|
Photovoltaic
(PV) panels produce electricity from sunlight using silicon
cells, with no moving parts. They have been mass-produced
since 1979. They are reliable that most manufactures give
up to a 25-year warranty they work well in cold or hot weather.
Solar
water pumps are specially designed to utilize DC electric
power from photovoltaic panels. They must work during low
light conditions at reduced power without stalling or overheating.
Low volume pumps use positive displacement (volumetric)
mechanisms, which seal water in cavities and force it upward.
Lift capacity is maintained even while pumping slowly. These
mechanisms include diaphragm, vane, and piston pumps. These
differ from a conventional centrifugal pump that needs to
spin fast to work efficiently. Centrifugal pumps are used
where higher volumes are required.
A
surface pump is one that is mounted at ground level. A submersible
pump is one that is lowered into the water. Most deep wells
use submersible pumps.
A
controlled or current booster is an electronic device used
with most solar pumps. It acts like an automatic transmission,
helping the pump to start and not to stall in weak sunlight.
A
solar tracker may be used to tilt the PV array as the sun
moves across the sky. This increases daily energy gain by
as much as 55%. With more hours of peak sun, a smaller pump
and power system may be used, thus reducing overall cost.
Tracking works best in clear sunny weather. It is less effective
in cloudy climates and on short winter days.
Storage
is important, three to ten days storage may be required
depending on climate and water usage. Most systems use water
storage rather than batteries, for simplicity. A level sensor
can turn the pump off when the water tank fills, to prevent
overflow. A similar control can turn the pump off if the
water source is drawn too low.
Compared
with windmills, solar pumps arte less expensive, and much
easier to install and maintain. They provide a more consistent
supply of water. They can be installed in valleys and wooded
areas where wind exposure is poor. A PV array may be placed
some distance away from the pump itself, even several hundred
feet (100 m) away.
What is
it used for?
Livestock watering: Cattle ranchers in North America,
Mexico and Australia are enthusiastic solar pump users.
Their water sources are sources are scattered over vast
rangeland where power lines are few and costs of transport
and maintenance are high. Some ranchers use solar pumps
to distribute water through several miles (over 5 km) of
pipelines. Others use portable systems, moving them from
one water source to another.
Irrigation:
Solar pumps are used on small farms, orchards and gardens.
It is most economical to pump PV array direct (without a
battery), store water in a tank, and distribute it by gravity
flow. Where pressurizing is required, storage batteries
stabilize the voltage for consistent flow and distribution,
and may eliminate the need for a storage tank.
 Domestic
Water: Solar pumps are used for private homes, villages
medical, clinics, Schools etc. A water pump can be powered
by its own PV array or by a minimal system that power lights
and appliances. In a combined system, more configurations
are possible. An elevated storage tank may be used or a
second pump called a booster pump can provide water pressure.
Or, the main battery system can provide storage instead
of a tank. Rain catchments can supplement solar pumping
when sunshine is scarce. To design a system, it helps to
view the whole picture and consider all the resources.
Thinking small
There are no limits to how large a solar pump can be built.
But, they tend to be most competitive in small installations
where combustion engines are least economical. The smallest
solar pumps require less then 150 watts, and can lift water
from depths exceeding 200 feet (65m) at 1.5 gallons (5.7
liters) per minute. You may be surprised by the performance
of such a small system. In a 10 –hour sunny day it can lift
900 gallons (3400 liters). That’s enough to supply several
families, 30 head of cattle or 40 fruit trees!
Slow solar pumping lets us utilize low-yield water sources.
It also reduces the cost of long pipelines, since small-sized
pipe may be used. The length of piping has little bearing
on the energy required to pump, so water can be pushed over
great distance at low cost. Small solar pumps may be installed
without heavy equipment or special skills.
The most effective way to minimize the cost of solar pumping
is minimize water demand through conservation. Drip irrigation,
for example, may reduce consumption to less than half that
of traditional methods. In homes, low water toilets can
reduce total domestic use by half Water efficiency is a
primary consideration in solar pumping economics.
 A
Careful Design Approach:
When a generator or utility mains are present, we use a
relatively large pump and turn it on only as needed. With
solar pumping, we don’t have this luxury. Photovoltaic panels
are expensive, so we must size our systems carefully. It
is like fitting a suit of clothes: you need all the measurements.
Here is a guide to the data that you will need to
determine feasibility, to design a system, or to request
a quote from us SUN’NRG.
Solar pump
Design Questionnaire
1.
Well depth or description of water source
2. Depth to water surface: Does it vary?
3. Yield of well in gallons per minute
4. Total vertical lift from water surface to
outlet
5. Inside diameter of well casing
6. Water requirements in gallons per day according
to season
7. Will other sources of water be available
8. Use of water. Home Livestock Irrigation
9. Describe any existing system at the site.
10. Quality of water: Clear Sandy Mineralized Other
11. Is pressure required for delivery?
12. Can a storage tank be located higher than the
point of use?
13. Will the pump be located near a home/battery system?
Distance?
14. Geographical location of system, plus any solar
data available.
15. Solar access: Describe any obstructions at the
system site.
16. Complex terrain? Include a map or diagram
17. Gravity feed System
Our
first choice for a domestic water system is gravity feed.
With gravity feed, water is stored in a large holding tank
above the house and ideally is filled from a water source
above the point of storage. (For every foot of elevation
get 45# pressure.) If a site does not allow for direct filling
of the tank then an AC or DC pump will have to be used.
|
