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If you have an EV and a rooftop solar system you can often reduce your charging costs by charging from solar. More importantly you can help the planet and feel good at the same time whilst driving around on the green electrons that came from the solar panels on your roof.
There are three options we know of for charging your EV from your home solar:
First up we’ll provide a quick overview of the different approaches, and then we’ll look at some of the different factors you should consider in choosing which solution will work best for you.
Solar EV chargers are similar to a standard EV wall charger with the addition of solar monitoring and control systems. The charger may have one or more sets of sensors called current clamps (often referred to as CT clamps) which monitor the power flows in your home to detect when excess solar is available.
The EV charger can use the measurements from the CT clamps to adjust the rate of charging on your EV to match the excess solar available or according to other user preferences.
If you also have a home battery installed, you may need some additional CT clamps to monitor the battery.
Some common models include:
Some solar inverter manufacturers offer inverters with either an integrated EV charger or an add-on charger with strong integration with the solar inverter.
For such EV chargers, the inverter is already aware of the solar production so additional CT clamps may not be needed.
If you’re installing a new rooftop solar system, upgrading or expanding an existing system at the same time as your EV charger these may be worth considering.
Lastly - some such models may be capable of advanced functions such as controlling an EV charger, a home battery system, hot water or home heating systems. Such models may offer more advanced control than is possible with less integrated configurations. On the flip side, it may require that you purchase or replace many of these appliances at the same time.
Charge HQ takes a different approach to solar EV chargers. It communicates over the Internet with compatible devices (solar inverter, battery, energy monitor) in your home which are already measuring energy flows. It then communicates either directly with the EV (in the case of Tesla) or with a supported OCPP wall charger to control the charge rate to match.
If you have a compatible EV, charger and or solar system, Charge HQ will work with the hardware you already have.
See our list of
Every user has different priorities and every home energy system is configured differently so there’s no single recommendation that will work for everyone.
A very brief summary table follows, but after that, it’s a really long article. If you can make it to the end it does cover all the factors we think you need to consider so that the solar EV charging solution you choose does everything you hoped it would once the installation is complete.
There is one caveat to this… if you already have a Tesla, and a supported solar data source, you can try Charge HQ free of charge and see if it works for you. We think this no-cost option is always worth a try. If not, keep reading!
For each factor, we’ll consider the solar EV chargers with local CT clamp sensors (we’ll refer to them simply as Solar EV chargers from here on) and Charge HQ. The features and functionality of different makes and models of solar chargers vary and we won’t attempt to compare them all, rather we’ll highlight the issues that we think are worth checking when deciding what to buy.
Currently, we’re not aware of many users with integrated solar inverter EV chargers so we won’t consider them in this article but may revisit the topic in future. Many of the factors raised for the regular chargers will still apply.
If you have a home battery or think you might install one in future, it’s important that your EV charger is aware of the battery and its behaviour. Battery awareness ensures that:
The solar/battery data API is used to obtain information about current battery charging and discharging rates. In addition, the API can also inform the current state of charge (or % full) of the home battery.
For all supported batteries, Charge HQ will allow you to choose whether to prioritise charging the home battery or the EV. This is true for both AC- and DC-coupled batteries.
For AC-coupled batteries - Charge HQ will work if the battery is supported.
For DC-coupled batteries - Charge HQ will work if the solar inverter it is connected to is supported.
At the time of writing, there are no home wall chargers which can determine the state of charge (e.g. what percentage full the EV battery is) automatically.
This information is either available by communicating directly with the vehicle via an API and Internet connection, or if both the wall charger and the EV support a new communication standard called Plug & Charge (ISO 15118).
Commonly the EV will allow the owner to define a charge limit - the percentage full they would like to charge their EV to - via an app or in-vehicle controls.
Without knowing what the state of charge of the EV battery is at any time, the wall charger can either charge until the vehicle indicates it has reached the set charge limit, or provide a specified amount of energy (e.g. 30 kWh) when plugged in.
If your goal is to automatically maximise the amount of charging you do from your own solar this is a big deal. Charging only up to your minimum required level each day makes a big difference to how much solar energy you can consume the next time it’s available.
As a wall charger, they generally won’t currently know the state of charge unless both the charger and the vehicle support the upcoming Plug & Charge standard.
You can manually control grid and solar charging by setting your solar aware wall charger / EV to a charge limit of say 90%, and then control charging by choosing when to plug the charger in.
If the EV is above your minimum required level (say 50%), leave the charger unplugged overnight, but plug it in anytime during the day when solar is available.
For control via OCPP implementations, Charge HQ relies on the wall charger and, like solar EV chargers, won’t be aware of the state of charge of the EV, unless the vehicle is a Tesla.
For Tesla vehicles where a direct API integration is used, Charge HQ has constant visibility of the state of charge of the battery. Granular controls can be used to set different charge limits for solar charging vs scheduled charging.
