Heat only boiler - hot water feed

[desktop987456]

Hello,
I have an old heat only gas boiler (35kw). I recently installed PV system at the roof, this will be my first winters (hopefully) with PV system!
I have an immersion heater 50 litres right next to the boiler feeding hot water to a bathroom.

My question is that if I feed hot water from immersion heater to my gas boiler and use boiler for ciruclation of hot water only to radiators, would this work? The idea is to save on heating bills (via gas) and utilize PV generation for space heating.

Thanks in advance.

 

[CBW]

A 35Kw heat only? Are you sure about that?

 

[oldbutnotdead]

Short answer- probably not. 50 litres is too small for your sole dhw supply anyway.

 

[desktop987456]

A 35Kw heat only? Are you sure about that?

Yes, it is an old non condensing boiler, it says 120,000 btu

 

[desktop987456]

Short answer- probably not. 50 litres is too small for your sole dhw supply anyway.

I don't intend to use this (50 litres) for my DHW if what I am trying to do is doable

 

[oldbutnotdead]

Apologies- meaning really was that 50 litres is too small to be an effective buffer tank to capture 'spare' PV energy.
Assuming a nominal 4kw PV system your 50 litre buffer will be boiling in about half an hour- PV energy will then be going to waste until you use some of that water. Typically space heating kicks in during the evening when there won't be any PV.

 

[JohnD]

Solar panels collect very little electricity during winter, so you will find it an expensive disappointment.

Energy from gas is much cheaper than energy from electricity so the cost saving is also small.

From your readings, how many kWh per day did you get in September? And how many in October?

 

[desktop987456]

@JohnD , Solar generation in Sep 40 kw/day, in Oct 40kw/day for 12 days so far.

 

[desktop987456]

@oldbutnotdead, spot on. I have an 11kw PV system, and surplus units goes back to grid which are net off at the end of each month. Last Feb it produced 900kwh.

 

[martygturner]

I use my excess solar to feed the grid during the summer but the feed in rate is a thing of mystery now that FIT has ended. In winter solar tends to have its peak at 10 til 2pm ...and they octopus rate is 5.2p during that time. So we heat an immersion tank with our solar during that time if we are out, a tank full of hot water is a pretty good energy store. Its in the roof space and feeds the hw system via a diverter valve,its on a manual switch at the moment so when the tank runs cold we can pop back to the combi supply.

If you fancy like being brave add some battery storage and throw it back to the grid at 15p a kw at peak...my 4.5kw system gives about 120kw a month back to the grid during winter, so if if stored it and sent to the grid at 15p a kw peak its not exactly mega money £18 a month.

The point being is that solar can really cut you grid usage...exporting lecc to the grid is useless you have a monster array its just a bit of fun. Better to use the lecc yourself and save 34p a kw. Even during the darkest days on winter we get 4 hours free a day, hot water made, laptops charged, power tool batteries charged, if we are not at home. If we are then we cook our meals..we get about 2.7kw out of 4.5kw array during winter, if we keep the panels clean. That's enough to run our house mostly.

Our neighbour has two storage heaters in the hall upstairs and down...charges them during the day. The thing with micro generation is being clever about using the energy you have made, selling it sort of misses the point during winter.

 

[desktop987456]

@martygturner - I agree with your views on FIT, where I live our Peak rate is from 6p.m - 10 p.m and then its non peak after 10 p.m so the units from solar credited during the day can be offset after from 10 p.m till sunrise. Not sure how it is like in UK.

I like the idea of a diverter valve for hot water to boiler during the day. Batteries are pretty expensive and I have to change the inverter to install these.