Can Diverting Solar To Air Conditioning Help Reduce Overvoltage? Paladin Says Yes.

With a smart 3rd party controller, your air conditioner can help a solar-laden grid balance supply and demand.

While regulators fret about the impact of solar power on low voltage distribution networks, developers are looking at ways to use household loads to relieve the stress.

Last week, I chatted to an NZ-founded company called Paladin, whose focus over the last four or five years has been a controller that diverts excess power from PV to a customer’s electric hot water service. It’s a double-win: the customer gets cheap hot water, and the diverter provides a load to soak up electricity that would otherwise stress the grid.

Innovations like this solar diverter are important at a time where AEMO has decided SA Power Networks needs the power to switch off customers’ solar systems if needed to avoid “negative demand” events (a power it says will be used only rarely).

As Paladin boss Mark Robinson pointed out, power companies don’t want exports happening between 10 am and 2 pm, because that’s when the overvoltage happens – when local areas reach 257V, inverters start shutting down.

The Genesis Of An Idea

With the advent of the COVID crisis and while Paladin’s chief developer Ken Smith was working on giving the controller a wireless interface to the water heater’s temperature sensor, he also pursued the idea that air conditioning can do the same thing as a hot water service – act as a load that consumes excess solar energy on-site.

For the wireless, Smith said, he wanted to avoid WiFi because it asks too much of the owner. Instead, he turned to the radio standard called LoRa, a low-power long-range wireless standard (here’s the Wikipedia entry).

“It fits roughly in the same frequency band as old pagers – excellent range, but low data rates. Once I got around the limitations of LORA, without compromising the performance, I can send a short data stream telling me all Paladin can see.”

That fed into Smith’s thinking about making use of air conditioners. For some time, he said, modern air conditioning units have included a “Demand Response Enabling Device”, or DRED.

The DREDs were implemented at the request of electricity companies so that if there’s a shortage of power (for example, during a heatwave or when electricity supply is disrupted), the network can turn air conditioners down or off.

Smith told us his idea was the inverse of what the networks do – turn the aircon on or up to soak up excess solar electricity from a household PV system.

He said at first glance it looked like a really knotty problem, because the air conditioner’s compressor has so many possible settings using different amounts of power.

“It took a couple of sleeps and a few pots of coffee to realise – the complexities don’t matter. We’ve developed a box that receives the broadcast [from the existing Paladin controller – SolarQuotes]. Just turn it on, and you’ve got control over the aircon.”

The Paladin controller “modulates the compressor power that matches the sun, so you don’t have to spend a lot of money at peak rates.” For the end-user, most of the air conditioning can happen using 12 cent (per kWh) electricity instead of 30 cent electricity.

And, just like diverting excess solar to the hot water service, it helps the grid, because it reduces the export during peak times.

“And you can run multiple units – when compressor one backs off, the second unit can start, and so on.”

There’s another benefit, he said: by matching the power of the aircon to the excess solar, getting a house to the desired temperature might happen more slowly than without the controller, but a big unit with a 4kW compressor won’t hit the customer’s bills so hard.

Paladin boss Mark Robinson added that the Paladin controller responds quickly enough to a whole household’s load that “as clouds go over, it reacts” – or if someone puts the kettle on, the controller cuts the amount of solar electricity going into the air conditioner.

Coming Soon To A Home Near You

Paladin states development has gone smoothly and Smith said the first units are in the Paladin workshop now.

Robinson commented: “After final testing, we hope to have this on the market by Christmas.”

He said the timing is important as just a couple of years ago, feed-in tariffs were high and curtailment unheard of, so there was no real need to divert power to local loads. But so much household PV is now live (and more is coming), the situation has changed.

Smith said until recently, users have focused on “how much we made from export”.

“If you’re exporting, you’ve got it wrong”, he stated. “The conversation should now be how much I can consume of my own power because I’m managing it better.”

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. I know that catchpower have a hot water solar diverter.

    Curiously, they have a new product coming out soon in about 60 days, called “Solar Relay” to power any electrical load

    I’m very intrigued about how this product works…….. as a opposed to a variable power diverter.

