Solar Immersion - my experience !

[danesol]

Ours too is in the airing cupboard "miles away" from the dno meter / Henley Block so using a considerable amount ofcat5 via the loft and down the gable end, the length of tbe cable shouldnt actually matter unless it exceeds that of cat5.

The only issue we have if you can call it that is that once the SI unit kicks in no RT clamp / monitor records the true electrical consumption properly but this has been discussed before possible on this thread?

As yet I am yet to find a monitor system that can wirk alonvside this unit and measure accurately the true consumption

hth

 

[tdrees]

Again - thanks for the feedback! .

I have noticed the same thing, the Electrisave monitor that we have is hopeless when the real power draw is close to zero, as you would expect. Its very hard to measure a magnetic field that does not exist! It seems to revert to "last reasonable measurement" which is invariably something large caused by the kettle having been turned on.

 

[Worcester]

And then you guys still wonder why we wont fit these particular units!

ImmerSun's and Apollo's for us Choice is dependent upon the functionality needed. - As we fit more and more heat pumps, we're doing more and more solar, and more and more ImmerSun's - Standalone we find the Apollo's difficult to beat on value and performance.

 

[Steve_rutland]

For anyone who has solar, I would definately recommend an Immersun. I haven't used any gas since mine went in!

 

[danesol]

Again - thanks for the feedback! .

I have noticed the same thing, the Electrisave monitor that we have is hopeless when the real power draw is close to zero, as you would expect. Its very hard to measure a magnetic field that does not exist! It seems to revert to "last reasonable measurement" which is invariably something large caused by the kettle having been turned on.

The real stupid situation I have is that I am currently using two complete E-On energy monitor systems ( Current Cost ) , one hooked up to the tail after the Henley, but feeding the CU and the other on the tail between the DNO meter and the Henley Block.

........ now this is the interesting bit !

When the SI unit kicks in when the consumption in the property is less than the generation and that generation is around the 2kw mark - the value of the two monitors gives the precise consumption with one been alot higher than the other, ie one appears to measure what the SI is sending to the water heater and the other is what the standby useage... LOL


When the PV system is generating far less than this amount - the two read very similar figures !

As I can only connect one of these to my PVO uplink system - the figure I record / send is inaccurate but over the course of a mth isn't that far out ... now work that out !


edit:- Forgot to mention - I also try and measure the load on the positive tail from the SI to the Immersion Heater to try and see how much is been diverted - I use an old British Gas wireless unit for this which is also hit & miss for the very same reason. I know this is the case as I can see what im generating, what I'm using and can also see the DNO meter is stationary so know exactly when its lying to me and not recording diverted electric to the IH !

 

[MikeWBC]

I have a very similar setup to trdees, and I'm getting exactly the same effect. I have a Solar Immersion feeding a 3Kw immersion heater and East/West solar PV installation. Even if I have 1800W being generated, with a base load of 300W, the monitor measuring total consumption varies between 300W and 3.5KW. The SI oscillates between 8% and 13%.
I only installed the SI 2 months ago, and with fairly stable weather conditions, I could get an accurate comparison before and after. Measuring the gas saved and the extra Solar power used, it appears the Solar Immersion imported 25% of its power from the grid.
So I've saved 79p in 2 months.
Support at Solar Immersion have said this new model now uses the burst fire (power burst) form of control, which I believed could cause flicker problems, rather than phase control.
Hasn't Immersun just gone the other way?
All Support at Solar Immersion can offer is to swap the unit for an old model.

 

[Sunstroker]

I’m confused! It appears that some are suggesting that their SolarImmersion units may at times be importing from the grid. Surely this can’t be so?


Up until now I have assumed that when the SI display indicates a diversion percentage this is the proportion of total available solar power that is being diverted, not the percentage of potential demand being supplied to the load. How can the SI unit “know” the wattage of the load?


In my case Heater 1 is a 3 kW immersion while Heater 2 is presently a 2.7 kW storage heater. There is surely no way that the SI unit can detect these differing loads, so the display can only be indicating the percentage of total generated power being diverted at any given time. If there is no surplus from the PV system then nothing goes to the load and nothing is imported. That is the whole purpose of the system.


On a different point, MikeWBC states that Support at Solar Immersion have said the new model now uses the burst fire (power burst) form of control, which could cause flicker problems, rather than phase control. This would possibly explain my previous observation that my replacement unit causes the immersion switch neon to flicker, while the original unit in my son’s house produces a steady neon irrespective of the rate of diversion. I have to say however that I have not noticed any problems of flicker in my house lights.

 

[MikeWBC]

Thanks for your comments, Sunstroker. To answer your points, as I understand it, the percentage shown on the display is the percentage of the full sinusoidal waveform that is being fed to the load. In a phase switching system (like the old SI unit) the output thyristor (probably a Triac) is fired so only a percentage of the 50 cycle waveform is fed to the load, so for 20%, the triac fires late in the cycle and for 50% it fires at the mid point. A problem with this is that the fast switching injects harmonics into the mains, which can cause electromagnetic interference unless filtered out.
Burst fire is different in that it feeds full cycles to the load, but only intermittently. So for 13% only one in 8 cycles are fed to the load. This means current is being taken in 20mS bursts every 160mS which is about 6 cycles a second, well within the visual “flicker” range, but is only likely to manifest itself if the supply to the local group of houses is relatively poor. And your neighbours have got their lights on. If you’re on an estate or in town, you’re unlikely to experience any flicker problems.

