The Standards Gap Holding Back Solar Homes Becoming Smart Homes

inverter wirelessly communicating with smart plugs

Want your inverter to wirelessly control some smart plugs? It ain’t easy…

This week’s post was inspired by a question asked by Malcolm via e-mail:

“Do you know of any ‘Smart” home systems/software that can be used with a Fronius Inverter/Smart Meter to direct surplus solar power to home appliances and/or heaters via smart wifi plugs?”

It’s a good question, and one that doesn’t yet have very many good answers. The world’s full of “smart home” control systems, but even so, you don’t have to look very far to find some pretty extreme examples of “makers” putting together DIY systems to get what they want, because what they want doesn’t come off-the-shelf.

The YouTube video below is probably our favourite of the genre.

What the YouTuber, CWNE88, wanted was to charge his Tesla from his solar power system, only when there’s solar electricity to spare – so the car is never charged with electricity imported from the grid. It’s such a simple and obvious question, I’m amazed it’s not a tickbox in the Tesla control software.

Instead, the intrepid CWNE88 has had to write software for a Raspberry Pi, get power for the RPi, and use the fortunately-standard RS485 serial bus as the control interface. As you can see from the video, it’s not excessively difficult – but it’s not for the faint-hearted (or those fearful of warranty warnings!). If you want to see the whole thing, he’s got the software, designs and documentation here at the open source software distribution site, GitHub.

Malcolm’s request is really straightforward – if the system is importing from the grid, keep the heater off; if the system is exporting with enough spare capacity, turn the heater on.

And as is so often the case, the really straightforward request isn’t answered because it involves two fragmented industries: on the left, Fronius, Enphase and other solar inverter suppliers; and on the right a dizzying number of smart home controller companies, and in the middle …

… people like CWNE88 above, hacking up his own solution, because the Tesla kit doesn’t have that capability out of the box.

Here’s another example: an acquaintance of mine who is an IT systems administrator and solar owner told me of the difficulties he had with a similar question – how to constrain his pool pump to only operating when there was sufficient solar power. In a series of direct messages, he told me:

“At the moment, you need a hub/gateway that’s specific to whichever vendors’ products you are using. Some can interact, but very broadly.


“Then you have a different app for each vendor needed to configure their particular thing.


“It’s all good fun as a hobby, in the sense it will constantly consume time and money to make it work, and that’s cool if you like playing with tech, but it’s a long way from my wife or parents making a whole of home IoT solution tie neatly together.”

He succeeded in getting the pool pump powered when there’s lots of power coming off the roof, but only after he’d managed to pull data from his inverter, uploading it to the PVOutput metering-sharing service, using the open-source Home Assistant software to download the data again, and mapping a Home Assistant action to the PVOutput data.

As he wryly noted:

“There are probably more direct methods, but this works.”

What Malcolm, CWNE88 and the sysadmin want are two things: a standard way for the inverter to communicate its status (a smart WiFi-enabled power point for Malcolm, between different Tesla systems in CWNE88’s case), and a product that makes it easy to make decisions based on inverter status.

Inverters Talking to the Outside World

Researching this post took me into the world of API documentation. The API, or Application Programming Interface, is the language the inverter’s computer uses to talk to the outside world. A smart home vendor needs to get the inverter status, to find out whether power is being imported or exported, and whether there’s enough solar power to drive a particular load.

To get that information over the wire, you send a request to the inverter (an API call, for programmers) and read the response.

I looked at the API documentation for just two inverter makers – Fronius and Enphase – and it won’t surprise you to know the API calls are different. If you’re running a Fronius inverter, the request seems to be GetInverterRealTimeData (if you’re interested, you can download the document here); if you’re using Enphase, you send a request called Summary (if I’ve read Enphase’s API documentation correctly).

Two inverters, two different commands to retrieve inverter status: that’s why we need standards if the solar home is to become a full member of the smart home.


Standardisation is on the way, via a multi-year industry effort called SunSpec (interestingly, Fronius is a member but Enphase isn’t yet). Companies that join the industry group can, once they’ve built products that use the SunSpec API, get the group to certify their compliance.

At this stage, however, SunSpec’s effort seems to me to be mostly “grid-facing”. As the group explains,

“SunSpec standards address operational aspects of solar PV power and energy storage plants on the smart grid

(emphasis added).

