[RE-wrenches] AC coupling induction generators (was Solar and pumped hydro)

[Brian Teitelbaum]

Hi Phil,

I do a fair amount of hydro system designs, but have never run into a scenario where AC coupling of the hydro unit would work or make sense. While all of the brushless microhydro units on the market (nano-hydro? pico-hydro??) do have three-phase AC output, it's at wild voltage and frequency. It's certainly possible to rectify that to high voltage DC and run it through a grid-tie inverter for use in an AC coupled system (or direct grid-tie), but it's really easier and cheaper to just run that DC into the battery, and use a diversion controller, as long as you already have a battery bank.

The other issue that you run into is the voltage spike that occurs if the hydro/grid-tie inverter system is disconnected from the AC line, either because of a grid failure, or to regulate the battery charging. This requires the use of a rather expensive voltage clamping device, which greatly adds to the system cost. Without the clamp, you will likely have damage to the system if and when the AC is disconnected. In an off-grid system, you could just use a diversion load to control the battery charging (rather than interrupt the AC connection to the grid-tie inverter), but if you ever have the battery-inverter shut off, you will likely have damage. It's really just safer to connect the hydro unit to the DC system directly.

Brian Teitelbaum
AEE Solar




From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Phil Schneider
Sent: Tuesday, August 25, 2009 4:17 PM
To: RE-wrenches
Subject: [RE-wrenches] AC coupling induction generators (was Solar and pumped hydro)

Jay mentions a topic that I've had a question about.  Has anybody AC-coupled an induction generator (wind or hydro) with a conventional battery based inverter?  On the surface it seems that it would work fine as long as there were appropriate means included in the design to avoid over-charging the battery.  Maybe one of you off-grid hydro Wrenches has done this.  Thanks for any insights...

Phil

On Tue, Aug 25, 2009 at 5:00 PM, jay peltz <jay at asis.com<mailto:jay at asis.com>> wrote:
Hi Keith,

Sorry about #4, should have said " pumped storage just isn't practical for small systems.

So the long version is that to get away from batteries, you would need whats called an AC direct hydro.
This hydro would power the AC loads directly, no inverters, no batteries.
What gets tricky is that since the hydro has to power EVERYTHING including surge it needs to be pretty large for many of todays loads.
So 8 kw would be pretty small ( about a 4kw inverter system ) and 15kw+ not uncommon for an AC direct system.
Which means you need a lot of water/drop to get this kind of watts from your hydro.

In getting away from batteries, inverters etc its a very cost effective and reliable system, and really about the ultimate system.  Typically these systems run for years, decades without problems, with a bit of maintenance of course.

Besides the turbine you need a controller system that will keep the voltage constant.  These use SS controls with diversion loads to keep the voltage constant under all loads ( within the parameters of the system) so you don't blow things up when the compressor turns off or on for that matter.
One benefit of these dump loads is that you can make hot water for domestic and space heating, air conditioning, leave lights on, you name it.

Hope this makes sense,

jay

peltz power

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