Immersion heater enhancement

[Bob j]

Hi I'm new to solar pv system ownership and this forum but I'd like to pass on some info on a little control system that I've just built to control my immersion heater. I installed a Solar iBoost unit to use excess power to heat water but was torn between staying with the 11" element that was already installed and having a small amount of ready use hot water or installing a longer element and having more water of a lower temperature as background heating to save on gas heating.
In the end I fitted a dual element immersion heater with a manual switch over but this meant keeping an eye on the iBoost to see when it was time to switch over elements. I have now constructed an auto changeover system using a 20amp SPNO / SPNC relay. The relay is switched by the short element thermostat so when the first 16" of water reaches temperature the thermostat breaks the relay feed so the relay drops out switching off the 16" element and switching on the 30" element. I've been testing it today and it works really well. The parts cost about £20. I'm amazed that something like this isn't available commercially but hey for £20 who cares

[russ]

Only in the UK where the crazy FIT pays you for what you use does this piece of junk make sense.

[Bob j]

Only in the UK where the crazy FIT pays you for what you use does this piece of junk make sense.

So you think it's a piece of junk eh Russ? I wasn't expecting hostility this early on

[russ]

So you think it's a piece of junk eh Russ? I wasn't expecting hostility this early on

No hostility - it is only in rare situations that electric resistance heating makes sense - in the UK where you get paid for the production you use yourself (I believe) is one of those.

If this was an attempt at advertising the junk - don't do others the dis-service

[Bob j]

The Feed in Tariff in the U.K. has all but disappeared so it's no longer a good reason in itself to install a PV system; it just helps to reduce the payback time a little. The iBoost only switches on the immersion heater when you start to export electricity so it uses electricity we would have been paid about six cents a unit for. We try to make the best use of our solar generated electricity by running high consumption appliances during the day and let the iBoost eat up the surplus when it can by auto sensing the import/export situation. I agree that heating water with an electric element is inefficient but at six cents a unit (kwh) it's cheaper (in the UK) and cleaner than gas. The switch over relay means that we can still get nice hot water quickly without the iBoost switching off prematurely. Which if you think about it makes a lot of sense.

I'm not trying to advertise anything, I am freely sharing information which is what I thought this type of forum was all about. If you think calling someone's honest efforts junk isn't hostile Russ I don't know what is.

[pleppik]

The Feed in Tariff in the U.K. has all but disappeared so it's no longer a good reason in itself to install a PV system; it just helps to reduce the payback time a little. The iBoost only switches on the immersion heater when you start to export electricity so it uses electricity we would have been paid about six cents a unit for. We try to make the best use of our solar generated electricity by running high consumption appliances during the day and let the iBoost eat up the surplus when it can by auto sensing the import/export situation.

I think the term for what you're trying to do here is "opportunity load," and when you get paid a lower rate for selling power to the grid than it would cost to buy at a later time, it makes a lot of sense to look for opportunity loads to make local use of your excess generation.

There's been some discussion of this on the forum, but mostly in the context of off-grid, where storage is very expensive. However, if net metering gets replaced by something more like a wholesale rate to sell power to the grid, I think you'll see a lot more interest.

The great thing about storing excess power as heat is that it's cheap and easy to do (assuming you were going to use the heat anyway). On the other hand, electric resistance heating is not nearly as efficient as alternatives like heat pumps, and PV to resistance heat is much more expensive than straight up solar thermal.

On the other other hand, there are lots of places where people still use resistance heating for domestic hot water, and preheating a big tank of hot water is one of the simplest and most flexible opportunity loads you can imagine. So I see nothing wrong with what you're doing.

[Bob j]

The great thing about storing excess power as heat is that it's cheap and easy to do (assuming you were going to use the heat anyway). On the other hand, electric resistance heating is not nearly as efficient as alternatives like heat pumps, and PV to resistance heat is much more expensive than straight up solar thermal.

On the other other hand, there are lots of places where people still use resistance heating for domestic hot water, and preheating a big tank of hot water is one of the simplest and most flexible opportunity loads you can imagine. So I see nothing wrong with what you're doing.

I take your point entirely about heat pumps vs resistance heating. I've worked on two way compression heat exchange and vapour compression distillation systems in the past. I'm going to be taking a look at heat pumps and solar thermal over the next couple of years.

[kr15m4tth3ws]

solar iboost / optimmersion install working alongside combi ? can it be done?

hi all,

I've got a 4kw system installed and am looking into using either iboost / optimmersion to heat a tank of hot water whilst im in work all day and my system is exporting to the grid.

what i would like to know has anyone installed a immersion tank along side a combi boiler ?

my combi bolier is quite new and during the winter months where im not generating as much would like to keep the efficiency of a combi but during summer would like the option to be able to swap to a immersion tank to enable me to use up the excessive energy.

has anyone attempted to install anything like this ?

cheers

[russ]

hi all,

I've got a 4kw system installed and am looking into using either iboost / optimmersion to heat a tank of hot water whilst im in work all day and my system is exporting to the grid.

What is the advantage to you - this is in the UK