Immersion Heater - PV electricity

[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!