Download FIELD TESTING OF PHOTOVOLTAIC ELECTRO

FIELD TESTING OF PHOTOVOLTAIC ELECTRO-CHLORINATION
APPLICATION IN SALT WATER SWIMMING POOLS
Kame Y. Khouzam
School of Electrical & Electronic Systems Engineering
Queensland University of Technology
GPO Box 2434, Brisbane, QLD 4000
AUSTRALIA
Telephone:
+61 07 3864 2483
Facsimile:
+61 07 3864 1516
E-mail:
[email protected]
Abstract
The process of electro-chlorination by photovoltaic was demonstrated for producing liquid chlorine
in swimming pools. The system comprises a PV array, an electrolysis unit made of specially designed
anti-corrosive electrode, and associated instrumentation. Results showed that proper matching can be
achieved by carefully selecting the PV parameters w.r.t. the electrolytic load. Using PV for water
chlorination is an effective method to semi-automate the input of chlorine into the pool. The process
offers technical and environmental advantages, and savings in electricity bills. This project aims to
develop commercial PV chlorinators for application in private and public swimming pools for local
and export markets.
1
INTRODUCTION
Most chlorine is industrially produced by the electrolysis of salt water (sodium chloride). This involves the passage of
direct current through salty water to produce chlorine gas at the positive electrode. Chlorine and its compounds are
used extensively for disinfecting municipal water supplies, for bleaching in the paper and textile industries, for
household bleaches and germicides, and for the production of many organic and inorganic chemicals.
In this project, photovoltaic (PV) power was applied to specially designed electrode cells for the production of liquid
chlorine (sodium hypochlorite) for use in in-line chlorination in salt water swimming pools. Several systems were
installed in public and residential pool sites. Each system comprises PV panels, electrolysis cell, associated control and
data acquisition and are monitored for twelve months. Data include voltage and current, solar radiation, temperature,
chlorine level, pH, water temperature and quality, and pool usage.
The PV-based chlorinator project received funding from the Office of Sustainable Energy Industries, Environmental
Protection Agency under state approved “Queensland Sustainable Energy Innovation Fund”. A feasibility analysis
began in 2000 to develop an alternative PV power source to replace mains power for the production of chlorine in salt
water swimming pools. The new system must offer the same level of performance (if not better) as offered existing
commercial power units. The proposed PV chlorinator system must be simple to operate, safe and cost effective. The
testing phase of the project was concerned with the chlorination parameters and the economic study. The second phase
of the project seeks to:
•
•
•
•
Install the world’s first PV-based chlorination systems for water treatment in public and private pools.
Analyze electro-chlorination parameters, solar radiation, and correlation to pool usage for optimum performance.
Get customer feedback for further development of PV chlorinators and boost confidence among consumers in the
product.
Develop a commercial turn-key package suitable for domestic and public pools and facilitate the marketing of PV
based chlorinators.
Field Testing of Photovoltaic Electro-Chlorination Application in Salt Water Swimming Pools
K.Khouzam
Allchlor Pty Ltd, project partner, with Queensland University of Technology have been working on the development of
the PV-chlorinator system and on experimenting of electrolytic parameters and electrode materials and coatings. Work
is also underway to develop a new electrode to better match the PV characteristic to provide for higher performance.
Several types of electrodes (low and high voltage) are being experimented and further enhancement will be made to
design a choice electrode. Additional funding has been provided to achieve the following goals:
1.
2.
3.
2
Expand the use of PV power to water pumping and filtration.
Improve overall system performance. This includes integrating the system to the grid. Other backup options will
also be considered.
Consider alternative electro-chlorination methods.
SWIMMING POOL CHLORINATORS
Salt water chlorinators have been in the market for over thirty years and their technology is well known. The principle
of operation is as follows: salt is added to the swimming pool water, bringing its salinity to a level of between 5,000
and 9,000 parts per million. Salt is periodically added since the salinity level may drop due to flooding, or when water
is lost through overflowing. Evaporation of water will only concentrate the salt level and will be diluted when water is
added. A chlorination cell consisting of anti-corrosive plates is installed within a sealed unit in the pump line, so that
when the pump is operating water flows through the plates and salt water is electrolyzed. In practice the plates are
titanium with the anode often being coated in platinum. Platinum serves as an effective catalyst, that speeds up
chemical reactions but is not itself changed in the reaction.
