Fitting a 27 inch 1Kw Immersion Heater Element

[phobe]

I am contemplating replacing my 3Kw element with a 1Kw in order to take advantage of the spare electricity from my solar panels during sunny days. My plan would be that I would use off-peak electricity to top-up the heat on dull days. I see that it is now possible to buy 27 inch 1Kw elements, which could give a decent amount of hot water in the top end of my large insulated copper tank. Two questions:
1. Would a such an element be able to heat enough water overnight for a couple. (We don't use excessive amounts f hot water)
2. I see that there is limited headroom above the tank. Is there any flexibility in these elements so that I can bend it slightly to fit it. Or will I have to raise floorboards in the room above and cut a hole in ceiling of the airing cupboard?
thanks for any tips.

 

[mrStat]

Why not just fit an Immersun style unit? Something like the Solic and then you can use a standard immersion and still boost as needed.

1) Depends on how big your tank is.
2) No, they should not be bent. There is a small amount of flex, but they are not designed to be bent or flexed and can break.

 

[JohnD]

it sounds like a nice idea, but just to check: Do you currently heat your water by electricity, or have you got a gas (or other) boiler?

What colour is your hot-water cylinder?

 

[ScottishGasMan]

2nd for an Immersun suggestion. Keep the 3kw heater and in the better weather the solar panels can give you maximum benifit of HW, and can still use any potential power produced in lower solar gain times

 

[JohnD]

I know the daily cost of the gas I use to heat my HW cylinder in summer.

I also know the cost of an Immersun or similar.

I divided one into the other.

It was not a good business proposition.

 

[MeldrewsMate]

I know the daily cost of the gas I use to heat my HW cylinder in summer.

I also know the cost of an Immersun or similar.

I divided one into the other.

It was not a good business proposition.

JohnD, I'm surprised at your low opinion of the various energy diversion gadgets available (Solic, Solar iBoost, Immersun, etc.). I have installed Solar iBoosts at both my dad's house and at mine. In the summer months (April to September) we both get ALL our hot water free from the Sun. My unit has just totalled 3.5 MWhr over the 5 years it has been fitted, dad's has topped 4.5MWhr in total. That's over 8000 kWhr (units) of electricity saved and, at a cost of 15p/unit, about £1200 worth of electricity saved.
Now I concede that gas is cheaper at about 5p/kWhr, but when you take into consideration the efficiency of the boiler to convert gas to heat, the losses through the transmission system (pipe heat emissions), I estimate that it takes about twice as many 'units' using a gas based indirect water heating system to direct electrical heating of that same water, thus the true monetary saving over those 5 years is about £800 in hard cash terms. To put it into perspective, that's the £500 initial outlay recouped after about 3 years.
That sounds not only a great business proposition to me, that's also 8,000 units of energy that didn't have to be generated by burning fossil fuels.

OP, I highly recommend a solar electricity diverter. Leave the 3kW element installed. As previously stated it will enable you to use more of your self generated electricity at home, and the 3kW standard elements are widely available and most probably much cheaper than the 1kW option.

MM

 

[JohnD]

. My unit has just totalled 3.5 MWhr over the 5 years it has been fitted, dad's has topped 4.5MWhr in total.

And is that what your metered electricity usage has dropped by? I bet not.

Is summer, when my boiler runs only to heat the HW cylinder, average daily use is about 0.75 cu.m/day.
Which is about 8kWh.
I currently pay 3.122p per kWh
so about 25p a day for the gas to heat the HW
I must have a full cylinder first thing in the morning, and in the evening. Immersun will not heat it overnight.

Lets suppose we have 6 months of sunny weather, though not all days are sunny even in summer. Let's suppose that in summer, an immersun could halve the amount of gas I use for the HW.

That would save me about 12.5p/day x 183 days = £23 a year.

And the device costs about £230 (plus fitting)

So after 10 years I would not have made a profit, but would have covered the purchase price. I would be out of pocket for ten years. After that I would make a return of £23 a year for as long as the thing worked.

Maybe an Immersun lasts 10 years, maybe it doesn't. They don't seem to have a repair service. Once worn out it is worthless. Let's assume it depreciates to nil over ten years.

If I had put my £230 in a savings account, I would break even on the first day. I would not ever be out of pocket. If I had invested it in shares of, say, National Grid, ten years ago, my £230 would have grown to £326 and i would also be getting annual dividends of (now) £17.95, so I would have done much better.

