Export is 5kw per phase I should say.

Dilbonius:

We already do use the heat pumps all day. 

The EECA calculator is pretty useless. I don't have a power bill to feed it so it way over estimates what I'm paying per power and tells me 7 years to pay is back and a savings of $2500 a year. Even with solar we'll be on the standard user rates due to an EV and lots of other loads. If I shift a couple kwh of hot water heating to the sunny hours with a timer then the savings are more like $1200/yr or a 9% ROI = 11 year pay back. So the EECA calculator is off by about 50%. Other factors are if the cost of electricity goes up we win more, or if the cost of solar panels drops we lose.

I'm more interested in which hardware is the better value for money the JA+Fronus stuff or Solax/Huawei.

So the biggest thing i can see is if you get a single phase system is putting on a phase where most of your daytime load is, and depending on that load will depend on how much you can end up exporting or self consuming.

The 3 phase system on your spreadsheet is the most expensive, and only gives you 6kw of panels. also be aware of the max single phase output of the solax 3 phase inverter.

Most inverters allow you to over panel them by sometimes up to 30% meaning though its a 5kw inverter you could connect 6.5kw of panels to it and work without issues.

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

That leads to battery storage. The cost of AGM (per kWh) is still cheaper than lithium (even taking into account ~50% depth of discharge for AGM, ~90% for lithium) On aliexpress I can get 20kwh AGM (10kwh or so usable) for about $5k landed. For a 10kwh lithium around $9k or so. 

For AGM you gotta consider extra maintenance and shorter life.  Your lithium price seems a bit high when you can get 15kwh locally for NZ$5K  e.g. https://www.micromall.co.nz/solar-batteries/lifepo4-batteries/48v-51-2v-340ah-lithium-battery-lifepo4-battery-deep-cycle-solar-battery

Then look at how much your total battery setup is going to cost, expected lifetime charge cycles, effective cost for each kWh you store.  Is it actually less than the difference between your feed-in-tarrif and your import rates?  Maybe for peak $0.40 import - $0.15 export.  But probably not for shoulder.

I'm thinking small battery maybe <2kWh.  That will cover base load during the morning and evening peak, and act as a buffer during the day so if the spa is heating on a cloudy day the battery is going to discharge as a cloud passes over and recharge when the sun comes out again.

would it be worth holding off battery install until sodium batteries come out?

they are in small scale production at the moment and large scale production factories are being built at the moment. so its a little way off. unfortunately won't know cost until large scale production fires up, but they are meant to be far cheaper, can handle cold weather, but suffer from lower power density. all things that make it a good option for solar storage where size and weight of batteries is not a big issue. would also need different chargers and possibly inverters (different charging voltage and can be drained down to 0v).

 

For AGM you gotta consider extra maintenance and shorter life.  Your lithium price seems a bit high when you can get 15kwh locally for NZ$5K  e.g. https://www.micromall.co.nz/solar-batteries/lifepo4-batteries/48v-51-2v-340ah-lithium-battery-lifepo4-battery-deep-cycle-solar-battery

 

Then look at how much your total battery setup is going to cost, expected lifetime charge cycles, effective cost for each kWh you store.  Is it actually less than the difference between your feed-in-tarrif and your import rates?  Maybe for peak $0.40 import - $0.15 export.  But probably not for shoulder.

 

I'm thinking small battery maybe <2kWh.  That will cover base load during the morning and evening peak, and act as a buffer during the day so if the spa is heating on a cloudy day the battery is going to discharge as a cloud passes over and recharge when the sun comes out again.

 

No extra maintenance for AGM. As long as charge cycles are frequent and consistent they will last ages. It's undersizing and depleting them too low that kills longevity. And for that link you provided that's $5700 for 7.5KwH. You need 2 to get the 15KwH. Sneaky advertising I think??? If not, thats very cheap!

Not interested in exporting, very little point. 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.

And re 2kWh, I guess battery size varies depending on everyones use case. I have a largeish house (or rather I should blame it on my teenagers) with pool and spa so usage is high at 60KwH a day, with spa using a fair amount (9kWh per day according to Home Assistant) I really gotta create an Excel calculator for this but its gonna be pretty complex I'd think, and coz everyday power consumption and solar power generation varies, it can only work on a daily average based on usage over a year. 

chimera:

 

.....

 

Not interested in exporting, very little point. 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.

 

......

 

This is a comment about the world in general, not anyone on this thread or even GZ in general: Why do so many people only do things if they can convince themselves they'll save or make money from it?  What's wrong with "I'll do this because it's the right thing to do", or "because it's good for the environment", or "because it provides a safety margin in the case of extreme events"?  And this applies to things like public works, "we're going to do this and it'll create 500 jobs and bring in $50M in tourism income".  No it won't, you've just made those figures up, but for some reason you have to do it because saying "we're going to do this because it'll benefit the community" isn't enough.

 

Might be worth revisiting your export data. Octopus are offering 40c/kWh FIT for export during peak periods during winter months, and their Saving Sessions promo can be used to gain $2.00/kWh for reduced import over their nominated peak periods which if usage is manipulated by way of clever export scheduling effectively amounts to a $2 FIT.

 

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?

neb:

 

This is a comment about the world in general, not anyone on this thread or even GZ in general: Why do so many people only do things if they can convince themselves they'll save or make money from it?  What's wrong with "I'll do this because it's the right thing to do", or "because it's good for the environment", or "because it provides a safety margin in the case of extreme events"?  And this applies to things like public works, "we're going to do this and it'll create 500 jobs and bring in $50M in tourism income".  No it won't, you've just made those figures up, but for some reason you have to do it because saying "we're going to do this because it'll benefit the community" isn't enough.

 

Because the reality of life are death and taxes. Unless you have zero debt and excess money, or simply don't like throwing money at big corporate energy companies, or have somehow convinced yourself that you're going to get solar to save the planet (when the irony is that NZ is already over 80% renewable energy) then that is exactly why. 

chimera:

 

 

Might be worth revisiting your export data. Octopus are offering 40c/kWh FIT for export during peak periods during winter months, and their Saving Sessions promo can be used to gain $2.00/kWh for reduced import over their nominated peak periods which if usage is manipulated by way of clever export scheduling effectively amounts to a $2 FIT.

 

 

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?

 

In our case we upgraded from 5kW to 8.2kW (fed with ~10kW of panels) in order to feed our 7kW EVSE without grid input. We don't have batteries with our HWC and 2 EVs serving as energy storage, and waiting for V2G to become possible/viable with our Leaf.

In a word, 'seasonality'. A solar installation that has sufficient capacity to fill your consumption needs in winter will be producing far more than you can use in summer, unless you have found a source for batteries that hold charge for months.

 

In our case we upgraded from 5kW to 8.2kW (fed with ~10kW of panels) in order to feed our 7kW EVSE without grid input. We don't have batteries with our HWC and 2 EVs serving as energy storage, and waiting for V2G to become possible/viable with our Leaf.

 

So effectively that means your initial argument on "Octopus are offering 40c/kWh FIT for export during peak periods during winter months" is null and void. 

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.

chimera:

 

In a word, 'seasonality'. A solar installation that has sufficient capacity to fill your consumption needs in winter will be producing far more than you can use in summer, unless you have found a source for batteries that hold charge for months.

 

In our case we upgraded from 5kW to 8.2kW (fed with ~10kW of panels) in order to feed our 7kW EVSE without grid input. We don't have batteries with our HWC and 2 EVs serving as energy storage, and waiting for V2G to become possible/viable with our Leaf.

 

 

So effectively that means your initial argument on "Octopus are offering 40c/kWh FIT for export during peak periods during winter months" is null and void.