Water Storage for Solar Water Pumps12.5
Storage Tank Capacity Generally, storage capacity
should equal 3 to 10 days of average water consumption,
or more. This depends on the climate and usage patterns.
For domestic use in a cloudy climate, 10 days is minimal. In
a sunny climate, this allows for a generous safety margin.
For deep irrigation of trees (where the soil holds moisture
for a week) 3 days’ storage may be adequate. For irrigating
a garden, 5 days may be adequate. You cannot store too
much water!
Storage Tank Plumbing This illustration shows many
options. They are not all required, but are illustrated for
purposes of discussion.
We suggest that you place your normal point of discharge
higher than the bottom of your water tank, in order to hold
a reserve so that the tank does not run completely dry.
You can lose your water supply under any of these condi-
tions:
a period of low sunshine and/or excessive water 1.
demand
an electrical or mechanical failure in the system2.
a leak in the tank or piping3.
an accidental discharge of stored water4.
Place a second outlet valve at the bottom level of your stor-
age tank, to use the reserve supply in case of emergency.
Pipe sizing The pipe from the pump to the tank may
need to be larger than the pump outlet, depending on the
flow and the length of pipe. A single pipe may be used for
both fill and discharge. In that case, size the pipe for the
maximum discharge that you want to accomplish. You
may oversize the pipe if there is a chance that you may
install a second pump, or larger pump in the future. Sizing
the pipe larger than necessary will NOT influence the
performance of the system. See section 13.3, Water Pipe
Sizing Chart
Air Vent
Required if top of tank is sealed,
particularly if the tank is buried
Inlet Pipe (optional)
Feed well water in at this level if you want the pipe
from the well to drain after the pump stops (see
“Freeze Protection”). Your choice of inlet here at top of
tank will not significantly effect pump performance.
Overflow Outlet
If float switch is used: this drains excess water safely
away in case the float control system fails. If float
switch is not used: this can send water to additional
storage or irrigation.
Refresher Valve (optional)
A slow leakage of water at this level will cause the
pump to refresh the water periodically during times
of low demand.
Main Shutoff Valve (normally open)
Reserve Shutoff Valve
Drain / Cleanout Valve
To Water Distribution System
In-/Outlet Pipe
A single pipe can handle water going both into and
out of the tank. Note the relatively large size of the
main discharge pipe This facilitates gravity flow with
minimal pressure loss.
Monitoring Valve
(optional)
Water Well
Water Meter
(optional)
Check Valve
(spring-loaded type)
Pressure Sensor for
Wireless Level Control
Float Switch
on
off
cable to pump controller
If you plan to use gravity-flow to supply water from the
storage tank, be sure the discharge pipe is large enough to
allow sufficient flow to meet the maximum water demand
without excessive friction loss.
Pressure of delivery Every 2.3 ft (0.7 m) vertical feet
of drop produces 1 PSI of pressure, minus any friction loss
(10 m produces 1 bar). The volume of water stored in the
tank does not effect the pressure delivered.
Water Purification Check local health authorities
and/or plumbing codes to ensure you will comply with
requirements for using a storage tank that is open to the
atmosphere, for potable water. Sanitation by means of
chlorination, ozone or infrared system may be required or
recommended.
Wireless Level Control for Full-Tank Shutoff
(optional) This eliminates float switch and cable. It uses
a pressure sensor on the pipe. See Automatic Control for
Full-Tank Shutoff.
Water Storage SystemFigure 34:
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