    • Graham,

      A variable power diverter is for resistive loads. like big heating elements. It varies the power from say 0 – 2.8 kW depending on how much excess solar is available. For example if 1.45 kW of solar would otherwise be exported, the diverter only sends 1.45 kW to the element. It does this on a second by second basis.

      A solar relay is an on/off switch. You tell it how much power the device draws and it only switches the appliance on if there is at least that much spare solar. For example – if you have a 1.2 kW pool pump, it will only switch on when there is at least 1.2 kW of excess solar available.

      The catch power relay may be more sophisticated – and measure the actual power usage of the appliance, and it may have smart logic that will ‘boost’ the appliance from the grid under certain circumstances. I’ll contact them to find out the details.

  2. Where do i sign myself up? During winter my consumption skyrockets due to AC use, and during summer we are prudent with AC use, trying to maximize savings.

    However, one grows tired of always going without. if there was a way to be sure AC was run from solar, essentially for free, being my homes largest influence, I would be all over that

    • If the sun is shining aren’t you running your ac for free anyway?

      • Hmmm……how does one work out how much energy a large ducted AC unit consumes based on specs? For example Actron 23Kw model has a variable output between 4.5kW and 23.5kW for heating and a stated input of 6.9kW. I assume that input isnt fixed but rather varies as output varies so is the max input? The reaosn for my question is I’d like to understand PV sizing to ensure powering the AC during day to warm up house before getting home in evening and conversely cooling it down in summer before getting home.
        At max power of 6.9 this means my PV needs to produce 6900Wh for ay given hour I want to run the AC and effectively not paying for it?

        • ‘At max power of 6.9 this means my PV needs to produce 6900Wh for ay given hour I want to run the AC and effectively not paying for it?’

          Not quite…

          Firstly, you are using excess PV that you would otherwise be exporting at your FIT rate. However as that decreases over time, this is an attractive tactic.

          That is the beauty, inadvertently, of DRED. With any compressor the DRED control waits until you have 50% (the minimum) of rated value + a buffer as a mean ‘excess solar’ (Generated – House load) before it allows the AC to start. As the compressor ramps up over the next minute or so, the DRED protocol limits the maximum power draw to 50% of rated (3.45kW in your case). As the compressor starts more slowly, the head unit will obviously not deliver the full cooling / heating that it might at 100%.

          However, after the slower start the compressor eventually gets control. As the excess PV rises the DRED controller will schedule 75% even 100% as available. If the sun goes in the allowed power will ramp down and even turn off until the PV goes back into range..

          On the face of it it can be as complex or simple as you wish, but with decent smoothing tactics and a sensible buffer at the bottom end, it works well.

          Indeed you can run multiple compressors at the same time and watching these in concert is quite fascinating. The first unit on (or smallest) gets powered to 50% first and as it comes on speed and backs off, even though it may get a DRED 75% it will not be using that power, so the second unit sees this and starts at 50%. Round and round it goes, and they will often swap 75%/50% positions as time goes on. Obviously it all depends on the amount of excess solar and room temps etc.

          The whole process is counter intuitive and I have now fitted a screen display to show the state of the internal Tourbillon software analog that does the controlling.and damping.


          • Marcus madrid says

            Hey Ken,
            As an off -grid householder I have a question, currently were in our 4 month of our off-grid system adventure and I can say I wound never go back to Grid tie (even if I could). Specs: 10.5kw Panels, 20.5KWH lithium batteries.
            So far winter to spring our battery usage hardly drops below 60%, and its charged to 100% in a cloudy day by 11am, On a warm sunny day by 9:30.
            I wanted to know if something like this would be possible/ efficient for us.
            With Summer approaching i’m thinking that incorporating a small/medium split system with that only utilises PV power after the batteries have charged would be amazing.

          • Marcus. That is actually quite a simple task – with a big IF.

            IF you have direct access to battery voltage (ie the terminals) .

            You can then use a voltage sensitive switch to turn on anything. In the case of the AC, using the DRED is very straight forward.

