Home Solar EV charging explained
One of the big drawcards for those with rooftop solar is the ability to charge an EV using your own power. Charging with your solar-generated electricity can essentially eliminate the ‘fuel’ cost of an EV. However, this is not always as easy as it sounds in practice. In this article, we discuss the various home EV chargers available, analyse different solar charging options, determine how long it will take to charge an EV using solar and address some of the issues with using rooftop solar and batteries for charging. For those interested in Vehicle-to-load (V2L) technology, we have a detailed article about using V2L for backup and off-grid power.
How to charge an EV at home using solar
Charging an EV using your rooftop solar can be relatively easy, but it depends on several factors, the most obvious being the size of your solar system, the time of day, and the weather. If you want to charge an EV quickly using solar only, you’ll need a large enough solar system and some help using a smart charger, which we will describe in more detail later.
How easily an EV can be charged using solar depends on the following:
Type of charger used - Charger speeds can range from 2kW to 22kW
The size of your solar system - Typical rooftop solar systems can range from 5kW to 15kW
EV battery level - How low is the EV battery, and how many kWh do you need to charge?
Distance travelled - How often do you drive, and how far do you travel?
This might sound complex, but fortunately, we have built a free solar and EV charging calculator so you can estimate how much solar you need to charge an EV based on your driving distance and charger type used.
If you don’t drive often, charging an EV using home solar can be easy with a simple portable plug-in (level 1) charger and a relatively small 5kW solar system. However, as explained later, solar EV charging using a more powerful 7kW (level 2) charger can be tricky, even with a much larger solar system. The problem arises as the solar will often not generate enough to cover a level 2 charger at full power during cloudy or bad weather. Luckily, this is where smart EV chargers can help, along with several other solar charging options explained below.
How many solar panels do you need to charge an EV
This is a common question, and the answer differs for everyone depending on how far you drive and how often you charge. Due to the high power consumption of EV chargers, a much larger solar array is required than a typical household. For example, an average household generally requires 6 to 8kW of solar, or 14 to 18 solar panels, to cover the daily power requirements throughout the year. In contrast, an average household with regular EV charging may require 10 to 12kW of solar power or 24 to 28 solar panels. This is around 50% bigger than the average solar size.
However, solar EV charging can be easily achieved in some cases using a much smaller solar system (6 to 8kW) if the charger is a low-power 10 or 15A portable charger. It all depends on the daily energy consumption and charging rate, as explained in more detail below.
Using a smart EV charger with a solar-only charging function is the best way to charge an EV using your own solar.
EV battery capacity and driving range
Before we get into too much detail about the different types of chargers and charge rates, it’s necessary to understand EV battery capacity and range. Battery capacity is measured in kilowatt-hours (kWh), and electric vehicles are available with a vast range of different battery sizes, from 24kWh up to 100kWh or more. Most common EVs have a battery capacity of around 65kWh, which generally provides a driving range of about 350km, depending on the conditions and how efficiently you drive. Each kWh of battery capacity will deliver around 5 to 8km of driving range. For a real-world comparison, lighter, more efficient EVs can use as little as 12kWh per 100km (1kWh = 8.2km), while larger, high-performance EVs can use 20kWh or more per 100km of driving (1kWh = 5km).
EV Driving Range - An average EV uses roughly:
16kWh of energy per 100 kilometres (1.0kWh = 5.8 km), or
26kWh of energy per 100 Miles (1.0kWh = 3.8 Miles)
Driving at higher speeds reduces driving range due to increased aerodynamic drag. However, most EVs also have regenerative braking, which recovers much of the energy typically lost during braking to slow the vehicle. Regenerative braking is particularly beneficial in city start-stop driving, improving efficiency and reducing brake dust and air pollution.
