Genset to Power Grid

If you wish to synchronize with the grid, this will involve some fairly expensive equipment (and probably some negotiation with your electrical utility). If you can find some loads that match your biofuel generation capacity, and remain stand-alone with those loads, it will probably be simpler. No one solution fits all cases, but it will be good to research this as well as you can.

Tornado, what would be the downside of generating a DC voltage to feed a grid-tie inverter? I know it's converting twice, doubling the inefficiency, but at least he's getting something out of the waste oil and it's easier than trying to synchronize a genset.

Maybe you could rethink your savings scheme in terms of removing equipment from the grid and using the genset for power in a standalone fashion.

The simplest grid tie route is to use your engine to spin a standard AC induction motor faster than it normal runs when connected to your AC lines. It then becomes a self synchronizing grid tied generator system.

Start your engine and bring it up to speed and then connect to the lines, thats it.

I will let the legality and safety Nazi's/worrywarts take it from here.

I had an 8000 watt pull recoil start genny. It had one 120 volt duplex receptacle and one 240 volt receptacle on it. On occasion I would back feed my home breaker panel, 240 volt genny to 240 volt service via a 30A, 2P circuit breaker. With no load I would watch the utility meter run backwards. When I would initially bring it on-line, the generator RPM would rapidly fluctuate up/down 50 - 100 RPMs. After about 30 – 40 seconds, the rapid RPM fluctuation would begin to smooth out and within 60 seconds, the generator would be running perfectly smooth. Never popped a circuit breaker nor the on board push button reset. Was this luck or was the genny able to sync up because it was producing such a small output? Obviously, connecting to the grid without the proper equipment is dangerous but theoretically, couldn't shanewaldoc connect directly to the grid as I did?

For your information :-

1. Connecting a generator 180 degrees out of phase to a big-rating supply takes twice as much current as short-circuiting it. This causes four times the bursting force in the windings compared to a short circuit. Big generators are only designed to survive short circuit.
2. Small generators are less efficient than big ones - they have relatively more resistance to limit the current. There is also more weight of copper (better able to absorb the excess heat) in a small machine relative to rating.
3. You were obviously running at the right speed, else this would have been worse (a generator is a very bad motor for self-starting - without special provision like an auxiliary induction motor winding, although once synchronized they make good motors).
4. The rpm fluctuation was because the synchronizing forces on the rotor cause an angular oscillation of the rotor about the final speed which takes a long time to damp down.
5. You are probably at the end of a long local line which means you get voltage dips if you apply exceptional loads - this limits the current.
6. Depending on the class, a 30A breaker can take 100s of amps to trip it off instantly. Below this, in its thermal overload mode, the breaker is designed to trip for over what the feeder cables can take.
   
7. Small things are stronger - if an aeroplane flies into a building, both are wrecked. If a wasp flies into a window, it bounces off and tries again!
8. Theoretically, couldn't shanewaldoc connect...... If his supply is much stiffer it could be wrecked generator and breaker.
9. If I had to do it, I would put electric fire bars in the feed to the generator, rated for full voltage (Short-out with switch once it all stabilizes) : equalize voltage, speed/phase, as close as possible using voltmeter and synchronizing lamps before closing breaker. The firebars are a precaution against gross error, it worked for Mr Westinghouse (without firebar) over a century ago!
   

What is your business? Lighting loads should be fairly constant. Waste heat AND electricity could heat your water for dishwashing, clean-up, building heat. Twenty liters isn't much energy. What's the diesel consumption at 8kva? Work out the cost of converting the fry oil to biodiesel. It's complicated and messy. Better to sell the oil and pay your electric bill. And look into solar thermal water heating for restaurant business. It's the best payback time.

shanewalddock; Go for it. you could use light bulbs for synchronizing the gen set, one your locked in, speed up your engine till you see your output from the gen set, this should slow down your watt-hour meter. DOWN SIDE!! if your power company were to lose power to your building, you would be feeding power back into the power co. line & injure or kill a employee! MAYBE the circuit breaker on the gen set would trip with the increases load. perry

The lamps for synchronising need to be twice the circuit voltage, (to take the mains plus alternator voltage at 1890 degrees). The supply co here would prosecute you if you were caught; seems a big risk.

Bigger downside; If your supply feeder breaks your alternator could feed wiring and shock or electrocute someone. Maybe manslaughter!

Better feed a diesel vehicle or isolated electrical load.

Thanks to all for your fantastic help and support. We're leaning towards using the genset as a pwr backup to the cold rooms.

What a great site and thanks again!

Would like to use waste oil as biodiesel through my small (8kva) genset and provide energy to the power grid reducing our power bill.

For the simplest and most financially viable alternative, convert the waste oil to biodiesel and use it in one of your diesel company vehicles!

Initial equipment costs are much, much lower (no expensive grid-tie inverter needed) and some double conversion inefficiencies are also removed. Additionally as it would be used for a company vehicle it can be classed as a business expense.