiply it with different power plans to work out your ROI. - But it's complicated - in my calculations I missed the nuances between sunny and cloudy days and how clipping affects the yield. If anyone has a year of hourly data please do share.

We're probably going to get 8%/yr return on our system after adjusting for the green loan effectively discounting the cost by 12%. Which is decent but there are heaps of assumptions baked into this of course.

Ge0rge

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#3259232 14-Jul-2024 09:40

@Dilbonius - despite the detailed explanations on previous pages, I still don't think you're quite getting why you have an excess of panels over inverter capacity.

Yes, your system will clip for a few hours each day in the middle of summer. However, as you have said you have north facing panels, you really do want this to happen. The angle of incidence of the sunlight hitting the panels has a huge effect on the output. When it's not 90°, output begins to drop away significantly.

The output of you inverter plotted over a day, with no other shading effects, trees etc, will look like a nice bell curve. If your system had 5kW of panels for your 5kW inverter, the peak of the bell curve would rise to reach your max at midday, and then drop off again. However, that rise would begin quite late in the morning, and drop off again fairly sharply in the early afternoon - by 1500 you'd be making negligible power.

By increasing the panel capacity relative to the inverter, you are able to get that rise to begin earlier in the day, and last for longer into the evening. The clipping that you get at midday will be offset by the fact that you will be making more power for longer over the entire day.

That's all before we start talking about winter, with the sun lower in the sky, not up for as long, and the prevalence of cloudy days. I have a 5kW inverter with 6.8kW of panels in two strings. As I write, it's pouring with rain, but I'm making just on 500W - enough to cover my base load on a crappy winter's day. If I had 5kW of panels, Id be importing power right now.

Your system is fine, stop worrying about it and go watch your export meter.

Jase2985

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#3259291 14-Jul-2024 10:27

How long was it making 4.9kWh for? Looking at your graph, it was maybe an hour to an hour and a half. in summer, it could be 4-5 hours, if you had 5kW of panels in summer it might only be like what you are seeing now.

It's good to be seeing it almost clipping in winter, and it sounds like you have the near perfect orientation, which also helps things. In summer, it will make max power for longer, but it will also make more power in lower sun conditions, so on a cloudy day it will make more power.

LightbulbNeil

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#3259292 14-Jul-2024 10:31

Different installers have different ideas of what they think your needs are. The difficult part is researching what you actually are wanting from your solar install, and the roof design or the area being used for the panel install. When we got our house designed, one of the aspects we wanted was to in the future install solar. My late brother in law, had shared his experience with solar, as he was an early adapter of it, around 2010. His goal was to reduce his power bill in winter which it did. We based our system on the winter demand, not the summer capability. We don't have a battery either, but may consider that in 5 years time. Unsure if it will happen. We moved into the home in Jan of 2020 and installed solar in Oct 2023. My goal was to never have another power bill again. It has certainly done that and now we are running a 2nd hand, excellent condition, spa pool that we just got 2 weeks ago.

If you are on a rural connection, some only allow a max of 5kva (4.66kw) even if over 3 phases. So supply charges will still be there used or not, and charges for any power that you import as well. A battery will allow you to use more of the solar generated at another time, and will give some resilience to a power outage for sure. The more energy efficient your home is, the lower the amount of power will be required in winter for heating etc. One thing that had a larger impact than I first realised was the type of glazing in a home, and the type of curtains as well. The better the thermal properties of the glazing as a whole, was very significant for the thermal retention in winter and the thermal insulation in summer.

Our East West arrays, 5kw each side , is effectively an 8 kw array compared to the north facing 5 kw array viewed as 100%. We have a low 15deg pitched roof and although there are 10kw systems on a higher pitch roof and better aligned making as much or more throughout a whole year, the advantage we have is the 3 phases allows for more export in summer. This aspect is not available to rural customers.

Some people are very handy at doing electrical work very competently , and have added their own battery systems and controllers to their inverters and are able to make it all work. I am not in that area of expertise so I am not playing with something I know little about. For retail end users of adding a battery , they seem to me to cost in the vicinity of $1200-$1500 per year to fund a 13kwh battery.

