Immersion heater regulator

TechyTim said:

As explained in other posts on the main Solar PV thread, although cost of gas is usually 3p to 4p, the cost of heat to the hot water is much higher as the losses in pipework and boiler cycling are significant when heating hot water only.
From my days in Britsh Gas R&D, I estimate actual cost is closer to 7p with a 60% overall efficiency and annual saving in region of £50 to £100.
I am marketing the SolarHeat controller which doesn't try to vary the output but simply switches on the immersion when the output exceeds 2.5kW, and even allowing for a small amount of import can give worthwhile savings.

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I'd even suggest setting at 2kW for beginning to charge the hot water.

Running the immersion on electric for an hour might cost 36p (at 12p per kWh). Gas might cost 21p.

So running with 2kW from the solar and 1kW imported, puts the cost of an hour's hot water at 12p: still a big saving on 21p for gas.

Assuming a few household appliances ticking-over (e.g. fridge etc) and consuming 0.5kW of power, even having 1.5kW of the 2kW solar output going to the immersion and 1.5kW imported makes a cost of 18p for the imported power, which is still fractionally cheaper than gas once the heat losses of gas burning are considered.

It would broaden the market for the product to those with medium-sized arays, and still make a saving on heating the water.

FB. said:

I'd even suggest setting at 2kW for beginning to charge the hot water.

Running the immersion on electric for an hour might cost 36p (at 12p per kWh). Gas might cost 21p.

So running with 2kW from the solar and 1kW imported, puts the cost of an hour's hot water at 12p: still a big saving on 21p for gas.

Assuming a few household appliances ticking-over (e.g. fridge etc) and consuming 0.5kW of power, even having 1.5kW of the 2kW solar output going to the immersion and 1.5kW imported makes a cost of 18p for the imported power, which is still fractionally cheaper than gas once the heat losses of gas burning are considered.

It would broaden the market for the product to those with medium-sized arays, and still make a saving on heating the water.

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FB.
Your thinking is exactly in line with my original design, the controller can be configured to switch at 1.5kW for small systems and 2.5kW for larger ones. Next version will have a switch on the PCB for the installer to make this choice.
Tim.

Check out this thread: http://www.electriciansforums.net/...tml#post551986

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Quick summary: threshold based systems (relays) are a waste of money as they are not efficient.
Expected annual savings from a full proportional system: £ 28 in gas (very conservative, likely more), or £ 80 in electricity.
So yes, a proportional system is worth it, provided it is cheap (and cheaply installed)

bommels said:

Quick summary: threshold based systems (relays) are a waste of money as they are not efficient.
Expected annual savings from a full proportional system: £ 28 in gas (very conservative, likely more), or £ 80 in electricity.
So yes, a proportional system is worth it, provided it is cheap (and cheaply installed)

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Yes, the price must be right.
If we take my earlier example where 2kW of solar PV is used, along with 1kW of grid power, it's a saving of 9p per hour compared to gas.
If the hot water heats for an hour, once in the morning and once in the afternoon, most solar arrays will only be close to peak power in one part of the day (e.g. SE peaks mid-late morning and drops off in the afternoon, while SW has only a trickle in the mornings and peaks early afternoon).
So the device can probably only be used once per day.
And only about half of days would have reasonable sunshine.
So realistically we can save 9p per day, for 180 days of the year. £16 of savings.
If we're lucky, we might be able to save twice that: £32 per year of bill savings.

So, yes, a device needs to be cheap, or very-long-lived, to justify its purchase.

I don't trust much to be long-lived these days as there's always an incentive for companies to cut corners - and who would try to claim a new device thre years down the line?.
So I guess that cheap is better than high-price with a claim of long life which we have to trust.

links123 said:

The price of immersion heater regulator is too high, it should come down.

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Agreed, and it probably will like all other new technology products.
I have the power reducer fitted now and the immersion is using about 1 to 1.2kw.
Its very easy to fit, just a live in and live out wire, that's it !
We'll probably get one of the automatic regulators fitted once they come down in price.

FB. said:

Yes, the price must be right.
If we take my earlier example where 2kW of solar PV is used, along with 1kW of grid power, it's a saving of 9p per hour compared to gas.
If the hot water heats for an hour, once in the morning and once in the afternoon, most solar arrays will only be close to peak power in one part of the day (e.g. SE peaks mid-late morning and drops off in the afternoon, while SW has only a trickle in the mornings and peaks early afternoon).
So the device can probably only be used once per day.
And only about half of days would have reasonable sunshine.
So realistically we can save 9p per day, for 180 days of the year. £16 of savings.
If we're lucky, we might be able to save twice that: £32 per year of bill savings.

So, yes, a device needs to be cheap, or very-long-lived, to justify its purchase.

