Immersion Heater - PV electricity

[pauldreed]

PV is dead. RIP PV :- (

--- It's because it's dark!

 

[pmcalli]

Hi, Ive been dircted to this thread from a discussion on the PV forum and have spent hours sifting through all the pages and some very interesting idea. I'm a little confused about your CT's and wondered if could you elaborate a bit on how everything is connected in your system. Do you simply have one CU with PV fed in via RCBO and immersion fed from MCB or is the immersion feed separated off from the CU. I've been trying to work out what the result is from your CT set up with up one on PV+Incoming and another on the PV?
I've currently got everything connected into the CU so have thought of putting a CT around all the house circuits (excluding immersion) and another on the PV thereby enabling me to calculate the excess power or maybe adding a Henley block to my set up to keep everything separate but is your method a cunning way to get round all that?

Its probably all very simple but its late and my brains dead
Cheers
John

My system balances the house load inc immersion with the solar gen. Your assumption is correct I have one CU with PV fed in via RCBO. PV plus incoming gives you all house load as PV current is flowing in opposite direction. I have since added a second cu for the solar and split the tails in a Henley block as I wanted some extra mcb outlets both ways work well. The system has been working well for the last month and my feed in has dropped to 20 percent from 60.

 

[inie meanie]

Hi Guys
I am going to have an extra long immersion heater made. 3 KW but 48 '' long. The majority of heat will be biased at the lower end. As some of us are now getting free hot water it makes sense to try and use the whole tank. If anybody else is interested in one let me know because the more they make in one go the cheaper it will be for all of us. I have asked for a quote for one and five units to see what the difference is. It must be better than drilling into the side of the tank and risking damaging the whole thing.

 

[pmcalli]

Hi Guys
I am going to have an extra long immersion heater made. 3 KW but 48 '' long. The majority of heat will be biased at the lower end. As some of us are now getting free hot water it makes sense to try and use the whole tank. If anybody else is interested in one let me know because the more they make in one go the cheaper it will be for all of us. I have asked for a quote for one and five units to see what the difference is. It must be better than drilling into the side of the tank and risking damaging the whole thing.

I have just changed mine from a 27 to a 36 and only just got away with it beacuse it goes in at a slight angle. 48 would hit the boiler coil. An immersion coil where the heat is applied lower down would be of great interest.

 

[JohnBoyZ]

I have just changed mine from a 27 to a 36 and only just got away with it beacuse it goes in at a slight angle. 48 would hit the boiler coil. An immersion coil where the heat is applied lower down would be of great interest.

Rather than using an extra long immersion, have you considered using a pump to simply circulate the water around the cylinder, T off from the H/W outlet at the top of the cylinder and route via a pump and a non return valve down to the C/W input at the bottom of the cylinder, switch the pump on whenever there is enough excess PV power to run the pump and immersion.

 

[pauldreed]

Rather than using an extra long immersion, have you considered using a pump to simply circulate the water around the cylinder, T off from the H/W outlet at the top of the cylinder and route via a pump and a non return valve down to the C/W input at the bottom of the cylinder, switch the pump on whenever there is enough excess PV power to run the pump and immersion.

Good idea....I like your lateral thinking....

 

[pmcalli]

Rather than using an extra long immersion, have you considered using a pump to simply circulate the water around the cylinder, T off from the H/W outlet at the top of the cylinder and route via a pump and a non return valve down to the C/W input at the bottom of the cylinder, switch the pump on whenever there is enough excess PV power to run the pump and immersion.

Excellent idea
probably a good idea to have a non return valve in the C/W input as well to prevent possiblity of pushing hot water into the cold system.

 

[JohnBoyZ]

Excellent idea
probably a good idea to have a non return valve in the C/W input as well to prevent possiblity of pushing hot water into the cold system.

Yes but if its being fed from a header tank, make sure there is enough pressure to operate the check valve.
Taking the idea one stage further, I've actually seen a circulation pump used in a large house where there was effectively a h/w ring main around the house so the H/W was pumped around the ring and back to the bottom of the cylinder so didn't have to wait for hot water at any of the taps or showers regardless of how far they were away from the cylinder. Obviously this required copious quantities of pipe lagging but very effective.

EDIT: Looks like a spring loaded check valve might be too restrictive on a header tank C/W feed so maybe a horizontal flap type check valve might be the way to go. Haven't found any with standard 22mm compression but have found these imperial threaded ones http://www.ukpumpsupplies.co.uk/browse.asp?cat=10/106/1062/1062-2

 

[inie meanie]

Rather than using an extra long immersion, have you considered using a pump to simply circulate the water around the cylinder, T off from the H/W outlet at the top of the cylinder and route via a pump and a non return valve down to the C/W input at the bottom of the cylinder, switch the pump on whenever there is enough excess PV power to run the pump and immersion.

Hi well done for the abstract thought. I have just had the quote. £150 + vat for 48'' with 6'' dead zone. Hmm quite a lot really. The pump would need to be controlled carefully so that you didn't disperse useable heat if it was a low pv day.

