Future Proofing Solar Installation

Forums › Home Workshop DIY › Future Proofing Solar Installation

insane

3324 posts

Uber Geek
+1 received by user: 1006

ID Verified

Trusted

2degrees

Subscriber

#295355 23-Mar-2022 14:45

I've been looking at getting a solar system to predominantly offset daytime loads, but may in future add batteries to extend some of the benefit into the evening/night too.

I've seen that there are two types of Solar battery installation designs, these being DC or AC coupled.

My limited understanding is:

NZ has some 5kw limit on how much power you can send to the grid at any time.

DC coupled requires a battery charge controller, and allows the full wattage of the inverter to be used to power the home or sell back to the grid. If you have more solar gen capacity than your inverter e.g 7kw of panels and 5kw inverter then you can draw the maximum 5kw through the inverter and charge batteries at 2kw from the excess from the panels.

AC coupled is connected to your mains and uses some comms to the inverter to work out when to charge or dump power into your house. The drawback being that your inverters capacity is used for both powering your house and charging your batteries, so adding batteries at a later stage could limit the amount of power you can draw in the rest of your home.

Question time...

The Tesla Powerwall 2 looks to be an AC coupled design, as are a handful of others. Sunvolt and others are DC coupled. What design do you guys with solar + battery setups have?

Harrison's Fronius inverter doesn't support DC coupled, so trying to understand if I'm limiting my future battery options to expensive AC options like the Powerwall.

1 | 2

13730 posts

Uber Geek
+1 received by user: 6202

ID Verified

Lifetime subscriber

#2890851 23-Mar-2022 16:44

5kw limit? its more than that with some providers could you please provide a reference to your limit?

https://www.mysolarquotes.co.nz/about-solar-power/residential/solar-power-buy-back-rates-nz/

frankv

5705 posts

Uber Geek
+1 received by user: 3666

Lifetime subscriber

#2890858 23-Mar-2022 16:57

I don't know squat about solar, but am interested. But I'd hope that if the inverter was the limiting factor in an AC coupled system, it would limit how much went into your battery rather than how much was used in your house. Bear in mind that if the battery charging is from AC, you will need a rectifier to convert AC back to DC to charge the batteries.

compound

89 posts

Master Geek
+1 received by user: 43

#2890910 23-Mar-2022 18:45

We have a 10kW limit to sending back to the grid. It was the limitation set by the network, not the retailer. We could have gone bigger but that required more paperwork, whereas 10kW was pretty much tick the box and the application was accepted. To get to a 10,000 watt export we would have to be using no power at all and that never happens. System is set up for a battery but we haven't bought one as yet and probably wont unless the cost comes down further. We use a good proportion of the energy we make and we could self use more if we had battery storage but the cost of the battery is likely to only return a break even result over its lifespan.

eonsim

403 posts

Ultimate Geek
+1 received by user: 192

Trusted

#2891005 23-Mar-2022 20:19

As others have said export limit depends on your local network utility (not power company), and potentially how much paper work you want to fill out.

With regards to Batteries they're all technically DC, but it depends on the DC connection is directly connected to your inverter/solar system, or the battery has it's own built in inverter to switch between AC > DC > AC. If you are getting an on grid hybrid system (battery + Solar + Grid) your options generally are a Hybrid inverter which can link directly to a DC battery and Solar panels while converting them both to AC or a normal inverter which can't link directly to a DC battery.

Hybrid inverters tend to be more expensive and thus they're only really recommended if you plan to install a battery at the same time as the solar system, or your absolutely certain you will install it in the next year or so. Effectively the hybrid inverter has a DC side which receives DC power from the panels (anything from 80V - 1000V commonly) and converts it to the correct voltage (12/24/48/400V etc) that it can send it directly to a DC battery system (charge it) and retrieve DC power from the battery (discharge it). The DC power from either source or both sources can then be sent to the AC side of the inverter which will convert it to AC. If you look at something like a Fronius Symo 5kw hybrid inverter it can be connected up to 8kw of Solar panels plus a battery, but it can only ever convert 5kw of power directly to AC, so if the solar panels are generating 8kw it could convert 5kw of that to AC, and then push the rest into the battery assuming the battery isn't full. Once the battery is full the max power it can generate is 5kw, if the solar is only producing 1kw and the house is drawing 5kw then depending on the battery linked to it, it could pull up to 4kw out of the battery.