I don't trust much to be long-lived these days as there's always an incentive for companies to cut corners - and who would try to claim a new device thre years down the line?.
So I guess that cheap is better than high-price with a claim of long life which we have to trust.

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FB,
I think you have understated the potential as an average 100 litre tank of water needs 9kWh to heat through 50 DegC. If you assume that most of a tank is used in the morning (probably heated with the existing system), this gives an opportunity to re-heat the tank during the day with PV, giving a potential saving on your figures of 27p.
So for 180 days a year that is a saving of at least £48.
If not reheated with PV, the existing system kicks in at the end of the day to give hot water for evening use.

My SolarHeat controller is professionally built and simple to install with a relay warranted for over 100,000 operations which is probably 10 years or more and gives a payback within 5 years at £50/year.

A proportional controller would easily double these savings but at what cost? The only ones I have seen which are avaialble on the market (ignoring e-bay kits) are £800 or so which pushes the payback to at least 8 years. They are also more complicated to install and usually require an electronic meter to monitor the import/export.

Tim.

TechyTim said:

FB,

A proportional controller would easily double these savings but at what cost? The only ones I have seen which are avaialble on the market (ignoring e-bay kits) are £800 or so which pushes the payback to at least 8 years. They are also more complicated to install and usually require an electronic meter to monitor the import/export.

Tim.

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I am about to build a fully proportional system to a design by trader9 and the parts for it have/will come in at around £80.

Mind I have the ability to make/fit it myself, and many do not.

I think this has been mentioned before on another thread but this is a cheaper device (£30) that uses a light sensor to switch on the immersion.
A few people have bought them and have left positive comments regarding them on the sellers feedback ...
IMMERSION WATER HEATER CONTROLLER TO USE SURPLUS SOLAR PV POWER | eBay

Due to cost of parts, maunfacturing, CE approval, I think you'll get it will be a while before you get better than this:
fully proportional control, ce approved: £395
Solar PV heating switch

Worcester said:

Due to cost of parts, maunfacturing, CE approval, I think you'll get it will be a while before you get better than this:
fully proportional control, ce approved: £395
Solar PV heating switch

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This actually sounds good, except for this part:
"Our Solar PV heating switch patiently waits for these consuming units to reduce consumption below generated power, and switches all available surplus power to the load or loads."
If I read this correctly, you have to decide what is more important/economic - setting your washing machine/dishwasher etc to come on during the day (as usually advised when having pv fitted) and accepting that only a limited amount of generation will end up going to the immersion. Or don't optimise the household use in favour of the immersion. Surely this still only makes sense if you use electric to heat your water anyway?

Worcester said:

Due to cost of parts, maunfacturing, CE approval, I think you'll get it will be a while before you get better than this:
fully proportional control, ce approved: £395
Solar PV heating switch

Click to expand...

Way too expensive and their claim it will pay for itself in 2 years is well out.
I would have thought it would closer to 10 years at that price.

Worcester said:

Due to cost of parts, maunfacturing, CE approval, I think you'll get it will be a while before you get better than this:
fully proportional control, ce approved: £395
Solar PV heating switch

Click to expand...

This unit has a number of issues:
1. From what I can see the flying lead to the CT is not very robust (as those with earphones will tell you, the connectors are very fragile);
2. It relies on being able to sense the whole house use with the CT - this is impossible with many consumer units as the clamp has to be fitted between the PV connection and the main feed and there is no room;
3. The unit seems to be hand assembled from "breadboard" circuits giving potential reliability problems with soldered joints;
4. The cost of £395 seems very high for an on-off controller.

But then as a competitor, I would say that wouldn't I!

Tim.

If my math below is wrong, please point it out

@TechyTim
1) The CT lead is fine, we've used one of those CT's for years, it doesn't get moved around like an earphone.
2) It is possible, you only need to monitor the main incoming lead before the CU and before the PV, so it doesn't matter wether the PV is wired via henley blocks or into the CU, it monitors that actual incoming / export with a single CT (just like CT meters do) - never found a place yet where there isn't room to put a CT on the incoming
3) Time will tell
4) Yes Tim, however, this isn't an 'on/off' contrioller it's proportional, your isn't -

From your site, "When the sun is shining strongly and the power generated by the PV panels exceeds 1.5kW or 2.5kW (depending on model), the feed to the Immersion Heater will be switched on at the consumer unit." i.e. it takes no account of base load, or other units that may be consuming power

Just so Tim doesn't get accused of selling on the forum, I'll post the link to his product .:Energyfactor UK:. - Energy consultancy

"A simple low cost controller which switches on the immersion heater when the sun is shining and your PV panels have sufficient output to give low cost hot water"

That's the point - It's horses for courses and pays ya choice.