On our old house, a 5-6kw system, no battery, single phase has a payback time of 15 years for solar installation. So we are not getting solar on that house. To me, it should have a payback of 10 years or less as we are 6 years from retirement. If planning on staying somewhere for longer than 15 years that may well be acceptable to have a lower bill over a longer timeframe.

Many of the companies doing quotes etc have access to great software that simulates what a particular system is likely to generate for you, and in summer the excess it will produce and in winter when raining what is likely to be produced as well. Ask about different system configurations and sizes and have a play with panel location etc as well. Keep in mind, that the panels will require cleaning at least once a year and consideration to cleaning them is worth while also.

Dilbonius

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#3259318 14-Jul-2024 11:47

Ge0rge: @Dilbonius - despite the detailed explanations on previous pages, I still don't think you're quite getting why you have an excess of panels over inverter capacity.

Yes, your system will clip for a few hours each day in the middle of summer. However, as you have said you have north facing panels, you really do want this to happen. The angle of incidence of the sunlight hitting the panels has a huge effect on the output. When it's not 90°, output begins to drop away significantly.

The output of you inverter plotted over a day, with no other shading effects, trees etc, will look like a nice bell curve. If your system had 5kW of panels for your 5kW inverter, the peak of the bell curve would rise to reach your max at midday, and then drop off again. However, that rise would begin quite late in the morning, and drop off again fairly sharply in the early afternoon - by 1500 you'd be making negligible power.

By increasing the panel capacity relative to the inverter, you are able to get that rise to begin earlier in the day, and last for longer into the evening. The clipping that you get at midday will be offset by the fact that you will be making more power for longer over the entire day.

That's all before we start talking about winter, with the sun lower in the sky, not up for as long, and the prevalence of cloudy days. I have a 5kW inverter with 6.8kW of panels in two strings. As I write, it's pouring with rain, but I'm making just on 500W - enough to cover my base load on a crappy winter's day. If I had 5kW of panels, Id be importing power right now.

Your system is fine, stop worrying about it and go watch your export meter.

No - I get it. Some excess is fine but there is a point at which you're throwing away energy worth more than it'd have cost to put in a larger inverter. I'm only interested in ROI, I don't particularly care about self-sufficiency during the early and late periods. It comes down to how much inverter capacity costs vs panel capacity. I'd guess it makes sense to over panel by 20-30% but we have 42% on a system which places all bets on the same sun direction.

"and the prevalence of cloudy days"

Exactly this - the more variation there is in daily panel output the worse the clipping is. On a productive July day, at a 28 degree pitch we're already hitting 4.95kW for 2 hours. I am home during the day and have a lot of summer loads like A/C and irrigation I can shift into the sunny hours.

"enough to cover my base load on a crappy winter's day"

Oversizing your panel capacity to cover cloudy days and save 18c/kWh (for me) isn't a winning game ROI wise. I'd be better off investing the difference in stocks or something more productive. Unless you have to be off-grid then aiming for self-sufficiency isn't financially smart.

Jase2985

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#3259320 14-Jul-2024 11:50

sounds like you put solar in for different reasons to the rest of us and didnt do enough research.

Did you make it clear to the installer what you wanted from the system?

HarmLessSolutions

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#3259378 14-Jul-2024 14:11

paultaupo:

HarmLessSolutions:

@paultaupo, The Zen setup doesn't sound great as the inverter is going to limit production from 10kW of panels to only 5kW so I don't understand their reasoning there. A 7kWh battery will fully charge in no time so that's not the answer and do be sure to sussout the ROI of including batteries in your installation as they add considerable expense to the project and if your use model doesn't fit them you may never see their cost repaid. Also for both 10kW systems (if the Zen system upsizes their inverter) the next limitation you may strike is if you have single phase supply installed, and/or a single phase inverter is the export cap that your lines company stipulates, typically 5kW/phase. A reputable installer should be across these issues so if you don't get satisfactory answers from Zen or Harrisons do some more shopping around. SEANZ are a good resource for finding local PV installers/providers.

thanks for that - basically what i thought so good to hear it from others. Still not sold on battery as the ROI is hard to make work but we do want some resilience as we are rural

Plenty of aspects to think about in the intervening posts but from my perspective we are also rural so the occasional power outage is part of life, and it results in no pumped water while it's out. We didn't see the extra cost of a battery as being cost effective and since last September when our present installation was completed our installer has doubled down on his original advice to us that our consumption model is such that a battery would not be viable. We were in credit with Octopus for 5 months during the summer months which included almost all of the charging required for 2 EVs, pumped water, 2x 700L freezers and other home consumption.

