Solar options for home in 2022.

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506 posts

Ultimate Geek

#3252541 24-Jun-2024 14:33

eonsim:

chimera:

You have perfectly iterated my initial point. Why size / invest in a MASSIVE solar array spending a heap more on panels up front JUST to have excess solar that then needs exporting to the grid? Why not concentrate on sizing batteries first and then solar panels to suit? That makes considerably more sense to me. Everyone seems to concentrate on solar panels first, or maybe that's just solar company sales and marketing?

Solar panels are probably easier to add in a single batch (needing matching panels, and getting people up on the roof multiple times is expensive), and the output is variable depending on the weather (so additional panels always give you some benefit, even if you can't export).

A battery system it's a bit easier to add or expand after the fact, they're designed to be expanded. Also having a massive battery system with insufficient solar means you end up running the battery off the grid which reduces the savings (buying energy at 12c to use when it would cost 30c isn't as good as storing energy that's 'free' or worth -8c to replace energy that would costs 30c).

The cost per extra panels is marginal vs the cost of the labour, also adding extra panels after the fact may require a complete redesign of the strings and rewiring (inverters have max input AMPs and Voltages as do panels), potentially a change in inverter. Also it's not great if your panels are very different, adding 40V panels to strings of 30V panels can complicate things. Or having panels that can do 500W mixed in with 400W panels means you are wasting potential with a string inverter.

Also you may require scaffolding during the install, in which case you end up paying for that twice.

Also even if you can't use all the power from your 15kW array in summer, in winter that 15kW array will be producing alot less power and you are likely to be able to use it all. If you are going for a 5kW array then in the middle of winter during crappy weather you may only get 2-3kWh a day so there is no spare power for your battery to store.

Seems you have missed or not read my initial post, or perhaps are misunderstanding the angle I'm coming from. At a high level - don't use solar to charge your batteries, use night rate when grid power is at the cheapest. Get a large enough battery setup to run all your peak needs. Use solar to supplement the house usage during the day, or charge batteries with any excess. So invest in batteries first, then solar second. Obviously everyones needs are different so YMMV. All I'm saying is as an alternate approach, test by calculating the numbers based on batteries first with solar to supplement your setup.

eonsim

398 posts

Ultimate Geek

Trusted

#3252546 24-Jun-2024 14:37

chimera: About to get solar myself. Thinking out loud here…

Based on several mates solar setups plus data I’ve read online (in Auckland with between north west to north east facing roofs) a rough guide over a year you will get 4 times the size of your panels in kWh. So example if you have 5KW of panels over a year you will get an average of 20kwh per day, 8KW of panels will get 32kwh generation per day. Obviously over summer more, over winter less, but nonetheless a good rough guide.

The difference between seasons is really substantial especially if you don't have perfect north facing view for Solar.

We for example have a 5kWp array in the Waikato, In summer we can get as high as 35kWh with an average in the mid 20', while winter we get as high as 15kWh but an average of more like 8-9kWh, with crappy weather being more like 2-5kWh.

June/July will often be a third of December/Jan, if you build for the year average or December/Jan you will have very little solar power in Winter.

chimera

506 posts

Ultimate Geek

#3252550 24-Jun-2024 14:40

eonsim:

chimera: About to get solar myself. Thinking out loud here…

Based on several mates solar setups plus data I’ve read online (in Auckland with between north west to north east facing roofs) a rough guide over a year you will get 4 times the size of your panels in kWh. So example if you have 5KW of panels over a year you will get an average of 20kwh per day, 8KW of panels will get 32kwh generation per day. Obviously over summer more, over winter less, but nonetheless a good rough guide.

The difference between seasons is really substantial especially if you don't have perfect north facing view for Solar.

We for example have a 5kWp array in the Waikato, In summer we can get as high as 35kWh with an average in the mid 20', while winter we get as high as 15kWh but an average of more like 8-9kWh, with crappy weather being more like 2-5kWh.