Vendors in the smart-home sector have their own set of standards to work with, making it unlikely they’d welcome another, but perhaps some there’s a gap in the market for someone to build a bridge between the two worlds – SunSpec on one side, a smart home standard on the other, to make the connection from the solar inverter to the smart home as plug-and-play as Malcom’s WiFi power point.

About Richard Chirgwin

Richard Chirgwin is a journalist with more than 30 years' experience covering a wide range of technology topics, including electronics, telecommunications, computing and science.


  1. The only project that seems to achieve what he wanted is the ´Open Energy´ monitor. Unfortunately, only a kit or self-build, but they also have an Open EVSE that interfaces to their monitoring so that an EV can be smart charged.

    In the future, I hope this project expands to include a virtual power station. All the base hardware is there, it just needs the software!

    Here is a link:

    regards, Doug

  2. Or he could just use a Zappi which just uses CT clamps and will direct excess solar or wind to charge the car.

  3. Also, I forgot to say that many Fronius Inverters have a programmable output that can switch a Solid State relay. This is ideal for turning on Hot Water systems or other resistive loads. (But not so good for running things like pools where you want the power to be constant.)

  4. Geoff Rehmet says

    For the kind of application described, you should be able to use the RESTful API of a Fronius inverter, together with the API provided by a smart plug such as the TP-Link HS100 or HS110.
    You would need to trawl the Fronius API documentation to find the right endpoint to give you the amount of power being exported. To be able to get that would also require that you have a Fronius smart meter installed to measure the amount of export.
    The API of the TP-Link HS100/HS110 is not documented, but there is a Python module available for it on GitHub.

  5. Standardizing getting information from the inverter is very worthwhile, but I think the bigger need is on the appliance side having some standard way that information about how the appliance should consume electricity being able to be fed in.

    Some appliances can be controlled by switching them on and off entirely, but it would be great if air-conditioners could adapt to the availability of solar power and use exactly the amount that is available.

    While much more minor, it would be great if the heating element in my dishwasher could wait until the cloud passes by and there is solar power available before it starts heating the water. These things can only happen if the controller is embedded directly in the appliance and there is a standard method for it to receive information about available power and its going to take many years to both get a standard, then many more years to get it adopted into appliances and then more again for people to replace their appliances to ones include this control. We need to get this started now because it will take a very long time for it to be widely adopted.

    The control needs to be more advanced than what comes directly from the inverter as well. Some houses have multiple inverters and then there is measuring the import/export directly which could be with a different device like Solar Analytics. And there’s potentially considerations about battery charge and the state of the grid as well, probably moving more and more towards time of use or even completely dynamic tariffs based on the current wholesale price of electricity at the time.

    Maybe I’m dreaming, but one day it would be nice if all these things would work togeather in a simple way to get the best price outcome for consumers and increase the reliability of the grid without consumers having to think much about it, but there’s a long way to go if we are going to get to that point.

  6. Tim Lawson says

    Have just gone through this trying to find clever ways to boost my solar hot water system from PV at the most efficient time.

    I did a ton of research into what was available

    I investigated using a Raspberry pi and doing some coding to make it work.
    Also Green catch power.

    At the end of the day I decided to roll the dice chose a timer instead. Trading off the desire for a hot shower when I want it and the most effective use of electricity.
    There has got to be a market for some smartypants to package CWNE88’s solution with some smart switches.
    Modern inverters are wifi Smart switches are WiFi (not many are Australian compliant) Raspberry pi is Wifi.
    Most great inventions, are the creative combinational use (or misuse) of existing technologies.

    • Hey Tim! —> “Have just gone through this trying to find clever ways to boost my solar hot water system from PV at the most efficient time.”

      Try sticking a roll of black polypipe in a treated-pine box with a sealed glass lid.
      This’ll get water quite hot even on a moderately cloudy day.
      Attack one end of the pipe to a garden tap, and the other end to an old insulated HWS tank you can pick up anywhere.
      A big tank will provide all the stored hot water you need, but to build-in a guarantee stick in a regulated instantaneous gas HWS between the tank and you delivery-pipes.
      In the event of the non-rising of the sun or a nuclear winter either enjoy the legitimate reason for not showering, or do what a recently-previous generation did as a matter of course: light a fire under a metal bathtub full of water in the backyard.

