Immersion Heater - PV electricity

[inie meanie]

The owl on the house load reads about 10% high because it's conversion of the current transformer does not work accurately on non sine wave currents. The meter confirms that over the last three months I have only exported 5%.

Have a look at the AD637 Rms to dc converter. I have ordered a couple as I hope to buffer the house signal then compare the same way with opamp. I hope this will improve the acuracy and reduce any export. I will post as soon as they turn up. Christmas post and all that.

 

[bradburts]

I thought that the B Gas kit is already available.
Its only a relay switched from what I can understand, no phase control.

 

[pmcalli]

Have a look at the AD637 Rms to dc converter. I have ordered a couple as I hope to buffer the house signal then compare the same way with opamp. I hope this will improve the acuracy and reduce any export. I will post as soon as they turn up. Christmas post and all that.

Good luck I have used them in the past and they have limitations on crest factor and sensitivity. rms even if it is derived accurately is only an approximation. to get an accurate imitation of the meter you need to integrate the current over a cycle. interested to see your results when availble

 

[pmcalli]

I thought that the B Gas kit is already available.
Its only a relay switched from what I can understand, no phase control.

I haven't seen any offering yet only press statement about acquisitions and trials.

 

[bradburts]

May be wrong, and have lost the link, but check the company who supply the BG monitors.
They have a control product on their site as well. From memory it was <<£100.

 

[Sunnydaze]

Does anyone have a smart meter yet? I just wondered whether they do actually sense current direction. I can't find any model info / technical specs.

 

[sharpener]

Surely that is exactly what sharpener is proposing, by using an analogue multiplier to multiply the CT output with the voltage waveform?

Correct. The analogue multiplier will multiply the current and voltage waveforms correctly whatever they are. This is a better approach as it uses the actual voltage waveform, rather than a square wave as in synchronous rectification or a synthetic sine wave as the openenergymonitor people do, and so averaged over one cycle gives true instantaneous power.

Also the cost to me is zero because I still have a few AD532s from when I used to use them a lot in laser scanning systems. One of the difficult situations is when the immersion heater is drawing half power, as the current will change sign abruptly at the 90 deg point in each cycle when the triac fires. But with suitable scale factors I expect it to handle this OK as the bandwidth is several hundred kHz.

BTW thanks suntrap for the links to Home | OpenEnergyMonitor, which I am still exploring (using Chrome not Firefox, I hope you approve <g>). I will use a separate winding for the voltage sense input and the transformer will be very lightly loaded, which will I hope avoid the phase shift issue in both primary and secondary. By using true precision analogue computation a lot of the other problems the Arduino community have encountered should be avoided too.

Does anyone have a smart meter yet? I just wondered whether they do actually sense current direction. I can't find any model info / technical specs.

They have to or they would not be able to discriminate between imported and exported power! There is a teardown report on one here Elster REX2 Smart Meter Teardown - iFixit but it is mainly concerned with the physical construction, has anyone got a more informative link?

 

[UKMeterman]

Hi all,
If you have the cash consider puttin a nemo96 in a plastic box and use a Hobut 100A|5A clip on tradional CT

 

[Rogerhillside]

Hi
Have just has 3.55kw PV system fitted. While I have a combi boiler hence no water tank. Intend to fit water tank with 2 3kw immersions and want to buy a controller as outlined in this thread. But would like it to also control a valve for in winter or dull days when the water is cold is uses the combi. Any suggestions?

 

[suntrap]

Are you aware that as this will all be under mains pressure, you can't use a standard hot water cylinder but need an expensive high pressure system? It will take an awful long time to recoup the cost. Also, is the idea of two immersion heaters that you will use them in parallel when you have >3kW spare? This will only be for very short periods in high summer when you're likely to have far more spare capacity than you can use, so I wouldn't worry about a second one. You'd also have to make sure you divert all power to the lower one most of the time (if at different heights) or you won't heat the whole tank.

 

[Rogerhillside]

Suntrap Thanks for the quick reply
I have bought a direct unvented tank already and only intend using one of the immersions at a time. The lower one from the excess solar and the upper one for occassional warming up. The tank was used so not so expensive and only 140l.
[email protected]

 

[suntrap]

OK sounds good. I suppose in theory you could feed the tank straight into the boiler but that's probably not allowed...

 

[pmcalli]

Suntrap Thanks for the quick reply
I have bought a direct unvented tank already and only intend using one of the immersions at a time. The lower one from the excess solar and the upper one for occassional warming up. The tank was used so not so expensive and only 140l.
[email protected]

I run two vented tanks in series the first tank is an economy 7 tank ie with two immersions the second with an immersion in the top and gas heated coil in the bottom. I run the controller via a daisy chain of relays so it heats the second top of tank first then a std cylinder stat set high on the tank switches via a relay the controller to the top of first tank another stat switches it to bottom immersion when hot. This way I always have the max quantity of hot water if you heat the bottom one first and its a dull day you just get a lot of Luke warm water. The relays cost about £3. I don't see why you couldn't use the same idea with the first relay enabling the combi boiler via the nc contact of the relay.

 

[echase]

This may be relevant. I have a granny annex with its own combi boiler for water heating. I’d like to draw its feed off the solar cylinder in main house but the pipe would be long. I am thinking that best bet may be to install a thermostat half way up the cylinder switching the boiler feed from this cylinder to mains (although one is mains pressure and other loft tank fed). If it’s above a certain temperature, like 40C, it’s a sign that there is lots of hot water higher up the cylinder so there is spare to send to the combi. For short combi runs this hot water may not reach it before run time ends, so is largely wasted. For longer runs like baths it will reach it. But don’t want to use it if little spare in cylinder, so the thermostat prevents this.

In these solar installations you need to consider legionella. Opinion is divided but heating all or at least the top part of cylinder to 60C regularly (daily/weekly) is needed to kill the bacteria. There is the risk that unless a good top up heating system is used this 60C is rarely reached in dull periods.

http://www.solartwin.com/solartwin-...l-to-a-combi-boiler-combination-boiler-geyser partly covers all this. They use a 60C mixing value to stop the water into boiler being too hot.

 

[sharpener]

Can anyone who has used the Crydom 10PCV2425 controller or similar confirm that they are optically coupled so there is complete isolation between the input and output sides? Also, what current does the control input draw at 10V and what are the voltage limits? Some circuits published here seem not to have any overvoltage/reverse voltage protection for the control input!

Lastly can anyone point me at a supplier for the Crydom polycarbonate terminal cover (pictured earlier) and heat sink pad? Farnell have a good price for the controller but don't seem to stock the accessories.

TIA