On Apr 12, 7:44*pm, David Nebenzahl wrote:
On 4/12/2011 9:47 AM g spake thus:

On 11/04/2011 23:17, harry wrote:

On Apr 11, 8:01 pm, David
wrote:

You don't "push" electricity from your solar installation into the grid
by raising the voltage, as someone here postulated. It just don't work
that way.

Yes it does. *Electrical current flows from a point of higher
potential to a lower point. *The very first thing you learn. Ohm's Law.

So, you don't increase current by raising the voltage, but you increase
current by having a higher potential.

No, no, no: increasing the current doesn't increase the potential
(that's voltage). It increases the *flow* of electricity (= current), at
least the maximum possible current. But that's not the same thing as
potential difference.

Example: Let's say you run your house off 12 volt batteries (just for
illustration). The *potential* of your power circuit is 12 volts
(assuming the batteries are fully charged, and they'll actually be
closer to 13.something, but let's call it 12).

Now let's say you add some more stuff to your house and find that your
lights are going dim because the battery can't provide enough *current*
(= amps) to the load. So what you do is add another battery in parallel
with the first one. This doubles the available current (= amps), but it
does *nothing* to change the voltage; it remains at 12 volts (nominal,
as explained above). This is true no matter how many batteries you add
*in parallel* with each other. But each battery increases the
*available* current (= amps) you can draw from your power source.

Notice that adding more batteries does not "push" more current through
the system; it increases the amount of current that can be "pulled"
(drawn from) the batteries.

Which is exactly the situation when you connect your photovoltaic system
to "the grid". It increases the *available current* to the grid. It does
not change the voltage of the grid; there's no need for it to be at a
higher voltage than (but it needs to be at about the *same* voltage as)
the grid.

Now, difference in potential is voltage?

Yes. Please refer to any good basic guide to electricity for more details..

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The explanation for the above is that the battery too has internal
resistance. This why it's output is limited. The internal resistance
varies with the load and state of charge too.
"Potential" is an obsolete and confusing term, see EMF. (Electro-
Motive Force).

http://en.wikipedia.org/wiki/Electromotive_force

Emf is the driving force behind the whole system (measured in volts)
Voltage is the difference (or potential if you like) between any two
points in the system.