[RE-wrenches] Sandia study - WAS Strings and series of batteries with reverse return linkup

jay peltz jay at asis.com
Sat Dec 5 07:19:53 PST 2009


HI Allan,

Here is an interesting way that statistics can make bad results.

It might be that 64% of all solar batteries are VRLA, but I would guess that most of the those "systems" are single battery ones.
Such as road call boxes, lighting etc which number in the 10's of thousands of systems but only have 1 or 2 batteries per system.  

So while I cannot validate the numbers they could be both correct and also very misleading.

jay
peltz power
On Dec 4, 2009, at 9:42 PM, Allan Sindelar wrote:

> There's an interesting "back story" to the 1996 battery study you cite,
> Joel. It illustrates the pitfalls that can occur when you don't ask the
> right questions of the right people.
> 
> I reviewed that study a few years later, and was surprised to read that Mr.
> Hund's survey suggested that 64% of batteries used in PV systems were VRLA.
>> From that study:
> 
> "Table 1 presents a preview from the battery survey listing total flooded
> and VRLA
> battery sales from the 21 PV system integrators for 1995. The data indicates
> that
> 64% of the PV batteries sold are VRLA with a dollar value of $3.4 million." 
> 
> My own observation suggested that this number was way off: I knew of
> virtually no one who used sealed batteries for typical residential off-grid
> homes.
> 
> I had the opportunity to question Mr. Hund about this at some technical
> forum. When he explained that this number came from a survey of RE
> wholesalers' battery sales, it all made sense. Sealed batteries can be
> shipped; flooded batteries are generally delivered by trucks operated by
> battery wholesalers. If you only ask RE distributors what they sell, the
> answer will reflect this reality. Mr. Hund asked the wrong people, and drew
> an erroneous conclusion from the answers he received. 
> 
> A year or two later I was talking with someone in tech support at
> Morningstar; I think it was about how easy it was to default the charge
> voltage setting on an early ProStar controller to the VRLA setting. If you
> ever disconnected battery DC to the controller, it repowered up at the lower
> VRLA voltage, and must be reset each time to the higher settings needed for
> flooded batteries. The technician defended the structure by referring to a
> Sandia study that found that nearly 2/3 of batteries in PV systems were
> VRLA. When I explained the fundamental flaw in the study that led to that
> conclusion, the Morningstar technician was pretty surprised. A year or two
> later, the second-generation ProStar was released, that is still in current
> production, with a rotary switch setting that is set once and returns to the
> same setting - gel, VRLA, or flooded - when powered up.
> 
> I have long remembered this as a good lesson in how poorly crafted research
> can result in unintended consequences.
> 
> Allan Sindelar
> Allan at positiveenergysolar.com
> NABCEP Certified Photovoltaic Installer
> EE98J Journeyman Electrician
> Positive Energy, Inc.
> 3201 Calle Marie
> Santa Fe, New Mexico 87507
> 505 424-1112
> www.PositiveEnergySolar.com
> .members.re-wrenches.org
> 




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