Main Types of EV Chargers
Tesla home EV charger is rated up to 7kW (single-Phase)
For those with solar installed, the first thing that comes to mind after purchasing an EV is what charging options are available and whether they are compatible with a rooftop solar system. Before we get into detail, it’s worth pointing out that most level 2 chargers, also called wallbox chargers, are relatively simple devices that can be installed on any home or business with or without rooftop solar. The main difficulty is whether your utility grid connection has enough spare capacity to support a level 2 charger, which generally requires a 32A supply.
Technically, there are three levels of EV chargers, of which only the first two can be used at home. Level 1 is a basic portable (granny) charger plugged into any ordinary 10A power socket, or a larger 15A power socket. Most EVs come equipped with a small 10A charger as standard. Level 2 are compact wall-mounted chargers permanently installed on homes and businesses. Level 3 are very large, powerful, fast DC chargers generally found at dedicated roadside EV charging stations.
Level 1 - Home 10A to 15A portable chargers from 1.4kW up to 3.6kW (10A to 15A). Often referred to as granny chargers.
Level 2 - Home wall-mounted chargers from 5kW up to 22kW (Wallbox charger). Single-phase and/or 3-phase varieties are available depending on your home grid connection.
Level 3 - Roadside EV charging stations from 50kW up to 350kW. Commonly called DC fast chargers.
Home EV Chargers
EV chargers used in most homes are either level 1 portable chargers or level 2 wall-mounted chargers. Households cannot install large DC fast chargers due to the enormous power requirements and cost. Some large commercial buildings can install DC fast chargers as they have the power capabilities required. The three main types of home EV chargers are described in detail below:
Portable plug-in (granny) chargers - 1.4kW to 3.6kW
Single-phase home EV chargers - 3.3kW to 7.4kW
Three-phase home EV chargers - 7.0kW to 22.0kW
1. Plug-in (socket) EV charger
The standard Nissan Leaf 10A plug-in EV charger
Most EVs come equipped with a basic portable charger that can be used with any common 10A wall socket. These small, granny chargers generally require 12 to 36 hours to fully recharge an average EV, depending on the battery size and initial battery state of charge. Most portable chargers draw around 2.2kW but, due to losses, typically only charge at 1.7kW to 2.0kW, which adds around 10km to 14km of range per hour. More powerful 15A portable chargers are also available, which are much faster and relatively cheap to buy, but require a dedicated 15A outlet to be installed in the home or garage.
Power rating: 2.0kW (10A), or 3.2kW (15A)
Charge rate: 12 km (7.5 miles) of range per hour
Portable charger price range: $250 to $600
Charging from solar: An average residential 6kW solar system can generate 2 to 3kW even during partly cloudy weather, so solar EV charging using a 10A plug-in portable charger is relatively easy.
2. Single-phase Home EV chargers
A standard home 32A wall-mounted EV charger (level 2)
Level 2 single-phase EV chargers can be wall or post-mounted and come in various options and designs. Most are rated at 32 Amp, equivalent to 7.4kW of power, and can provide a vehicle with a range of 40 to 50km per hour at the max charge rate. However, most chargers allow the charge rate to be adjusted from 8A to 32A using a mobile App. Given that the average person drives less than 50km a day, in theory, you will only need an hour or two to recharge a vehicle daily. An average EV can be fully recharged in 8 to 11 hours (overnight) using a regular single-phase 7kW Wallbox charger set to the maximum charging speed.
Power rating: adjustable from 2.0 to 7.2kW (32A)
Charge rate: up to 45 km (28 miles) of range per hour
Single-phase charger price range: $500 to $2400
Charging from solar: Charging using solar and a single-phase EV charger (7kW) at full speed is possible using a larger 10kW+ solar system during good weather. If the charger is set to a lower charging rate of around 4kW, solar charging using a smaller 6kW system is possible. However, a smart EV charger is the best option as it can dynamically adjust the charging rate to match your solar generation.
