Immersion Heater - PV electricity

[JimJo]

Hi hobbo, I would PM pmcalli. He's been extreamly helpfull to me. I'm an electrician, not an electronics technition. But with his help Ive just started building his circuit. And he answers to his emails. Good luck

Hi Hobbo
I've just found and joined this forum because your requirements for a system to switch an immerssion heater on around noon to use generated current instead of exporting it is just the system I want - I am also willing to purchase such a system as it should have a reasonably quick payback. Is anyone out there that can design, manufacture and sell such a system - if so let us Know?

 

[flyman]

while you're waiting for the ultimate, with the summer months coming this may be a cheap solution that those with a small DIY ability might consider. Water Heating with Surplus Solar PV - Solar

At under 32 quid, payback should be quick.

 

[echase]

At under 32 quid, payback should be quick.

Not at all. If you use it with a 3kW element you may well import a lot to heat your water. And with a 1kW element there is the added cost of element plus not a lot of actual PV generation transferred to that element. See all the posts on page 51. These switched type systems, particularly ones that do nto actually measure the amount of house export, have an unproven benefit and many of us think they won’t pay back any time soon, if at all. They are just creating an illusion of diverting enough PV to the immersion to be saleable. You need one that tracks export and puts variable power into the immersion.

 

[flyman]

Not at all. If you use it with a 3kW element you may well import a lot to heat your water. And with a 1kW element there is the added cost of element plus not a lot of actual PV generation transferred to that element. See all the posts on page 51. These switched type systems, particularly ones that do nto actually measure the amount of house export, have an unproven benefit and many of us think they won’t pay back any time soon, if at all. They are just creating an illusion of diverting enough PV to the immersion to be saleable. You need one that tracks export and puts variable power into the immersion.

Echase,
Possibly so but there seem to be a number of new enquiries from people with limited skills wanting something that doesn't yet exist in a commercial form. Whilst some may be competent in producing something that meets the requirement others might be looking for something that is available now even if just an an interim solution.
Naturally circumstances vary for each case dependant on size of system and usual source of water heating. Personally with the small system I have (1.5kwh) and being out most of the day I'm happy to explore the options of utilising a low power immersion to offset the cost of water heating with the gas boiler. I have no problem identifying the yield of my particular installation as I am familiar with PIC, PICAXE and Arduino microprocessors. I've been datalogging on an Arduino with both CT's and pulse counting directly from my Elster A100C export meter and switching loads remotely for months. During the last few days the excess yield over 1kwh has been prolonged or consumption to the point where I'll start to look at the economics of a new immersion.

I appreciate that not everyone has the time or inclination to look at a DIY solution but there are several option available or due to be available. Payback time will depend an many factors and in many cases will be impossible to calculate. I wonder sometimes if the desire to wring out every watt available isn't overtaken by the financial benefit.

 

[echase]

I wonder sometimes if the desire to wring out every watt available isn't overtaken by the financial benefit.

I accept the principle that paying for a Ford rather than a Rolls Royce is fine if you are prepared to accept some performance compromise in return for a lower price. But what you don’t want is a Ford that never actually moves forwards, but only goes in reverse. Some of these stepped controllers, particularly if not set up properly (and who has the patience or necessary test equipment to do this?) could actually use more grid electricity than the amount of export they will save.

A well designed controller will deliver the right amount to the immersion with no setup or special knowledge needed by the user. With that £32 one you have to choose a PV generation level to set it at. Those of a worrying disposition may be constantly wondering whether they go it right as it’s very subjective and likely to need altering summer to winter or indeed several times a year. Unlike altering your house thermostat, where heat can be sensed by one’s body, electricity is not something easy to measure/visualize so it’s easy to make a mistake in the setting.

 

[legoman]

Hi,
New to this forum. Got an immersion question.. anyone know if there is a problem fitting an incoloy 1kw immersion to a stainless steel cylinder. I have been told that if the 1kw immersion has a copper stat pocket there may be a reaction with the stainless steel.Has any one done this/had problems? I have an old copper cylinder now and would like to renew it.
Stainless cylinders are cheaper than copper ones and also have a 10 year warranty. I would like to fit a 27inch immersion in the top of my new cylinder, also an 11inch one in the bottom through the 1/2 in drain.
I cannot find either with a incoloy stat pocket.

 

[markthorpe999]

Didn't know that by trying to help people, I would be told I need to know the laws of physics. Quite a rude and kurt response to a new member?.

 

[pauldreed]

Didn't know that by trying to help people, I would be told I need to know the laws of physics. Quite a rude and kurt response to a new member?.

I don't think that the response you got from pmcalli was rude and kurt?
He gave you an accurate and comprehensive reply, and yes, the rules of physics need to be understood otherwise you could be wasting money on a heating element that would not fulfil your goal.

 

[David Bowen]

Hey guys,

I've taken a look at how much money I could save using solar PV to power my immersion heater:

How much water can I heat with spare Solar Power?

Notably, I've also run simulations for these device types:

* Switch that triggers based on solar output
* Switch that triggers when there's sufficient spare power
* Controller which ramps up the immersion in proportion to the spare power

 

[suntrap]

Very impressive article - well done.