Rather than batteries we have a Paladin diverter which on most fine days sends the first 3kW of our 'excess' generation to our HWC. That component is the single most cost effective part of our installation. We virtually never use grid supply for our HWC. Our Evnex EVSE is then second in line for 'excess'. Both are aimed towards self consumption and minimising export as the golden rule of PV is that the best ROI you can get is by consuming your own generation, followed by storing it if you can make the numbers work in your favour.

Our intention into the future is to put an EV into duty on a V2H purpose effectively making that our power backup strategy. Just waiting for bidirectional charging, V2G/V2H to start rolling in NZ for that to become possible. Good to see an increasing number of EVs being offered with bidirection charging ability so hopefully appropriate EVSEs at reasonables prices will follow. I can't see the sense in spending ~$20K on a Powerwall or BYD box when a Leaf with moderate SoH can serve the same purpose, as well as mobility.

Looking at the SEANZ directory it seems Taupo is in no man's land provincially. I don't think our installer Solar One operates outside Taranaki but may be worth approaching them as closer than many of the other options based in Tauranga, etc. I have no hesitation in recommending them even if just as a referral source.

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

dantheperson

174 posts

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#3259523 14-Jul-2024 21:11

Ge0rge:
By increasing the panel capacity relative to the inverter, you are able to get that rise to begin earlier in the day, and last for longer into the evening. The clipping that you get at midday will be offset by the fact that you will be making more power for longer over the entire day.

Rather than compare 7.4 kw of panels on a 5kw inverter to 5kw panels on a 5kw inverter, you could look at it the other way and compare it to 7.4 kw of panels on a 7.4kw inverter. As you say 7.4kw of panels will still get you up to 5kw output earlier in the day and for longer than 5 kw of panels would, but the peak 7.4kw output in the midday wouldn't be lost.

Yes that midday peak is the lowest bit of ROI on inverter cost, as you only hit the peak for a couple of hours, and not at all in the middle of winter, but how much does that extra inverter capacity cost? You've already paid for the panels, the racking, the DC wiring for 7.4 kw, all the labour, complaince costs. I'd suggest the cost for a slightly larger inverter is quite minimal in the overall project cost. Perhaps a heavier gague wire could be need to carry the AC to your panel, depending on how long the run etc, but that cost should be minimal.

Fronius pricing isn't very transparent, but other brands are, if we look at Deye Sun grid-tie inverter, the cost to upgrade from 3.6kw to 6kw is only NZ$300, Or a growatt example, 5kw to 6kw upgrade costs $150.

The other consideration is the export limit, if you have a 5kw limit then you want to be sure you have enough loads to use that extra midday production, or else your 7.4kw inverter will just be throttling back to 5kw anyway...

EgorNZ

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#3259533 14-Jul-2024 21:58

On the subject of batteries - your choice of electricity plan can make a big difference to the economics.

I'm with Contact on their Good Nights plan which provides three hours of free power every night (9pm-12am), which is enough to fully recharge the Tesla Powerwall. Put that together with solar and I can pretty much bank on filling the battery twice every day for free.

The battery has a capacity of 13.5kW but I keep 25% in reserve (in case of a power outage - common here), so the usable capacity is about 10kW.

At my unit price of 27.7c/kWh, a free 20kW each day is worth $5.54. Over a year, that's roughly $2000 earned from having the battery. And if NZ power prices keep rising at 3% per year, after 5 years that 20kW will be worth $2300.

The install cost for the Powerwall was $17k, so it should pay for itself in about 8 years, in my case.

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