If you want a controller that specifically monitors wether power that would be exported is available and you want to proportionally control the output to that heater without changing the element and NOT to heat it when the base load is consuming all generated power, then its £400, if you want a switch based on what you are generating its Tim's £200 or other similar ebay models.

The real savings maths have to take into account trigger point, base load etc.

Taking four simple examples, and two scenarios:

1) Proportional control, with a 200W trigger point, dumping all load to heating elements
2) 1.5kW trigger from Tim, dumping to a 1.5kW heating element
2) 3kW trigger from Tim, dumping to a 3kW heating element
2) 1.5kW trigger from Tim, dumping to a 1kW heating element

Scenarios
A) No base load (never the real case)
B) 600W base load

With the 600W base load, examples 2 and 3 will of course mean that some electricity will actually be imported as the base load needs to be supplied, so that results in an import cost, hence example 4, effectively allows for a 500W base load.

Best 'saving' is from a proportional control with no base load, next best is using a 1.5kW trigger with a 1.5kW load with no base load on a 4Kwp system.

As far as ROI is concerned, the MOST money will be saved by the proportional control, and the key thing is that both have an payback period in the region of 2 -3 years allowing for the install costs - ALL so long as you can use the excess power.

Figures attached are based on the 5 minute data from the real output of a system on 28th June (its as good as any day )

Worcester said:

If my math below is wrong, please point it out

@TechyTim
1) The CT lead is fine, we've used one of those CT's for years, it doesn't get moved around like an earphone.
2) It is possible, you only need to monitor the main incoming lead before the CU and before the PV, so it doesn't matter wether the PV is wired via henley blocks or into the CU, it monitors that actual incoming / export with a single CT (just like CT meters do) - never found a place yet where there isn't room to put a CT on the incoming
3) Time will tell
4) Yes Tim, however, this isn't an 'on/off' contrioller it's proportional, your isn't -

From your site, "When the sun is shining strongly and the power generated by the PV panels exceeds 1.5kW or 2.5kW (depending on model), the feed to the Immersion Heater will be switched on at the consumer unit." i.e. it takes no account of base load, or other units that may be consuming power

Just so Tim doesn't get accused of selling on the forum, I'll post the link to his product .:Energyfactor UK:. - Energy consultancy

"A simple low cost controller which switches on the immersion heater when the sun is shining and your PV panels have sufficient output to give low cost hot water"

That's the point - It's horses for courses and pays ya choice.

If you want a controller that specifically monitors wether power that would be exported is available and you want to proportionally control the output to that heater without changing the element and NOT to heat it when the base load is consuming all generated power, then its £400, if you want a switch based on what you are generating its Tim's £200 or other similar ebay models.

The real savings maths have to take into account trigger point, base load etc.

Taking four simple examples, and two scenarios:

1) Proportional control, with a 200W trigger point, dumping all load to heating elements
2) 1.5kW trigger from Tim, dumping to a 1.5kW heating element
2) 3kW trigger from Tim, dumping to a 3kW heating element
2) 1.5kW trigger from Tim, dumping to a 1kW heating element

Scenarios
A) No base load (never the real case)
B) 600W base load

With the 600W base load, examples 2 and 3 will of course mean that some electricity will actually be imported as the base load needs to be supplied, so that results in an import cost, hence example 4, effectively allows for a 500W base load.

Best 'saving' is from a proportional control with no base load, next best is using a 1.5kW trigger with a 1.5kW load with no base load on a 4Kwp system.

As far as ROI is concerned, the MOST money will be saved by the proportional control, and the key thing is that both have an payback period in the region of 2 -3 years allowing for the install costs - ALL so long as you can use the excess power.

Figures attached are based on the 5 minute data from the real output of a system on 28th June (its as good as any day )

View attachment 13422View attachment 13423View attachment 13424

Click to expand...

Impressive! Well im sold.

How does it connect exactly? One CT lead and you have to fit both the pv feed and main live incomer in the same coil?

Then for the box. Does it go in line with the existing immersion feed? If so how does it override if, for instance, there is no sun and the water needs to draw from grid to heat up?

Thanks

Dan

The CT goes on the main incomer and the logic maths tries to reduce the current flow through it to zero, by measuring also the voltage and phase angle, and using solid state relays on phase angle and / or burst fire control , it can do this incredibly quickly, so you don't import

So it doesn't matter if the PV is wired in via Henley blocks or into the CU just make sure the CT is 'upstream' of it all.

Yes the Immersion feed does go through the box, (it needs to measuer voltage and phase angle, so it may as well take it from the Immersion feed) so you may want to install a 'bypass' switch, or wire it in parrallel along side existing timer and boost controls, and let it act as a bypass/booster to those. So if you're worried you wont have hot water in the evening put the timer controls (either boiler or immersion as per your choice of paid for fuel) on for late afternoon, and if it's not up to temperature, the timer will kick in.

as Sergei would say, "simples"