[RE-wrenches] PV powered music festival

Wed Apr 27 20:26:16 PDT 2011

Benn,

I totally agree with everything Brian and Jason said, especially the aspect of the chronic and *significant* UNDER-estimation of the power needs by the sound equipment crew.

Earlier comments in this thread from Larry (Starlight Solar), Ray Walters, Jason (Fafco Solar) are also spot on.  They all clearly know of what they speak.

I also absolutely want to reinforce Brian's recommendation that you use a *quality* sine wave inverter -- one that's capable of reacting fast enough for the wild swings in power demand placed on it by large audio amplifiers.  As Brian mentioned, the Exeltech MX will do this.  I've been using MX inverters to provide power for Grammy award winning bands.  I have feedback from every audio engineer who's ever used solar power from the Shuttle -- and they all agree (yes, 100% of them) .. the power from the MX is cleaner than any power they've ever used, including at their recording studios.  Keep in mind .. just because an inverter has sine wave output doesn't mean it's capable of reacting quickly to keep the output voltage stable.

Brian .. by the way .. don't worry about running the MX in the red.  This is an indication of the inverter being called on to deliver its max power, not an overload condition.  The MX are rated to run in the red at 100% of their rated power 24/7, and they'll do it for as long as your DC source holds out.  The inverter wasn't clipping the AC waveform in the red, even at less than 24Vdc input.  What the sound guy heard was distortion in either the amplifier(s), speakers, or both.  This could have been caused if their extension cords from the MX inverter were too light for the load current .. but wasn't the MX inverter.  It'll deliver a sine wave down to less than 22 volts, and will turn off due to DC undervoltage before the sine wave begins to clip.  Since it continued to operate .. you were getting a clean sine wave the entire time.

Benn .. I've been powering outdoor events for more than 10 years.  Here's a link to a PDF on my solar trailer (the "Solar Shuttle"):

http://www.txses.org/NTREG/dnld/SolarShuttleInfo_2010.pdf

If you wish to see photos of the Shuttle under construction, here's a link:

http://www.txses.org/NTREG/projects.htm

The Shuttle has 2150 watts in PV, dual Blue Sky Energy MPPT charge controllers, 20 kWh in battery, and 12 kW in Exeltech MX sine wave inverters.  It's all been flawless, including operation at over 100F.  Full specs are on the last page in the PDF.

The trailer will power events for up to 15,000 people (+/-) depending on a number of variables.  The largest event it's ever powered had 18,000 attendees.

Things to avoid at all cost:

Incandescent stage lamps.  Period.  (Dan from FoxFire and Jason from Fafco are 100% on target on this.)

* Tube amplifiers of any kind.
* Class 'A' amplifiers (tube or solid state - doesn't matter).
  Most sound people and musicians are clueless about this aspect
  of their equipment. You'll have to either get the make and model of
  the amps and talk with the respective manufacturers .. or go to a lot
  of trouble to measure idle power for each.

* Events at night.  For events after dark, you're running totally on battery.
  This can be a pain.  For significant power draw at the event, you'll need
  very *BIG* batteries.

As Brian mentioned, amplifier "idle power" can be a killer.  I provided power for a soundstage last Saturday for a small Earth Day type event that ran for 10 hours, and attracted 5,000 people.  The stage had 7 kW in audio amplifiers, plus mixers, monitor amplifiers, and other electronics.  They frequently hit 10 kW+ on audio peaks, and consumed 1.8 kW just sitting there.  Thankfully, we had pretty good sun and the PV was able to keep up much of the day.  This was a *small* sound stage.  Brian T. and Dave Katz have handled some monster stages by comparison.

Remember too .. headliner bands tend to be the loudest and most power-hungry of the groups.  They're generally the last ones on stage, just when the batteries are really getting tired.

Jay's comment about blowing fuses also merits a comment.  Fuses are appropriate in many applications.  I don't feel that applies here.  I used DC-rated magnetic hydraulic breakers with appropriate amperage and AIC ratings in the Solar Shuttle systems.  They're very expensive but aren't affected by temperature (as are fuses and ordinary breakers).  Breakers aren't as fast as fuses during an over-current protective event, but they can be turned off .. or re-set.

Powering events can be a lot of fun yet nerve-wracking all at the same time.  One excellent benefit .. you get a front-row seat for the music.  You also sit there and hope the batteries hold out -- you're a front-and-center target for the music fans if they don't.

If you want to discuss the Shuttle in detail, and/or powering events in general, contact me off list and I'll be happy to cover whatever info I can.

Dan

--- On Wed, 4/27/11, Brian Teitelbaum <bteitelbaum at aeesolar.com> wrote:

From: Brian Teitelbaum <bteitelbaum at aeesolar.com>
Subject: Re: [RE-wrenches] PV powered music festival
To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
Date: Wednesday, April 27, 2011, 8:13 PM

Benn,  I have a little experience from about a decade ago. Don’t know how useful it will be though.  AEE and DC Power used to team up to supply power for a three-day outdoor music festival in Mendocino Co, CA in the mid 90’s and early 2000’s. Music from 5-8PM on Friday, and from 11AM-10PM on Sat and Sun.  I don’t know how big the crowd was  - 5-6000 I would guess.  We would bring a rack-mounted 12kW Exeltech MX inverter set-up (24V and not even N+1 redundant) and 5-6kW of PV (a lot of 120W modules). DC Power would bring two big tractor-trailer loads of industrial wet-cell batteries (I have no idea what the total amp-hours were, but a hell of a lot).  The sound crew would show up each year with a bigger set-up, even though we warned them that the power supply was limited. Stage lighting was left on generators running biodiesel.  The last year that we did it, the sound guys showed up with a sound system rated at 14kW. It drew 6kW just being
 on with no sound. Not even a hint of buzz or hum from the inverter power. The MX is good stuff.  I nervously watched that Exeltech all weekend as the bar graphs on each power module stayed in the red over-load range for most of each band’s set. When the drummers or bass players would go nuts it was all red lights. We were measuring up to 600A of current flowing through the four pairs of 4/0 cables coming from the batteries, and a good bit of voltage drop as the cables were at least 30’ long. The inverter was seeing less than 24VDC most of the time. The cooling fans on the MX modules would run for 20-30 seconds, and shut off for a minute or two and then come on again. This is with temps in the upper 90’s, and the inverter sitting on the ground under the stage. Even with all this torture, the Exeltech never even hiccupped, which was quite impressive. The sound engineer was hollering at us that the inverter was clipping off the high notes, but
 neither I, nor the audience ever noticed. All I could do was shrug and tell him that he was warned about limited power availability. The music was great.   By the end of the weekend, those batteries were pretty drained, so it’s hard to actually say that the show was “solar powered”. Sitting around with a few beers afterwards, we all agreed that the ranch owners could install a 2kW grid-tie system on a tracker at the concert site and that system would produce all the energy needed for the show in a year’s time, likely including the energy use for the lighting and by the vendors. This would have required that utility power be brought to the site, which would have been a rather expensive deal, but would have made more sense, and would have made it a more truly solar-powered event.  Brian TeitelbaumAEE Solar  From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of benn kilburn
Sent: Wednesday, April 27, 2011 3:51 PM
To: Wrenches
Subject: [RE-wrenches] PV powered music festival  Wrenches,I have been asked about sizing PV systems for a couple different music festivals that have been run solely off of generators in the past.  The problem i'm having is determining the energy consumption of music/stage (amps, speakers, lights, etc...?) loads as well as concession.  The organizers have never considered the kwh of electricity used and it has never been metered.  I believe the attendance of one festival is expected to be in the range of 5000 and the other closer to 15000 over the course of a weekend.  Do any of you have any experiences in this area?  How were the loads determined?  No doubt that generator back-up will still be needed, to what extent, will be determined.  So what we're looking at would be a temporary off-grid PV system with generator back-up...  Any suggestions on how to proceed with this one?  benn

DayStar Renewable Energy Inc. benn at daystarsolar.ca780-906-7807 HAVE A SUNNY DAY     
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