[RE-wrenches] PV driven air compressor

[Phil Undercuffler]

In my experience, there's few problems in the world that can't be solved
with more PV -- including running pumps with permanent magnet/brush motors
array direct.  However, there's a couple things to be aware of -- first,
sizing the array.  Although the pump may be rated to draw 90 watts when
running, you need to oversize the array to ensure 90 watts will be available
under normal daily conditions.  The exact amount of oversizing depends upon
many factors, but without further testing I'd ballpark an additional 30%
over rated running watts.  Also, the array needs to be larger if the pump
starts under load, which is highly likely with an aerator (probably doesn't
have an unloader valve, if those work with aerators at all).  So far,
everything leads one to say, rock on with the 180-200 watt modules.

But, it's sometimes not so easy.  Most 190-200 Watt modules available today
have 60 cells, and don't nicely align with 12 or 24V "nominal" voltages.
 Does your aerator come in two flavors, 12V or 24V, please specify your
preferred voltage upon order?  Or does it have electronics built in, and
will take anything in a range between 12V and 24V (unlikely, but possible)?
 If the former, then you really need to find some module combination that
provides 36 or 72 cells in series -- otherwise, you'll either run the pump
under or overspeed, which will impact longevity and performance.  If the
latter, make sure it will be happy with the voltage the module puts out --
over the full range of conditions.

Empirical testing can sometimes be the best approach with a project like
this, but it's a good idea to do a little homework beforehand, to best know
what the expected behavior should be.  Good luck with it, it sounds like a
fun project!

Phil Undercuffler






On Tue, May 25, 2010 at 9:30 PM, Howie Michaelson <howie at suncatchervt.com>wrote:

> Hi all,
>
> I have a project to provide PV power for a small diaphragm air pump (1/8
> hp, 12 or 24 vDC, 6.2 or 3.5 running amps, 90 watts).  As it turns out,
> pricing from my distributor is cheaper for 180-200 watt modules than for
> anything smaller.  I don't spec PV driven pumps except for SHW, so I'm
> just checking for any reason to not use the larger modules.  The pump is
> being used to aerate a pond, so no problem with excess pumping.  I will
> most likely use a linear current booster to improve output, but mostly to
> limit voltage.  Any advice would be welcomed.
>
> Thanks,
> Howie
> --
> Howie Michaelson
> NABCEP Certified Solar PV Installer™
>
> Sun Catcher, LLC
> Renewable Energy Systems Sales and Service
> VT Solar & Wind Incentive Program Partner
> http://www.SunCatcherVT.com
> (cell) 802-272-0004
> (home) 802-439-6096
>
>
>
>
>
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