3. Three-phase Home EV chargers
Level 2 three-phase home EV chargers generally look identical to single-phase wall-mounted devices and are typically rated at 32 Amps (per phase). However, due to having three supply phases, they can supply three times as much power as the single-phase version, which is roughly equivalent to 22kW of charging power. This can provide a vehicle with a range of 120 to 150km per hour at the maximum charge rate. So, fully recharging an average EV could be possible in around 3 hours using a 3-phase Wallbox charger. However, it’s important to emphasise that not all EVs can accept 3-phase AC charging. Many EVs have limited AC charging from 7kW to 11kW single-phase, so AC charging speeds up to 22kW are not possible with all vehicles.
Power rating: adjustable from 3.6 to 22.0kW (32A 3-phase)
Charge rate: up to 130 km (80 miles) of range per hour - compatible EV required
Three-phase charger price range: $600 to $2500
Charging from solar: Solar-only EV charging using a powerful 3-phase charger (up to 22kW) is difficult, even with a much larger 15kW+ solar system, especially during cloudy weather. Solution: A three-phase EV charger set at a lower charge rate (such as 12kW). However, a smart EV charger is a better option as it can dynamically adjust the charge rate to match the solar output.
Fast Home DC Chargers - Direct Solar Charging
While level-3 rapid DC chargers are used at most roadside charging stations, smaller level-2 DC chargers for home use are either unavailable or prohibitively expensive. However, this is about to change, with several inverter companies working on utilising hybrid inverters to enable fast solar DC charging at speeds of up to 22kW at home. While this sounds quite innovative, it is not technically a new technology. Hybrid inverters have been used to charge high-voltage batteries, like those used in EVs, for many years directly from solar. The main benefit of the direct DC charging approach is bypassing the home's AC infrastructure and the limitations of the car's onboard charger, enhancing both efficiency and charging speed. Two such companies with affordable Home DC chargers in the final stages of development are SolarEdge and Sigenergy.
The SolarEdge DC charger will deliver DC fast charging up to 24 kW, harnessing power simultaneously from solar, a home battery, or the grid. The charger supports both 400 V and 800 V EV systems via a standard CCS connector and, more importantly, will be bidirectional and enable a vehicle-to-home (V2H) by utilising the EV battery to serve as a home energy storage solution for backup power during outages.
The Sigenergy SigenStor hybrid EV charging system offers single-phase and three-phase models from 5kW to 25kW. Battery capacity is scalable, utilizing 5kWh and 8kWh modules stacked up to six units high, providing a maximum capacity of 48kWh. The Sigenstor is an all-in-one modular solar energy storage system that is V2H ready for bi-directional EV charging and supports DC EV fast charging at capacities of 12.5kW or 25kW using the additional EV charging unit.
Already have solar installed?
If you already have a solar system installed, chances are you also have an energy (CT) meter and a solar App that provides information about your solar generation and household consumption. If this is the case, using an EV charger from the same manufacturer as your solar inverter makes sense and easily lets you set up a smart EV charger. Likewise, if you have a hybrid (battery storage) system, you will already have an energy meter, so these are also compatible with smart EV charging. The only catch with these existing solar systems is that you must use the same brand of EV charger as your solar inverter, such as Fimer, SolarEdge, Enphase, Fronius or Sungrow, as shown in the image below.
If you have solar already installed consider using a EV charger which is compatible with your solar inverter
For example, if you have a Fronius solar inverter, then you should consider installing the Fronius Wattpilot EV charger. Likewise, if you have a SolarEdge system, you might want to get the SolarEdge EV charger. Doing this can reduce the cost of installation and enables you to monitor your solar and EV charging all the same App.
Smart EV Chargers
Smart EV chargers offer various smart charging modes to optimise when and how your EV is charged. Charging options include scheduled charging to charge during off-peak times automatically or when electricity prices are low, boost charging and solar-only charging. If you have rooftop solar installed, you can use a smart EV charger to maximise your self-use of solar. These smart app-controlled chargers can monitor your solar generation and divert it to your EV charger instead of exporting excess solar to the electricity grid. This way, you don’t end up drawing power from the grid to charge your EV, even during poor or intermittent weather.
