Local power generation and selling to utility company

[GigaNews]

Here's a question I've had for a long time. I've read of people who
generate their own electrical power with various means and sell the excess
to the utility company. Somehow they are pumping their excess power into
the utility grid. How is this done? How can a small generator pump his
electrons "upstream"? Wouldn't this be like trying to add water to the
city's resevour by pouring a glass of water into a fire hydrant? The
pressure would cause the water to flow the wrong way.

Thanks,
Tom

 

[SQLit]

Actually they have backflow preventers in fire hydrants, and all other "city"
water supplies for exactly that reason. If the pressure (aka voltage) is
higher, the current will flow up stream. Most meters will run backward if this
happens but when you do have the proper severse energy system this is done a
little more "officially". It requires the correct metering equipment plus the
proper charge controller in the alternate energy interface to the service.

Most electric meters will not run backwards any more. They fixed that like
15 years ago when people were turning the meters upside down and letting
them run backwards to lower the bill. I am sure there are a few ancient
ones out there somewhere but most have been change out years ago.

 

[Andrew Gabriel]

Here's a question I've had for a long time. I've read of people who
generate their own electrical power with various means and sell the excess
to the utility company. Somehow they are pumping their excess power into
the utility grid. How is this done? How can a small generator pump his
electrons "upstream"? Wouldn't this be like trying to add water to the
city's resevour by pouring a glass of water into a fire hydrant? The
pressure would cause the water to flow the wrong way.

If you generate a fractionally higher voltage than the supply
voltage, you will feed the supply. In the UK, electricity
suppliers are required to allow domestic customers to do this
and they pay the customer for the energy fed back, as part of
a government scheme to encourage alternative energy sources.
It requires changing the metering equipment, and in the one
example I've seen, the metering was all electronic and includes
all sorts of safety features too, such as making sure you don't
backfeed if the mains supply has failed, nor connect your
installation whilst self-powered to the supply unless the phase
is in sync. I suspect deployment is very thin on the ground at
the moment. I don't know who is expected to pay for the metering
equipment.

 

[Pocho]

If you generate a fractionally higher voltage than the supply
voltage, you will feed the supply.

I believe that voltage is not a main issue here. If you imagine a electrical
motor (of any kind) connected to the grid, and with mechanical power
increase its original speed, you will feed the supply in that case. If you
invest mechanical power, you will get electrical (very simplified, but the
main fact here). Behaviour of the voltages in this case is consequence, not
a couse.


___
Broken English is better than a broken leg

 

[daestrom]

I believe that voltage is not a main issue here. If you imagine a electrical
motor (of any kind) connected to the grid, and with mechanical power
increase its original speed, you will feed the supply in that case. If you
invest mechanical power, you will get electrical (very simplified, but the
main fact here). Behaviour of the voltages in this case is consequence, not
a couse.

Well, you're both right.

If a motor is forced faster than its synchronous speed, power will flow back
into the line. But a solid-state inverter, such as those used by home PV
setups doesn't have a mechanical input, its all electronic. By sensing the
supply frequency and phase, and triggering the electronics correctly, power
can be made to flow into the grid. But for that method to work, the
inverter must have a voltage higher than the AC sine wave (at least some
parts of the cycle).

daestrom