Designing a Combined Solar, Battery, and EV System in Singapore

Solar, battery, and EV charging are usually explained as three separate decisions, each with its own sizing logic. Designed together as one system from the outset, the right sequencing and sizing actually changes, and getting the order right avoids paying for capacity that goes underused.

What order should these three decisions actually happen in?

Solar system size first, since usable roof area and the property's electrical supply phase are hard physical constraints, covered in the roof suitability checklist. Battery capacity second, sized to the household's evening and overnight loads, covered in the battery storage sizing guide. EV charging strategy last, since when and how a car charges should adapt to what the solar and battery system already provides, not the reverse.

Does charging an EV from solar directly change the calculation?

Yes, meaningfully. Charging directly from solar generation during daylight hours captures that energy at essentially no additional cost beyond the electricity already being generated, without needing battery capacity, inverter round-trip conversion losses, or storage cost to shift that energy to a later time. This is generally the most cost-effective way to combine solar and EV charging, covered in full in solar and EV charging, charge your car for free.

Does an EV charger compete with solar and battery for the same electrical supply capacity?

Yes, and this is worth understanding before assuming solar, battery, and EV charging simply stack without interaction. A typical home EV charger draws a meaningful load of its own, commonly around 7kW for a standard AC unit, on the same single-phase or three-phase electrical supply that also governs how large a solar system the property can support. On a single-phase supply already sized close to its practical ceiling for solar alone, adding a substantial EV charger load is exactly the kind of scenario worth discussing with an electrician or your installer before assuming the existing supply comfortably handles all three simultaneously, since electrical capacity, not just battery or panel budget, is a genuinely shared, finite resource across all three systems.

Does adding an EV charger trigger its own separate approval process?

Often yes, and it is worth checking rather than assuming your existing solar approval automatically covers it. A significant EV charger load can require its own notification or approval step with SP Group, separate from the EMA and SP Group process your solar system already went through, since it represents a meaningful new load on the property's electrical supply rather than a generation source being added. Wiring for the charger circuit itself also needs to meet Singapore's SS 638 electrical installation code, the same standard governing the rest of a solar and battery system's wiring.

How much does adding EV charging actually change battery sizing?

Substantially, if overnight charging is the goal. A single EV can draw considerably more overnight than typical household evening loads combined, so a battery sized only for lighting, refrigeration, and general use will not meaningfully cover EV charging on top of that without a real capacity increase. A household planning to charge overnight from battery should size specifically for that load, not assume a standard household-sized battery has spare room for it.

Does adding all three at once affect inverter choice?

It can. An inverter selected only for the panels may lack the capacity or configuration to also manage battery charge and discharge and EV charger integration added later. A homeowner planning to eventually add battery and EV charging, even if not immediately, should raise this with the installer when the solar system is first designed, covered in solar inverter sizing and clipping, so the initial inverter has headroom rather than requiring replacement later.

Have any of Sunnify's own documented installations actually combined all three?

Not yet as a single documented package, worth being upfront about rather than implying otherwise. Sunnify's publicly documented installations to date are solar systems, several sized generously enough that a future battery or EV charger addition remains realistically on the table, but none currently paired with a battery or EV charger in the same project write-up. That is a genuine, honest gap in the portfolio today rather than evidence that combining all three is somehow impractical; it simply reflects where Sunnify's own documented project history genuinely stands at the time of writing, and the sizing principles laid out above still apply regardless of whether a specific combined example exists yet.

Run the Sunnify solar estimate to establish the solar system size first, the right starting point for designing battery and EV charging around it.