TedM

Yep, I've never paid more than £100 on any of mine - all bought on eBay. (although if you have an EV then the eddi works in conjunction with the zappi charger to utilise your PV generation even better - I think this adds value to the eddi)

I don't think so - and the external boost [by applying any voltage to a special 'port') is a game changer and, I think, limited to Immersun and the Eddi. (Immersun came out quite a long time ago but went out of business but you can still find the units for sale on eBay. Myenergi bought Immersun and based the eddi on it - it's extremely similar but has a couple more bells and whistles) Literally any cheapo electric convector heater (without a fan) will do. The Immersun and Eddi can output a maximum of 16A (you can actually throttle the eddi back if you wanted) so pretty much any heater will do.

Ummm .... not really! Well, yes it has but the heater is located effectively at the bottom of the stairs which lead to an open plan kitchen and living room and it never gets hot enough downstairs to trip the thermostat - and, as it's there to dump excess power I don't really want it to switch off. There is a bit of an exception to that though The upstairs has quite a lot of south facing glass (inc. floor to ceiling sliding doors) so it benefits from a lot of solar gain if the sun's out. This is great generally but if we're not there [the doors/windows are all closed] and it's a very sunny day the combination of the solar gain plus the extra heat from the PV dump heater downstairs can push the temperature upstairs to over 30c 😬 I fixed that last year by adding a relay in the feed to the PV dump heater that disconnects it from the Immersun if the upstairs temperature gets too high - surplus generation is then sent out to the grid. Is that a thing? Maybe. My inverter is currently outputting 260v but it ultimately all feeds into the house consumer unit which is running at 250v. Screenshot below shows the current readings from the power going into the CU from the PV and the small amount being exported by the Immersun: If your diverter has dual outputs (i.e. Immersun or the Myenergi Eddi) you could set the top element to be heated first and then the bottom element - but TBH I'd just go with the bottom element (hot water rises anyway) and then a heater wired directly to the second diverter output. ... Correct - it's not a clever way to do things as the heater would always be on (thermostat dependant) 🤦‍♂️ Two solutions: 1) Wire it directly (and exclusively) to the diverter then anything that would have been exported is sent to the heater.... even if it's only 100/200/300W 2) Put a wireless plug on the heater and have it switch on then the exported power is over a certain amount. The issue with this method is that the heater will draw the maximum it's set to so it may well end up drawing a load of power from the grid if the exported power is not monitored constantly. For example you have a heater that on it's lowest setting draws 1kW - you could set up a system that would switch that heater on if > 1.2kW was being exported (gives a little headroom), but if a cloud comes over and the generation drops then the heater will continue to pull 1kW unless it's switched off by your monitoring system. I use Shelly power monitor and wireless relays to control various devices now as they don't need an internet connection to operate - signals can be sent via your house LAN - and they constantly check the amount of power going into or out of the house and react very quickly.

I'm doing something very similar with my [electrically heated] holiday place in Wales that is occupied 90% of the time during May to Mid September. We have a south facing 3kWp array on the roof and a 210L Megaflo tank with hot water usage basically being showers - no baths. I've set up an [old] Immersun diverter to heat the tank and when that is satisfied any spare generation going into a single electric wall heater in the hall which is only connected to one of the Immersuns' outputs - it's an upside down house so it heats open-plan upstairs as well as the hall. I like using the Immersun because, not only does it have two outputs, it can also be remotely boosted by applying any voltage to a specific connection. Unfortunately there will be periods, even in the summer' when that's not going to happen. I also run a Pi that monitors various house temperatures including the hot water. This checks the water temperature very early in the morning (say 5am) and, if it's below a threshold that I've set, it switches on a wireless plug that sends power to the Immersuns' remote boost port so there's enough hot water ready for morning showers. This is pretty important at a holiday let where guests expect hot water all the time! You don't have to use a Pi to achieve this - I'm moving quite a lot of stuff over to Shelly relays which are simple to set up. Our array and this setup supplies all our heating needs for 6 months of the year. The one change I do want to make is to add a further 4 ground mounted panels that face west which would give us some very handy generation past 4pm during the summer. I'll be adding another inverter to handle this power as the original array is on a very attractive FIT so I'm not going to mess with it!