June/July will often be a third of December/Jan, if you build for the year average or December/Jan you will have very little solar power in Winter.

Indeed. Maybe the calculator needs to be split into seasons, then work out the best setup for each season, then aggregate and average the lot. Getting more and more complicated :-)

eonsim

398 posts

Ultimate Geek

Trusted

#3252552 24-Jun-2024 14:44

chimera:

Seems you have missed or not read my initial post, or perhaps are misunderstanding the angle I'm coming from. At a high level - don't use solar to charge your batteries, use night rate when grid power is at the cheapest. Get a large enough battery setup to run all your peak needs. Use solar to supplement the house usage during the day, or charge batteries with any excess. So invest in batteries first, then solar second. Obviously everyones needs are different so YMMV. All I'm saying is as an alternate approach, test by calculating the numbers based on batteries first with solar to supplement your setup.

What you are describing isn't really a Solar install, it's a battery time shifting install. Every time I've run the numbers for that sort of setup (using lithium) it doesn't pay for it's self. If you halved the cost by switching to another battery tech, you often need to double the capacity of batteries, which again means it doesn't pay for it's self or needs 15 years to do so (at which point the batteries are dead or dying).

If you aren't concerned about it paying for it's self then yes the system will work and you'll make some savings. You will also need a lot of space for the batteries and the inverter, likely undercover and potentially ventilated. You maybe able to make the numbers working for you, but it'll be tight and makes the assumption that we will continue to be able to get time of use electricity charges with a substantial difference between peak and night.

chimera

506 posts

Ultimate Geek

#3252557 24-Jun-2024 14:50

eonsim:

chimera:

Seems you have missed or not read my initial post, or perhaps are misunderstanding the angle I'm coming from. At a high level - don't use solar to charge your batteries, use night rate when grid power is at the cheapest. Get a large enough battery setup to run all your peak needs. Use solar to supplement the house usage during the day, or charge batteries with any excess. So invest in batteries first, then solar second. Obviously everyones needs are different so YMMV. All I'm saying is as an alternate approach, test by calculating the numbers based on batteries first with solar to supplement your setup.

What you are describing isn't really a Solar install, it's a battery time shifting install. Every time I've run the numbers for that sort of setup (using lithium) it doesn't pay for it's self. If you halved the cost by switching to another battery tech, you often need to double the capacity of batteries, which again means it doesn't pay for it's self or needs 15 years to do so (at which point the batteries are dead or dying).

If you aren't concerned about it paying for it's self then yes the system will work and you'll make some savings. You will also need a lot of space for the batteries and the inverter, likely undercover and potentially ventilated. You maybe able to make the numbers working for you, but it'll be tight and makes the assumption that we will continue to be able to get time of use electricity charges with a substantial difference between peak and night.

Correct, batteries with usage by rate shifting and solar panels sized correctly to supplement the setup. I have already done rough numbers with AGM (accounting for 50% DoD) and it works out better than a large solar array. Not so much with Lithium. This is averaged over a year though. I need to account for seasonal changes and work it out again, but that would be little different to a large solar array and seasonal changes.

tweake

2391 posts

Uber Geek

#3252558 24-Jun-2024 14:51

chimera:

Seems you have missed or not read my initial post, or perhaps are misunderstanding the angle I'm coming from. At a high level - don't use solar to charge your batteries, use night rate when grid power is at the cheapest. Get a large enough battery setup to run all your peak needs. Use solar to supplement the house usage during the day, or charge batteries with any excess. So invest in batteries first, then solar second. Obviously everyones needs are different so YMMV. All I'm saying is as an alternate approach, test by calculating the numbers based on batteries first with solar to supplement your setup.

one of the advantages to that is now you can have high drain devices running off the battery setup. most nz homes are only have 60 amp connections and some lines companies etc won't allow upgrades. one way to do fast ev charging (or large amount) is to do it from another battery.

have the home battery charge slowly (and/or by solar etc) so it can be used to charge the cars and/or the house.

