We have oil CH that also deals with our hot water which is stored in a megaflo pressurised cylinder (about 9 years old) which has a single immersion heater element about half way up the tank and, I think, a further blanked off heater location towards the bottom of the tank.

If I were to go with a solar hot water installation to reduce my oil use how would it integrate with the existing system?

YG a question on PV’s on the other thread.
Our water panel needed a new tank as we didn’t have a spare heat input hole. Ours runs totally independently of the CH system but uses the same hot water tank.

Tricky without a dedicated solar cylinder.

You may be best off looking to take it via a buffer but to be honest time you’ve done that buy a dedicated solar cylinder (Oso Hotwater as good as Megaflop, maybe better, but cheaper) and eBay your existing cylinder.

There are other ways but you will still need to buy stuff and probably not as good as dedicated cylinder.

you can buy (or indeed make) your own solar coil to fit in an immersion port.

http://www.ebay.co.uk/itm/Solar-Panel-Hot-Water-Immersion-Coil-Heat-Exchanger/271298634641?_trksid=p2047675.m1850&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D11%26meid%3D2140190829306956291%26pid%3D100011%26prg%3D1005%26rk%3D2%26rkt%3D5%26sd%3D271169128142%26

You could use that to connect the buffer to your megaflow. NOt sure how effective it would be though.

http://www.solarcoil.co.uk/products.html

Is a buffer a second cylinder? If so how would it work with the existing cylinder?

A buffer allows the solar energy to accumulate and “concentrate” by stratification so that you can produce water of a more uesable temperature.

Bear will correct me if Im wrong, but the idea is to use an indirect coil in your buffer to transfer energy from your solar collectors into the cold part of buffer water, near the bottom. This gives the greatest temperature gradient (and hence most efficient) for collecting the solar energy.

The water in the buffer stratifies over time, with the energy concentrating near the top. This energy can then be transferred into the top of your hot water tank via another coil, I guess controlled by a tank stat to make sure it only ever transfers water hotter than the water at the top of the hot water tank.

BTW, some more to read here. REUK is a bit yoghurt knittingy, but there’s some cool projects on there:

http://www.reuk.co.uk/Solar-Hot-Water-Heat-Exchanger.htm

So can’t I just connect a solar panel to a coil in the spare inlet on my megaflo?

If I understood the above, you’d risk transferring heat from your tank up to your roof.

You can connect straight to the tank (effectively that’s what mine does), and you rely on a solar controller not allow your pump to send hot water outside. BUT your megaflow tank isnt very big, which means you wont get much stratification, which in turn means you wont get the most efficient use out of the solar array. Mine works well because my tank is 7′ tall and holds over 700Litres of water so the bottom section can be kept cooler.

Hmmm…. right *rubs chin*

OK so I’ve done some reading up and had a quick check on my existing (250L) cylinder – it does have two immersion ports; one right at the bottom which is being used and another half way up which isn’t.

Please correct me if I’m wrong but I think I’ve got two [reasonable cost] options and a few questions:
1) Swap the current immersion heater to the upper port and use the lower port to set up an indirect system using just my current cylinder.

2) Buy another cylinder and heat the water in that with the solar panels and pump hot water from solar cylinder to the main cylinder as it heats [is this the buffer system?]

I quite like option two as MrsSB thinks we don’t have enough hot water capacity and with three growing girls I suspect she may be right. But option one is waaay cheaper.

So if I added a 120l cylinder as the buffer I’d potentially get 370L of hot water?

If I went down this route would it be OK to locate the buffer in the roofspace above the main cylinder (which is in main bathroom).

Presumably the second tank would also have to be unvented as the we are on an unvented system?

Go on Ebay and buy a second cylinder then plumb that in tandem with the existing cylinder so that the cold water entering the house gets pre-heated by the solar panel before entering the main cylinder. This requires only one small modification to your plumbing.

what about external plate heat exchanger?

http://www.solarproject.co.uk/Install%20Tips%20and%20Tricks.html#coils

What have you done to reduce the HW you actually need? Have you got a low flow shower head and taps? Does the washer / dishwasher have a HW feed?

