You could leave your existing immersion in place and have them mains connected. Buy a Willis heater (£40ish), replace the element with the one above. Connect between the cold and hot DHW connections on your cylinder.

@johnmo Interesting idea!

Unfortunately, it can only be used on vented cylinders, and the heating element thread is 2.1/4" BSP.  But worth a check. Thanks!

Why not get your local workshop make a suitable adapter the instructions say you can thread length up to 90mm, so plenty of room to have an adapter.

Don't get it made in stainless as galling may occur quite easily, get it made in brass.

Posted by: @johnmo

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Why not get your local workshop make a suitable adapter the instructions say you can thread length up to 90mm, so plenty of room to have an adapter.

Don't get it made in stainless as galling may occur quite easily, get it made in brass.

An adapter would work - but I would be hesitant to fix it up to an unvented system - from what I have read elsewhere, some Willis heaters state on them that they can't be used on unvented cylinders. I've seen some posters elsewhere that they have been unable to get an installer to fit a Willis heater to an unvented system. Interestingly though, I saw that one person installed it to the internal coil of a cylinder!

Possibly the easiest solution would be to get a programmable switch for choosing between two AC sources, but that means having to buy an invertor too.

Posted by: @graeme

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I would also appreciate any other thoughts on heating DHW from the sun.

Solar thermal panels are at least 80% efficient,
whereas the max. possible efficiency from a (single sided) silicon PV panel is 23%.

I have 30 vacuum tubes in my solar thermal collector, outlined in red below:

If you still want to go for electric immersion heater, then talk to TP Fay in Kirkby.

They really understand the background physics behind immersion heater elements, and can offer some unusual solutions.

Over a decade ago they supplied with a 1kW immersion heater which could operate as a directly-fed dump-load from a wind turbine.
Although the turbine generator was rated to charge a 24v battery, they correctly calculated that it could generate 50v when the battery became 'full'.
So I needed a heater element capable of running at 60v in order to provide a margin of safety.

Posted by: @transparent

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Solar thermal panels are at least 80% efficient,
whereas the max. possible efficiency from a (single sided) silicon PV panel is 23%.

[nice setup btw]

I know! I have three problems - [Having already used up all my main roof for conventional PV] (1) I now have limited roof space - I have space on (a) south facing roof for about 3 pv panels - shaded after 12 noon and (b) another south facing roof for about 3 PV panels - shaded until 12 noon. (2) Both these locations are not good for piping to the HW tank. (3) Dont have sufficient space to increase HW tank size to accommodate lower temperatures.

Thus PV with its lower efficiency - may have some advantages with its flexibility.

BTW - As a reminder. My existing DHW is currently heated by my primary PV's for 6 summer months and Gas for 6 winter months.

Thanks for the pointer to TP Fay in Kirkby. - Appreciated.

Graeme

Yes, I agree that cables from PV panels offer a flexibility which cannot be matched by the insulated pipework required for a solar-thermal array.

Over the past few years I've been having conversations with Councillors from my Local Planning Authority.
Those have elicited some interesting insights about what is or isn't addressed by the Planning Act.
For example:

Unless you're in a designated Conservation Area or the property is Listed, you don't require planning consent to install PV panels.

Those panels do not have to be placed on your main roof.
They can be on an arbor at the bottom of the garden, or a chicken shed.
But there are height restrictions which apply to any structures within 2.4m of your boundary.

Ground-mounted panels are permissible.

There don't appear to be any restrictions on PV panels which are held in place by frames or tubs which can be moved.
You can buy plastic 'tubs' precisely for that purpose... although they seem to be as expensive as the panel itself!

Bi-facial panels do not have to face the sun because both sides generate electricity.
Some farmers in the West Country are looking into using bi-facial panels vertically, where they would double up as livestock fencing.

The aluminium frame of a solar panel isn't that much different to the aluminium used to build a greenhouse.
Some of the greenhouse sections could reasonably be 'built' by bolting PV panels together.

Just a few thoughts... 😎 

Posted by: @transparent

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Just a few thoughts... 😎 

And good thoughts too! Thinking flexibly is important. My main roof is East/West. Which makes the PV's only 75% efficient as South facing. However, as I have double the usable roof space - I can achieve an output of 150% as a similar South/North facing house. Additionally, the input from the panels is flatter, with higher levels first in the morning and later in the evening.