Charge HQ doesn’t have any additional hardware components, relying instead on data provided by existing monitoring points, so there are no additional CT clamps to be installed.
As the app is often setup independently of the home solar or battery or EV charger installation, little control exists over the wiring and monitoring points. To maximise compatibility with different wiring configurations, flexibility is provided at the software level.
For example, the monitoring of the household loads may or may not not include the load from the EV charger itself, which can be compensated for in the app settings.
Per the section above on EV charger CT clamps, solar EV chargers do their own monitoring of energy imports and exports from the grid to enable solar charging.
Relies on the data feed it receives including information about energy imports and exports from the grid. By default, all solar inverters we connect to provide us with information on total solar production. All inverter brands also offer an optional add-on energy meter which allows monitoring the grid import/exports and household consumption.
To adjust the EV charging power to match the amount of excess solar available at any moment, Charge HQ requires one of:
If the solar installation does not include an energy meter, Charge HQ can adjust the EV charging power to match the amount of solar generation, with a configurable "margin" to allow for the other household loads. Such a setup is not able to react to the actual amount of excess solar at each moment.
Since they rely on local sensors, solar aware EV chargers typically detect any change to available excess solar generation very rapidly (e.g at the single second level), and can then alter the rate of charge fairly quickly.
This allows the charger to closely track the amount of excess solar to minimise any exporting of energy to the grid, or consumption from the grid in solar charging mode.
Since Charge HQ relies on the collection of solar generation data over the Internet, there is a delay in receiving the data and the EV charging rate cannot be updated as quickly. Typically we see a 1 minute delay in updates but it can be 5+ minutes depending on the equipment. See Solar Data Delays for more details.
This means Charge HQ will often undershoot or overshoot its target charge rate for short periods. In aggregate, these delays only have a small impact on the efficient use of excess solar energy.
For both solar EV chargers and Charge HQ you’re able to install a single phase or three phase charger if you have a 3 phase grid connection. The choice between them is usually dictated by what speed EV charger you want.
If you have a 3 phase grid connection, it’s important that the CT clamps on your charger monitor the correct phases.
This might mean monitoring all three phases, or if your solar inverters or batteries are only connected to a single phase you may just need to ensure the correct phases are monitored.
The API data feeds aggregate power flows across all three phases which ensures all energy flows are captured.
If you have a 3 phase grid connection, you can use either a 3 phase or single phase charger with Charge HQ provided that these phases are all monitored by your solar data source.
Where a 3 phase wall charger is used, Charge HQ will usually detect it automatically, or it can be configured in the app.
It’s not uncommon for homes to have multiple separate solar inverters. Often this occurs as a small system was initially installed and then more capacity was added later by way of a second independent solar PV system, leaving the original one in operation.
Per the discussion on CT clamps above, if you have multiple solar inverters, check where the solar EV charger is monitoring.
Currently, Charge HQ can accept data from a single solar data source. In many cases, it’s possible for a single source to report the production of multiple inverters but this depends on the equipment and how it was installed.
Charge HQ can also support an unmonitored second inverter provided that the grid connection is monitored correctly. This configuration is reasonably common in homes that have added a second, newer inverter, which does not monitor the old one.
AC-coupled batteries rely on monitoring total solar production and so when used as a data source generally provide coverage of multiple inverters.
We’re not aware of any solar integrated EV chargers which include a button to unlock the charge port on a Tesla. Without this button, you will either need to unlock the charge port from within the vehicle or via the mobile app.
Charge HQ is compatible with the Tesla wall charger and mobile chargers which include the release button to unlock the charge port.
Since all monitoring and control occurs within the charger itself, they’re not dependent on an Internet connection for normal EV charging from home solar.
If you use a smartphone app with the charger, it may require an Internet connection to operate or require the phone to be close by if using Bluetooth.
All control and monitoring depend on a reliable connection to the Internet. Ideally, your EV or wall charger would be within range of your home WiFi network. For Tesla vehicles, control is possible via built in mobile connectivity, but WiFi connectivity is preferred given the frequency of communication.
OCPP support won’t be required for solar charging of your electric vehicle. It may be a nice to have feature if you wish to connect your charger to other smart charging services in future.
OCPP is not required for vehicles with direct API control such as Tesla. For all other vehicle models, a supported OCPP EV charger is required.
Both solar aware EV chargers and Charge HQ rely on software to operate. In the former this software lives on small embedded computers in the charger itself, for Charge HQ it lives on computing services in the cloud.
We’re conscious that this article is comparing our product with that of competing products. Our broader mission is to enable EV adoption to help accelerate the transition to renewables and so our first goal is to help people charge their EV from renewable energy. If this article helps you find and choose a solar integrated EV charger, that’s a great outcome.
We’ve made every effort to present the options in an unbiased way, but our knowledge of home solar EV chargers isn’t as high as it is with our own product. If you’re familiar with these products and notice any errors please let us know so we can improve this guide.