Solar PV to immersion diverters.

[Chris B]

I am researching solar PV to immersion diverters. There seem to be several on the market but this one by Marlek looks like one of the easier ones to retrofit and seems to be fully stand-alone without any direct integration with the inverter or other smart systems. Also having a remote wireless export sensor means that the control unit can be close to the HW tank (desirable).

Does anyone have any comments on

A) The technology. Does it work? (can't see why it won't). Reliability? Does all of the on/off switching of the immersion heater significantly shorten its life?

B) Personal experiences good or bad with any particular brand/model.

Thanks.

[Peter Johnson]

I've had an iBoost for several years, must be an older model without the standalone repeater. Never had any problems with it. The batteries in the sensor last a long time. The first year I had it I ran from June until September without using any gas, Ovo thought the meter was faulty, but we've not had a summer like that since. It's put 2.4Kw into my immersion today, about 10Kw in the last week.

[Chris Green]

I presume you mean 2.4kwh and 10kwh respectively. Even at the new prices that's about 72p and £3.00.

[Chris B]

If we assume that as we are currently close to the equinox and £3.00 per week is "average" that is a very healthy £150/year return on a £300 investment.

Although as we are now replacing paid gas water heating with free electricity water heating it is gas price we should be using for comparison. I think 10Kwh of gas is more like £0.40 rather than £3.00. This reduces the annual return to £20/year. Not quite such a no brainier as we are now into reliability issues - will the device last long enough to pay for its-self?

I will have to look back through old bills and see how much gas I typically use in the July/Sept (no space heating) period. When I would hope this device could do most of the heavy lifting for water heating.

[Andy Burns]

My cast iron lump obviously uses most gas autumn->spring, but it provides my hot water all year round, last time I worked it out, during summer when the heating never cuts in, the cost of running the pilot light and heating water for 30 mins/day was about 50p/day ... that was a 2-3 years ago.

[Vir Campestris]

Surely the correct way to heat your hot water from the sun is to use a water heater? It'll be far more efficient.

There must be better things to do with high quality energy like electricity than to use it for resistive heating.

Charge something?

Andy

[Theo]

Yes, but installing a solar hot water panel on your roof isn't very straightforward: you need the panel, pipework full of glycol, pump, heat exchanger, controls... I'm sure in a commercial building that would make sense, but for the relatively small amount of domestic hot water demand the amount of hassle can outweigh the 'free' hot water. Plus another wet system will eventually perish and leak, and somebody has to go on the roof to fix it.

Meanwhile PV just does its thing, with essentially no maintenance. All that comes off the roof is a couple of wires, which you just run off to the inverter mounted whereever.

There are integrated solar hot water units with their own tank/heat exchanger that sit on a frame on a flat roof - they are probably easier to manage than the bespoke systems that we tend to have mounted on sloping roofs, but it's not an aesthetic we're used to:

That's the benefit of PV - when you have something else you can use electricity for, use it for that. When you don't, the diverter will put the energy into your hot water tank. It has a better payback than the rate your utility will pay you back for it (and if you DIY your solar install, the payback from the utility is 0p/kWh).

It would be better to have a battery, but £100 for a diverter against £5K* for a battery?

Theo

• actual battery costs are about 0/kWh at the moment but costs of systems are a lot more, for unknown reasons

[Andy Burns]

That's about my level of thinking, just have PV on the roof, not any plumbing.

[rick]

I have one been in place and working for 4 years. Not the model you mention, I have:

I put an Hr meter on it to see how much gets diverted - it is significant, and worthwhile as I still get paid for the generation.

[The Natural Philosopher]

ROFLMAO!

Until the builder next door blows cement dust all over it, the birds shit on it, lichens and algae cover its surface and the plastic mountings crumble in sunlight and the connections corrode in the rain...