            To get control of your AC via DRED you will need access to the 4 wires that connect to the DRED interface. These are just low voltage (5-21V) signal currents, so any small wire will suffice.

            The connections are labeled 1,2,3,common. DRED is activated by connect either 1,2,or 3 to common.

            The DRED states are :

            1 – common = OFF
            2 – common = 50% of max
            3 – common = 75% of max
            No connections = Full

            Connect 1 to common and use the remote to start the indoor unit as normal. The unit will open the vents, but not run. There will probably be a flashing light to indicate DRED control. Check your manual.

            The simplest solution is to use the voltage sensor to change the connection from 1 to common when the battery voltage rises above say 95%, that is holding the compressor OFF, to no connection at all. This will allow the compressor to start at full power.

            There has to be a ‘gap’ between the ON and OFF voltages as the battery voltage will sag somewhat as the compressor pulls power off the system. How much depends on many things, but mainly the capacity of your battery and the point on the charge / voltage curve you decide to work with. Near the top (90%+) the is a better slope to make this work.

            If the battery voltage drops below a set threshold (say 90%) the voltage sensor makes the connection from 1 to common again – turning the compressor OFF.

            This can all be done with analog preset units. Search AliExpress for ‘voltage switch’. You will need one that works in your battery voltage range (48-58V?).

            To be more precise (which may not be required given the size of your system), you will need to do a little programming and use an Arduino and a relay pack. There are many examples of voltage sensing circuits and code on the ‘Net. The voltage sensing is just 2 or 3 resistors for a bridge to get the sensing voltage into the Arduino’s range (0-5V) and some simple C++ code. Activating a small relay pack is simplicity itself.

            Even if you have no idea what I am talking about here, research it and give it a try. You can practice with a small lead acid battery, a charger and a few light bulbs as a simulator.

            If your inverter/charger is web enabled, you might be able to use IFTT or similar to do the same thing. However, this may well be harder to do and produce less satisfactory results than a little code and ingenuity.

            I have done this many times to control things around the house. Currently I am doing just this with my garden waterfall pump. It is a single small panel, a 12V, 5aH lead acid and a 30W pump. I use an Arduino UNO and a relay to do the switching and a 100 Ohm and 270 Ohm for the bridge.

            To fully implement the DRED and control the AC really ‘nicely’ – you will need a 3 relay pack and a bit more code. But all this is like eating an elephant – one bite at a time.

  3. Not sure I get it.

    AC is a different kind of load compared with heating water, the latter being a form of energy storage. HW storage makes sense. Turning stuff on for the sake of it doesn’t.

    If I don’t want/need the AC to be on, e.g. as happens during most of Spring when this low load/high solar export problem occurs, then why on earth turn it on?

    Even if it is on it ain’t going to suck up much power cooling/heating a home that’s already naturally at a desirable temperature during the mildest time of year. Which is why people are not using AC much during that season.

    Incentivising some industrial loads and more grid storage would be a much better solution I’d have thought.

    • I agree with Alex, why does something that isn’t needed have to be switched on. It’s not going to help I think. Maybe the electricity generators could schedule maintenance shutdowns in spring when their demand is reduced.

      • Michael Shaughnessy says

        A well insulated house (maybe with some thermal mass) can be used like a battery. Warm it or cool it now so you don’t have to later

  4. Paul Tranter says

    All this technical stuff I am afraid is well above my little brains ability to understand. But a couple of questions.

    I understand the concept of the low voltage increase between say 10am and 2pm due to feed in to the local grid from rooftop PVs. Why though do they need to turn off roof top PV Panels. Won’t that just send the system back to coal and gas generators for power?

    Also regardless of the reason for excess PV generated Power why use it to turn on an air conditioner or decrease temperature of an air conditioner if most people aren’t home. Seems a waste to me.( and yes I understand the effects of Covid at the moment relative to a lot of people being at home who normally aren’t but hopefully that is en passant.)

    I suspect these questions will highlight my ignorance however is it possible to provide a simple overview in answering my queries above.

    • Paul Tranter says

      I also meant to ask surely diverting excess power to a battery bank would make more sense than using it to power an air conditioner in an empty home?

