Immersion Heater - PV electricity

[echase]

Hi Whip1971,

It is really not a proportional controller but it is a smart unit.
Juraj

How does it relate to www.totalpowershop.com which seems to be same thing at higher cost with better website?

Fundamentally though you have a problem in how to match the loads against the export. You can’t say rapidly turn on and off a washing machine to try to track the export as the machine will not like it. And a straight heating load like an immersion does not track export at all accurately with this system. Best bet could be three 1kW elements progressively switched in, but what hot water tank has room for 3 elements? And these three are a significant extra cost

You might get back £20 per year in saved gas/electricity so it is £150 capital mostly wasted as far as I can see.

 

[Trader9]

Look at the OpenEnergyMonitor forums - it seems at least for some meters you can use burst firing of complete cycles as they average over a whole watt-hour so will not charge you provided you take less than one watt-hour out of the mains before putting it back. No need to worry about filtering.

Hi Suntrap

Sorry to jump on your post but I have been using the OpenEnergyMonitor sketch with an Arduino to divert solar into my 3kW immersion heater since Dec 2011.

There are a number of ways to do this using the PWM output from the Arduino driving a LED which is heat shrunk together with a LDR which then drives a SSR-25 VA. Basically, by varying the LED brightness you can control the LDR resistance and thus the SSR. You can do this either proportionally as most people seem to want or in say 50W steps. Obviously its not as simple as that, but it can be done for little cost if you are prepared to put in the effort.

Pm me with your email address and I will send you all the basic detail you need to get started including the Arduino sketch for the proportional system. Almost no electronics only the sensor interface and LED/LDR components.

Regards, Trader9

 

[suntrap]

Thanks for the offer, and I'm impressed with your innovative way of making use of a cheap "potentiometer controlled" proportional controller, but if I do it I'll go down the burst firing route. My mains supply is good so it shouldn't make lamps flicker, and I won't need a filter. My PV is also not on a separate consumer unit so I need to measure power flow direction in a meter tail. I'm "eof" on that forum - you can see my thoughts on using a zero crossing detector and synthesised voltage waveform to get what I believe should be a very accurate power measurement.

 

[jbella]

How does it relate to www.totalpowershop.com which seems to be same thing at higher cost with better website?

Hi,

it is indeed exactly the same controller Home Energy Monitoring and Control System Solar Version with automatic operation function manufactured by Sailwider but sold for double price as on eBay Solarcontrol | eBay and supplied with two socket sensors instead of three as on eBay,

Fundamentally though you have a problem in how to match the loads against the export. You can’t say rapidly turn on and off a washing machine to try to track the export as the machine will not like it. And a straight heating load like an immersion does not track export at all accurately with this system.

I do not have yet immersion heater yet but following this thread to get ideas how to do it.

Best bet could be three 1kW elements progressively switched in, but what hot water tank has room for 3 elements? And these three are a significant extra cost

What about this: 27" Dual Element Dual Stat Immersion Heater - QVS Electrical Supplies | Electrical Wholesaler ?

You might get back £20 per year in saved gas/electricity so it is £150 capital mostly wasted as far as I can see.

You might be right but for me it is not all just about the money. I am considering the greenhouse gases impact too. Basically trying to do my small bit.

Juraj

 

[cryo]

Hi all I'm seriously considering using a system as described by Trader9 to run some background heating during the sunnier colder months March.April.Sept.Oct although this year such a system could have run up to today. A lot of people have Solar PV but the majority of modern and a fair number of older houses have Combi systems with no hot water tank which leads me to suggest a system using one or more oil filled radiators (resistive load) for background heating. Do you think this is feasible to assist the general household heating working on a proportional loading system with the heat source placed centrally in the house. I definitely feel a project coming on after reading this very long but interesting thread and looking through ebay for parts etc.

Ken.

 

[suntrap]

Best bet could be three 1kW elements progressively switched in

Even more best bet would be a 1kW and a 2kW element switched in a binary fashion, which would achieve the same result.

You might get back £20 per year in saved gas/electricity so it is £150 capital mostly wasted as far as I can see.

There have been some interesting thoughts that you might save a lot more than that if in the summer your gas use is low enough to be down into the range of the initial more expensive units which are there in lieu of a standing charge.

 

[suntrap]

You might be right but for me it is not all just about the money. I am considering the greenhouse gases impact too. Basically trying to do my small bit.

Unfortunately you might be doing the opposite - by using your generated electricity to displace relatively efficient use of a fossil fuel to heat water you are no longer using it to displace electricity possibly generated by less efficient means. But it's still a fun project!

