Tom’s Solar, Battery And EV Tech Struggle – Can You Help?

Meet Tom, a solar tech tinkerer who’s had a heck of a time getting his solar system’s inverter, home battery, EV charger and other related gear to play nice with each other.

Tom’s house in Gawler, just outside of Adelaide, is bursting with all sorts of solar power related devices. Among them are 7.8kW of solar panels on his roof, a 6kW SolarEdge inverter export-limited to 5kW, a Sonnen battery, a Zappi EV charger and a Nissan Leaf electric car.

An early adopter and pretty clever fellow, Tom’s focus is on solar energy self-consumption. But he’s had more than his share of headaches trying to coordinate all the different-brand components to properly communicate with each other and do his bidding.

The Sonnen battery, which should be the “brains” of the setup, is being under-utilised.  It has multiple programmable outputs, but only one is being utilised to “talk” to the hot water system. And getting that happening wasn’t easy.

Tom is also on an Amber electricity plan, which exposes him to wholesale electricity prices. This means when the wholesale price goes negative (which is happening more often these days), he is penalised for exporting to the grid. However,  it would be a great time to charge the Sonnen battery and his electric car from mains power.

But there’s no real digital communication between the Zappi and the SolarEdge inverter. And there’s no digital communication between the Zappi and the battery.

There have been some wins – for example, controlling the hot water load. The addition of a SwitchDin Droplet has also enabled Tom to instruct the battery to do whatever he wants – but it’s done in a rather brutal way.

While it *should* be relatively easy to get a solar inverter, battery, hot water load, an electric car charger and a wholesale electricity provider like Amber to all talk in order to coordinate loads – it turns out it isn’t.

One Solar Brand To Rule Them All

The major issue is Tom’s various components are manufactured by different companies. Tom’s advice at this point of his journey for anyone looking to invest in this sort of setup: stick with one manufacturer for the solar inverter, battery and EV charger.

For example, SolarEdge manufactures inverters, EV chargers, a battery controller (StorEdge), a hot water controller, smart switches; and not far off is a home battery – the SolarEdge Energy Bank. Fronius is halfway there with various products, and SMA will have an EV charger soon.

Watch the video get a better handle on Tom’s trials, tribulations, successes, failures and goals. He has put in plenty of hard yards and is still keen to get things happening as he desires with the gear he has.

“If anyone watching this has solved this problem, please jump on the comments, let us know how you’ve done it,” says Finn. “We’d love to talk to you and we’d love to solve this problem together.”

About Michael Bloch

Michael caught the solar power bug after purchasing components to cobble together a small off-grid PV system in 2008. He's been reporting on Australian and international solar energy news ever since.


  1. Wayne Bissett says

    I can’t help Tom but I also am finding it difficult to get answers on the next phase of this dilemma which is integrating vehicle to grid (V2G) and vehicle to home (V2H) into the solar/EV equation. A wall mounted battery makes no economic sense in my situation but a significantly sized battery in an EV that provides me with transport, peak evening power and blackout backup is a no brainer. I would buy an EV tomorrow if I knew it was compatible with such a system.

    However, when I talk to my solar supplier and electrical engineering friends about the magic box to make this happen they quickly change the subject. I have 12kW of panels feeding through two SMA 5kW inverters and an SMA home manager. Any insights into how to make V2H work or where it’s up to in development would be appreciated.

    • Have a look at the ARENA REVS project in ACT. They will be installing the hardware to do this for a fleet of Leafs in February next week. Hopefully the hardware will be commercially available soon after, Nissan Australia have been promising it for months. I read the hardware is already available in UK and Japan.

  2. I have seen others with the same problem turning to facebook groups etc for options. One I saw(Have not personally tried) had acheived some of this using a Raspberry PI and setting up an IFTTT network. Though programming the code etc is what has turned me off trying.

  3. FIMER (from Italy) manufactures solar inverters, battery systems and EV chargers for residential use that all talk to another using a simple RS-485 connection.

  4. I (electrician) installed a 1.8kW element in my storage hot water cylinder and plugged it into a smart plug. It comes on during the off-peak period in the middle of the day only.
    The smaller element means the electrical load is more likely to be satisfied by the solar.
    It is also small enough to be switched by a $27 smart plug.
    I know this is peanuts compared to the ambition in the article, but it was also $50 total and a couple of hours of work.

    We also use the delay feature on appliances to run them during off-peak.