      • Martin Sheppard says

        Of course if a battery is available then it makes more sense to divert it there, but people often don’t have a battery at all or are going to produce more power than the battery can hold even if they do have one.

        Using an air-conditioner when nobody is home will reduce the need to use it later when people do come home. There’s a balance there between the wasted energy of cooling or warming a home only to have it leak out vs the time of use and availability of power. It definitely can be worthwhile to do, but won’t always be and will depend on many factors such as insulation and when people are going to be home.

        It is also possible for the air-conditioner to use less power overall by pre-cooling or pre-warming and overcome the thermal losses that will occur. This is because the efficiency of the air-conditioner depends on the differential between the outside temperature and the inside temperature and on how hard you are driving the aircon. If you can run the aircon at 50% load by running it before you get home as well as once you get home it may use less energy than running it at 100% when you get home. And particularly in winter, doing some of the heating before it cools down outside can use less energy then switching it on when you get home after it has cooled down. But whether it uses more or less overall energy is very complicated and depends very much on individual circumstances.

    • “…why use it to turn on an air conditioner or decrease temperature of an air conditioner if most people aren’t home.”

      I would have thought it logical to stop the house getting hot in the first place, by running the air-con during the day (using solar energy and assuming the domestic batteries are fully charged) rather than walking into a warm house and turning the air-con on. If it’s too cold inside then it’s easy enough to put on a jumper and socks until the house warms up a bit.

      I occasionally have found it useful after a hot day (or series of them – eg 4 consecutive days with 44 degree maxima) to run the air-con during off-peak at night when grid power is cheaper. This means that my batteries aren’t discharging too far and can start to recharge in the morning. By not discharging the batteries too deeply, the life of the batteries (SLA) is extended by a few years, which means I will be saving money down the track by not having to replace them so frequently. My present batteries were installed in 2014 and are still capable of handling the loads they handled initially. I should think that a life of 15 years would not be an unreasonable expectation.

      • It’s all very well to talk about pre cooling or heating and “stop the house getting hot in the first place” but this grid load imbalance scenario mostly occurs during the mild temperature seasons of Spring and early Autumn when aircon just isn’t needed let alone pre-heating or cooling.

        Even if aircon was turned on it wouldn’t draw much power anyway since homes at this time of year are mostly already at a comfortable temperature.

        The grid’s load imbalance problem isn’t so severe in Summer because aircon is needed more and more energy is being used.

        As for pre-heating/cooling when temps are high/low, it’s a pretty crummy strategy for most as it wastes a lot of energy and costs a lot of money.

        If a distributor wants me to turn on a load I don’t need, they can pay me to do so.

  5. Mark Symonds says

    I simply had my off-peak Hotwater meter removed, Hotwater wired back into the main circuit via a circuit breaker and a battery backed up timer. Ive set the timer to come on between 10am and 2pm (when the sun is out). In Warmer months I might adjust it to 9am to 3pm, but that might not even be necessary. So unless its real cloudy or I’ve had a super long hot shower (never), I almost always will be using solar to heat the hotwater (free!).

    • It’s not “free” if you have foregone feed in income. IOW the cost of heating the water is the feed in tariff. Unless you would have been prevented from exporting that energy for some reason.

      In many parts of NSW the FIT is equivalent to (sometimes less) than the hot water off-peak tariff hence there is little to no incentive to move hot water heating to use daytime solar.

      • Mark Symonds says

        At the time the feedin tarriff was about half the offpeak hot water tarriff. So it was costing me more to run at night on grid power. However I didnt atticipate the full cost. eg. Origin charged me $198 to give them back the meter on the behalf of energex. So all up it probably wasnt worth it. But probably compariable to these other devices that are being talked about here. Now in QLD the retail feedins are still less than the offpeak unless you get a special retentions deal, so day to day im still saving a little, which overall I thought was the point of this post. One of my collegues got the hotwater relay timer rolled into the install of his solar so it was proabably cheaper for him.

  6. Patrick Comerford says

    Surely when EVs start to become visible as a load on the grid and as home charging including V2G(H) becomes an actual thing all these problems ie over voltage and export curtailment will simply go away.

