At long last, here is a synopsis of the Bobolink Mobile Solar Water System.
The BMS consists of three components:
1. Solar module
Two 64 watt amorphic polycarbonate solar panels mounted on an
adjustable-tilt frame. These are mounted on a standard wooden freight
pallet, which can be easily moved with the fork attachment on the
tractor loader, or by two husky people. Also on the pallet are a 100
amp-hour 12 V deep-cycle marine battery, a battery charge controller, a
+-10 amp current meter, and a 4 joule 12V fence charger, to keep nosy
cows from looking to see what's under the pallet.
The solar module can be placed in the middle of the pasture, to get
full light. It is attached to the rest of the system by #12 braided
pair copper cable rated for ground contact. This is the type of cable
that is usually sold for hooking up low voltage garden lights, so it can
be gotten at any store that sells frivolous crap. the #12 is better
than the #14 for long runs, as there can be significant voltage drops at
12 volts over long distances.
2. Pump module
This module is meant to be set on the river bank, in the shade if
possible. It has a 10 ft suction hose for drawing water from the creek,
a 5 gallon per minute (20 lpm) positive-displacement pump, some
plumbing, a 0-60 PSI well pressure gauge, a well pressure switch
(contacts close on pressure drop), and a 10 amp fuse to protect the
pump. The pump is fitted with a dry-run switch, a thermally-activated
breaker which protects the $450 pump from self-destruction if the creek
drops and the inlet runs dry.
I chose the more expensive positive displacement pump over a much
cheaper centrifugal pump because the PD is very, very energy efficient,
and therefore the system can pump all night and late into the season,
use lighter duty cable, be more flexible in terms of placing the solar
module further from the creek, etc. The bad news is that PD pumps
cannot tolerate any sort of grit in the water, so you have to filter the
inlet.
3. Inlet module
This is the part that goes in the creek: it consists of a 30"
spun-poly filter mounted inside a perforated 6" septic field pipe. The
ends are capped with drain grill fittings, held in place by large
stainless steel hose clamps. The poly filter is connected to the
suction hose via a foot-valve, which keeps the pump from losing prime
when you move the system.
So far, I've built two of these and have had little trouble with them.
There is no need for a pressure tank if you use garden hoses to connect
the pump to the float valves on the water trough: a 50 foot hose has
enough volume and elasticity to keep the pressure switch from
chattering. The filter needs changing when the pump begins to run
noisily, or when the dry-run switch shuts the pump off. From a very
silty creek, 40 young stock took a month to silt up a filter, which I
replaced with a new one ($5 each). The old filter was allowed to dry in
the sun and then I blew it clean woth an air compressor and got another
month out of it.
Connected to a 100 gallon trough, this system kept 40 calves, yearlings,
and 2 year olds quite happy through a very hot June and July. The
trough was never empty, not even before daybreak. This was with the
solar arry in partial shade, aimed haphazardly towards the south, set at
the correct angle for October.
In theory, the pump take 20 minutes to fill the trough, and the 100 amp
battery should provide ten hours of pumping overnight. The 128 watts
of solar panel can supply the 8 amps to run the pump while still
charging the battery.
Sorry about the roughness of this description, but I'm pressed for
time. a more polished article on the subject will be forthcoming,
probably in Stockman's Grassfarmer.
--
Jonathan & Nina White, cheesemakers
Bobolink Dairy & Bakeyard
Vernon, NJ USA
