3 Phase Solar Setup Recommendations

Hi snowfly

My situation is not too dissimilar to yours, so I’ll briefly describe my system, then comment on the points where you’re looking for recommendations.

I have an all-electric 3-phase home with two single phase heat pumps, a hot water heat pump and a base element in the cylinder, a spa pool and a single phase 7kW EVSE. I don't have any 3-phase appliances.

My solar system was installed in late 2022 and consists of:

AlphaESS Smile T10-HV – a 10kW 3-phase inverter
2 x 8.2kWh DC-coupled battery packs
40 x 400W Trina solar panels split over NE and NW aspects
Stats and control via web and mobile apps
Home Assistant modbus integration over Ethernet.

My retailer is Electric Kiwi, and I heavily exploit the free “Hour of Power” which I’ve set at 6-7am (typically pulling 40kW over this period), and do a force discharge to grid to take advantage of peak hour FIT rates if I can top up with solar.

The system is working well for me. The 16kW of solar panels is about right, but I could handle more inverter power (5kW per phase rather than 3.3kW) and an additional battery pack would guarantee getting through the evening peak hour if we’re cooking up a storm in the kitchen.

Now for your questions:

Ideal 3 phase inverter size to support house size / ducted heat system? (e.g. 10, 15 or more KW?)
I’d go for a 15kW system giving you 5kW per phase. More if you can afford it

Unbalanced / Asymmetric capability, to spread load between phases - avoid exporting on 1 phase, and importing on another phase
Absolutely. The inverter must work in unbalanced mode. It’s frustrating enough that even within half hour billing periods retailers will apply usage and FIT tariffs independently rather than net usage

Hybrid inverter, with at least 1 battery (5KW) and ability to add another in future if required
Yes hybrid. Battery energy storage is measured in kWh. If you mean 5kWh of battery storage then you will quickly find its limitations. If you can afford it, go for 15kWh or more. Battery technology changes over time so get all the batteries at once. Don’t expect to get a compatible battery in three years’ time.

App/web/API access (modbus?)
Yes, especially modbus so you can keep monitoring, alerting and control local and you have full access to all the control registers in the inverter. For example, the Alpha app doesn’t allow force discharge to grid in NZ, but I can do so via HA/modbus.

Number of panels? (inverter size above would help dictate that)
Install to the maximum capacity of the inverter. The incremental cost of additional panels is small. Spread over NE and NW aspects to maximise PV over the morning and evening peaks, and avoid a big unusable PV hit in the middle of the day. Even so you will be in clipping territory on sunny days where the inverter can’t handle the full PV input, and the MPPT circuitry will scale it back. Implementing force discharge to grid in anticipation will free up battery capacity to absorb the solar (assumes DC-coupled inverter).

I know some people recommend against loading the inverter to its full PV spec but to my mind it’s better to accept/manage clipping than suffer inadequate solar PV on dull days. Just make sure your installer checks all voltage/current/power limitations to ensure nothing is exceeded.

Suggested brands / ecosystems to use or stay away from?
I’m happy with Alpha. It’s popular in Australia but the NZ agent (Solar Group) went into liquidation recently. I believe Sunshine Solar now sell and support Alpha kit. Do your research on that one – there are lots of good brands, and it really comes down to your local installer.

Any suggested suppliers / installers in Taranaki region
I’m in the Waikato so can’t make a recommendation other than to propose you use a well-qualified and well-established local installer selling good quality kit. Membership of SEANZ is good. Get three quotes and compare them rigorously.

Other considerations
Consider what happens during a grid outage, especially if you live rurally. Have a transfer switch (automatic preferred) installed or an inverter design that keeps selected circuits live. Keep loads low on these circuits, even during normal operation. Size your battery accordingly.

Implement a home automation system to monitor and switch your high-power devices – heat pumps and hot water in particular. Depending on your electricity retailer and their TOU tariffs, you can have endless fun controlling energy consumption and generation to minimise your ongoing costs.

Phase balancing is important - work with your sparky on that.

And be warned - you will be prone to shaking your fist at clouds once your system is installed.

Cheers - Steve

snowfly

SteveXNZ

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