    This is the low hanging fruit. To get more complex either requires an expensive integrated system or for the user to craft a custom computer (Pi) by hand and program it themselves. Great for amusement, not worth it from a $ perspective.

    • Ronald Brakels says

      That’s excellent, Brendan, and not peanuts at all. What you’ve done will shift more demand to the middle of the day and save more money than a small battery that would cost several thousand dollars.

      • I had planned to take my electric hot water off controlled load and use my daytime solar PV (11kW).

        From a $ point of view it’s not going to save us anything (off peak is still cheap) but it will have a modest net reduction in CO2 emissions (NSW grid is more fossil heavy at night than during the day) and also help lower my typically high grid supply voltage.

        But the solar installer is not interested in setting up my Fronius relay control, and nor can we find an electrician available to install a timer/contactor. Diverters like Catch are far too expensive to make sense and are no good on our 3-phase supply anyway.

        The sad reality is there’s just no availability of skilled, qualified licensed people to do such things. It’s the same with a whole range of building related trades – no one has any availability. Most jobs are quoting at least a 12 month’s wait. When someone is available, they have never done anything like this before so you have to convince them to have a go but they don’t want the hassle.

        • Grant Hewitson says

          Hey Alex, Grant here, my sparkie got our hot water off controlled load in a flash by adding a “contactor” (which is really only a relay to reduce the load on the timer contacts so we can leave the 3KW element in the system) and a timer to our electricity panel. We set the timer to turn on at 8:30 am and I think off at 4:00 It also has a convenient manual override switch on the timer if we need to flick it on in the evening.

          To provide full disclosure, our hot water is two flat panel solar collectors/electric and I’m in QLD so the electric element will probably only come on in winter when we have a number of days in a row with no sunshine.

          • Thanks Grant
            Yes I’m aware of the timer + contactor option. I include that in the list of things that’s a challenge to find someone qualified to actually come and do. Getting any tradespeople is nigh on impossible at the moment. We have a long list of projects for which we are on long wait lists, or they just refuse to make any commitment.

        • Tom, I have not solved your problem. First my comment to Alex, I have gone the same route as Grant & fitted 2.4Kw elements to my HWS. It is possible to have a ´Smart´ switch, either controlled by software or Grid export monitoring, but it is easier & cheaper to use a timeswitch. Turn on the HW at ~10AM & off at say 2PM, & there is enough energy to heat 300L tank. Occasionally your solar will not generate enough energy so you draw from the grid, but the cost seems to be minimal. I recommend ALWAYS using a contactor to switch loads such as HWS, because the slight teactance can spark & weld switch contacts. (Even using 20A timeswitch, on 2.4Kw load).
          At home I have the opren Source Open Energy Monitor monitoring all my circuits (in fact a TaWatt which is good value if you source your current transformers from China). I have by-passed my EV charging circuit so it is not part of the system sensed by the Victron Inverter charger I have that is hooked to 4 of 1,93Kw Zenaji batteries. Up to now, I have only used the 2.4Kw Hyundai Kona chasrger, charghing off the solar system by pl\ugging the car in in the morning, then disconnect at 17:00. (I am retired, so this works for me). I have an OpenEVSE under construction, which will enable software control, but yet to be commissioned (it will be plugged into a 32A power outlet.) My Kona does not have EV>H capability..

    • Ditto for me too (as a sparkie). I did the same thing, swapped out my 3.6kW element for a 1.2kW element and connected a WiFi Smart plug, I did that about 8 years ago. Ditched the Controlled Load meter, went onto a ToU plan. The WiFi plug mostly only comes on to turn on the 1.2kW element during the winter months during the day as I have a solar thermal hot water system (where 9 months of the year, the sun does most of the water heating for free). When I do need to boost it, it comes from either from spare solar PV generation or from my PW2. I try and switch on the WiFi plug after lunch to let the sun thermal do most of the preheating. The thing about the PW2 is that it covers any short burst of cloud cover and the 1.2kW element doesn’t overwhelm the solar system or PW2.

      I’m really surprise how well my 3 different branded solar inverters (of different ages) work well with the Powerwall 2 battery.

      No issues with the PW2 for last 4 years.

      My biggest gripe is not being able to capture all that summer solar for winter use. Shame we can’t store hot water for a lot longer (but requires a very big and well insulated tank to hold the hot water for 6 months from January to July.