  7. Standards are good, but I suspect for most of us not the main answer. The problem I see it is with proliferation of many vendors and different types of equipment that could all benefits from being able to talk to each other to make more sensible decisions. Once you are trying to do this, you have a massive N x M sized problem where vendors might be chasing their tail trying to write software of every other vendor or at least device try than they want to support. Standards can reduce the complexity, and hopefully through standards a smart pool pump vendor would more easily be able to support a wider range of solar inverters. But the problems still exists to some extent.

    To me a simpler and more promising path is through platforms like IFTTT. If solar inverter manufacturers and smart pool pump makers each implement an interface into IFTTT, then users can easily setup whatever rules they want. eg If “Solar Export is over 2kw”, then start the pool pump. It means that vendors only need to provide 1 interface to ITFFF and through that can unlock interaction with LOTS of other devices and vendors. IFTTT is already very widely supported by lots of companies. Take the pool pump problem. There are already lots of smart power points like the Belkin WEMO smart plug (or many others) that are already integrated with this already. So all Enphase/Fronius needs to do to unlock this capability is implement IFTTT interface and it is already there. I have sort of solved this problem myself using a 3rd party energy monitor (Energomonitor). Unfortunately they do not support IFTTT. So I need extra steps. But with Energomonitor I can send an a email alert when usage hits various thresholds, and then I use the gmail IFTTT interface to monitor for this alert, I can use this to turn on and off the Belkin WEMO switch. But it would be MUCH simpler and more reliable if Enphase implemented IFTTT to simplify this.

    The more vendors that get onto the whole IFTTT else thing, the richer the interaction between different IoT devices.

    • Leigh Phillips says

      The industrial controls industry has a world wide standard IEC 61131-3 which is for control system programming uses commonly used protocols ladder logic, function block, structured text, sequential function chart. These are common programming languages used by control system integrators for machine control, this would be an ideal standard to be used as most industrial electricians have knowledge/understanding of these protocols

      • I’m with you, Leigh.

        My industrial control systems engineering brain can’t get past how easy all of the requirements for a domestic application could be handled by a PLC, however there would be a few barriers for home hackers.


      I agree with Matthew IFTT seems the simplest and easiest way to facilitate WiFi communications between the Inverter and Wifi enabled domestic appliances and/or smart plugs like Belkin. I looked at using IFTT with my Fronius inverter and SmartMeter but gave up. It is all a bit too complex for the average PV system owner and the inverter suppliers need to make it much simpler. Their Hot Water system relay may be OK for resistive loads but it is unsuitable for most domestic appliances. Maybe we should be lobbying Fronius to adopt IFTT and provide a simple, user-friendly interface via their platform that enables users to switch on smart Wifi-enabled domestic appliances when there is surplus solar power available? Malcolm.

    • ….um….. “The problem I see it is with proliferation of many vendors and different types of equipment that could all benefits from being able to talk to each other to make more sensible decisions.”

      Wasn’t that the inspiration behind politics/politicians?? 🙂

  8. Malcolm Crout says

    As Doug mentioned above, with a Fronius Inverter and Smart meter a hot water service can be turned on and off to utilise excess solar production, but try and find an installer with the know how to fit the relay and make the software adjustments. After waiting for 12 months and no solution from my installer, I just fitted a timer to turn the service on and off when solar is likely to be producing maximum output. The same installer, who did a pretty good job of the panels etc, then started sniffing around to fit a battery – wtf?
    Anyway, the point I’m making is that installers might be great at sticking panels on roofs but they seem to know bugger all about the software enhancements needed to make the most of excess solar production. It’s about time these installers were properly trained on all aspects of inverter capabilities and the salespeople made aware of the potential uses of the inverter. Until then all I hear is chirping crickets whenever I ask questions.

    • I use openhab2 on a raspberry pi to control appliances when the solar is generating power.
      Openhab has a plugin for the fronius and lots of other things. I use it to turn the dishwasher on and off via a zwave smart plug when there is solar power available.

      Well worth a look if you’re at least a bit technical.

