Stability of 240v supply under FIT tarrif?


J

jim

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
 
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J

John Williamson

jim said:
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?
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.
 
D

Dave Liquorice

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).
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.
 
T

Tim Watts

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
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.

--
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H

harryagain

John Rumm said:
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.
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.
 
T

The Natural Philosopher

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?
smoke, and mirrors. :)


however the imdeance of the mains supply is pretty low...

--
Ineptocracy

(in-ep-toc’-ra-cy) – a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.
 
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H

harryagain

jim said:
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?
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.
 
B

Brian Gaff

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
 
B

Brian Gaff

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
 
R

Roland Perry

In message <[email protected]>, at
17:30:56 on Sun, 22 Sep 2013, Dave Liquorice
A domestic PV array in bright sunlight produces less than 4 kW, only a
bit above a rapid boil kettle...
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...)
 
H

harryagain

Brian Gaff said:
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
The inverters in use these days are around 95% efficient. (No transformer)
I think mine uses around 3w on standby.
 
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T

The Natural Philosopher

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.




--
Ineptocracy

(in-ep-toc’-ra-cy) – a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.
 
V

Vir Campestris

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.
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
 
D

Dave Liquorice

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!
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.
 
R

Roland Perry

In message <[email protected]>, at
09:07:34 on Mon, 23 Sep 2013, Dave Liquorice
Greenwash...
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.
 
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M

meow2222

In message <[email protected]>, 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
 
D

Dave Liquorice

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.
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...
 
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T

The Natural Philosopher

Whilst the former is a matter of debate, a lot of the latest
inverters have no transformer, like this:

<http://www.sma-uk.com/en_UK/product...000tl-5000tl-with-reactive-power-control.html>

"...the new transformerless Sunny Boy is the ideal solution..."

Chris
just because the sales blurb says it is transformerless doesnt mean it is.


--
Ineptocracy

(in-ep-toc’-ra-cy) – a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.
 

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