Options for EV charging from solar

Options for EV charging from solar

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:

  1. Buy a solar-aware EV charger
  2. Use Charge HQ with a supported wall charger and any EV
  3. Use Charge HQ with a Tesla and any charger

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

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:

Solar inverter integrated EV chargers

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.

Options include:

Charge HQ + supported EV or OCPP charger

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

Which option should you choose?

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!

Summary

Factors to consider in choosing a solar EV charger

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.

Battery awareness

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:

  • your charger can distinguish between solar generation and battery charge/discharge
  • you can prioritise EV vs home battery charging
  • if your battery is enrolled in a VPP, battery exports can be distinguished from excess solar generation exports

Solar EV chargers

  • If you have an AC-coupled battery, can the charger monitor it via an additional CT clamp?
  • If you have a DC-coupled battery, a Solar EV charger can only provide limited battery-related functionality, because it's not aware of the battery. At best, you may be able to specify a "margin" that may enable some control over whether the battery or the EV is charged first.

Charge HQ

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.

EV battery charge level

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.

Solar EV chargers

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.

Charge HQ

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.

EV Charger CT Clamp installation

Solar EV chargers

  • We recommend confirming the monitoring points for the charger, it may either:
  • Use a single clamp on your grid supply to monitor import and export, OR
  • Use one clamp on the home load and another on the solar generation.
  • If you also have an AC-coupled battery, you may also need to install a CT clamp on the battery circuit with a cable running back to your EV charger.
  • A data cable for the CT clamp(s) must be run from the EV charger to the monitoring points. Often this is the same cable route that is used for the EV charger supply power, but it may not be if for example power is supplied via a sub-mains switchboard.
  • Some models of solar-aware EV chargers offer a wireless CT clamp device which is useful in cases where the cable runs are difficult or not possible.
  • Get your electrician to check that a) the charger includes the required CT clamps, b) there is access to and space available to install the CT clamps at the monitoring points required for the charger, and c) that it is practical to run any required data cables or investigate wireless options.

Charge HQ

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.

Grid consumption monitoring

Solar EV chargers

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.

Charge HQ

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:

  • An optional grid consumption monitor that is integrated with the solar inverter, or
  • The presence of a supported home battery system since they all include a grid consumption monitor to support their own operation, or
  • An independent energy monitoring system, eg Solar Analytics

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.

For more details see our article on solar vs grid vs home battery monitoring as well as the solar data support register.

Solar monitoring frequency

Solar EV chargers

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.

Charge HQ

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.

3 phase grid connections

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.

Solar EV chargers

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.

Charge HQ

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.

Multiple solar inverters

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.

Solar EV chargers

Per the discussion on CT clamps above, if you have multiple solar inverters, check where the solar EV charger is monitoring.

  • If it monitors the grid connection point it will automatically pick up any generation from both inverters
  • If it monitors on the generation and load independently, the system wiring may need to allow for a single CT clamp to monitor both systems. Check with your electrician.

Charge HQ

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.

Tesla charger release button

Solar EV chargers

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

Charge HQ is compatible with the Tesla wall charger and mobile chargers which include the release button to unlock the charge port.

Connectivity

Solar EV chargers

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.

Charge HQ

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

Solar EV chargers

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.

Charge HQ

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.

Future upgrades

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.

Solar EV charger

  • The software can be updated via the vendor issuing firmware updates.
  • If the wall charger is connected to the Internet, these might be over the air, if not there may be a more manual process involved.
  • Changes to the software will be governed by the capability of the hardware or computer in the device which never changes. This can both limit the ability to provide upgrades but can also provide opportunities since the vendor has intimate knowledge and control over all of the relevant components.
  • As the vendor builds newer versions of their devices over time, it’s not uncommon for the older versions to stop receiving software updates, or receive fewer of the new features. A similar situation is often experienced in other devices such as laptops and mobile phones.

Charge HQ

  • Since the software lives on cloud servers, the capability of these and the software itself can constantly be upgraded and updated without needing to make any changes to the physical EV charger. The charging experience will continue to improve without needing to buy a new wall charger.
  • Where direct vehicle control is used, upgrades to the software and capabilities on the vehicle may provide the opportunity to upgrade the capabilities of Charge HQ. For example, we currently can only offer direct charging control on Tesla vehicles, but many other EVs come equipped with an Internet connection and APIs, if the vehicle manufacturers add remote charging control via over-the-air updates we’ll be able to offer support independent of the wall charger.
  • Charge HQ is a single application, which can potentially control any charger with OCPP support or any EV where direct vehicle charging control is possible. We’re biased, but we believe that this very large potential user base will support the development of a more feature rich smart charging service than one which is only developed for a single make of EV or EV charger.

Disclaimer & Feedback

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.