 

[JohnBoyZ]

Hi well done for the abstract thought. I have just had the quote. £150 + vat for 48'' with 6'' dead zone. Hmm quite a lot really. The pump would need to be controlled carefully so that you didn't disperse useable heat if it was a low pv day.

Yes, good point, how about a cylinder stat or even a relay controlled off the immersion stat so that when the stat gets up to temp the relay turns on the pump would then circulate enough until the temp drops and the stat switches to heat again.
Oh and by the way, I definitely don't like the sound of a 6" dead zone LOL.

 

[pauldreed]

I don't know if different 'power' pumps are available, but I would think it would only need a low flow rate to effectively circulate the water as there is only about a metre head of water and short pipe runs.

 

[suntrap]

Many pumps have electronic speed controls and you'd probably use it at the lowest setting.

 

[suntrap]

There's actually no head to overcome - just a minute difference in pressure caused by the difference in water density. An alternative would be to have a short piece of large diameter tube from the bottom of the element to the bottom of the tank, which would result in the water from the bottom being drawn up, but that isn't controllable.

 

[pauldreed]

There's actually no head to overcome - just a minute difference in pressure caused by the difference in water density. An alternative would be to have a short piece of large diameter tube from the bottom of the element to the bottom of the tank, which would result in the water from the bottom being drawn up, but that isn't controllable.

How would that work?
Wouldn't the water temp in the tube vary between the tank temp at the top, and cold at the bottom (same as the tank) and remain motionless in tandem with the tank?

 

[JohnBoyZ]

I don't know if different 'power' pumps are available, but I would think it would only need a low flow rate to effectively circulate the water as there is only about a metre head of water and short pipe runs.

From what I can see there are numerous pumps available low power, low voltage etc but they always seem to work out more expensive than a cheap central heating circulation pump. A standard CH pump removes any problems with odd sized connectors and can be simply connected using 22mm pipe and a standard 22mm check valve, set it on slowest speed and away you go. Should get the whole thing up and running for less then 50 quid.

 

[suntrap]

How would that work?
Wouldn't the water temp in the tube vary between the tank temp at the top, and cold at the bottom (same as the tank) and remain motionless in tandem with the tank?

If there is any temperature gradient in the water inside the top of the tube where the bottom of the element is placed, it will move and draw water up from the bottom of the tank.

 

[echase]

I've actually seen a circulation pump used in a large house where there was effectively a h/w ring main around the house so the H/W was pumped around the ring and back to the bottom of the cylinder so didn't have to wait for hot water at any of the taps or showers regardless of how far they were away from the cylinder. Obviously this required copious quantities of pipe lagging but very effective.

I had a 1975 bungalow like that but the pipes were set into the concrete floor with probably no lagging so it had been disconnected by previous owner as not efficient. There was a standard CH type pump to pump it round.

Regarding the deadness of PV due to proposed FIT change can I encourage you to protest to relevant people as government is allegedly open for consultation. Chances are it won't kill the industry but slow it down a lot. As PV prices fall its likely that in 2-4 years the new FIT level will again return more than 5%. But they could reduce FIT further by then.

The December cut off is very unfair as many people have spent significant money on the planning process and now can’t get it installed in time to reap the full benefits, even if they have just got to the end of the porocess.

Governments of all hues have blighted the low carbon industries by stop start grant/subsidy policies.

 

[inie meanie]

I had a 1975 bungalow like that but the pipes were set into the concrete floor with probably no lagging so it had been disconnected by previous owner as not efficient. There was a standard CH type pump to pump it round.

Regarding the deadness of PV due to proposed FIT change can I encourage you to protest to relevant people as government is allegedly open for consultation. Chances are it won't kill the industry but slow it down a lot. As PV prices fall its likely that in 2-4 years the new FIT level will again return more than 5%. But they could reduce FIT further by then.

The December cut off is very unfair as many people have spent significant money on the planning process and now can’t get it installed in time to reap the full benefits, even if they have just got to the end of the porocess.

Governments of all hues have blighted the low carbon industries by stop start grant/subsidy policies.

Absolutely shout as loud as possible. It will kill off many companies and stop people installing. They should have slowly reduced the tariffs not like this. It just shows that the MPs live in a bubble not the real world!
Green peace are going to launch an action in the courts on Friday

 

[Red Defender]

The circulating pump needs to be a bronze one. Normal CH pumps are cast iron and will rust and discolour the water in the hot water cylinder.

 

[Red Defender]

Hi all, Im new to this forum and have read everything with great interest. I was due to have a 4 Kw system fitted today but been put back to next Thursday. I have been looking for ways of optimising my consumption of my PV output and accept that using it to heat water and store it seems a good idea. The point I raise is a standard 36" x 18" cylinder will have about 25 gallons of water and from cold will take less than an hour to be heated to 65 degs. What are you going to do with the rest of your output on a clear long summers day?

My first thought was to use a low power element in the very bottom of the cylinder, say 400 watts, and using a timer, and the output profile, have the element switched on during peak hours, say 1000 to 1500 for a south facing roof. this should heat the water without importing any power from the grid and allow other surplus to be consumed by other activities.

Just a thought!