  7. Kerri Moore says

    Yes I’m in. As we already have a power diverted for our hot water. Works great. Can’t wait for this to come out

  8. Samuel Aragone says

    The simplest way to absorb excess solar power in summer is to crank up the desalination plants that exist in every state and keep them running at peak capacity during the middle of the day and wind it back at night.
    Ease water restrictions and divert excess water into existing reservoirs.

    • In 2007 I acquired a “water-from-air” condensing and treatment machine which cools humid air and creates drinkable water, with multi-stage filtration and sterilisation, including reverse osmosis (as in the desal plants). I also use this system to treat water from my rainwater harvesting tanks. Thirdly, during hot periods I use a portable refrigerated air conditioner to cool inside my house. This also produces water which I push through the condenser. On a “good” day, (ie sunny and humid) I can have up to 8 litres of water treated.

      I ride a bicycle (indoors or out) every day and in summer I can drink up 4-5 litres of water (including coffee/tea).

      All of this process is powered by my rooftop arrays and domestic batteries.

      So I look at savings on several levels here. Firstly, and relevantly, both the condenser and the air conditioner are solar powered, so I save money on not importing from the grid, as well as CO2 reduction. Secondly the “excess” power doesn’t go into the grid thereby reducing the “strain” on the grid. The batteries soak up some power and the water some more. Thirdly, looking at some shops I see bottled water selling for $1 for a 500 ml bottle. If I drink only 4 litres a day, then potentially I could be saving up to $8 a day not buying in bottles*. Lastly, by not buying bottled water I’m saving the environment by not having these single use bottles being dumped into landfill.

      So using our excess power to run desalination plants sounds like a “win-win” game.

      *At 4 litres a day, that’s just under $3,000 a year.

  9. Hi,
    I have a different problem. Not sure if this solution could help me. I live in an RV with 4 x 327W Sunpower panels on the roof. These load the batteries. Once the batteries are full, I would like the AC to turn on to stabilise the temperature inside the RV, so we do not have to run everything when we get there later. Do you think this unit will work or is there another off the shelf solution?
    Thank you

    • Leon,

      I will soon publish a blog post about the Catch Power Solar Relay. This $250 device could work for you. If your inverter uses frequency shifting the relay can detect when the batteries are full and switch on your AC via a contactor,

    • Leon, Your RV situation is not quite the same, and does not require this type of controller, which is grid mains specific.

      What you need is a simple voltage switch on/off that you can monitor the battery voltage and use that to cycle your RV AC.

      Switch it ON at max voltage and switch off a volt or two under. You will have to play around with the OFF voltage value as it will dip under AC load – it depends on your battery size / condition.

      But it is simple and cheap to do – I use one of these :

      To control a battery charger in the ‘shed’. I screwed up the undervoltage value to just under 14V and the relay closes on anything above that to run the charger. You could, I think, use the same method to run you AC as the batteries come up to full voltage (14.4).

      It really depends on the voltage drop as the compressor starts. Still it would only cost you around $5 to find out !!

      Hope this helps


      • I’m not sure that would work too well … once the batteries get to 14.4v the relay will turn on, but the A/C will then bring the voltage down, turning the relay off at which time the voltage will come back up … (repeat, repeat, repeat) … ?

        • Julian, it’s called “Hysteresis”.
          You set the cut-in voltage higher than the cut-out voltage so it doesn’t thrash back and forth.

  10. Sebastian Silverwood says

    I actually already do this with my 3x split systems using a combination of Home Assistant, Broadlink IR blasters, Fronius API, thermal-shielded blockout curtains and some custom Python scripting. Using the solar to pre-cool the house while there’s excess generation has been incredibly effective in reducing peak load requirements once we get home.

    If you live in WA, this really is a no-brainer considering how ridiculously low the FIT rates are there.

  11. Mike Belfield says

    As an alternative, during the solar peak of summer, couldn’t an air conditioner’s evaporator cool (or heat in winter) a tank of brine to almost freezing and then during the afternoon peak, the brine be pumped into a “radiator” i.e. an air to brine heat exchanger installed in the room to be conditioned.