A normal inverter 5kw inverter (say a Fronius Primo 5kw inverter), can take up to 7.5kw of solar panels. It will then convert upto 5kw of the power generated by the solar panels directly to AC. If you want to add a battery to such a system you need to add an AC battery with a AC > DC inverter. The AC battery system would then be linked up so it can communicate with the inverter. Then when the Solar inverter pushes power out into the house wiring the AC battery will take that energy and feed it into it's AC > DC inverter, then use the DC power to charge it's batteries. Later if the battery detects a load and has power available it will then draw DC power from the batteries send it to it's DC > AC inverter and push it out into the house wiring. As the battery has it's own inverter it will tend to cost a bit more than a standard DC battery and you will have two inverters at your house.

There are advantages and disadvantages to both.

A Hybrid inverter with a DC battery will tend to be more efficient and you'll get more usable power for the same amount of solar panels. As each time you switch between AC and DC you lose 2-5% of the power. So with a hybrid inverter you will have one DC/AC step so if the efficiency of the inverter is 96% you'll get about that out of what ever solar you generate. However, with an AC battery you can have up to three conversion steps Solar to AC, AC > DC, DC > AC so 0.96^3 you can get as little as 88% of the solar power you generated as usable AC. Potentially important if your in an off-grid situation.

One advantage for an AC battery is that it has it's own inverter, and is independent of the main solar inverter. Thus if either the solar or battery inverter breaks down the other will still function. Also this means you can have a higher total load from the system, if both your battery and solar inverter can do 5kw then the house can draw up to 10kw without having to use grid power (often higher for short periods as battery inverters usually have surge capacity another kw or two for a short amount of time). While a 5kw hybrid inverter with DC battery will only ever be able to deliver 5kw.

An AC coupled battery can also happily charge from the grid, so if the weather is bad for a while and thus no solar generation, or you have free hours of power at night (or really low rates) you can charge the battery off the grid at free or cheap times and then use the battery at peak times.

insane

3324 posts

Uber Geek
+1 received by user: 1006

ID Verified

Trusted

2degrees

Subscriber

#2891013 23-Mar-2022 20:38

Interesting, was told by Harrison's that the limit is set by Vector (lines company here), and that if I installed an inverter larger than 5KW that I'd have to install an export limit meter e.g Fronius 63A-1 Smart Meter.

Interested to hear if anyone in Auckland is exporting more than 5kw, and extra points for being with Harrison's!

The inverter size in an DC coupled system I guess would limit how much power could be fed into the home (and/or back to the grid).

@frankv you're right in that an AC coupled battery system could feed more into the house directly depending on what the battery / built in battery inverter is capable of pushing out. And could charge from the grid at lower cost times at a high rate. Most are quite low though, think the Powerwall is towards to higher end and it's only like 5kw sustained.

Maybe AC coupled isn't so bad after all, even if it does have an extra AC/DC conversion.

Jase2985

13730 posts

Uber Geek
+1 received by user: 6202

ID Verified

Lifetime subscriber

#2891015 23-Mar-2022 20:47

https://www.vector.co.nz/personal/electricity/distributed-generation/10kw-or-less

read that for Vector 10kw or less

para 4.6 of the first ref might apply.

New World

Shop on-line at New World now for your groceries (affiliate link).

insane

3324 posts

Uber Geek
+1 received by user: 1006

ID Verified

Trusted

2degrees

Subscriber

#2891043 23-Mar-2022 22:12

Jase2985:
https://www.vector.co.nz/personal/electricity/distributed-generation/10kw-or-less

read that for Vector 10kw or less

para 4.6 of the first ref might apply.

Thanks for that, where did you find para 4.6?

eonsim

403 posts

Ultimate Geek
+1 received by user: 192

Trusted

#2891067 24-Mar-2022 00:05

This doc
https://www.vector.co.nz/kentico_content/assets/55223b76-c902-4e40-be13-8cf50786b97d/ESP009_Small_Scale_Tech_Inverter_DG.pdf

Effectively they're saying you can't export more than 5kw on a single phase. If you use 3 phase it looks like you can do at least a 15kw system.

insane

3324 posts

Uber Geek
+1 received by user: 1006

ID Verified

Trusted

2degrees

Subscriber

#2891070 24-Mar-2022 00:37

eonsim: This doc
https://www.vector.co.nz/kentico_content/assets/55223b76-c902-4e40-be13-8cf50786b97d/ESP009_Small_Scale_Tech_Inverter_DG.pdf

Effectively they're saying you can't export more than 5kw on a single phase. If you use 3 phase it looks like you can do at least a 15kw system.

Ah right yeah I did see that one, was assuming there was another similar doc for > 5KW.

Whats not clear to me is whether the limiting is done as a setting in the inverter or through the Fronius 63A-1 "smart meter". Perhaps the answer lies in the device name!

