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.

 

[suntrap]

Yes - you could have discovered this by typing it into the search box at the top of the page. And "not cheap" is an understatement.

 

[echase]

I can't bring myself to read all 35 pages

Not cheap but very effective.

I sympathise, but it shows the popularity of the topic (congrats to Paul for starting it) and the excellent solutions being offered all of which are much cheaper, but many work as well.

 

[scoobiedoo]

My Intelligent Immersion unit from echase is working fine easy to build and install, also a good price. :santa3:

 

[suntrap]

How much, and does it have a mains filter? Oh, and can it cope with the PV being on the same consumer unit as the rest of the house, i.e no way to measure house current directly without threading several wires through the current transformer?

 

[scoobiedoo]

You will have to speak to echase for any Technical advice on this unit.

 

[suntrap]

OK then, what's the price? You're stating publicly that it's "good" so it's only right that you tell us what it is. The point about a filter is important: things like EMMA may be overpriced and overspecified for this application, but they comply with regulations regarding the electromagnetic interference they generate, a problem which may not be obvious to users of alternative systems and which has caused misunderstandings on this thread (e.g. a snubber network is not the same as an EMI filter).

 

[scoobiedoo]

You will have to speak to echase for the price on this unit.

 

[suntrap]

Is there a rule against punting stuff on this forum then? Or worries about infringing patents? Why so cloak and dagger?

 

[sharpener]

Sorry if this has been answered before, has anyone found a true power sensor at a reasonable price? I want to measure the actual power exported to the grid and use this to control a Crydom controller (as others have done). Hopefully this approach will be more accurate than deriving the small difference between two comparatively large currents, and also maybe cheaper.

If there isn't a commercial solution for <£100 then I will try a current transformer/Hall effect current sensor and feed the output of this together with a stepped down version of the supply voltage into an Analog Devices analogue multiplier.

This when averaged should give me true rms power (with sign!) which I can then use to drive the Crydom unit, and also a panel meter giving me an instantaneous import/export display.

Anyone out there tried any or all of this and can recommend components etc for it?

TIA

 

[suntrap]

You would be wise to read the openenergymonitor.org forums about this. People have spent a lot of time on it, and found gotchas like phase shifts in transformers for measuring voltage causing inaccuracies in the calculation of true power.

 

[pauldreed]

OK then, what's the price? You're stating publicly that it's "good" so it's only right that you tell us what it is. The point about a filter is important: things like EMMA may be overpriced and overspecified for this application, but they comply with regulations regarding the electromagnetic interference they generate, a problem which may not be obvious to users of alternative systems and which has caused misunderstandings on this thread (e.g. a snubber network is not the same as an EMI filter).

...I find it quite remarkable that folks are prepared to buy and fit unknown electrical devices to their home from strangers, and know so little about them...

 

[sharpener]

You would be wise to read the openenergymonitor.org forums about this.

Have tried, but it repeatedly and consistently crashes my browser (plain vanilla IE7).

People have spent a lot of time on it, and found gotchas like phase shifts in transformers for measuring voltage causing inaccuracies in the calculation of true power.

Am alive to that one, may well use a resistive or capacitative voltage divider instead. Have made another little device which uses a capacitor dropper in the power supply too, for low dissipation. Not too worried about using mains neutral as the 0V DC rail, it's all going in a steel box anyway.

The CT I propose to use (Magnatec SCT 0400-050) has 1% linearity from 5 to 65A and a max phase errror of 2 deg, do you think that is suffiently precise?

I do not plan to be too greedy, it will be fine if 90% of the output goes into the immersion heater and I end up exporting 10%, this will give me simple proportional control with no appreciable lag and no long-term drift.

 

[suntrap]

Download a better browser - there are far more important reasons for it than being able to read those forums.

I was actually talking about the voltage transformer. I do recommend you do make the effort to look at those forums because it may save you a lot of wheel-reinventing. I would probably build something like you're proposing as I don't have the PV on a separate CU so can't measure house current directly. That is, unless I went down the digital route. But as the saving is so small (of the order of £50 a year if you're on mains gas?) I've shelved the project for the time being.

 

[inie meanie]

But as the saving is so small (of the order of £50 a year if you're on mains gas?) I've shelved the project for the time being.

Just a quick comment I checked my gas consumption over a month with no heating and I reckon I will save about £150 per year. I guess I need the kids to get out of the shower a bit quicker

 

[pauldreed]

Just a quick comment I checked my gas consumption over a month with no heating and I reckon I will save about £150 per year. I guess I need the kids to get out of the shower a bit quicker

...Just lower the water temp, and the shower times will get shorter!