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

[Allan Sindelar]

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

-----Original Message-----

Here's some good info:
http://photovoltaics.sandia.gov/docs/battery1.htm

or 
http://www.osti.gov/bridge/purl.cover.jsp;jsessionid=CC366D87BBE1C7C3BCBEEAF
D87A3D0D7?purl=/402426-htwdT8/webviewable/

or 
http://www.osti.gov/bridge/purl.cover.jsp?purl=/125071-E7W1qQ/webviewable/

Joel Davidson