To get sign off from Vector they need to cite the main voltage and frequencysettings via screenshot or similar within 10 days of installation.

Now I've spotted that Fronius have launched a modern Hybrid inverter in the Primo Gen24+. Seems about $2k more, but does appear to have a lot more smarts and can run in the advent of a power outage without a battery, covering my UPS needs during generation hours.

eonsim

403 posts

Ultimate Geek
+1 received by user: 192

Trusted

#2891095 24-Mar-2022 08:27

insane:

Whats not clear to me is whether the limiting is done as a setting in the inverter or through the Fronius 63A-1 "smart meter". Perhaps the answer lies in the device name!
...

Now I've spotted that Fronius have launched a modern Hybrid inverter in the Primo Gen24+. Seems about $2k more, but does appear to have a lot more smarts and can run in the advent of a power outage without a battery, covering my UPS needs during generation hours.

The inverter will limit the power production but it needs the smart meter to work out how much power the house is using. If you had a 10kw system on a 5kw export limit without a smart meter the inverter would only ever produce 5kw, though 2x the panels mean it would produce that a lot more often than a system with 5kw of panels. It would max out at this even if your house was drawing 9kw as it wouldn't be able to see what the house was using.

With the smart meter linked to the inverter, it now knows what the house is using, and how much it's exporting. Thus it can adjust it's self to cover the house usage and still export 5kw. So say the house was drawing 4kw, then the 10kw inverter would produce upto 9kw, 4kw used by the house and 5kw exported. The inverter always controls things, but the meter tells it about what's happening with the house and grid.

The Fronius Gen24+ inverters look very nice, up to 3kw of emergency power if there is a power cut. You would want a lot of panels on such an inverter though. Getting a 6 or 8kw model and maxing out the panels to 9-12kw (can add 50% more panels than rating). That would maximise the production at all times, and give you the maximum chance of getting the full 3kw backup power out of the inverter during less than ideal weather or the middle of winter.

Ge0rge

2114 posts

Uber Geek
+1 received by user: 2060

Trusted

Lifetime subscriber

#2891153 24-Mar-2022 09:02

Where and how do microinvertors fit into this picture? (apart from physically behind the panels of course)

Dyson

Shop now for Dyson appliances (affiliate link).

insane

3324 posts

Uber Geek
+1 received by user: 1006

ID Verified

Trusted

2degrees

Subscriber

#2891167 24-Mar-2022 09:24

eonsim:

The inverter will limit the power production but it needs the smart meter to work out how much power the house is using. If you had a 10kw system on a 5kw export limit without a smart meter the inverter would only ever produce 5kw, though 2x the panels mean it would produce that a lot more often than a system with 5kw of panels. It would max out at this even if your house was drawing 9kw as it wouldn't be able to see what the house was using.

With the smart meter linked to the inverter, it now knows what the house is using, and how much it's exporting. Thus it can adjust it's self to cover the house usage and still export 5kw. So say the house was drawing 4kw, then the 10kw inverter would produce upto 9kw, 4kw used by the house and 5kw exported. The inverter always controls things, but the meter tells it about what's happening with the house and grid.

The Fronius Gen24+ inverters look very nice, up to 3kw of emergency power if there is a power cut. You would want a lot of panels on such an inverter though. Getting a 6 or 8kw model and maxing out the panels to 9-12kw (can add 50% more panels than rating). That would maximise the production at all times, and give you the maximum chance of getting the full 3kw backup power out of the inverter during less than ideal weather or the middle of winter.

Thank you, that's the part I was missing!

My 'backup' needs are very very minimal, well under 1kw from what the Genesis' app shows me - but understand that's an hourly average and does not reflect micro peaks.

In that scenario would only be 4 monitors, couple docks, router, switch, aps, cameras and led lighting, appliances standby power loads and the fridge. Don't need anything else on. Also not sure what happens when demand > supply, I'm guessing a blip or total power outage unless the backup loads are on a dedicated breaker?

So I was only looking at a dozen or so panels, a shade over 5kw to begin with as in general my average usage would be 2-3kw. Not sure how well that will work in autumn or winter or if I'll need more panels to help prop up cloudy days.

I see the inverters are good for 1.5x of their rated wattage, is it safe (also inverter longevity) to always count on 'boost' or should I try to minimise that and just get a bigger inverter to begin with?

Ge0rge:
Where and how do microinvertors fit into this picture? (apart from physically behind the panels of course)

Don't think that implementation design is used much anymore these days. Just more things that could break and possibly not needed due to the use of Tigo optimisers and duo panels?