      The other plus for Openhab, it’s all running in my private network so no outside servers needed. But if you want it can work with both alexa and Google home. It can work with pretty much anything you can think of.
      If you want to link it to the openhab servers you can use the mobile app.

      I use the web page/ app via VPN from my phone for added security.

    • Dave Bray says

      I also use opehab2 on a raspberry pi. I can download the solar production stats of my SolarEdge inverter using an api and then use logic to control the devices I want.

      I like to DIY so I use a MySensors network of nodes for sensing and control.

  9. I already do this. I use homeassistant and efergy clamps. And also s20 wifi switches. Works via delta of solar vs consumption and then can turn on a power socket.

  10. If you run Home Assistant you can create as much automation as you want for controlling power usage based on solar generation. All it takes is to integrate the inverter and some smart plugs to Home Assistant and then create the automations to suit your needs. A far better solution and not some hacky setup

  11. Off topic. Can the suppliers manupilate the Smart meter? I feel that my meter shows less power being produced and fed into the grid as time goes on. It is 6 months old. A stone in the bush and hoping something jumps out.

  12. Parklea solar says

    I also can do this by using Reposit which monitors the power produced by my PV.
    Reposit uses ITTT to control my Homeseer HA system. I use Insteon switches for both GPO and most of the lights in the house.
    It can also turn the AC on or off automatically via Google home.

  13. Andrew J Goodman says

    The pool pump sucks a lot of energy, we changed ours to a full solar pool pump. Initial cost was about 3000 but we needed a new pump 1500 anyway. It starts up when the sun comes up and runs while the Sunnis out – working slightly slower in winter and flat out in summer.
    No problems with it to date – after 3 years!

  14. Ray Havill says

    Auzimax….Mark Leckenby Enopte ,Sunshine Coast

  15. I use a z-wave current meter (clamp type) to monitor solar feed into the grid. I then use other ZigBee or zwave devices via Hubitat Elevation to program anything imaginable.

  16. If you are serious about a “smart home”, I have had great success using the Indigo home automation system running on Mac OSX machines (see
    The basic infrastructure is expensive (I use a second hand Mac Mini, plus the Indigo software that runs to about $1K) but can operate the whole house including remote access.
    A “plug-in” is available to access data from the Enphase Envoy system, and the Fronius data can be accessed using their published API.
    The PV data can then be used to trigger any of the devices controlled by the Indigo system, including smart plugs. The data can also be presented on a control page – the Enphase data to individual panel level (see example at or in a graphical manner (see example at

  17. ahem! The smartest piece of ‘smart home softeware’ is that which 4 billion years of evolutionary trial-and-error has installed in the cranium. (admittedly TOO soft in some craniums and too underweight in others!) It has provided us with the means to ‘think’ (I know that’s an alien concept to some), and has directly resulted in the evolution of ‘fingers’, which (among many other uses!) allows us to flick a bloody switch.

    Added benefits include the non-requirement for any ‘suppliers’ (who’d then have to go out and get a ‘real job’ ~ remember those??), and also the disestablishment of hordes of assorted ‘experts’, ‘bureaucracies’ and ‘authorities’ (including taxmen’ who can rejig whatever rules/fees/charges they choose once they have you by the balls).

    And the really adventurous seekers of ‘air-conditioning’ could take a lead from Ron’s horse (or, more accurately, the tail on Ron’s horse’s arse) and start flicking.

    And for the super-dooper sophisticated hi-tech-o-philes, one might point out that ‘excess sunlight’ is an oxy-MORON (sic). Since the sun is set to produce a few trillion-gazillion kilowatts every millionth of a second for about another 5 BILLION years the concept of “excess sunlight” is an absurdity.

    …particularly at the price, (including delivery).

  18. Stuart Allinson says

    You might want to take a look at carbonTRACK – intelligent monitoring and control. It should do what you are looking for.

  19. Hi guys, the fronius smart switch has had an update, and now has 4 load management switches that can be set by priority. Each will need a relay to control each circuit. And it still incorporates an open ended time clock.

  20. Lawrence Coomber says

    There is another important aspect of system monitoring and control not mentioned yet, but ties into this discussion.

    Solar PV Installations Monitoring & Control technology (it’s not just for system owners)!