HarmLessSolutions

969 posts

Ultimate Geek

Subscriber

#3252559 24-Jun-2024 14:51

@chimera, Can't help but think you're trying to 'reinvent the wheel' with your theorising. Any reputable solar designer and installer will have the info you require so suss out one in your area.

As a guide our best generation from 9.5kW of panels, with ~1/2 of them being bifacials, through an 8.2 kW Fronius single phase inverter was ~65kWh in a day in early January (with ~1,300kWh for that month) but we've seen days this month with <10kWh and we'll struggle to crack 500kWh for June. Our arrays are mounted on trusses on a shed roof so optimally sloped and orientated with minimal shading losses.

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

LightbulbNeil

57 posts

Master Geek

#3252695 24-Jun-2024 16:52

If using 430kwh a week, 22000 kwh in a year, over 10 years it seems an expenditure of 55k at 25c per kwh including daily charges.
For 8 years of power , will get a very large system.
I have not been able to calculate batteries to last or pay for themselves .
Batteries do give redundancy for a power failure however. Which is the only reason I have been looking at batteries etc. The price of batteries is in the $1200 per kwh of usable energy. Some need about 50% in reserve, while otgers can be 90% discharged. It looks like batteries have a continual cost of about $1200 a year for something in the 14Kwh range.
Our outlook has been very different. We started with about 9 years to break even to in actuallity break even is going to be 6.5 years.
Since being installed, we do not have a power bill to pay.
You should be able to get the pool heating done mainly in the day time and that will reduce your evening heating costs. With the cover off it's surprising how fast the pools cool down.
The amount of roof space and area to place panels starts to become an issue.
We have a huge excess in summer and not enough for winter if we intended to be off grid.
A 15kw system should be able to save you 4k or so a year , around 18,000 Kwh for the year.
I have also looked into directly importing a battery. Finding a certified installer to install to keep the home insurance valid was a problem.
Being your consumption is in the commercial range, seek out a company to look into your needs and what solution that is a good fit for your location.
Neil

dantheperson

174 posts

Master Geek

#3252698 24-Jun-2024 17:07

chimera:

And for that link you provided that's $5700 for 7.5KwH. You need 2 to get the 15KwH. Sneaky advertising I think. But still not too badly priced.

If that's the price for one, then that's not sneaky advertising, its plain false advertising. It clearly says in the titlle "48V 51.2V 340Ah" and in the description says it's for 2x units. There's a separate listing for a single item: https://www.micromall.co.nz/solar-batteries/lifepo4-batteries/48v-51-2v-150ah-170ah-lithium-battery-lifepo4-battery-deep-cycle-solar-battery

Export always going to be lower than import, sizing the solar to suit charging battery and powering the home during peak sunshine hours will give better ROI.

Batteries wont give a better ROI if the cost of your battery install is greater than the difference between your import and export rate.

For me the night rate is only 1 cent difference with the export rate. My thinking is there no point spending thousands on batteries to cover night usage that is only going to save 1 cent per kwh in comparison to export and buyback. Thats why i'm thinking small battery to cover just peak baseload.

Some people here on EV tariffs actually have a lower night rate than their feed in rate, so they make a profit on each unit that is exported and then bought back at night.

Jase2985

13457 posts

Uber Geek

ID Verified

Lifetime subscriber

#3252772 24-Jun-2024 19:00

i use the grid as a battery, my export (12c) is more than my night rate(11c), so i try to do everything at night as my export covers that. Summer might be a different story when I'm hitting the export cap.

eonsim

398 posts

Ultimate Geek

Trusted

#3252789 24-Jun-2024 20:25

chimera:
So I want to concentrate on spending the bulk of my $20k budget first on batteries, and the rest on panels and inverter etc. So (ballpark) $10k to get 40kwh batteries (20kwh usable) and $10k on everything else (prob 4-5kw of panels) So setup would be using peak solar (arguably 10am til 2pm) during day to power house (any excess to charge batteries) morning and late afternoon to use batteries (as well as any additional solar available), early evening off batteries, night rate (cheapest) use grid to power house overnight and charge batteries. Only downside of the whole setup is need to take into account ~25 years for panels, but only ~10 years for batteries, so ROI needs to consider power savings vs battery investment.

