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Demonstration of Generator Support

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ChrisOlson:
It is surprising how many people I have talked to (most of whom have Outback inverters and have never heard of it) that do not understand what generator support is all about in an off-grid inverter. And I've talked to other folks who have heard of it but don't think it's all that important to have. And yet others who have heard of it and would like to have it, but have never seen it work in a real live installation.

So I took the opportunity to make a video with a live demonstration of how it works.

//www.youtube.com/watch?v=KMBdaukbahE--
Chris

Frank S:
 Chris Thanks for posting I am truly impressed which is not to say much because any good system design engineering impresses me, since I so seldom see it anymore.  Just looking at your video it would seem to me that you have a state of the art system now.
 And when you set up your co-gen with the AC compressor you will have a system of dreams.
Maybe if the folks at Outback or the others were to see this whole new mind set for off grid energy production might be perused with more possibilities of plug & play multiple AC & DC input sources
 I believe you now have  a large solar + battery bank with water heating dump load coupled with more than a few wind generators  and your Honda all coupled together  with the probability of a go-gen with the 4bt in the upcoming summer  And you may have other solar usages  installed as well I don't remember .
 Great work

ChrisOlson:
I would bet that if you did a random survey and asked people what the most expensive thing is about living off-grid that you would not get the right answer from most folks. It is batteries. Not solar panels, or inverters, or controllers, or generators, or fuel in the generators. Batteries.

Where generator support in an off-grid inverter comes in, is allowing you to buy the bare minimum in battery capacity to run your normal daily loads and let the generator help with the big stuff instead of just throwing more batteries and solar panels at the problem. Many folks consider it the "pinnacle" of off-grid to not have to run their generator. In reality, that generator fuel is a lot cheaper than the extra battery (and RE generating) capacity it takes to never run the generator.

In most off-grid homes the normal loads are pretty light, and the heavy draw stuff is very intermittent. Instead of spending the extra money on batteries and multiple inverters to meet the peak demand, generator support is a lot cheaper. So it not only saves you money on batteries, it also saves you money on extra (or bigger) inverter equipment.

And the last thing it allows you to do is save money on generator fuel. Too many off-grid people have a 10, 12 or 14 (and some even over 20) kW generator on a XW6048 inverter or similar. This is ridiculous. The generator should not be any bigger than required to get either maximum charging amps from the inverter, or C/10 charge rate for your battery bank, whichever is smaller. Running a 8 or 10 kW generator to charge batteries with a 6 kW inverter is like using a semi to haul an armload of wood

Inverters that only have generator pass-thru support (aka Outback FX-series or Magnum MS/MS-PAE) are limited to either what the inverter can run, or what the generator can run. And that means if you want to power a 6 kW load with a 4 kW inverter you need a 6 kW generator - and you have to run that 6 kW generator for charging when you only need 3,500 watts to max out the charger in the inverter. With gen support you can save the gen fuel and run your 3,500 watt generator for battery charging, and still power that 6 kW load with ease.

It's not about having the biggest there is.  Generator support is about using the smallest inverter and smallest generator combination possible to run the biggest loads with the minimum in battery capacity required.  When you live off-grid if you subscribe to the "Go Big or Go Home" theory - you will pay dearly for your mistake.  It is much more prudent to apply proper engineering and equipment to the job to get it done at peak efficiency and least cost, because living off-grid is anything but cheap.
--
Chris

kevbo:
Chris, you never fail to impress me with looking at the big picture, system view, whatever you want to call it.  When the fuel is free it is all too tempting to overspend on what is needed to "burn" it.  Because the fuel is free, you must pay close attention to the capital and maintenance costs.

Even when you look at large utilities they often have some expensive plants to carry peak loads...which used to be natural gas fired turbine plants, but now that gas has gotten a lot cheaper, they are not so reluctant to bring them on-line as a few years back.

You are also adding diversity to your system, so you are not without power when the once-in-500year ice storm takes all your windmills off-line.

One thing I haven't heard you mention is the time-value of whatever money you tie up in the system.  Even if you don't borrow money for the energy-system, that is money you could devote, or not borrow for other things, so you really need to tack an interest rate onto the cost of system even if you don't borrow to pay for it.  Of course your cheaper-is-better approach just means that when you consider this, you are even better off.

ChrisOlson:

--- Quote from: kevbo on January 10, 2013, 06:47:34 PM ---One thing I haven't heard you mention is the time-value of whatever money you tie up in the system.

--- End quote ---

Indeed the money outlay for equipment has to have both depreciation and interest figured in - none of the equipment lasts indefinitely.  The most expensive is batteries - assuming our bank lasts 7 years the battery cost is slightly over $100/month.  I figured it out once and we would have to easily double our bank size (along with bigger inverter equipment and more RE generating capacity) to never run the generator.  And then at 7 years you take it in the shorts with a $17,000 bill to replace a big battery bank.

That sort of puts in perspective how cheap using generator support to run the peak loads is, looking just at the cost of batteries.
--
Chris

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