 

[echase]

There have been some interesting thoughts that you might save a lot more than that if in the summer your gas use is low enough to be down into the range of the initial more expensive units which are there in lieu of a standing charge.

Partially true. My estimate that for a gas user a proportional controller saves £50 to £100.

A switched controller is minus £30 to plus £30. £20 was a guess within that range. The minus is because, if you set it up badly you import more than you save, especially with 3kW loads. For oil, LPG and peak rate electricity the figures are up to 4 times better.

 

[fredfred2]

Thanks to Juraj redirecting me to this forum page, where it appears my quest to find one and the same thing as everyone else is popular! Whoever makes these is going to get rich or get sued by the gov for breaking FIT rules... (no longer 50% feed in with this thing fitted).

Here's a pic of a unit I found on my travels, but sadly I don't know who makes it. From what I understand, it's a proportional device, where the power provided to a bog standard 3kW immersion heater tracks the solar PV panel's output precisely (minus what the house is using). The panels produce less than 2kW. There was no transformer between the box and the immersion. The immersion was a standard mains 3kW 240V thing.

This thing was fitted to a house that has a 2kW PV array back in Summer last year, and works well. That's all I know. Oh, and I'd like one.

I have found 10 different types out there on the internet, but this little unit looks like it ticks all the boxes for me, but I know little more.

Does anyone know who it's made by?

thanks,

fred

 

[Keith Walker]

Hi,

Details of Trader9's circuit and other peoples ideas can be found at Home

Cheers, Keith

 

[echase]

From my knowledge of Electricity and Electrical appliances an immersion heater has two components that huge amount of electricity so it reduces the efficiency.

What do you mean as not correct English? An immersion heater is 100% (or very close to it) efficient as almost every watt delivered goes to heating the water. Tiny losses in the connection terminals and wires plus heat losses through the cover could be taken off that. Say 99%.

 

[runthangs]

Hey guys,

I need some electronics advice. I have the cheap ebay 3800w dimmer triac circuit mentioned earlier (inkFrog) that "dims" the power supplied to my immersion heater, the dimming is controlled using an AC potentionmeter (model: wth118-1a).

I now need to programmatically control the potentiometer. Aside from getting an SSR and redoing the circuit, etc., I have explored using a servo motor controlled via USB to turn the pot, but have discovered that 5v/100ma from USB isn't strong enough for the motor to turn the knob (plus very inaccurate) - I want to avoid external power supplies etc. Is it possible to instead send a 5v current down a USB directly (via some conversion circuit of some sort) to one of the terminals of the potentiometer and thus vary the resistance (i'm looking for the simplest solution possible). I am happy with a binary "high power" and "low power", i.e. 5v and 0v from usb. This would allow me to at least step the potentiometer/dimmer circuit one level up when solar pv generation is high.

Thanks.

 

[thushar]

My electrician just installed the new Mark II version of the solar immersion switch from Intelligent Solar Immersion Switch - Use Surplus Solar PV Power to Heat Water and it's working brilliantly. It comes with a differential control, compare the house load and the pv production to turns on the immersion. This will make sure no power is imported from the grid even when a kettle is turned on when the immersion is on . a quality product at a very affordable price.

 

[Trader9]

Hi Runthangs

Have you considered an eight way 5V relay printed circuit board from Ebay for about £9.00. It has eight, 5V relays on which only take 70ma each. Also each relay could have a different resistance connected to its contacts so in effect you could have eight different levels on your dimmer. Also the contacts would give you isolation from the potential high voltage on your dimmer potentiometer which it would replace. How you would operate each relay I am not sure unless you use something like an Arduino.

Regards, Trader9.

 

[echase]

My electrician just installed the new Mark II version of the solar immersion switch from Intelligent Solar Immersion Switch - Use Surplus Solar PV Power to Heat Water and it's working brilliantly. It comes with a differential control, compare the house load and the pv production to turns on the immersion. This will make sure no power is imported from the grid even when a kettle is turned on when the immersion is on . a quality product at a very affordable price.

As the device measures grid export only what happens when the load is turned on? Say export was 3500W and set threshold is 3500W, so when load turns on export becomes only 500W. To stop it immediately turning the load off again it needs to know that the load consumes 3000W. Is there a control to set the load power?

To provide reasonably complete consumption of the spare power the switching needs to be frequent which must play havoc with the reliability of the element and relay. Never gets close to consumption of a proportional controller so their £100 pa claimed savings, especially on the Mark 1, is very unrealistic.

Their £49 power reducer (halves it) has 2 wires so is probably just a diode. Surely this is “illegal”. If it’s a triac set to phase control at 50% it’s also illegal as the EMI will be too large.