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Single vs 3 phase when EV charging from solar

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If you’re just charging your EV from the grid, the main difference between single and 3 phase wall chargers is your maximum rate of charge and the cost of installation. A 3 phase charger will cost more once installed but will give you a higher maximum rate of charge (assuming your EV supports it)

When charging from solar there’s another consideration.

The rate of charge for EVs is set in amps, and can only be set in whole numbers. Most EVs and chargers will have a lower limit around 5 A (since charging at very low speeds becomes in-efficient) and upper limits based on the wall charger, circuit or onboard chargers in the car. For a single phase charger the upper limit is often 32 A and a 3 phase 48 A (being 16 amps on each of 3 phases).

In between the upper and lower bound you set the charge rate, incrementing in whole numbers only.

A single phase charger can usually charge at 5, 6, 7, 8, 9, 10… 30, 31, 32 amps.

A 3 phase charger can usually charge at 6, 9, 12, 15… 42, 45, 48 amps.

On the 3 phase charger since amps are set per phase and must still be whole numbers per phase, the power delivered to the car adjusts in 3 amp increments. A single phase charger on the other hand adjusts in 1 amp increments.

At 240 Volts, 1 amp = 0.24 kW, and 3 amps = 0.7kW. A single phase charger will need to see only 0.24 kW of excess production before it ramps up whilst a 3 phase charger will need to see 0.7kW of excess before it ramps up another step.

As a result, the single phase charger is able to track the constantly varying output of a solar system more accurately than a 3 phase charger.

In practice the amount of excess solar available for EV charging won’t look like the smooth graphs above. Output will vary rapidly from cloud cover and in response to varying load in the home. Being able to make small (1 A adjustments) will result in much more accurate tracking of excess production.

Conversely, if you have a larger solar system that regularly produces more than 7 kW, and you have an EV that can charge at speeds greater than 7 kW, you may be able to consume more of your excess solar with a faster charger.

Factors to consider when comparing 3 phase and single phase EV chargers for solar charging

There’s no simple answer in choosing 3 phase vs single phase, but from a solar charging perspective it’s worth considering:

  • Larger solar systems (> 7 kW) will benefit more from a 3 phase charger.
  • Smaller solar systems (< 4 kW) may be notably less efficient at solar tracking on a 3 phase charger.
  • Are you likely to install more solar capacity in future?
  • How fast do you actually need to be able to charge at home? Do you need to charge at speeds higher than 32 A? Do you think you will have an EV that supports charging at speeds higher than 32 A now or in future?
  • Do you have the option of using either a single phase or a 3 phase power supply with the same charger? For example, the 3rd Generation Tesla wall charger can be wired in either configuration.
  • What is the minimum rate of charge on the 3 phase charger you’re considering - some may not support charging below 6 A per phase (18 A total). Alternately, can the charger dynamically shift from 3 phase to single phase to support lower charging speeds?

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