h a l f b a k e r yNot so much a thought experiment as a single neuron misfire.
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Stand-alone inverters exist - they produce AC from DC.
Inverter generators exist - they produce unregulated AC from fuel, DC from unregulated AC, using a rectifier, and regulated AC from DC, using a built-in inverter.
It seems obvious to me that you should be able to feed in DC (or even unregulated
AC) from an external source, such as photovoltaics, with or without the fuel engine running, and use the inverter generator's electronics to produce regulated AC, thus eliminating the need for a (redundant) stand-alone inverter. But apparently, you can't.
The benefits would be great - apart from the reduced system cost, it could simplify the combining of, and switching between, power sources.
Outback Thingy
http://powerelectro...d-grid-applications
Thingy with DC and AC input [the porpoise, Mar 31 2014]
[link]
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For photovoltiacs, the problem you describe may
have something to do with the fact that while solar
cells produce a constant voltage, their amperage
varies with the amount of sunlight. |
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Perhaps the solution is a relatively simple
intermediary capacitor bank. You want so many solar
cells that the bank is always "full" --and if the bank
feeds a DC-to-AC inverter, its output should be
pretty stable/consistent. |
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[Vernon] The problem is simply that if I bought an inverter generator I would still need to buy a separate inverter, even though I would already have a perfectly good one. |
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[bigsleep] Sorry, 'modular' may have been a bit misleading. It's not combining 3 into 1; that's already been done. It's using a subsystem (the inverter part of an inverter generator) independent of the engine. |
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If I had a horse and cart, I would expect to be able to use the cart independent of the horse. If I had an inverter generator, I would expect to be able to use the inverter independent of the engine. I'm surprised that no manufacturor seems to have allowed for that. |
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[link] I have no idea if this is what you're talking about, but it seems to do the same thing. |
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Nah on second thought, it doesn't look like it has the inverter generator bit. |
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It seems to me that the reason they don't make these is that they can keep the cost down on the inverter because the inverter input from the generator is pretty tightly controlled. I'm guessing that most inverter generators also use some feedback from the inverter to control the field on the generator since all generator types without inverters (that I'm aware of) control the field to regulate the output, even "unregulated" generators. |
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So theoretically someone could build a modular system with a cheap unregulated generator, AC-DC converter, and AC inverter, but there is quite a bit of efficiency that can be gained by tightly integrating the inverter with the generator. [+] |
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So I'd guess that a modular generator would need to be a bit more expensive to have a slightly more versitile inverter, and it might be good if the inverter had "Maximum power point tracking" to allow efficient use with solar. Of course you might then want a separate model for grid intertie vs. off-grid. |
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Maybe even better (but probably more expensive) would be to design a standard "smart generator" interface that could be implemented on inverters and generators. A "Smart generator" compliant generator might be even cheaper than an "unregulated" generator since it would have very few built in controls, but could be controlled intelligently by any compliant inverter. The inverter could be selected based on peak generator power or the peak solar power and on features such as grid intertie or battery energy storage backup. Generator manufacturers could make this model efficiently by basically just selling their high-end inverter model without most of the electronics. |
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[the porpoise] Thanks for the link, but no, that's not what I had in mind. |
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[scad] Thank you; you have understood my intent perfectly. I suspect that you are right about cost and efficiency; of course, I'm banking on the difference being less than the savings on the extra inverter. It probably also comes down to the fairly limited market. Few people would pick the $3000 inverter generator over the $2000 one, because few people want that versatility, much as few people want mechanical power takeoffs on their vehicles. |
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I've noticed that inverter generators cost roughly the same as high quality (off-grid) inverters of similar power ratings; it seems on the face of it that they're throwing in the engine for free, or we're being fleeced for the inverters. |
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//all generator types without inverters (that I'm aware of) control the field to regulate the output// ... except permanent magnet generators. |
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//Maybe even better// That's the truly modular approach. |
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// except permanent magnet generators. // I was not aware of permanent magnet small engine powered generators. Thanks!! I just now managed to find a few online, but it's hard to tell how common they are since "permanant magnet generator" mostly finds just the mechanical to electric converter, not units with an attached combustion engine. |
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// or we're being fleeced for the inverters // thinking about this some more... We may be being fleeced somewhat since there aren't that many players in that market yet. I'm guessing that the thing that's stopping Honda from pulling hteir inverter off their genset and selling it separately gor home solar installations is the grid intertie feature. Technically, making a grid intertie doesn't seem like it should add that much manufacturing cost to the system, but I suspect it's difficult to get it certified so the electric utility will let you hook it up. Since grid tied home solar installations have been taking off for a couple years, hopefully there are many new inverter products in the pipeline about to be released that will help bring prices down. |
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