As an investment, an Immersun is a non-starter.

 

[JohnD]

Incidentally, my solar generation has been 14,430kWh between 31/12/14 and 31/12/18

so about 3600 p.a.

so calculating 5-years to compare with yours would be about 18,000 kWh

It will vary by size, location and orientation

Presumably your array is twice the size of mine.

The last 12 months have been below average, at 3,286

 

[MeldrewsMate]

And is that what your metered electricity usage has dropped by? I bet not.

Well no JohnD, I use electricity in preference to gas purely because it IS free from the solar. Without the diverter I would use the cheaper option of gas, however I have just put a Solar iBoost into a 4 bed house presently heated by warm air: their water is entirely heated by electricity and they're not on economy 7. In their case it most definitely would come directly off their metered charges.

....so about 25p a day for the gas to heat the HW

At present prices, and I think we all know that prices are only going one way.

I must have a full cylinder first thing in the morning, and in the evening.

Your choice of course, though minor changes to your lifestyle can bring large improvements to your energy consumption. I deliberately set my 'gas' tankstat to 40C so that I use little or no gas first thing in the morning - 40C is hot enough for an 'adequate' shower. The sun will give me a full tank by midday in summer, and by avoiding baths after dark the tank is usually still over 55C by morning. BTW I have additional measures in place to guard against legionella, so this is perfectly practical for me.

Lets suppose we have 6 months of sunny weather, though not all days are sunny even in summer. Let's suppose that in summer, an immersun could halve the amount of gas I use for the HW.
That would save me about 12.5p/day x 183 days = £23 a year.
And the device costs about £230 (plus fitting)

If you insist on using up your hot water at night then it is clear that you won't have sufficient next morning, but you could easily increase your current 'saving' to £40 by avoiding waste and late night usage. Plus I find that the iBoost that I have will give a contribution all year around, and provide 90% of my hot water requirements from March to October (8 months).

So after 10 years I would not have made a profit, but would have covered the purchase price. I would be out of pocket for ten years. After that I would make a return of £23 a year for as long as the thing worked.

Did you forget about that warm inner feeling you get when you do your bit to save energy, saving a little for the next generation? Surely it can't all be about money? I suggest a payback, even for you, of just 5 years (with 5% fuel price inflation).

If I had put my £230 in a savings account, I would break even on the first day. I would not ever be out of pocket. If I had invested it in shares of, say, National Grid, ten years ago, my £230 would have grown to £326 and i would also be getting annual dividends of (now) £17.95, so I would have done much better.

And if you'd put that money into Polly Peck shares?
So did you put £230 into a savings account? From what I see, the return on savings for the last 10 years has been less than 1%, so that would be £2-30 per year return. Using your own figures from National Grid shares, the £23 saved by the diverter would outstrip the £18 from dividends, though dividends can be volatile or non-existent.

No JohnD, I remain a great supporter of the energy diverter, both on monetary and moral grounds.

 

[maltaron]

I use oil for heating, hot water and cooking. I have recently installed a solar diverter. We used to run the oil fired boiler on Sunday morning for hot water when the wife does all her baking and cooking. It's not switched on now as even on dull days we get a cylinder full of water at 55c from solar. I should also add that we get more cash from FIT than our electric bill, so electric cost is not counted. The evening boiler run for baths has also reduced as the cylinder is close to 55 from solar and the boiler cuts out at 60. Since installing the diverter and oil use has halved. (And that can be quite a saving depending on the Arabs for oil)

 

[phobe]

Thank you for all the comments and ideas, and apologies for the delay in acknowledging them. I have not been receiving notifications that there has been activity on my post (probably because of a recent change of email address)
On mature consideration I have decided to do nothing about my hot water heating after all.

My PV array is small (1.8Kw max), and because I got in early with installation now receives a generous FIT payment. I am on Economy 7 and so any fiddling about I do with diverting solar electricity only saves the low cost power.
All in all, with the disruption to floor and cupboard, and the plumping hassle I can see that the sensible thing to do is relax and go to the beach instead of trying to squeeze a few quid from whoever pays.
Thanks again.

 

[mrStat]

All in all, with the disruption to floor and cupboard, and the plumping hassle I can see that the sensible thing to do is relax and go to the beach instead of trying to squeeze a few quid from

Sounds like a solid plan to me. Although it’s pi$$ing down here, so I’ll pass on the beach thanks.