Solar PV Buffer Tank?

[Charley]

Hi All,

I'm new to this forum and not a plumber, although I did install our CH system 20 years ago. Hope you'll still advise me!

We're having solar pv panels fitted to our roof and will be generating up to 4kW. I got a energy monitor last week and we seem to be using between 200W and 750W most of the time, until we turn a device with a heater (kettle, microwave) on.

So potentially I'll have a kW to spare most days during daytime and maybe two on a sunny day. Not enough to turn on our 3kW immersion heater without buying energy from the grid so I'm thinking of fitting a buffer tank in the roof between our header tank and domestic hot water tank (our old Potterton boiler is still heating the water OK).

For the buffer tank I'd get a cheap direct vented economy 7 tank, then fit it with a couple of 1kW immersion elements (available for marine applications with the same boss size). If I get real clever I'll fit a sensor that switches the elements on when there is spare electricity but initially it will be manually.

From research it seems that it takes about 8kWh to heat 120 litres from cold, so one element would do it on an average crap UK day, with a quicker job on the day the sun shines (just kidding). Any increase in temperature will reduce my gas bills!

Any comments or suggestions on this idea? Problems or gotchas? Thanks for all comments, humorous caustic or otherwise - Charley

 

[ecowarm]

Why not have solar thermal fitted as well?

The electricity you dont use you sell to the grid for a lot more than you buy back any way>

 

[Charley]

Good question, long answer! I started out looking at thermal but it only makes real sense if I rip out my existing hot water tank which means major surgery on a shower room and bedroom.

I've chosen PV as an investment really. The system costs around £12K and will hopefully generate (sorry) a return of £2K per annum, guaranteed for 25 years (if you believe the government) and increased by RPi annually. The payments are based mainly on what I generate (approx 41p per kWh) plus 3p per kWh exported, but the latter is assumed to be 50% of what I generate unless I fit an export meter.

So any energy I use is "free", hence my interest in the buffer tank...

For interest, new panels are in development that combine pv with thermal, because the pv generation is improved if the panels are cooler, but my supplier said they're not commercially available yet.