Immersion Heater - PV electricity

[inie meanie]

Thanks for the replys. My first problem with any of the systems that have been developed here is distance. My mains comes into the middle of my bungalow where the main consumer unit is. The inverter is in an outbuilding som 30 meters away. The output from a clamp would be lost or degraded over that distance and therefore make comparisons more difficult. I guess the clamp output could be amplified and then re calibrated before it entered a comparitor but my days of electronic engineering where long past, OC71 transisters were replacing valves when I started.

Ok simple solution . Use a current clamp that gives you a milli amp output say 4 to 20 is industry standard. Current flowing in a circuit is the same therfore distance makes no difference, if you have 6 ma at the coil you will have 6 ma at your measurement. You can get these coils from LEM.

 

[inie meanie]

But it will be red if you are exporting 3kW and also red if you are exporting 3W, so how will you know whether there is enough residual power to run an immersion heater?

Yes, clip on current meters can determine which was the electricity is flowing, by comparing the voltage phase of the mains cycle with the current, at the same time as telling you how much current is flowing.

Good luck fella!!

Paul. I think that sums it up very well :- )

 

[inie meanie]

Hi all, have been reading all your posts, and very interesting, but (to me) far to technical,
Whilst I have an understanding of mains electrics, electronics are magic.
Maybe one of you learned gents can tell me if this would work:
Very basic but use something like Owl, Efergy meter with alarm, in place of buzzer fix a relay connected to whatever immersion /mains socket, set alarm at desired level, and hey presto when sun shines turns on relay, free electric.
Would need something to stop relay chatter.
Thoughts please....

Yes in a very crude way that would work. BUT! and it is a big but! You have no way of compensating for load on the house. So you maybe importing already. Ie the washing machine may be on . the oven running? then you just switch on 3 kw of load straight off the grid.

 

[pauldreed]

Thanks for the replys. My first problem with any of the systems that have been developed here is distance. My mains comes into the middle of my bungalow where the main consumer unit is. The inverter is in an outbuilding som 30 meters away. The output from a clamp would be lost or degraded over that distance and therefore make comparisons more difficult. I guess the clamp output could be amplified and then re calibrated before it entered a comparitor but my days of electronic engineering where long past, OC71 transisters were replacing valves when I started.

OC71?
You've just taken me back over 40 years when I started in electronic engineering!
But don't let the years hold you back - I changed career in 1979 and until the past 12 months never touched electronics. It's a steep learning curve, but the basics will hold you in good stead.
At some stage, the inverter must feed back to your consumer unit, and that's where the clamp should be fitted.
If not, you might consider using 2 of these. Which are microprocessors with RF capability, so they talk to each other, and the software provided by this site would deliver your goal.

 

[suntrap]

Have a look at openenergymonitor.org - there is a lot there including wireless sensors. Of course if the load in the outbuilding isn't significant, you can just measure the current at the house end.

 

[Sparqui]

But it will be red if you are exporting 3kW and also red if you are exporting 3W, so how will you know whether there is enough residual power to run an immersion heater?

Yes, clip on current meters can determine which was the electricity is flowing, by comparing the voltage phase of the mains cycle with the current, at the same time as telling you how much current is flowing.

Good luck fella!!

Thanks for your input.

As for your 3W v. 3kw point, my scheme will use the flash rate for feed-back. If the non-controlled house load goes up, or a cloud passes by, the led will begin to flash and the immersion heater loading will be reduced until equilibrium is restored. I've actually proved this to myself manually by selectively changing loading within the house, even down to varying load on 500W of dimmable lighting.

Interesting, I thought that the clip-on monitors only acted like a single turn transformer, I don't see how voltage phase is determined nor how it shows direction (I'm a now-redundant RF engineer working on this as a challenge, so I don't understand DC, such as mains! )

 

[suntrap]

Current transformers are indeed unable to give you current direction, but the point is you look at the voltage as well (invasive). That's why plug-in consumption meters are theoretically more accurate than the Owl (helped by actually being able to measure the RMS voltage as well as the phase).