Quinny

926 posts

Ultimate Geek
+1 received by user: 208

Trusted

#2891173 24-Mar-2022 09:37

I spent $36k. Tesla Powerwall 2 and 5kw Solaredge Inverter and 6.4 LG Neon 2 panels. System's solar output designed to be with 3% in 10 years time. I do understand you can no longer get LG panels. I am 5 deg from optimal. House uses 20-25kw a day on average as we love our electronic toys. I also have gas hot water and (some) gas heating along with 4 Heat Pumps.

I used the Westpac zero interest Winter warm up loan for 10k and this is totally offset by the savings on power bill. Last months power bill was $5 after the recent crappy weather. I also had house value increased with QV who gave me the 40k requested. I have had the home valued and the Powerwall/Solar is seen as a major sales plus.

Anyway here is real world data from it https://monitoringpublic.solaredge.com/solaredge-web/p/site/public?name=Quinny&locale=en_US#/dashboard

Would I do again. 100% yes.

insane

3324 posts

Uber Geek
+1 received by user: 1006

ID Verified

Trusted

2degrees

Subscriber

#2891178 24-Mar-2022 09:59

Quinny:
I spent $36k. Tesla Powerwall 2 and 5kw Solaredge Inverter and 6.4 LG Neon 2 panels. System's solar output designed to be with 3% in 10 years time. I do understand you can no longer get LG panels. I am 5 deg from optimal. House uses 20-25kw a day on average as we love our electronic toys. I also have gas hot water and (some) gas heating along with 4 Heat Pumps.

I used the Westpac zero interest Winter warm up loan for 10k and this is totally offset by the savings on power bill. Last months power bill was $5 after the recent crappy weather. I also had house value increased with QV who gave me the 40k requested. I have had the home valued and the Powerwall/Solar is seen as a major sales plus.

Anyway here is real world data from it https://monitoringpublic.solaredge.com/solaredge-web/p/site/public?name=Quinny&locale=en_US#/dashboard

Would I do again. 100% yes.

Interesting, that's a great comparison! My daily average over the year is also around 20kw+, and I'm the same with gas hot water, gas heater (not used) and 6 heatpumps (seldom all used at once).

I created a big spreadsheet and found payback period was longer than I'd want to stay in the house. Add batteries and it got worse as my nighttime usage is rather minimal.

Was your viability done on the basis of a low user daily power charge or a higher / standard $2+ per day daily rate? I heard that the low user plans will be grandfathered soon due to new legislation? That alone would make a $50 or so per month difference.

eonsim

403 posts

Ultimate Geek
+1 received by user: 192

Trusted

#2891596 24-Mar-2022 19:48

insane: In that scenario would only be 4 monitors, couple docks, router, switch, aps, cameras and led lighting, appliances standby power loads and the fridge. Don't need anything else on. Also not sure what happens when demand > supply, I'm guessing a blip or total power outage unless the backup loads are on a dedicated breaker?

So I was only looking at a dozen or so panels, a shade over 5kw to begin with as in general my average usage would be 2-3kw. Not sure how well that will work in autumn or winter or if I'll need more panels to help prop up cloudy days.

I see the inverters are good for 1.5x of their rated wattage, is it safe (also inverter longevity) to always count on 'boost' or should I try to minimise that and just get a bigger inverter to begin with?

Ge0rge:

Where and how do microinvertors fit into this picture? (apart from physically behind the panels of course)

Don't think that implementation design is used much anymore these days. Just more things that could break and possibly not needed due to the use of Tigo optimisers and duo panels?

So on really wet cloudy days like the last few, we have been getting between 5 and 9 kwh a day from a 5.1kw Solar system (with very good panels), that works to less than 1kw for most of the day and only a few hundred kws in the morning and evening. As such if you want back up power in winter, you probably want more panels than that.

I think your probably best to do a bit of both get a bigger inverter then overpanel it by 25-50%. 10kw of panels on a 10kw inverter will cost more than 10kw of panels on a 8kw inverter. Looking around pretty much everyone seems to recommend over panelling, otherwise your inverter spends most of it's time producing less power than it's rated for. For example a 5kw inverter with 5kw of panels generally produces more like 4-4.5kw of power at max during summer (the panels get too warm to produce max power) for 3-4 hours.

Microinverters (at least enphase ones) appear to be the deluxe option, they're more expensive but have a 25year warranty vs 10-15 for string inverters. They're also much better if you have a very complex roof (lots of different angles and directions) or a lot of shade on the panels as most inverters can only handle 2 different orientations. Though if you only have a little bit of shade there is apparently only a couple of % extra power generated for possible 10-20% higher cost.

1 | 2