Running the numbers briefly on NZ AGM pricing, I don't think it works very well.

AGM GEL - NZ$385 for 0.72kWh of usable charge, Total 40kWh (20kWh usable) = 27 batteries, 944kg, 1400 cycles (50%DOD), 1 cycle a day = 3.89 years life expectancy for the system, $41,960 (for 16 years)

LiPO - $5700 for 12kWh usable, Total 24kWh = 2 sets of 2 batteries, 252kg, 6000 cycles (80% DOD), 1 cycle a day = 16 years life expectancy, cost NZ$11,400 (for 16 years)

The lifetime costs massively favor the LiPO batteries, not to mention the difference between 4 units weighting 252kg, vs 27 units weighing 944kg. Even using more expensive LiPO batteries ($4500 for 4.5kWh usable) the initial cost doubles ($24k) but the 16 year lifetime cost is still alot cheaper than AGM (using NZ prices). That doesn't even count the extra bits needed, racking for 27 batteries (vs 4), high gauge battery cables for 27 batteries, BMS's for 27 batteries etc.

Unless you can get significantly better prices for AGM batteries with comparable capacity than I can see in NZ, the LiPO based on the prices at micromall make lot more sense. Not to mention just having less stuff to deal with, having a 15 year warranty and likely lifespan (given there rated cycles), would seem to make them a far better idea than AGM.

If you look at what you can save powerwise:

Assumptions:

12c per kWh difference between peak and night rates (about right for Octopus currently, assume difference is constant ignoring inflation).
Full charge and discharge cycle per day (20kWh per day, for life of battery system
Savings ~$2.4 per day

AGM 1400 cycles ~$3,400 saved for the life of each set of 27 batteries (assuming 100% capacity at 1400th cycle), $14,400 saved over 16 years:

LiPO 6000 cycles ~$13,000 (assuming 80% capacity at 6000th cycle)

AGM cost for 16 years $42,000 - $14,400 = $27,600 net cost.

LiPO cost for 16 years $11,400 - $13,000 = $1,600 saved!

LiPO at higher cost 16 years: $24,000 - $13,000 = $11,000 net cost.

In short unless you can do a lot better pricing the batteries or can get cheap good LiPO it doesn't add up on a purely financial case. Assuming both the night rates and peak rates increase at the same amount each year due to inflation (thus maintain a 12c benefit for night vs peak).

So it can work, but probably not with AGM/GEL.

chimera

506 posts

Ultimate Geek

#3252852 24-Jun-2024 23:12

I can get AGM from China cheap, but TBH I haven't seen Micromall before; their 48V LiFePO4 prices are pretty damn good

stuartgr

163 posts

Master Geek

Lifetime subscriber

#3252887 25-Jun-2024 09:05

Just been following this discussion and looking to take the next step to pricing this up for us. Any wellington based installers people can recommend would be welcomed. We've contacted Harrisons so far!

BlargHonk

147 posts

Master Geek

#3252892 25-Jun-2024 09:13

Has anyone here looked into Solar Zero before? Their system of Solar+Batteries and using them as a "powerplant" during times of high spot prices is interesting. Just not sure I would want to be locked in for 20years

Ge0rge

2052 posts

Uber Geek

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Lifetime subscriber

#3252894 25-Jun-2024 09:23

stuartgr:
Just been following this discussion and looking to take the next step to pricing this up for us. Any wellington based installers people can recommend would be welcomed. We've contacted Harrisons so far!

I'd recommend getting in Touch with Tony from SolarMan. Dealings with him for both my house and my parents have been fantastic.

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