How do smart EV chargers work
A standard home EV charger will draw at a fixed rate, typically 3.5kW to 7.4kW, depending on the type of charger and settings used. However, when charging from rooftop solar, the energy generated may be far less, especially during cloudy or poor weather. Smart EV chargers overcome this problem by using an energy metering device called a CT clamp mounted near the main electrical supply connection to monitor the energy flow to and from the grid. Once it detects excess energy flowing out to the grid from your solar, it will charge the EV at that specific amount. However, this can constantly vary due to changes in power consumption and solar generation, so the smart EV charger continuously adjusts the charge rate to match the excess solar generation. See our smart EV chargers article for more information.
How long does it take to charge an EV using solar?
This question is open-ended as it depends on the EV battery capacity and the solar size. Generally, it will take a long sunny day to charge an average EV from around 30 to 80% using a standard 6.5kW rooftop solar system. Naturally, the more solar, the better when it comes to EV charging from home, especially in colder, less sunny locations. Unless you drive more than 80km per day, EV charging from rooftop solar will be relatively straightforward using a regular rooftop solar system, provided you are home during the day. Try our solar and EV charging calculator to simulate EV charging using solar.
Average daily charge Time using the following size solar systems *
6.5kW solar system = 8 hours to charge from 20 to 80% (Hyundai Kona 64kWh)
10kW solar system = 5 hours to charge from 20 to 80% (Hyundai Kona 64kWh)
The actual charge time can vary significantly depending on how low the EV battery is, the type of EV charger and weather conditions. A larger 10kW rooftop solar array with a more powerful 7kW Type 2 charger could charge an EV up to 80% in 7 to 9 hours on a sunny day, while a more powerful 3-phase charger and a 15kW solar array could take as little as 5 hours. Many of these charging times assume the household load is low and weather conditions are sunny; however, things are not always ideal. This is where a smart EV charger can help if you want to avoid paying for grid power to charge your EV at home.
Average daily charge Rate using the following size solar systems *
6.5kW solar system = 4.0kWh per hour = 22 km (14 miles) of range per hour *
10kW solar system = 7.5kWh per hour = 36 km or (22 miles) of range per hour *
Note: * Average solar levels measured in Sydney, Australia - Similar to Spain or Southern California.
EV Charging Efficiency
The charging efficiency of a typical EV using a household EV charger depends on various factors, including the charge rate, ambient temperature, battery temperature, charging cable length, and conversion efficiency of the vehicle’s power conversion system (AC to DC charger).
Temperature can have a big effect on charging efficiency due to several reasons. High ambient temperature can mean a vehicle may need to run the battery cooling system while charging. In contrast, low temperatures below 5ºC may require the battery heating system to run while charging. During sub-zero temperatures, the charge rate may be drastically reduced in EVs without heating until the cells have warmed. Additionally, any charger will operate slightly less efficiently in high temperatures due to increased electrical resistance.
EV Charging Test Results
EV Charger testing conducted by Clean Energy Reviews using a BYD Atto 3 electric vehicle compared the charging efficiency of a small portable 10A charger with a 7kW wallbox EV charger at various charging rates. The results, shown in the chart below, indicate that a portable 10A charger's charging efficiency is almost 10% lower than that of a dedicated EV charger due to the lower charging rate and losses in the charging cable. Charge losses are also amplified if long extension leads are used with portable chargers.
EV charging efficiency chart comparing a portable 10A charger with a dedicated wallbox charger at different charge rates.
EV Charging losses explained
When using portable (granny) EV chargers, cable losses result from resistance and associated voltage drop as the electrical current travels through the extension cable. The amount of voltage drop depends on three main factors:
Charging current - Higher charging speeds (higher current) increase voltage drop.
Cable length - Longer cables increase voltage drop and cable losses.