The main difficulty, as I see it, is that we are limited by the DNO, as to how many panels we can connect up to the grid. So to be really flexible, you need to think of off-grid as well.

Cheers

Graeme

Posted by: @graeme

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we are limited by the DNO, as to how many panels we can connect up to the grid. So to be really flexible, you need to think of off-grid as well.

Indeed! We should be primarily considering the off-grid route.

The topic DIY solar upgrade - Considering adding more panels is actively exploring this route.

Two of the respondents there are been upgraded to 3-phase supplies by their DNOs, but the way in which it's subsequently been implemented within the home by the professional electrician has demonstrated that they haven't understood the fundamental basics of how 3-phase is intended to resolve the problems. Start reading at this point in that topic if you want to see how phase-imbalances can cause outages.

It's not the DNOs who are 'limiting' the deployment of grid-tied solar generation by policy, but the physics of what happens to the grid when we do so. The vast majority of UK housing stock is supplied by single-phase Feeds from the local substation. That's not the case elsewhere. Germany is rolling out 3-phase domestic supplies for good reason.

I have a partnership agreement with National Grid, which allows me access to their data and network maps.
That allows me to gather information on what's happening now...
... and what we should do in the immediate future.

Local battery storage within the home (or school, or farm) is a strategy which mitigates most the present energy problems.

Posted by: @transparent

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Indeed! We should be primarily considering the off-grid route.

[Then]...

Local battery storage within the home (or school, or farm) is a strategy which mitigates most the present energy problems.

Whilst I agree with the sentiment, I am not sure how realistic it is for most folk to be off-grid? In June, I exported 755kwh but last December I imported 287kwh.

@transparent - As you work with National Grid, you may help me with my understanding. As I understand it the DNO limits the size of PV installations (in this case on single phase) to prevent an overload from your PV to the Grid. Also, as a consumer, you can limit overloading from your PV to your invertor through clipping.

The DNO's interest is the integrity of the Grid, not your internal system.

Is there not some general way of clipping or even throttling power to the Grid. I don't need any higher yields in June - but I could do with a better yield in the winter months. In particular, a way that would satisfy the DNO and permit you to add more PVs to your system? [That is without going three-phase, which will cost in excess of £2K

Cheers

Graeme

Posted by: @graeme

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I am not sure how realistic it is for most folk to be off-grid?

Realistic in terms of price?
Or because of practical arrangements to have a storage battery installed?

The financial viability depends on what you're comparing with.

I've attended a number of regional briefings by National Grid companies, and I follow the requirements made of them by Ofgem (RIIO-ED2 Agreements etc).
They have a roadmap which charts the way forward for infrastructure upgrades.
Here's a slide from a presentation 11 months ago:

That slide refers only to the national Transmission Grid, operating at 400kv and 275kv.
How much do you think it's going to cost to increase grid capacity to these levels over the next decade?

That will have to be footed by rises in consumers' bills.

There are similar levels of increased capacity to be implemented on the regional Distribution Grid (132kV and below)
That will be paid for by increases in Daily Standing Charges as well as consumption bills.

These are levels of expenditure in excess of the HS2 rail project... which was curtailed because the UK couldn't afford it.

It would be lot cheaper to subsidise the installation of in-home batteries...
... starting with social-housing tenants, households in energy poverty and those with prepayment meters.

Since those households tend not to have access to Time-of-Use Tariffs, they have no incentive to spread their electricity demand.
Consequently they contribute greatly to the 'early evening peak':

National Grid are required to ensure that there is always enough power, so the infrastructure is designed to carry a level greater than the peak.

Having too much demand is not an option.
It would act as a drain on the 'rotary generation' sites, and the 50Hz frequency would drop.

Contrarywise, having excess supply isn't regarded as a problem.
The DNOs can make 'Offers to Connect' to thousands of potential generation companies, far in excess of what the infrastructure can support:

As a result, on days that are particularly windy or sunny, an Active Network Management mechanism kicks in, resulting in generation sites being removed from the grid, or their output curtailed. I think that's what you're referring to as "clipping or throttling power to the Grid".

An ANM plot for generation in a location where there are existing wind turbines looks like this.

Wind output is highest around the two equinoxes.

Instead of discarding that electricity, it could be usefully stored in home-batteries.
Obviously those batteries need to be close to the nodes where excess generation is going to occur.
But the data already exists to achieve such a solution.

What's lacking is the political will.