      Doesn’t need to have an overly intelligent automation system. No need for a Solar Power Diverter. Just some common sense and a bit of planning to see what the forecast will be in winter (to take advantage of low cost off peak at 11c/kWh to heat the water or precharge the PW2). Otherwise, the 9 months of the year, it’s pretty autonomous, no need to program anything.

      I could scrape together a preloved PV system and have it DC connected to the element of the HWS for winter hot water heating, reducing the need to use the grid tied inverter/battery, but not worth the effort/time at the moment.

  5. WARREN ROSS says

    On a slightly different line, I have a 6.6kw system feeding max 5kw back to grid with Thermosyhon 300 litre solar h/w [ like these as no moving parts ]with 2.4kw element with isolating switch inside to boost from pv or grid when required, had some issues getting pv approval but wish now we installed more panels and bigger invertor, but everything working well with power acc $ 52 last month
    Do see a company trying to sell Eveready battery into Victoria does anyone know of this system

  6. Yep, same problem here and the SolarEdge ZigBee controls simply did not work as advertised and have since been removed for a full refund. What I have done instead is install a $27 smart plug to control my pool pump and written some Python code which runs all day on my computer. Everything communicates over my local network and the internet. The SolarEdge API is really easy and well documented, as is the smart plug.

    BUT, I have discovered I cannot switch off and then on the charging to my car (Leaf) without manual intervention on my wallbox. Only solution is to either use the 10A charger or buy a different wallbox.

    FURTHERMORE I have discovered there is a maximum number of times you can use the SolarEdge API before they lock you out for 24hrs. I may have a solution for this, using ModBus over TCP (similar to RS485 mentioned earlier), I only received the necessary cable today so that will be this weekend’s project.

    By writing code to do this I have complete control over everything and can even use extra information and algorithms to choose where to send the power. The SolarEdge programming options are very currently limited.

    • Garry Busowsky says

      Hi Stirling – I have SolarEdge installation with an EV charger and ZIGBEE controllers. I use the SolarEdge app to charge my EV with excess solar and that works correctly. My gripe is that the 6.5kw panels are limited to a 5kw inverter output and ONLY 3.5kw of excess solar goes to the EV the rest goes to the grid … I have been pressing SolarEdge to explain why. If I switch on solar boost then I get up to 7 kw… !! This is frustrating as the ‘solar boost’ buys power and tops up with solar.

      Also the ZIGBEE controlled switches (Dry Contact SolarEdge ones) work for me as far as I can tell. I have them configured to only come on with excess solar and you can program the load power that is expected. For example 1 have one set to 200watts and the other to 2500 watts. So the lower one comes on when there is at least 200 watts excess and the other will come on when there is 200 + 2500 watts excess (since the first one comes on). I am keen to know what your experience has been…. Cheers

  7. George Kaplan says

    In related news, petrol prices have soared due to efforts to limit production. In one area on Petrol Spy, prices range from $1.45 up to $1.93 with most stations $1.90+!

  8. Malcolm Jacques says

    A heat pump is a better alternative than a conventional electric water heater. Relatively low power consumption compared to electric water heater. My 170 litre Chromagen Heat Pump uses around 800 w to produce hot water and can be set to operate during daylight hours only. Most days, except really dark Melbourne winter days, my 3.25 kW PV system will generate more than 800 w and as the Heat Pump is on the general house circuit it does not require any special switching or controls.

    Would a programmable switchboard be the simple answer to all the PV/battery/EV/Water Heater/dishwasher/ electric cooker/ reverse cycle AC/ etc, etc, control problems? Does anyone know if programmable switchboards exist anywhere in the world?

    • You can buy individual wifi switches in MCB DIN rail format. However they are NOT actually an MCB and cannot be used without one (you can imagine a circuit going live whilst being worked on). So IF you have enough space in your Distribution Panel you could add some of them alongside your existing MCBs. I have one controlling a Jaccuzi to filter/pump during peak solar. For A/C units I have wifi linked ‘Universal Controllers’ which can be programmed with your A/C remote and then schedules set up for eg timed use or weather / temperature related switching on/off. All simple stuff to set up and again utilise peak solar to cool down rooms and take the edge off of power demand later in the day. Works especially well with some thermal mass (eg concrete floors) to cool down.

  9. I have 13kW PV with 10kW string inverter, I’ve added heat pump hot water and battery is on its way. Needless to mention lots of standard home stuff – oven, microwave, dishwasher, fridges, aircon, etc.