I have also seen 12/24/36v DC immersion elements. Bung that in the bottom of the tank and connect up a couple of solar PV panels. That would provide some heat to the water and reduce how much heat your system had to add. That would be a much cheaper installation and maintenance would also be less. I know using PV to heat water has traditionally been seen as a poor use of the energy, but it could be a much cheaper retrofit against through-life costs.

Just read the wife and 3 girls bit. You’re screwed. Just get a massively over-sized system that goes against any logic a man would offer. Then you’ll just about be there. You have to suck it up.

What have you done to reduce the HW you actually need? Have you got a low flow shower head and taps?

Nothing, no and why would I want to? I’m happy to use the water, I just want to pay less to produce it.

Go on Ebay and buy a second cylinder then plumb that in tandem with the existing cylinder so that the cold water entering the house gets pre-heated by the solar panel before entering the main cylinder.

Would this work with an unvented system globalti? I like the sound of only one modification to the existing system! Although I can get a used unvented cylinder on eBay for about £100 I’m guessing there would be a fair installation cost as it’s a pressurised cylinder 🙁

Low flow shower heads ….. Great on paper , shite for showering.

My folks have a cylinder with a second coil and a pump with a thermostat that only runs when the panels have more heat than cylinder. V simple. The get 50 degrees on a cloudy scottish day, 70 degree plus when its Bright and sunny.

Nothing, no and why would I want to? I’m happy to use the water, I just want to pay less to produce it.

because in your first post you said:

If I were to go with a solar hot water installation to reduce my oil use

and the easiest way to reduce the energy you pay for is to reduce the water you heat. I’ll leave you to it then.

Shark bait……email me for my phone number if you want a chat sometime – I’ve done solar thermal personally and professionally. Email in profile.

You can plumb a second cylinder inline with the existing unvented cylinder but it should be done by a pro, unless you are very handy and can do it properly yourself. The viability of a standard coil used for solar depends on how much solar panel you intend to fit – most boiler coils don’t have enough surface area to work perfectly with a decent sized panel.

You can use the ‘hot rod’ shown above if you can still get them – they don’t have enough surface area to meet current boiler coil standards, let alone solar but it depends on the panel you are fitting.

If you are buying a decent solar collector, then don’t scrimp on the cylinder – do it right and it will do up to 50/60 % of your annual usage.

The finances are important though – a 210 litre cylinder needs approx 14kwh to heat to 65 degrees. Oil in a well serviced boiler costs 7 or 8p per kWh (.based on oil at 60p/l and 80% efficient) so a full tank of water costs £1..05 to heat. If you use a full tank per day, annual hot water bill is £385 so you could save £180 – £230 a year.

The cost of the system will determine whether you think it’s worth doing.

Hth.

Smudger – like your real world figures, although I’d say you are still on the high side as people don’t tend to use a full cylinder every day, and in the winter when boiler is running for heating too system is more effective too.

Ditto what I said really buy a dedicated solar cylinder.

Yeah — savings will depend on current. (And future) hot water use – my 14 year old daughter regularly uses a whole 210 tank in one shower! Luckily, half the time, it’s free!

I’m sure I’ve posted the formula before, but if anyone is interested…..

The energy needed to raise water is…

KWh = (litres x deltaT) / 858

Delta T is in centigrade.

Of course if you’re currently stuck with an immersion only HWC (like us) the math is even more compelling, as its 15p/kWh.

Smudger, what kind of area does the heat exchanger need to work with (say) 200L tank and (sensibly sized) panel?

–doubley post–

I’ve had an email fromPeter at Solarproject saying that on balance the best way forward for me would be to simply install a heat exchanger in place of the currently fitted lower immersion heater.
I’d still prefer more capacity but the cost of replacing the cylinder is too much when installation is included.

Are you getting the kit from him? Going for the silicone pipe and little 12v pump? or going to do a more substantial job with 15mm copper, grundfos circ pump and a 240v controller?

Not got that far yet Stoner, and seeing as it’s nearly winter I’m not in a rush – but probably get the stuff from him.
I’d prob go with silicon if it will stand the test of time but 240v for electricals see as it will be running mostly during daylight so our PV will pay for it 🙂