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13.4 Water Storage for Solar Water Pumps
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 re-
quired, 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 conditions:
1. a period of low sunshine and/or excessive
water demand
2. an electrical or mechanical failure in the
system
3. a leak in the tank or piping
4. an accidental discharge of stored water
Place a second outlet valve at the bottom
level of your storage 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 13.2, Water Pipe Sizing Chart.
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 feet vertical
feet of drop produces 1 PSI of pressure,
minus any friction loss (10m 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.
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
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
Float Switch
on
off
cable to
pump controller