    I believe I solved that.

    I used Home Assistant as middle-man simply because all vendors make closed systems unable to talk to the others on purpose. Something open opens the door.

    I started with friendly metering, after a bit of research I took on iotawatt as it reads locally, it can work with several backends, it stores massive data itself and best of all I could calibrate it. So I did calibrate it to be less than 0.5% off grid meter.
    Alright, I’ve got grid and all circuits metered. Then I’ve added number of smart sockets and plugs (deta, shelly and some less known stuff), many also metered. All certified. These having tuya (like deta) got flashed with alternative firmware as it all has to work without internet plus I am not keen to signal China what I switch on.
    Next step was to invent all rules. It took a while to observe what happens and define triggers. As an example:
    – when dishwasher and washing machine heats water at the same time and PV does not cover it, the dishwasher is being paused waiting for washing machine to complete heating.
    – hot water is started by scores – points for being less than 2C below forecast, points for passing forecast, points for lont export over 2kW, points for being off for long and at some point it hits the bar and turns on.

    Then, user awareness comes to play. Can I use oven now? I made a few colorful smart plugs and put them in various places. These lit various colors depending on power balance. If I see red – no more loads, if I see green, one 2kW item would be fine, I see blue? Well, there is over 6kW surplus, let’s kick oven and aircon together and burn some power…

    What if I don’t look? Well, speakers tell me. They play number of things such as please close fridge door or lights are taking 135.6W please turn some off. But for the balance they play when we pass 500W export saying what it is now and which direction it goes.

    Now DRED card is being installed in Aircon to let system throttle it to follow balance curve keeping 1kW spare. Then, once battery will arrive, inverter DRED will get connected to prepare for export throttle once I start paying export penalties.

    If I ever buy EV, it will know when to charge, unless I buy a socket deal such as $1 daily regardless of usage.

    But before EV, there is more fun. I participate in Origin’s “spike hour”. I let them control one of my TP Link smart plugs as they support them. Then system reads plug status. When they flick it off, speakers play message that we just started energy conservation hour. Fridges, tv-sets, microwave, even fans and some lights are put off and we are saving for fun and little profit. Then, when they turn it on, system reverts all changes and plays it’s been completed,now we can use as much, as we want…

    • Malcolm Jacques says


      Sounds fine, but how many Aussie householders are going to be able to do this sort of fix and get their existing PV/inverter/battery/EV/water heater/AC/etc/etc systems talking to each other?

      Until and unless there are some much simpler solutions on the market the true potential of PV to reduce GHG emissions and energy consumption in Australia will not be reached.

      Maybe this is what the various manufacturers of inverters, batteries and EV systems want in order to maintain their market positions, but they are doing nothing collectively for the owners of existing PV systems.

      They all seem to be following the Tesla business model. Buy 100% Tesla products for a complete system.

      Perhaps the Fed Govt could direct some of its zero-carbon money to provide a proper fix for this situation in Australia, after all we are the world champions in per capita rooftop solar installations. But I have my doubts, and expect to have to wait until the US or Chinese PV industry decide it is worth manufacturing the smart control systems needed, and Australia is a good market to test the products in.

      • I would say, as many, as attempt to do so. One important thing is to remember this is not about making things compatible with each other, this is about making things compatible with middle-man. Star-like solution. If product is being sold in reasonable number, there is enough people suffering from it and they will find a way to navigate around, Business won’t do it as letting people utilize own ideas is not what majority do for living. With few exceptions (such as Google) everyone makes closed systems. Business might be more or less malicious but never helpful. These who ignore open solutions working with their hardware help by not disrupting it and that’s pretty much all help available.
        I see in comments around all sort of trouble with proprietary solutions. Why on Earth I would buy one to suffer? Getting something friendly, starting with monitoring, solves first step – having data available with no clouds, no api limits, no Internet required, etc. Playing with solutions such as Home Assistant is not hard at all. There is lots of working integrations, just off shelf – Daikin, Tplink, Shelly, two options for Zigbee handling nearly any zigbee device, zwave (bit traumatic itself due to local radio regulations) to name a few. By buying right hardware, known to work, it can be simplified to something ready over weekend. And then, once everything works with middle-man using available integration, it works with each other.
        No need to write software to use it! Just ask for help, a bit of research and correct purchases.

        • Wow, really interesting idea. To be honest, I don’t think I can follow how I would implement this.

