Immersion Diverter(eddi) Vs smart immersion switch/relay

System

This discussion was created from comments split from: Domestic Solar PV Quotes 2022 - No PM requests - See Mod note post #1.

AmpMan

https://www.boards.ie/discussion/comment/121255217#Comment_121255217

A hot water diverter isn't just on or off.

deezell

https://www.boards.ie/discussion/comment/121255255#Comment_121255255

Correct, it's for life, not just Christmas. (Actually its a relay switch which is operated when the feed in exceeds sufficient power to supply the immersion, whence it, er, turns on and off. And on. And off....)

graememk

https://www.boards.ie/discussion/comment/121256966#Comment_121256966

No it's not just a relay switch, it varies the power to the immersion to match the excess from the solar, generally by modifying the voltage to the immersion.

But. I agree for most people they are better off just exporting the power. It will take a lot of kWh to pay for itself especially if you get 20+c for exporting. Especially if you have gas at 10c/kWh. 1 unit exported will pay for 2 of gas.

There is edge cases where convenience wins though, eg only heat from solid fuel, need a fire in the summer.

AmpMan

https://www.boards.ie/discussion/comment/121256966#Comment_121256966

No its, not. But if you wanted you could make that set up for 50e or less

deezell

https://www.boards.ie/discussion/comment/121257537#Comment_121257537

I suppose if you pay €600 for a diverter, then it's not 'just' an on off switch, unlike some much simpler Ali versions, or even the suggested 50€ home brew. The key is knowing when your panels are outputting more than the rated consumption of an immersion element, in the region of 2.4kw. Perhaps the measured output is available as an integer from the inverter Internet app, a bit like a smart stat, so straight away you could write a simple smart script to throw a 16a smart relay an connect the immersion.

The €600 jobbies do more it seems, @graememk says they can vary the power to the immersion, in other words, supply at a lower voltage. This would require switch mode power conversion of the 220v inverter/mains source, which at best would result in an immersion which only warmed the water. Half the voltage across the immersion element, say 110v, will reduce its output to a quarter, you might never get it fully hot unless the sun shines and PV output increases,or you're willing to let the diverter consume some mains in tandem with insufficient inverter output on a dull day. I must investigate if they do this. If it's the case, its hardly any different to wiring five 45v DC panels in series straight to an immersion. They will warm the water on low power, and and fully heat it at maximum output. This has been tried successfully if you go looking.

All this chopping and changing of voltage and current in the Eddie or whatever is likely to produce a fair bit of heat, and some inefficiency. In the end of the day, a cheap timer which bangs on the immersion when you're most likely to have full pv power, or else feed in at 20c and use your gas or oil at 10c as suggested. To me the Eddie is just another expensive box that will fail eventually due to its high voltage high heat circuits.

graememk

https://www.boards.ie/discussion/comment/121257827#Comment_121257827

I've seen the Eddi while running, it's no hotter than any other piece of equipment running.

A kWh of heat is a kWh, if it was put in at 100w or 3000w

Eddi uses PWM to vary the power, cheaper divereters use triacs as far as I know.

In the days before the export credit, an eddi just about made sense, but now with the FIT and costing your DHW on your night rate/oil/gas. Nearly could cost you money.

Say export is 20c, and night rate or oil is 15c

If you use an immersion diverter, it could save you 15, but if you exported you'd get 20c.

I've often used the argument that people on turf an eddi could be a convenience bonus with not having to light a fire in the summer, but if they have night rate, the tank could be heated at night. Tanks are well insulated now so the loss is minimal.

slave1

Diverters should still be considered depending on individual circumstances, you can have full hot water on night rate but this can be drained with morning showers and then required again for evening showers after exercise/training/sports etc.

For me I want the convenience of hot water all day so will continue to divert regardless of cost differentials although day rate heating of water in evenings will likely fall into the punitive peak usage rates for lots

tech

what are peoples views on Eddis these days? vs a smart switch for Imerrision

bullit_dodger

https://www.boards.ie/discussion/comment/122032523#Comment_122032523

I'm on the "it depends" mindset. If your coming from the cold hard fiscal viewpoint, then Eddi's these days don't make sense and you'll never make back your money. On the other hand (like me) and you value consuming as much as possible the energy you create from your panels and don't want to go over that €400/year limit in export and start to get taxed, then the make a bit of sense.

It's a luxury to have hot water 8 months a year and not worry about it. Yeah, it get the counter argument of it's not paying for itself, but that's not why I like it. I've paid the wonga and I'm "done with it" :0)

Latro

As long as the rate at which solar energy can be exported exceeds the cost of the cheapest energy imports, there is effectively no such thing as excess solar.

bullit_dodger

https://www.boards.ie/discussion/comment/122035842#Comment_122035842

Generally I'd agree with that statement, but when you go above that €400/year then instead of getting €0.24/kWh, you might be getting only €0.13 (after tax) it gets a little more complicated. I exported ~1500kWh last year which at €0.24 (Energia's FIT rate) that's €360. I'll be over €400 for sure this year as last year I was on deemed export and used as much as I could.

To the original question though. Smart switch + bit of home automation if you can do it and your good to go. Eddi is a luxury (one I really like), but it won't make you money even long term I reckon.

oaklands

You could heat your immersion @ ~7cents or less for 3 hours overnight on EV rate, and just export solar as normal for circa 20 cents per kWh and then save the cost of diverter + installation.