    On-Grid Solar installations already have in place rules and regulations (via a written contract already in place) that networks and electricity retailers are entitled to enforce with customers (commonly referred to as the network service agreement fine print). These contracts are all encompassing ones formulated by the networks and electricity retailers without negotiation with the customer.

    Importantly, these contracts involve customers agreeing to allow utilities to control the entire “system to grid interface” functionality of a customers solar /battery installation, and particularly system performance as it applies to grid feed in power and battery system charging and discharging logic controls.

    As the number of grid connect systems increase, the more sophisticated will become the “system to grid interface” control algorithms, applied to customers systems.

    Third party “approved by the network” monitoring and control systems (similar to the current network smart metering arrangements) will become mandated by networks to be fitted by customers to their systems (at the customers cost) in order to be eligible for an initial On-Grid connect approval. In the case of existing systems, the owners will be given a short period to retrofit a third party “approved by the network” monitoring and control system, to remain compliant as an On-Grid installation.

    We will be seeing moves from state legislators in this direction soon.

    Lawrence Coomber

  21. Ray Havill says

    Auzimax from Enopte

  22. All I wanted to do was avoid the grid because it costs money.
    I’d rather be off the grid completely and don’t care about any smart meter. I’d prefer to run my own electricity and retain privacy over how much and when I’m using it. Once solar and batteries get cheaper in the future this will be doable.
    I also like to run direct, and not rely on ‘the cloud’. That creates and extra point of failure, and your data once again has to leave your house.

  23. Lawrence Coomber says

    CWNE88: well expressing your aspiration about going Off Grid like you have is the necessary first step in the process to deal with, and you have moved through that step without any trouble at all it seems. Moving forward.

    You should now consider working through the important second step which is a technical analysis of your power plant technology options [which will be based largely on your individual situation and circumstances] with an experienced Power Engineer who specialises in Off Grid / Micro Grid Standalone Generation Solutions Design and Install.

    The objective being of course that you must end up with a best practice designed and constructed energy system which is: “semi-intelligent”, reliable, autonomous in its operation, enduring and maintenance free for all intents and purposes, and importantly cost effective, that will function 24/7 [permanent autonomy functionality].

    There is definitely a solution for your individual circumstances though, and all the best with your Off Grid project going forward.

    Lawrence Coomber

  24. Sorry. Back up a little. I thought the idea of a grid tied solar system was ALL of the electricity generated by the solar panels went into the grid? That’s the reason why I want one – to reduce my grid electricity bill. Are you saying there are times when this isn’t true? Under what conditions?

    As for off-grid systems, that’s a different story, and a system I would aspire too, but presently out-of-reach due to battery storage costs.

    Many thanks in advance for any responses.

    • Geoff Miell says

      Mark R,
      You state:

      “I thought the idea of a grid tied solar system was ALL of the electricity generated by the solar panels went into the grid?”

      There are two types of grid-tied metering:

      Gross metering: ALL electricity generated behind the meter is metered as being exported to the grid. ALL electricity consumed by the household/business is metered as being imported from the grid.

      Net metering: The household/business consumes any electricity generated behind the meter first, and any excess electricity left over is metered as being exported to the grid. If there is insufficient electricity generated behind the meter to supply the demands of the household/business then the shortfall is metered as being imported from the grid.

      Gross metering is beneficial for the consumer only when the FiT export rate is higher than the import rates.

      I’m not aware of any FiTs that are now higher than the import rates, so net metering should be the better regime for a grid-tied system. Check that’s what you have (if you already have a grid-tied solar-PV system) or intend installing one.

    • Mark,

      I made this video to clear up your confusion:

      Hope That Helps,


  25. Lawrence Coomber says

    Mark as we all know, the devil is always in the detail of course but you do have some options that you you haven’t considered yet, that are cost effective and able to satisfy most customers requirements such as yours.

    Have you considered adding an independent Standalone [Off Grid] PV/Storage Solution to your premises as well as maintaining your existing On Grid System. If not you should, and don’t forget that STC’s are available for any/all premises up to a maximum of 100 KW (total) of installed PV.

    This system design strategy is normal practice, and particularly in rural and small factory/business scenarios,

    Discuss this option with an experienced PV power solutions design engineer Mark is my suggestion.

    Lawrence Coomber

Speak Your Mind


%d bloggers like this: