Hybrid PV/Battery/Generator [RE-wrenches]

[Kent Sheldon]

If you have a Fluke 87 you can trust the RMS reading, as this Fluke is a
true RMS meter. Cheap meters assume sinusoidal, and calculate RMS from
.707 (root 2 / 2) of peak. These cannot be trusted. Also, using the peak
value to guess at RMS is not a good idea. If you've ever looked at a six
step waveform you will understand.

____________________________________________
Kent Sheldon
Manager, Industrial Power Systems
SMA America
ksheldon at sma-america.com
925 513 8813 Brentwood Office (Primary)
530 273 4848 Grass Valley Office




-----Original Message-----
From: Ray Walters [mailto:remotech at taosnm.com] 
Sent: Thursday, June 13, 2002 9:23 PM
To: RE-wrenches at topica.com
Subject: Re: Hybrid PV/Battery/Generator [RE-wrenches]

Hi Travis;

Have you tried the fast peak feature on your Fluke 87? You can catch the
voltage peak of the waveform, which gives you a fair idea if its
squaring
off or holding a sinewave. Its not as good as an O-scope, but its
another
parameter to look at. My old Honda was peaking at 135 under load even
though the rms voltage was still at 115. I beleive the the ratio for a
pure
sinewave is rms volts = .707 peak volts.  Somebody correct me if I'm
wrong,
but that would put peak volts at about 170 for an rms voltage of 120.

Ray

At 04:50 PM 6/12/02 -0500, you wrote:
>I'd be curious to know how a batteryless inverter would act with one of
the
>new "inverter" generators.  The ones that I've seen were all under 3kW.
I
>almost suspect that a batteryless inverter would not trip off line
until it
>overloaded the generator.  My crude testing showed that they output
some
>really nice voltage and frequency.  I don't know about the waveform
though. 
>Testing my 2800 watt Yamaha unit under various loads my Fluke 87 never
saw
>anything other than 60.0 Hz and never got outside of 118 to 122 volts. 
>Those measurements were taken continuously as I changed loads.  Very
>impressive little units.
>
>Travis Creswell
>Ozark Energy Services
>----------
>>From: Kent Sheldon <kentsheldon at sbcglobal.net>
>>To: RE-wrenches at topica.com
>>Subject: RE: Hybrid PV/Battery/Generator [RE-wrenches]
>>Date: Wed, Jun 12, 2002, 3:15 PM
>>
>
>>Brad, I know of a handful of installations that have tied SMA Sunny
Boy
>>inverters to generators. We haven't had any follow up phone calls
saying
>>they didn't work. The SB inverters rectify the AC voltage sense to DC,
>>so this will normalize any error caused by ripple or harmonic
>>distortion, assuming it isn't bad enough to skew the true RMS value
>>greater than +/- 10%. One thing to watch out for: The SB inverter will
>>attempt to deliver current up to the limit of the inverter(s) tied to
>>the generator. If the load is not large enough to consume the current,
>>the excess will backfeed the generator, causing it to trip offline on
an
>>over-voltage, or reverse current fault. This generally means that
>>grid-tied inverters are only tied to very large generators where the
>>load is known never to dip below the output of the available PV power.
>>In general, the larger the generator, the better its voltage fidelity.
>>
>>Regards,
>>
>>____________________________________________
>>Kent Sheldon
>>Manager, Industrial Power Systems
>>SMA America
>>ksheldon at sma-america.com
>>925 513 8813 Brentwood Office (Primary)
>>530 273 4848 Grass Valley Office
>>
>>
>>
>>
>>-----Original Message-----
>>From: Brad Bassett [mailto:bsbassett at earthlink.net] 
>>Sent: Wednesday, June 12, 2002 12:53 PM
>>To: RE-wrenches at topica.com
>>Subject: RE: Hybrid PV/Battery/Generator [RE-wrenches]
>>
>>Antony,
>>
>>The window of operation for a grid tied inverter is so tight now that 
>>the chances of one synchronizing with a generator is about nil. I saw
an
>>
>>attempt to get a 20 kW trace tech inverter to synch with a new 100 kW 
>>Kohler top of the line generator, and it never even came close. The 
>>longest I saw it try before an error on voltage (high and low) or 
>>frequency was about 3 seconds, and it takes 5 minutes of good power to

>>synch. 
>>
>>With a smaller generator such as would be used for a residence the 
>>chances would be even smaller. Still it might not be a bad idea to 
>>disconnect the inverter while on generator power to prevent any
possible
>>
>>backfeed of dirty power from the generator into the inverter (JB could

>>this be an issue with SMA?).
>>
>>Another option is to use a battery based backup system for critical 
>>loads, and grid tie inverters for the solar. I wonder if you could get

>>them to synchonize with each other!? (Put the grid tie on utility side

>>of backup inverter). Or a combination of battery based and straight
grid
>>
>>tie systems. With some musical relays you could transfer the solar
aray 
>>from the grid tie to the batteries during an outage. I'll let someone 
>>else do that science project!
>>
>>You also mentioned using a larger inverter, let me know if you find
one 
>>that's not a scince project in itself.
>>
>>Brad
>>
>>
>>Antony Tersol wrote:
>>
>>> 1. If we go with straight grid-tie batteryless PV, we would need a
>>> transfer switch downstream, so that the PV wouldn't be running in
>>outage
>>> situation when generator is on.
>>> 
>>
>>
>>
>>Brad Bassett
>>Schott Applied Power 
>>Tumwater, WA office
>>bsbassett at earthlink.net
>>
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>
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