Jay Summet via EV wrote:
It is technically possible, all you would need is a current sensor on
the main house feed. If the current is going in, your inverter would
start adding current to the house wiring until the current flow reached
zero. With modern electronics you could react very quickly if the draw
dropped (current flow started to go negative) and essentially never
backfeed the grid.
Yes, it's possible. But current alone isn't enough. There is also the
power factor to contend with. Most things in US homes are not power
factor corrected. So you will be drawing current even though the actual
wattage is zero or even negative.
The device needed is a directional wattmeter, or directional-power
relay, or reverse-power relay. They detect not just the current, but the
*direction* the current is flowing.
These have been around for 100+ years. The oldest ones are basically an
analog wattmeter. The pointer swings left when power flows to the left,
and right when it flows right. A switch contact can be provided to close
a switch when the flow is negative, or exceeds some set value.
The other old type looks much like a mechanical spinning-disk power
meter. But when the disk tries to turn backwards, it closes a contact.
Newer ones can be partially or entirely electronic. They have a current
transformer (to sense current) and a voltage sensor, and a circuit to
multiply the two instantaneous values together to get instantaneous
power. When the average of the instantaneous volts x amps is positive,
power is (on average) flowing out. When it's negative, power is flowing
back into the grid.
Lee Hart
--
When something bad happens, you have three choices: You can let it
define you; let it destroy you; or you can let it strengthen you.
-- Theodor Seuss Geisel
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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