Solar Immersion - my experience !

[Worcester]

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.

V=IR
Watts = VI

Alter the V, the I drops in proportion as R is the only fixed element so it only delivers a fraction of the "3kW"

Wetehr it's phase angie. PWM or burst fire the same maths applies.

 

[MikeWBC]

Agreed, but that assumes the unit controls the voltage to the load. I was under the impression (perhaps wrongly) that a burst fire system simply switched on one cycle every "n" cycles directly to the load, so both the V and the R are fixed for the duration of the burst. And hence the current. If it controlled the voltage, then there would be no need to burst at all. It then becomes a phase controlled system with smoothing to filter out the harmonics, and effectively reduces the voltage to the load. Which is the way, I think, the Immersun have gone with their latest product.

 

[Graham Hilton]

Agreed, but that assumes the unit controls the voltage to the load. I was under the impression (perhaps wrongly) that a burst fire system simply switched on one cycle every "n" cycles directly to the load, so both the V and the R are fixed for the duration of the burst. And hence the current. If it controlled the voltage, then there would be no need to burst at all. It then becomes a phase controlled system with smoothing to filter out the harmonics, and effectively reduces the voltage to the load. Which is the way, I think, the Immersun have gone with their latest product.

The immerSUN device I believe uses PWM and sinewave looking at their website,

You would need a filter the size of a fridge to make a device using Phase Angle comply with Harmonics, I am still surprised that this hasn't been addressed yet.

 

[Gavin A]

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.

no it won't, think about how averaging works, it's not coming from anywhere on the the other cycles, there's no power on the other cycles. ag if you want 20% power to match up with 600W of excess generation then 10 cycles out of 50 will be 100%, the other 40 cycles will be nothing, the average will be 600W over the 50 cycles each second.

 

[Gavin A]

V=IR
Watts = VI

Alter the V, the I drops in proportion as R is the only fixed element so it only delivers a fraction of the "3kW"

Wetehr it's phase angie. PWM or burst fire the same maths applies.

not really, well it does, but isn't really relevant to how Burst Fire works anyway,

 

[Gavin A]

The immerSUN device I believe uses PWM and sinewave looking at their website,

You would need a filter the size of a fridge to make a device using Phase Angle comply with Harmonics, I am still surprised that this hasn't been addressed yet.

problem is, there is no enforcement of these laws at the supplier level, or really at any level. I had to point this issue out to Immersun who had no clue what I was talking about until I actually referenced the specific regulations and showed how their mark 1 device couldn't possibly be compliant. Took them 18 months to bring out the mark 2 that fixed the issue, the process of which began with my emails, but for that entire time (and still) they continued knowingly to sell thousands of non-compliant units.

meantime, we get hammered at MCS inspection if there's a sticker missing, but not one of our supposed governing bodies has had a single thing to say about non-compliant devices such as these.

 

[MikeWBC]

no it won't, think about how averaging works, it's not coming from anywhere on the the other cycles, there's no power on the other cycles. ag if you want 20% power to match up with 600W of excess generation then 10 cycles out of 50 will be 100%, the other 40 cycles will be nothing, the average will be 600W over the 50 cycles each second.

Hi Gavin A,
I must admit I'm thoroughly confused now. How does a burst fire system work?

 

[Gavin A]

Hi Gavin A,
I must admit I'm thoroughly confused now. How does a burst fire system work?

it works by chopping the power on a per cycle basis, so 2% power = 1 cycle at full power 49 cycles at no power.

which is fine for low power control devices, but not for a 3kW immersion heater, which can result in serious voltage flicker at dangerous frequencies for those with epilepsy etc.

 

[MikeWBC]

it works by chopping the power on a per cycle basis, so 2% power = 1 cycle at full power 49 cycles at no power.

which is fine for low power control devices, but not for a 3kW immersion heater, which can result in serious voltage flicker at dangerous frequencies for those with epilepsy etc.

That's what I thought, so during the full power cycle, there's 250v sinewave across 3KW load, which results in a 12A sinusoidal current. If the PV can only provide say, 1A, the other 11A will have to come from somewhere (ie.the grid), otherwise the voltage would have to drop, and it can't as its connected through the Triac to the 250v grid supply.
For the rest of the "off" time, the PV will be exporting power.
Have I got this wrong?

 

[SibertSolar]

This may help those wishing to understand the differences between burst-fire, phase-angle and PWM control methodology. Basic but perhaps helpful nonetheless.

Proportional Control Technologies

 

[Gavin A]

That's what I thought, so during the full power cycle, there's 250v sinewave across 3KW load, which results in a 12A sinusoidal current. If the PV can only provide say, 1A, the other 11A will have to come from somewhere (ie.the grid), otherwise the voltage would have to drop, and it can't as its connected through the Triac to the 250v grid supply.
For the rest of the "off" time, the PV will be exporting power.
Have I got this wrong?

you've got it right, but missed the entire point I was making about the fact that the meter averages out the power over x amount of cycles rather than actually measuring each cycle individually.

so over a second the power in and out would be zero.

Possible there might be some meters that this doesn't entirely work with, but I'm not aware of any.

 

[Gavin A]

This may help those wishing to understand the differences between burst-fire, phase-angle and PWM control methodology. Basic but perhaps helpful nonetheless.

Proportional Control Technologies

Now I remember where it was that I saw the diagrams that made me thing that the PWM from the 4noks units would be working on the sine wave..... that document could do with updating to make it clear that the 4noks solution actually uses some weird form of PWM on a DC output.

 

[MikeWBC]

you've got it right, but missed the entire point I was making about the fact that the meter averages out the power over x amount of cycles rather than actually measuring each cycle individually.

so over a second the power in and out would be zero.

Possible there might be some meters that this doesn't entirely work with, but I'm not aware of any.

That's certainly true of the old electromechanical meters using eddy currents in a rotating disc, but not so sure for the solid state electronic meters where the voltage and current waveforms are sampled and then analysed by a DSP.

 

[Gavin A]

That's certainly true of the old electromechanical meters using eddy currents in a rotating disc, but not so sure for the solid state electronic meters where the voltage and current waveforms are sampled and then analysed by a DSP.

the metering standards are out there if you're that interested, but no standard meter I know of measures at the per cycle level, which is why these devices work the way they do.

 

[Steve120w]

Being new to this forum but very interested in solar immersion I'd like to add a comment.
The inverter is likely to have capacitors on the solar panel input. These will average out the current being taken from the panels. The solar panels will not be 'asked' to provide 12 amps for one cycle but the capacitors will provide this instantaneous current and this charge will be replaced by the panels over the next few cycles when nothing is being asked by a burst charge system.
The effectiveness of this will be determined by the capacity of the capacitors.