Maximizing Savings with Solar and Wind Power Generation

[Sparky_]

Greetings,

I'm seeing programs that allow solar, wind and other types of power generation to be connected to your house (or business) and you are still connected to your grid. The power company meters both - what they provide to you and what your private generation provides.

Your power company gives you a credit (or cash) for the difference.

Technically - is there a problem or danger in having both connected (I know the power company would have it wired correctly I just don't see how yet)?

Would or could the two sources "fight each other" or back-feed or something?

The only wiring diagram I've seen so far is both sources end up at your breaker box.

What if you are able to generate enough power on your own to meet your needs (or more than enough) - what keeps the power company's power happy and out of your house?

Thanks
Sparky_

 

[sophiecentaur]

Consider your house as a 'black box', with two terminals, connected to the mains. For convenience, let's say it all operates at DC. If you happen to be consuming energy then the voltage across your terminals will be ever so slightly lower than the voltage across the generator / source. So current will be flowing through the cables into your home (power being consumed). If your local generation system can produce enough power to meet your needs, with some left over, then the volts across the terminals will be a little bit higher than at the source. In this case, current will be flowing 'outwards, into the supply (power being produced). This is very much the same as when you float charge a battery, whilst it is being used: power can be either sourced or stored in the battery, depending on the capacity of your charger and the load demand.

When using AC there is another thing that has to be considered and involves sophisticated control systems. The phase of the home brewed and mains voltages must be synchronised, to prevent vast currents flowing and blowing up things, before actually connecting up your home and the mains. But whether power flows in or out will also depend upon a tiny difference in values of the instantaneous local and supply volts.

 

[Sparky_]

In the scenario where the local generation (solar, wind ...) is enough to meet my black box's (house) needs with some remaining - does what's upstream (my house's xfmer and up) care that I am putting power on the line?

will the two "sources of power" not fight each other?

Thanks
-Sparky_

 

[sophiecentaur]

I don't know what you mean by "fight each other" except that, if you take two fully charged batteries and connect them in parallel, you could say that they 'fight each other' in as far as each is 'pushing' equally hard so no current will flow.

The transformers / distribution system don't givadamn as long as not too much current is flowing. All that will happen, back at the substation or the generator, will be that less current comes from the generator. It is true to say that the speed of the generator could increase in response to this (needs to be dealt with) but the control circuitry will either change the current in the field windings or, longer term, feed less fuel to the turbine / boiler / reactor to maintain the right frequency / phase.

If you don't switch in your system in-phase then there is what you could describe as 'fighting' because each end of the chain is a low resistance source and, for a relatively small voltage difference, will allow loads of current to flow and cook things. I think, in the early days of AC power networks, there must have been some pretty dramatic incidents when the control wasn't as good. Lost of burst fuses and melted wires. Would that be enough of a fight for you?

btw, your Energy meter can quite happily go both ways.

 

[Sparky_]

gotcha!

thanks!