Please, can someone kindly elucidate how a domestic 240V house system maintains a stable voltage when connected to an FIT inverter fed from a pv panel?
One moment it's feeding amps into the local supply, the next it may be extracting them. To get a reversible current flow, there must be a pd (potential difference) between the 2 situations. How does it do this trick? (and avoid flickering lights etc).
Are mirrors involved?
TIA
It's all low impedance connections, so you need quite a large current change to make a noticeable difference in the suply voltage. Anything other than incandescent light bulbs or very old, non-stabilised power supplies for TV sets won't really notice less than about a 10% change in voltage anyway, which should need a current change of 100 amps or moreif all is in order. As most domestic PV panel sets can't generate more than about 16A, it's not a problem.
The potential difference required actually comes from a phase shift in the locally generated component. Depending on whether its leading or lagging the waveform supplied via the grid as to whether its drawing or feeding current. The RMS voltages of both grid and the output of the local inverter could actually be the same. The local grid tie inverter will adjust its generated phase relative to the grid voltage to achieve the required direction of energy transfer.
Not usually, and hopefully no smoke either ;-)
The volts do change but not enough to notice. The voltage here drops by about 8 V when the E7 kicks in and 11 kW is instantly applied. A domestic PV array in bright sunlight produces less than 4 kW, only a bit above a rapid boil kettle...
Do your lights flicker when you switch on the kettle? We don't notice the E7 coming on but then we don't have incandescent lights that would show it far more than anything else.
On Sunday 22 September 2013 16:38 jim wrote in uk.d-i-y:
Yes, there is a PD, probably in the form of a very slight phase lead/lag.
It is minute. The supply impedance will be less than 0.35ohms (L-N) so 10A FIT feed would be 3.5V or an equivalent phase shift. Not enough to be flickering lights.
What are you rambling on about? The previous poster is entirely correct. As the power output from PVpanels increases, the voltage at the AC output terminal of the inverter rises. So "stuffing the electricity back down the spout " so to speak. My PV panels causes a rise of around 5volts when on full power. There is no phase shift, the power factor is around unity at all outputs, there is no transformer.
smoke, and mirrors. :-)
however the imdeance of the mains supply is pretty low...
You take say four Kw out of the system and the voltage drops by a small amount. You stuff four Kw back into the sytem and the voltage rises by the same amount. (Everything else being equal).
Most of the energy stuffed back intot the sytem is used by nieghbours so in fact reducing the load on the system and making it more efficient.
As long as the PV systems are small sytems, dispersed and there are not too many of them there are no problems. Large system can present problems and as they become common the problems will increase.
This is another possible use for smart meters, the remote control of such systems.
Far more of an issue is synchronising the frequencies and putting crap on the local supply or even creating RFI from the inverter in my experience, which is not much here, but from those who rushed out and got it, there have been issues.. grin.
Brian
Of course a lot of these devices waste power when not a lot is being generated, and over time I'd suspect this adds up to quite a high amount. 5v is nothing, in any day the mains goes up and down far more than that amount. Brian
In message , at
17:30:56 on Sun, 22 Sep 2013, Dave Liquorice remarked:There's a big poster at my local Sainsbury's which says they generate enough electricity to boil every kettle in the town. But not simultaneously I suspect! And mine is a traditional one on gas hob, so that's a neat trick (maybe my share is the electricity to ignite the gas...)
The inverters in use these days are around 95% efficient. (No transformer) I think mine uses around 3w on standby.
Harry, the idiot who thnks inverters dont have any transformers.
Whilst the former is a matter of debate, a lot of the latest inverters have no transformer, like this:
"...the new transformerless Sunny Boy is the ideal solution..."
Chris
Locally perhaps, nationally unlikely. The big generators can't be easily throttled up and down, and lose efficiency when this has to be done.
Andy
Greenwash... if they are that proud of their solar PV why don't they have a big meter showing the total store consumption and what percentage of that is coming from the PV, both instantaneous and averaged over lets say a week.
In message , at
09:07:34 on Mon, 23 Sep 2013, Dave Liquorice remarked:Not the only example, they also say they are using LED lights in their (semi-underground) car park to save energy, but it's obvious they are fluorescents.
2 Leds in an emergency exit sign
weird how thats seen as a good thing
Are you sure? There are LED strip lights that fit standard florry fittings, not sure it would be very easy to tell what the light source is behind a diffuser...
What is weird about giving the true facts?
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