How to size solar panels, a home battery and an EV charger for a villa

Four parts of the system, four different jobs

Start with the question each item has to answer. Solar-panel capacity is shown in kW, but the owner's real concern is how much energy the array can produce over a day or year. The inverter's kW rating is about how much power it can move at one moment. Battery kWh indicates stored energy, while its kW limit indicates how quickly that energy can be delivered. The EV charger rating is the fastest power it may offer; the car, property supply and control settings can all reduce the actual rate.

This is why a product bundle can look impressive and still be poorly matched. A large charger may sit below its maximum most nights because the car has many hours to charge. A large battery may add little value if it is already full before midday and the home uses very little after sunset. A large inverter does not create more sunlight or battery energy.

Keep these four jobs on separate lines when comparing quotations. They come together in the final system, but they should not be justified by one headline number.

Add the car's daily refill, not its full battery size

An electric car may have a large traction battery, but most owners do not empty it every day. Planning the home around one full charge can make the solar array, stationary battery and inverter much larger than the daily routine requires.

Use recent driving instead. Find the distance normally travelled in a day and the car's energy use for that distance. The vehicle or charger app may already show how many kWh are added during a normal week. Divide that weekly figure by the number of charging days, then allow for the difference between energy drawn from the wall and energy stored in the car where suitable data is available.

Suppose the charger records 55kWh drawn across five ordinary charging nights. The planning figure is about 11kWh per charging day, not the car's full battery capacity. If the car is parked for eight hours, that 11kWh represents an average of about 1.4kW across the whole window. It may still make sense to install a faster charger, but the example shows why maximum charging speed and daily energy need are different questions.

Occasional long trips can be handled separately. The owner may accept a longer home charging session, use grid power, or use public fast charging rather than building the entire household system around a rare journey.

Estimate the solar array from the home and EV together

Add the home's normal daily electricity use to the energy usually drawn by the car. Then compare that total with realistic solar production for the roof and location. Roof direction, shade, temperature, panel layout and seasonal weather all affect the result. One generic “hours of sun” number is not enough for a final proposal.

Here is a simple teaching example. Assume the home uses 20kWh a day and the charger draws another 11kWh. The combined target is 31kWh a day. If an early estimate uses four equivalent full-sun hours and an overall production factor of 80%, the arithmetic is 31 ÷ (4 × 0.8), or roughly 9.7kW of panels. This is not a recommendation for a 9.7kW system. It only shows how the inputs connect.

A proper estimate needs local monthly production data and the actual roof. The winter result may matter more than the annual average if the owner expects a high share of home charging all year. The available roof may also set a hard limit. When the array cannot cover every kWh, the design can still be useful: solar supplies part of the home and car demand, while the grid covers the balance.

Choose the inverter and charger around busy periods

The inverter has to deal with what happens at the same time, not the total energy used across a day. Air conditioning, cooking, water heating, a pool pump and EV charging can overlap even when the daily kWh figure looks reasonable.

Write down one believable busy period. For example, the air conditioning and ordinary house loads may be using 4kW, cooking adds 2kW, a pump adds 1kW and the car begins charging at 7kW. The total is 14kW in this simplified example. That does not automatically mean the home needs a 14kW or larger hybrid inverter. With the grid present, the system may be allowed to import the difference. A smart charger may also slow or pause the car while cooking and the pump are running.

Charging control can be more useful than buying extra capacity for an overlap that lasts twenty minutes. Ask whether the charger can follow surplus solar, use a schedule, respect a whole-property power limit and restart sensibly after an interruption. Also check the car's own AC charging limit: a charger cannot force the vehicle to accept more power than it supports.

The property's supply and phase arrangement still matter. A single-phase and three-phase home can use the same total energy but need different equipment and load planning. The quotation should state the exact inverter and charger models, phase, continuous limits and what happens when the grid is available versus unavailable.

Size the home battery for a clear job

A home battery can move daytime solar into the evening, reduce purchases during expensive hours or keep selected loads running during a power cut. These goals can overlap, but the owner should say which one comes first.

For evening use, list what normally runs after solar production falls. For backup, make a shorter list of what must stay on. If selected loads average 1kW and the owner wants them for eight hours, they need roughly 8kWh delivered to those loads before allowing for reserve, conversion losses and equipment limits. That is a clearer starting point than choosing a battery because its brochure says “whole home.”

Do not assume the stationary battery must be large enough to fill the EV battery. Sending stored energy from one battery into another uses a lot of capacity and passes through conversion equipment. It may be a deliberate choice for a particular owner, but it should be priced and modelled as such. Many homes get more value by charging the car from daytime solar when it is parked, scheduling it for a suitable grid period, and keeping the stationary battery for household evening use or outages.

Battery power matters as well as battery energy. The exact battery and inverter pairing must support the intended charge and discharge rate. A large kWh number does not prove that air conditioning, pumps and vehicle charging can all run from the battery at once.

Decide how the system should behave before choosing models

There is no single best order for using solar energy. A home focused on bill savings may let flexible EV charging follow midday surplus. A home focused on backup may protect part of the stationary battery instead of using every available kWh overnight. Someone who needs the car ready early may allow grid charging even when stored solar is available for the house.

Write the priority in plain language. For example: “Keep 30% of the home battery for outages, charge the car from spare solar when it is parked, and use the grid if the car still needs energy by 11 p.m.” That sentence tells the system designer far more than asking for a “smart solar package.”

Before comparing equipment, collect the information below. It is enough for a useful first discussion without pretending that the final electrical design is complete.