          I am starting from scratch, so maybe I don’t need to? But I was leaning towards buying one ecosystem like SolarEdge Energy Hub to try and get everything working together.

          • Garry Busowsky says

            Hi Andrew – I went the SolarEdge route with a 5kw inverter and EV charger plus Zigbee and WiFi communications. All from SolarEdge. The Zigbee communication is a different wireless channel to normal WiFi and it is used to communicate with 2 “dry contact” devices. These o use to switch on when “excess solar” is available .. heating the spa for my grandkids and running the filter pump. The EV charger also is set for excess solar and I can set the ‘priority’ of these 3 outputs .. so house always has first go for power, then EV the the last 2 dry contacts .. Overall works perfectly. My only disappointment is the EV charger only delivers 3.5 kw even though there is more excess solar ..

  10. Luke Sutton says

    This is a really interesting one. I’m just looking through a few things whilst watching this video. Firstly, it looks like Amber have an API that allows you to pull price data into your own system. Since you’ve already got modbus comms working to the battery, it probably wouldn’t be a stretch to automate that control under certain price conditions.

    Does the Zappi have any sort of digital comms? If not, you could maybe hi-jack the CT input to get it to do what you want by sending it a bogus signal.

    Some Solaredge inverters can be configured for a demand response mode for 0 export.

    It sounds like you might just need an overarching system that can monitor your demand, there’s ways to manage control of each device.

    Following with great interest.

    Balhannah Solar and Automation

  11. I sympathise, even with a simple solar with battery system I’ve often thought that better control over aspects of solar systems with a battery would allow them to be run more efficiently. Being in SA, our export is capped at 5kw and so for a lot of months each year we have excess power around the middle of each day. As happens, instead of charging the battery to 100% first thing each day, I’d like the flexibility to choose to export early morning and to be able to choose when to charge the battery, so it can be charged from that excess power in the middle of the day. That would be better for us and better for the network, in providing more power at the early morning peak time. I asked Tesla about this but all they could offer was that maybe I could use Time-Based Control, I checked but that doesn’t do what I want.

  12. Hi All,
    I am at the beginning of what looks like a very steep learning curve.
    I am looking at installing PV (about 10kW) and have an EV.
    I would like to use the EV battery in a bidirectional system that charges the battery or powers the house.
    I am not able to program a Raspberry Pi or such arcane things. I can screw components together and have a basic knowledge of electricity (physics).
    Any suggestions?
    Info I have found:

  13. Ole Pedersen says

    If you own a Tesla ChargeHQ is an excellent app to coordinate charging of a battery and EV using solar and low tariff grid electricity. Works with SolarEdge and a couple of other inverters.

  14. Maybe an ARENA project?

  15. This maybe a long post but ill try and add everything i use to integrate/control Amber, Powerwall 2, Zappi v2, Sonoff Powr2 (mainly monitors Sanden heat pump), 3 x Daikin US7 RCAC here in Ausnet Vic.

    Firstly as others have mentioned Home Assistant is a very flexible home automation software along with Node Red.

    Firstly Amber have now integrated their api straight in HA without any coding, just requires an API key found here: (you have to be logged in). Whilst i have added this into Home Assistant, i still fetch the prices via Node Red.

    Amber Integration:

    Next i have the MyEnergi hub with an online account and use their API also via Node Red (to set schedules and monitor if EV is connected) but i have recently added via HACS (a community add on for HA). We have 3 CT clamps, 1 on Mains, 1 on Solar and 1 on Powerwall with the setting “not to discharge frm battery”

    GitHub account required for HACS:

    I control my RCAC directly from HA via the daikin integration (but not relevent to you guys)

    Powerwall 2 integration via HA is a bit annoying as every time a firmware upgrade happens, it fails and have to manually re enter the password to get it going again. I use the tesla cloud api to set reserve percentage of the powerwall to decide if i want to charge/discharge from battery or go into standby to use grid.

    Tesla API documentation (unofficial):

    we are fortunate enough here in Vic for customers before 15th April 2021 to still recieve the gov minimum FiT, so i dont have to worry about negative FiT. If this changes i will most likely replicate the local URL to set my enphase to zero export (havent explored fully yet)

    I have a Sonoff Powr r2 (flashed with Tasmota) to monitor our Sanden and occasionally use it too switch it on and off.

    For SolarEdge monitoring there is an integration in HA but mainly appears to be cloud API unless yours supports local API access: but im not sure as i dont have it.

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