Cable size - Larger cable size (copper core size) reduces cable losses.
Portable EV chargers with long leads
Longer cables and higher currents result in greater power losses. Cable resistance also increases with higher temperatures, resulting in voltage drop and reduced power. The real-world test results shown in the chart below conducted using a BYD electric vehicle highlight the losses associated with longer cables, particularly long extension leads used with portable chargers, which can result in significant losses. It’s important to note that the losses can also be amplified in high temperatures, especially if the charging cable and extension leads lie in the sun (on concrete).
Solution: To increase charging efficiency, it is recommended to use a shorter extension lead when using a portable EV charger. Also, use a larger size cable if a longer lead is required. Most 10A extension leads use a 1.0mm2 copper core size, while 15A extension leads generally use a larger 1.5mm2 copper core. A higher current 15A outlet and a larger 1.5mm cable will help improve charging efficiency if you use a portable granny charger and require a long extension lead.
EV Charging efficiency test results using a BYD Atto 3 electric vehicle - Charging efficiency of a portable 10A charger with different length extension leads and a wallbox EV charger at various charging rates.
Low charge rates = Lower efficiency
Most power conversion equipment (inverters or chargers) will operate more efficiently when working close to the rated power output, and EVs are no different. An electric vehicle's built-in charger needs to convert AC power from the grid to high-voltage DC power to charge the battery system. This process requires power conversion (via transistors) and powering auxiliary controls like battery cell balancing and temperature regulation.
For example, if a wallbox charger is rated at 7kW and the charge rate is set to only 2kW, the losses will be greater. Charging closer to 50% of the charger rating or higher will help improve charging efficiency. Unfortunately, as explained previously, when using portable chargers with extension leads, higher charge rates can also increase cable losses, so a balance must be made according to the cable length and charge rate.
Off-grid solar EV charging & challenges
Charging an EV using a typical home off-grid solar system can be challenging for several reasons, the most obvious being the limited amount of energy available during the day, especially during poor weather. Another problem lies in the limited EV charging window, as the most effective time to charge an EV is directly from solar. Overnight charging is possible, but this would generally involve running a backup generator or reducing the charge time or rate only to use a portion of the off-grid battery. EV battery capacity is very large in comparison to a residential off-grid system and would drain the battery if it was left charging overnight. For example, an average EV has a 65kWh battery, while a typical off-grid home may only have a 30kWh battery. In this situation, the high consumption rate using a 7kW home EV charger could completely drain an off-grid battery in 5 hours if it is not monitored or controlled correctly, resulting in system shutdown or excess backup generator runtime.
The Victron EV Charger is the first dedicated off-grid charger with battery management and control settings.
Off-grid EV Chargers and Solutions
Unfortunately, most smart EV chargers cannot be used to charge using solar only in an off-grid system, as there is no grid export for the charger (CT meter) to reference. Even in an AC-coupled off-grid system, this can be extremely difficult to setup and is not recommended. Fortunately, there are some simple solutions; most regular EV chargers can be used in an off-grid system if you reduce the charge rate to a lower level (3 to 4kW) and manage the consumption to prevent over-discharging the off-grid system. There are several ways this can be achieved, for example, using simple timers or smart controls to prevent draining the off-grid battery. Many modern off-grid systems have precise battery monitoring and can be programmed to activate relays (control circuits) to be
Currently, only one dedicated off-grid EV charger is available from Victron Energy. Victron specialises in off-grid power equipment, so it’s not surprising they developed a smart EV charger with off-grid functionality that can be programmed not to discharge the household battery below a pre-set level (min SOC). However, for it to operate, the charger must be connected to a Victron off-grid system containing a Victron GX device (smart control hub). Learn more about the Victron charger in the Victron EV charger review.
Charge HQ - Smart charging using OPCC
A recent technology is an intelligent app-based control system that integrates with an existing solar system to charge an EV. A startup company called Charge HQ developed the software, which is compatible with a number of popular solar inverters and energy storage systems, including Fronius, SolarEdge, Tesla, and Sungrow, plus energy monitoring platforms like Solar Analytics.