The unit doesn’t need to know the wattage of the load. As I understand it, the old SI unit simply increased the power to the load in 10% steps until the sensor detected the export power was in the minimum range set, and then checked it every second or so.

My guess is that the problems with the new burst fire unit are to do with the sensor. In the old system, the sensor circuitry only had to average out the current for a couple of cycles or so, say 50mS, to get a reasonably accurate reading of the current flowing.

It’s much more difficult with burst fire, where it needs to average over 20 or more cycles.
If they’re sampling much shorter than this, a likely scenario is that the unit sets an output, samples and sees power being exported, so it increases the load, samples again, still sees export and increases the load and so on until it hits a burst. By this time the load has exceeded the available solar power so some is imported.

I monitor and record my usage, generation and import readings, and my usage is fairly constant over the year. So it was fairly simple to see the change when the new SI unit was fitted.
For the two months before I only used gas for cooking and water heating. For the 2 months after, I turned the boiler off.
The extra solar energy used was 166KwH
The extra electricity bought was 64KwH
I saved between 7 - 8 Units of gas = 220KwH - 250KwH
So 230KwH seems about right for water heating.
So it's saved me 230x0.032 = £7.36
But it's cost me 64x 0.108 = £6.91 in extra electricity.

Sorry it’s such a long tome.
Mike

 

[Sunstroker]

Thanks for the comprehensive explanation, Mike. Your understanding of the complexities of electronic switching far exceeds mine, but I think I understand the gist of it. My degree, a long time ago, was in agricultural economics, and we didn’t cover sinusoidal waveforms!

I know how much my PV system generates per day (8.98 kWh on average since installation in Jan 2011) and how much I import per day (6.51 kWh over the same period). My daily average usage prior to PV installation was, incidentally, 12.53 kWh, so I’m happy that there is a considerable saving.

But I gave up trying to keep track of ongoing import and export when the SI unit was installed as the display on my NPower Smartpower monitor seemed fairly meaningless when the SI unit was diverting. I simply assumed, perhaps mistakenly, that the unit was doing its job. My water is hot, my storage radiator likewise, at least when the sun shines, and as far as I can see I’m not importing more than I did before the SI unit was installed, so in my case it does appear to be worthwhile. Perhaps if I had additional monitors to measure all the parameters I might feel less happy, but I think I’ll remain content in my ignorance for the present!

As regards flicker, my house is rural, with only one other property fed from the same transformer, and neither of us have noticed any problems with flickering lights since my SI unit was installed. My existing unit, an eventual replacement for the initial one which failed in September 2013, was delivered last November so I presume it is the latest burst fire type.

 

[SibertSolar]

Of course, you could always use an Elios4You and Power Reducer in tandem - you would have all the generation, consumption, import & export monitoring/data you could need, and a safe, compliant and compatible immersion controller designed by the same manufacturer, with no issues surrounding burst-fire or phase angle control....but then that's just me being biased....

 

[MikeWBC]

Thanks Sunstroker, it could be your replacement is still of the old variety. My original failed at the beginning of June (this year)and it took to the end of July to get a replacement out of them. Their excuse was that the new model was just coming in. I'll keep monitoring mine, but I don't hold out much hope of any resolution from them.
Cheers

 

[Gavin A]

Of course, you could always use an Elios4You and Power Reducer in tandem - you would have all the generation, consumption, import & export monitoring/data you could need, and a safe, compliant and compatible immersion controller designed by the same manufacturer, with no issues surrounding burst-fire or phase angle control....but then that's just me being biased....

and fit a NEDAP power router and 600Ah 24V battery pack in tandem with that to really exploit the full self consumption thing.....

 

[MikeWBC]

I’ve been looking at Power Burst or Burst Fire systems in more detail, and I’ve come to the conclusion that it’s inherently flawed and can never work properly. I was wondering if someone on the Forum could please check I have my reasoning correct?
In a Power Burst system, you feed power to the load for one cycle every “n” cycles, the ratio depending on the load wattage and the power available from the PV system. So, for example, with a 3KW Immersion heater, and say 1KW available power from the PV, you would burst one cycle every 3 to the load. During the burst, you’re providing 12A at 250v to the load. The PV has 4A available, and regulates this by dropping the voltage to compensate, so 8A has to come from somewhere, and is imported from the grid. Then for the next 2 cycles, while the burst is off, the PV exports 4A to the grid. So 667W (67%) of power going to the immersion is imported from the grid, and the PV has exported an equivalent back to the grid. With a digital import meter, it will register the imported power, but not the exported power, so you’re buying the extra power from the grid.

And it gets worse, the lower the amount of PV power available.
At 3KW available, nothing is imported from the grid.
At 2KW available, 33% is imported from the grid.
At 1KW available, 67% is imported
At 500W available, 83% of the power is imported.

Have I got this wrong?

 

[Gavin A]

the meters aren't sensitive enough to register consumption at the per cycle level.

but what you've just described is why burst fire systems can not meet the flicker regulations and are therefore illegal to connect to a 3kW load in many situations - ie higher grid impedance situations, or IIRC anywhere that a 3kW load would result in more than a 0.7V fluctuation in the grid voltage. I've known some places where 3kW would equal 4V swing, and where this does cause lights to flicker badly enough to send an epileptic person into fit, and properly did my head in while working to pull the unit back out again.

 

[MikeWBC]

Thanks Gavin A, but the power has to come from the grid, since the PV system can't provide it, so even if the meters average it out over many cycles, it will still register as a power import, even at a lower level. Perhaps that was why my system only indicated a 22% increase in usage.