    Under this condition, the compressor works when the PV is generating surplus energy and the room(s) are conditioned when the house is occupied when energy rates are high due to peak loadings..

  12. The Electric suppliers are banging on about their need to remotely switch off solar panels to avoid over-voltage.

    But surely all Grid Tie Inverters already do that automatically?

    What am I missing please.

  13. Thanks Ken. I take your point about missing the FIT however I think I am not viewing it from the perspective of selling to the grid but rather how do I size a system to comfortably run my home’s equipment at a net effective cost of zero to keep me comfortable. Not so much to make it smart and divert to the A/C but in a simple way if my consumption in a given hour is less than the output of the PV then it was ‘free sun energy’ as I dident need to import anything.

    So given say a 50% load on the A/C which equates to 4.1kW (COP of 3.4) + a HPHW of say 1.0kW for any given hour I generate more than say 6kW (added a 20% buffer) I know that i can run the A/C and the HPHW at no cost (no net import for that time period)? Is that right? If I only generated say 4kW in a given hour then my cost would be the 1.1kW imported right?

    To improve on that would be to install diverters to specifically direct energy to the devices once threshholds are met as you illustrated.

    • Yes that is just about right, it is all about compressor wattage draw. You can run under DRED at 50% of that 6.9kW Max load, at worst equals 3.45kW + your HPHW at 1 kW (at worst again). So an excess solar requirement of 4.45kW + buffer. Say 500W, so call it 5kW and everything can run.

      However if say you have 6kW peak then you can pretty much guarantee that you will have enough solar to start the HPHW 1 hour after sunrise, so that can just go on a timer.

      Once that starts to tail off and the solar starts to rise, you should get a compressor start by say 10am latest. It depends on the day and your other house loads.

      No the DRED unit it will not draw from the grid, except perhaps for the odd overshoot if a white fluffy thing comes by. It will either crank down or turn off until conditions are right to start again.

      If you have an element in your tank I recommend using the HPHW to a max of 40C (where it works best) and then using a diverter to take over at 40C to 73C or whatever the tank max is.

      The elegance there is that the diverter will soak up the buffer / balance when the DRED doesn’t need it.

  14. Thanks Ken. Just starting to read about DRED and checked that the A/C I am considering has this capability. I think you mentioned they were introduced so power suppliers could curtail demand but is there a ready way we can access/control that aspect of the device to the same effect as you described and is it currently economic to do so (maybe I missed this in one of the repsonses?) Please excuse my ignorance as juts learning and would love to size right for a nice outcome.

  15. Alek,
    absolutely easily.

    Under the same panel as the power goes to the compressor (so turn off the master switch before opening) is a small set of 4 (usually screw) terminal connections. (Some units have a small 4 pole socket – check the manual).

    This is just a signal voltage so nothing to harm. The connections will be labeled DRED 1 / 2 / 3 and Common. Here is the text from my software notes :

    // DRED #1 is ‘compressor off’ is the minimum required to meet the Australian standard AS4755.3.1.
    // DRED #2 must not exceed 50% of Capacity kW
    // DRED #3 must not exceed 75% of Capacity kW

    So connecting one of the numeric wires to Common will activate that DRED restriction to your compressor power draw.

    Simple as that. I ran a length of 4 core flat phone cable through the window to a set of switches when I was investigating this.

    DRED 2 is best to play with as you get a sense that something is actually happening.

    To make it all work, turn the AC on with the remote as normal and set the DRED. On my Panasonics the little GREEN light on the head unit flashes under DRED control – but that is about the only indication.

    The only caveat is ONLY use 1 wire to Common at a time. I haven’t any hard info as to what will happen if you double up, but why risk it?

    So you can now set the MAXimum power draw to your large compressor to a value nearer your excess solar. This has to make sense – even manually.

    Hope this helps.

  16. So what is now the status of this article, re solar & over-voltage?

    Confession: I Believed Solar PV Was Causing LV Network Over-Voltage Problems. I Was Wrong.
    July 6, 2020 by Richard Chirgwin

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