solar PV to heat water

p5x

I'm looking to replace my current combi boiler as I need something a bit better ([URL="https://forums.moneysavingexpert.com/discussion/comment/75282728#Comment_75282728[/URL]) and just wondered if there were any considerations/recommendations that would allow me to make the most of my solar PV system.

Do I need to get a dedicated solar cylinder such as the Worcester Bosch Greenstore?

pinnks

You need a tank but nothing special. Would be good if it has two heating elements - one at the bottom and one half way up - but not essential. I use my 1984 tank with a top-only but quite long element in a normal 190L (?) tank.

You'll need a diverter to pump excess solar power into the immersion heater(s). I have the immerSUN and am pleased with it. The firm went bust but the technology was bought and has been relaunched (I think). Then there is the Eddi, from the same inventor, and from a firm that also sells diverters for electric vehicles (Zappi). The two devices talk to each other so you can max out on charging your car and heating water if you have enough PV in the summer months. There is then the iBoost which many folk on here have and a host of other less well known versions. If you are good with electronics you can make one for yourself.

And that's it. All excess PV will be fed into the hot water and if that does not suffice (about November to about March) then you can either use the boiler to heat the water as well or use the boost function on the diverter to do the same. Generally using the boiler would be more efficient as it is running to power the heating anyway. My system is set to heat water in the winter only in the evening so that I still use any excess PV during the day and top-up with gas in the evening.

I save about £80 to £100 per year on gas by using a diverter for a household of 2. I now feed my underfloor heating as well as the immersion. Once one is hot the other one cuts in. Works well in the shoulder months but generation is too low in winter.

At the end of the day it comes down to investment v return on investment...

HTH

silverwhistle

Good summary by pinnks. I have an iboost and ordinary tank. The only difference is I don't use my central heating except in special circumstances as I have a log burner and scrounged wood, and it's a point of pride not to use the GCH (plus it's an extortionate unit rate with zero standing charge!).


For additional hot water I just shove it on to constant when I need it. Had it on last night which meant today I only used solar for 1.27kwh before it was hot again, otherwise I'd have benefited more from today's sun. I can't remember when I first used the boiler this last autumn, probably when I wanted a deep hot bath after football, but March to November is a reasonable guess, in a single person household.

gabitzul

I have the (also defunct) Wattson and it works. Buy a good immersion heater, ideally titanium coated, as it will be used more than usual compared to a GCH system.

pinnks

Good point, though I think the fact that it will be running cool for most of the time will help. I rarely see 3kW being pumped into mine, even in summer as the water is hot before i generate that much and may only get a few minutes top-up during peak production.

My immersion heater itself is 35 years old now, though virtually unused for the first 30. I must admit to wondering when it will go pop!

travellerboy

I use Solar diverted to an immersion with Immersun. I also have fitted a temperature monitor on the tank which tells me the water temperature as the tank is upstairs. I fitted the temperature indicator in the kitchen, no wires as it operates wirelessly. - https://www.clasohlson.com/uk/Coline-Wireless-Meat-Thermometer/Pr442239000

silverwhistle

I should add that harvesting is very variable at this time of year: nothing today but a very useful 3.45kWh yesterday.

Exiled_Tyke

Just to clarify the Worcester Bosch Greenstore is designed for thermal panels (i.e. where the panels heat water directly) and so as Pinks pointed out not necessary for a PV system which is using electricity to run a standard immersion heater and therefore an ordinary hot water cylinder will suffice.