OpenEnergyMonitor Community

Solar PV diversion options

Hi. I am getting solar PV installed next week and I am looking at getting an Emonpi. However, I’m a complete newbie when it comes to the level of tech that I am coming across on the forum. What I am interested in doing is monitoring how much electric I am producing/using and if there is excess I would like to turn on a smart plug (attached to washing machine or dishwasher) and any further excess to the immersion (can emon pi do this directly or do I need a solar iboost or equivalent?). In order to do this what do I need to purchase from yourselves and what smart plugs can easily work with this set up? I had originally been looking at Wemo but I have seen a lot about LightwaveRF on your site - if I need to use LightwaveRF do I need the Lightwave link too? Also, is the connection with the LightwaveRF sockets or the plugs?


Hi Sinéad,

Thanks for your interest. Yes, the emonPi solar PV will monitor your generation, consumption and gird - import export. See: https://

It would be possible to switch an immersions heater on/off using a light wave RF inline relay:

The inline relay can be controlled from the emonPi with OOK trasmitter, see: It would be simple to use nodeRED to write a little flow to turn on the immersion when for example more than 2Kw of solar is available.

However, the inline relay would only be able to turn the immersion on-off, it would not be able to modulate the power of the immersion based on solar PV output which I guess is how solar iboost works.

There is a community developed system called solar PV diverter MKII which was developed by members of the OpenenergyMonitor community. This can fully modulate the immersion heater output based on excess solar PV. It’s documented on our site: A kit can be purchased from @calypso_rae (the developer) via his website:

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I’m afraid only Mk2 PV Router kits for self-assembly are available at present. Please contact @calypso_rae via his website, or PM here, for details.

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One other thing to consider Sinead when you are thinking about using excess Solar is that you can only really use it on things like immersion heaters or other simple loads, lights etc.

Diverters work by turning the power on and off very rapidly so that small slices of the excess go to the device taking the power (unless you have a massive amount of excess that is).

Washing machines and dishwashers need to be powered all the time other wise they reset. So for instance if you put your washing machine on a socket powered by diverted power, you wouldn’t be able to set it up and start it unless there was enough diverted power and as soon as a cloud came along it would restart and need starting again with the start button. You can test this by turning the power on and off at the socket. Turn it off (as in no diversion 1st thing in the morning) and you won’t be able to do anything with it. Now turn it on (as in diversion during a sunny morning), once it’s running, turn it off and in all likelihood it will revert to it’s startup state where you need to press the start button to get it working running again.

So washing machines and dishwashers aren’t great for having connected to a diverter. What most people do is to make sure that they use these types of appliances serially, so they never have the washing machine or dishwasher on at the same time (or the iron, kettle, toaster or hairdryer etc.). This way any excess PV you have will be used by the appliance that is on at the time, as and when you use them. Takes a bit of thinking about to start with but once you’re in the swing of it you’ll do it automatically.

So your best bet for diversion is either one of Robin’s kits or a commercial solar diverter connected up to your immersion heater. That way and excess over and above your usage gets stored as warm water for use later. (Shower in the evenings of course). And if you work and can’t turn things like your dishwasher and washing machine on when it’s sunny then set them up on their built in timers to come on one after the other.


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I can’t speak for a commercial unit, but as Simon infers (but hasn’t spelled out in detail), Robin’s and MartinR’s diverters will both shut down (or trim back) the diverted energy as soon as another load comes on, and only divert as much power as would otherwise be exported.

I would not suggest using diverted power for lighting - unless you want the lights to come on when the sun comes out and go off when a cloud comes along. But storage heaters, and battery charging (given some caveats) are fine.

Thanks all. That was very useful. I was just being hopeful about the washing machine and dishwasher. Will look into the the diverter for the immersion but seeing as I have an inline relay at the minute I’ll have a play of that and see where that gets me.
Though as a complete beginner I’m just happy that I got the emonpi and emoncms setup and working today. Pairing the lightwave plug is my next challenge, but that’s one for a different thread.

On topic but at a slight tangent, I was thinking of getting one or more bitcoin miners connected via a UPS to generate bitcoin using my excess generation.

Has anyone done this? Stupid idea? Thoughts?

ps also considering putting a hot water tank in 'cos we don’t have one right now :smiley:

Given Bitcoin are now worth well over $1000 and have shot up in value since last year - that might be an idea.


Even the topic is old, have you thought about feeding your appliances with hot water instead of cold water. Most energy used by a washing machine or a dishwasher comes from the fact that water is heated in the machine. Devices are available to feed washing machines with hot water if your washing machine doesn’t have the hot water feed pipe.

That depends on where one is located. In the US, all washing machines use an external hot water source.

So in the US, they don’t use internal heating at all? And only hot water or does the machine use a thermostatic valve internally to mix water to the desired temperature? A search only got me this post “European Washing Machines Vs. North American Ones” from 20 years ago…

Mine has dual hot and cold inlets, but it’s quite old (1992). Most modern ones I’ve seen (and installed for friends/neighbours) have a single cold water only inlet.

Where mine is located, I have only cold water available, so I use a “Y” adapter to feed both inlets. From the instructions, I understand that it will mix to get the correct temperature, or use electricity to heat the water if necessary.

Correct. The machines have one inlet for cold water and one for hot water.

Mixing valve for cold, warm or hot.

Some machines have an economy warm setting as well which yields a water temp between warm and cold. The one I have has five settings: Tap cold, cold, eco warm, warm and hot.

In Canada there are smaller dish washers and clothes washer that have built in water heaters in them. I have them they work fine they are just generally smaller. as we generally do not use 240v for our washers they are generally 120volt. so I do not think anyone wants to wait twice as long for them to heat up the water - like my dishwasher it operate fine only with cold but it 150 minutes to do a load of dishes if you used only cold water cycle . compare if I used hot water I can do a load in 25 minutes