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#1
October 9th 05, 05:19 AM
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#2
October 9th 05, 01:15 PM
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Dave Heil wrote: wrote: Dave Heil wrote: wrote: Dave Heil wrote: If you're talking about electrical energy, any of it which is produced but not consumed, is wasted energy. I can turn off my appliances and lights, but if no one else uses the electricity I'm not using, it is wasted. Dave, Electricity supply doesn't work like that. The production adjusts itself to the load. If the load decreases, so does production. There is no waste from reduced loading. In fact, if the load goes down enough, utilities shut down their least- efficient plants. I accept your statements as fact, as far as they go. They go pretty far. However, if electricity is generated and not consumed, it is wasted. Where does it go? The utility doesn't put huge dummy loads on line. Actually, it does. No, they don't. They are in the form of transformers and wiring. Those losses are not dummy loads, they're inefficiencies. They are not connected to use up power others don't use. From what I've read, a little over 8% of generated power is wasted regardless of the load. 8% of 100 kVA is 8 kVa. 8% of 50 kVA is 4 kVA. As the load goes down, so does the waste. Of course the situation is somewhat more complex, because even with no load there is some loss, the loss is temperature dependent, etc. That allows no leeway for leakage. It includes "leakage". Copper loss, dielectric loss, skin effect, corona, etc. That's just the waste built into the system. The conversion from mechanical to electrical power is just a little over 41% efficient. That number is actually from the heat in the fuel to the final customer. It includes boiler losses, turbine losses, alternator losses, transmission and distribution losses, and all the electricity used to run the plant and auxiliary loads. It's actually very good compared to, say, a car. Generally, power is shifted to other parts of the grid if unneeded in one area, so that it is used where there is demand. Not really. If the load goes down, less is generated. If locally generated power was not connected to a grid, what would happen to electricity generated, but not used? It's not generated in the first place. If my home generator is run at full load, I might get eight hours of run time. If it is run at 50% load, I might get only ten hours of run time from the same tank of fuel. Doesn't this indicate that there is additional waste? What you're seeing is the inefficiency of the *engine* at light load. A perfect genset that burns X gallons per hour at full load would burn 0.5X gallons at half load, 0.25X gallons at quarter load and nothing at all at no load. But real engines aren't that good, so you might find that a real genset that burns X gallons per hour at full load burns 0.65X gallons at half load, 0.4X gallons at quarter load and 0.2X gallons at no load. The extra gas goes to run the engine itself - unbolt the alternator and the engine will still burn about 0.2X gallons per hour just to spin the shaft. Just like your car uses gas at idle. It's the engine, not the electrical system. This is where hybrids get their efficiency improvements. The engine in a hybrid is almost never idling. It's either driving the car, charging the battery or shut down. I don't know enough about controlling the total reactive component to address it. I do. Utilities always aim for unity power factor. They have auxiliary capacitors that are switched in to compensate. Some big customers can control their power factor and compensate the system as well. Ever hear of a synchronous condenser? 73 de Jim, N2EY |
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