Unfortunately the flash rate isn't much use because you never want it to be in that mode - you always want to prevent any power coming from the grid, especially if you're trading the immersion heater off against gas which costs so much less.

I've actually come to the conclusion that although it's very satisfying to heat your water from PV, it doesn't save you that much money and it's quite an environmentally-unfriendly way of doing it if you normally use gas - the electricity should be used to offset power generation rather than domestic gas consumption. Running fridge-freezers continuously off it might (might!) be a better idea.

 

[Sparqui]

Current transformers are indeed unable to give you current direction, but the point is you look at the voltage as well (invasive). That's why plug-in consumption meters are theoretically more accurate than the Owl (helped by actually being able to measure the RMS voltage as well as the phase).

Unfortunately the flash rate isn't much use because you never want it to be in that mode - you always want to prevent any power coming from the grid, especially if you're trading the immersion heater off against gas which costs so much less.

I've actually come to the conclusion that although it's very satisfying to heat your water from PV, it doesn't save you that much money and it's quite an environmentally-unfriendly way of doing it if you normally use gas - the electricity should be used to offset power generation rather than domestic gas consumption. Running fridge-freezers continuously off it might (might!) be a better idea.

In the past few months, I have monitored my weekly usage of peak, off-peak electricity and gas. For two weeks I heated water by off-peak only (i.e no solar PV to distort metering), and for another two weeks by gas only. There was very little difference in cost which surprised me.
I agree that using electricity, however generated, during peak periods (day-time) is less environmentally desireable than using off-peak. On the crude assumtion that any power I can put into the hot water tank will offset mains derived power later and that EMMA claims a theoretical return of about 8% for this alone on an expenditure of well in excess of £1500, I'm happy for me to press ahead with my home made scheme which should be almost as effective for one tenth the cost, beside its a challenge for the grey cells.
As for the flash rate, every time it records a flash, the power dumped into the immersion heater will reduce, I can live with a long period between flashes as this represents a consumption of just 1Wh.

I'll get back with my results in a moth or sos time and crow or eat humble-pie as appropriate.

 

[lioncrunch]

Thanks Inie Meanie for reply,
I agree with your comments but I was thinking mainly during the day when at work, house uses about 400w during day set alarm for 1500w fix heater/ hot water to come on then, just a thought, but thanks anyway..

 

[bumcrack]

This is far to much thread to digest, and I appreciate the electronics guys will be looking for the satisfaction of designing thier own control, but for the average punter, I would look to use one of these, they are ~£100 + the cost of LEM current transducer, and mains switching devices...

CAREL

Its actually a parametric refrigeration controller, but they come with analogue and digital inputs, and 4 x volt free output contacts.

You can set them up to cascade elements on or off based on export, and add switching delays etc....they are a great bit of kit, I use them to stop biogas compressors becoming inhibited due to low ambient temperatures.

 

[Maurice Sauer]

Hi echase,
Having read the last 20 pages or so of this thread I am intersetd to learn more about your controller system. I have no particular wish to reinvent, nor do I have the specialist knowledge to do so, but could put together from kit or go ready built. Please provide further info on options and prices. I can't find a direct link to your e-mail address.
thanks
Mo

 

[Vollster]

Message for EChase - yes me too - I have a customer who is particularly interested in a system to supplement a PV system we fitted recently. Could you send me some details

 

[sharpener]

As for the flash rate, every time it records a flash, the power dumped into the immersion heater will reduce, I can live with a long period between flashes as this represents a consumption of just 1Wh.

I'll get back with my results in a moth or sos time and crow or eat humble-pie as appropriate.

I like the approach Sparqui, and would be interested to know how you have been getting on since this posting.

Also would appreciate hearing from echase as to availability of his system or designs therefor (am capable of building most things from circuit diagrams).

TIA

 

[echase]

Sorry my inbox was full. Please try a PM again.

 

[CBR600]

I can't bring myself to read all 35 pages to see if anyone has mentioned one of these but they do exactly what seems to be required;

Igloo Solar Energy PV & Thermal Panels & Heat Pumps Essex London Cambridgeshire kent hertfordshire sussex surrey berkshire south east south west & midlands

Not cheap but very effective.