To function, Charge HQ needs to be able to control the EV charging over the Internet. It can either talk directly to your electric vehicle or the EV charger installed in your home. However, the EV charger must be an Open Charge Point Protocol (OCPP) compatible charger with support for external power control. If it does not support power control, the system can start charging when there is enough solar and stop when the available solar is below the set charge rate. EV chargers with OPCC compatibility can also be incorporated into smart home (IoT) control software.
Bidirectional chargers - V2G & V2H
A new technology that will become more popular in the future is vehicle-to-grid or V2G, using what’s known as a bidirectional charger. This might sound complex, but it simply allows two-way energy flow from your electric vehicle. Ordinary EV chargers send energy in one direction during charging. In contrast, if required, bidirectional chargers can also draw power from your vehicle to power your home or help balance the electricity grid in times of high demand.
Another emerging technology is vehicle-to-home or V2H. This is similar to the V2G, but the energy is used locally to power a home and enables the EV to function like a large household storage battery to help increase self-sufficiency using solar.
Vehicle to Grid technology using bidirectional chargers can allow an EV to be used for backup power.
For V2G to work, the EV must be able to accept two-way charging and there are only a few V2G compatible EVs on the market including the latest Nissan Leaf. This technology will become a game-changer in the near future and can offer a wide range of services including powering your home and storing excess solar energy. Learn more in our detailed bidirectional chargers explained article.
Vehicle-to-Load - V2L
EVs with vehicle-to-load or V2L technology are much simpler and do not require a bidirectional charger to operate. V2L allows electric appliances to be directly powered by the standard (10A) power outlets built into the vehicle. EVs with V2L technology can supply AC power and are used as a backup power supply in case of a blackout or an emergency. Considering the average EV has a 60kWh battery, a fully charged EV could, in theory, supply a regular household for several days non-stop. Another helpful feature of V2L is it can be used to top-up other electric vehicles if they happen to be stranded due to a flat battery.
EV charging using a home battery.
If you are away most of the day, charging an EV using rooftop solar can be challenging. However, this is where battery storage can help. Most average home battery systems are 10kWh in size, which can provide up to 80km of driving range, provided you can use the total battery capacity for charging. In reality, only half of the battery may be available due to household consumption requirements, so this may only provide 30 to 40km of driving range. However, this may be suitable considering that most of the population (who live in cities) drive short distances on average. For those who drive longer distances, a larger battery or off-peak charging will be required to recharge the vehicle. Smart EV charging systems such as the SolarEdge inverter EV charger can help manage and optimise your EV charging using solar and battery storage.
Single-Phase Vs 3-Phase grid supply
Two main grid connection types are available for homes, single-phase and 3-phase. Single-phase electricity connections are generally limited to a maximum of 20kW or 80A, while a 3-phase residential connection can supply up to 45kW (3 x 63A).
Most homes in Australia, Asia, the UK and North America have a single-phase, 220 to 240V supply. The maximum energy supplied to a home by the electricity grid is typically 12kW to 20kW (50A to 80A). However, you cannot utilise the full grid capacity to charge an EV, or you will not be able to use any other appliances simultaneously. If you did, every time you use a toaster or microwave, the grid supply switch would trip off due to overload. For this reason, most single-phase EV chargers are limited to 32A or around 7kW. This is not bad unless you need to fast-charge at home. However, higher charging rates can be enabled using an EV charger with a load-balancing function that monitors household consumption and adjusts the charging rate accordingly. Learn more about load-balancing in our smart EV chargers article.
Most commercial businesses have a 3-phase supply, so installing one or more high-power 22kW EV chargers is possible, depending on the building’s electrical connection capacity. However, multiple level-2 EV chargers could also overload a commercial grid supply, so smart load-balancing EV chargers are also recommended.