Commercial chlorinators require expensive power conditioning equipment to convert mains 240 V ac to a low volt dc
(between 7.2 to 9.6 V). When dc voltage is applied to the plates, current flows between them, electrochemically
transforming some of the salt water into chlorine gas, which instantly dissolves in the pool water forming the same
chemical compound present in liquid pool chlorine. The efficiency of chlorine production is dependent on a number of
parameters including cell design, water chemistry, temperature and salt concentration. The chemical losses incurred in
this process are in the range of 30 - 40%. Moreover, it was found that the electrical and magnetic losses in the power
conditioning unit amount to nearly 50%.
The process of water chlorination is safe and has no other effect on the pool water. The minimum recommended level
of chlorine is 1 gm/litres of water. Higher level of chlorine must be used at higher temperature and with heavy usage
of the pool. Super-chlorination must also be done (usually monthly) to increase the level of chlorine to at least 3
gm/litres.
According to manufacturers of pool chlorinators, savings of 70 - 80% can be made in the maintenance costs of a
swimming pool, by using salt-water chlorinators as opposed to granular chlorine additives. In other words, $25 worth
of electricity produces the same amount of chlorine, which is contained in $100 of dry chlorine. Further savings can be
achieved over the years if the power system is replaced with solar panels (Khouzam, 2000).
A salt water chlorinator offers the following:
•
•
•
•
•
3
Costs less than liquid or dry chlorine additives.
Automatically produces chlorine when the system is switched on, thereby eliminating the daily chore of adding
dry or liquid chlorine compounds.
Causes much less strain on the eyes than ordinary chlorine pools as salt balances the pressure on the eyes.
Eliminates stinging eyes, skin irritation and other health related problems.
Gives water softness and sparkle appearance.
CHARACTERISTICS OF PHOTOVOLTAIC MATCHING
The non-linear characteristic of PV panels can best be described with source providing ‘soft’ output. Unlike utility grid
(infinite bus) system, the operating point of a PV connected load (i.e. current and voltage) is determined by the
characteristics of both the PV source and the electrical load, with voltage and current limits. The PV characteristic
cannot be described as a voltage source but can be approximately described as a current source.
2
Proceedings of Solar 2002 - Australian and New Zealand Solar Energy Society
Paper
Field Testing of Photovoltaic Electro-Chlorination Application in Salt Water Swimming Pools
K.Khouzam
The quality of load matching in direct PV systems has been studied by a number of researchers including Appelbaum
(1987). These studies presented analytical work aimed at optimizing the matching performance. It was shown that
ohmic and in particular electrolytic type loads can offer performance advantage to the PV array if the respective
parameters are carefully selected (Khouzam 1990). The application of PV to salt water chlorination is no different.
Nevertheless, in order to get optimum performance, the following must be considered:
1.
2.
3.
Matching the array to the load via array sizing and, if practical, design modification to the electrolytic cell, so as
to maximize the load matching factor. There are two distinct issues to deal with: sizing of the array, and proper
load matching characteristics.
Devising a backup strategy to maximize reliability when the PV output is insufficient, e.g. battery, mains power,
other chlorine additives, or a combination. Most salt-water pools use another form of chlorination for boosting
(super-chlorination).
Devising a control strategy to maximize energy efficiency and optimize performance. This may be particularly
important in public operated swimming pools or where a backup system is employed.
A model has to be devised which quantifies the outcomes of various configuration concepts, in terms of reliability and
economics. It was found that the PV system offers these salient features:
•
•
•
•
•
•
•
•
Make use of the non-linear characteristic of PV generator; in its intrinsic matching quality.
No need for expensive power conditioning and auxiliary components.
Inherent over current protection; limited by short circuit.
Supply high quality dc (without ripple), which in turn offer more effective and sustained ion separation during
electro-chlorination.
Supply high current at required low voltage; a feature not readily available with conventional power sources.
Inherent gradual change in current and thus help protect the electrode cell and extend its life.
Inherent matching of incident solar radiation and chlorine production. This is true for the daily as well as the
seasonal variation.
Matching of chlorine requirement and solar availability in terms of location and usage.
The PV system must be sized (in terms of rated current and power) so as to produce the same amount of chlorine
required by the pool running using mains power as intended (usually for 8 hours). For example, since the average peak
sun hours (PSH) in Brisbane is approximately 5 PSH a factor of about 1.6 must be used to convert from conventional
system to PV system. This represents a reduction of the power system size by 20% when one accounts for the losses in
the conventional power unit. On the other hand, the electrode area must be sized to match the maximum allowed
current density expected at full sun.
The amount of chlorine produced is proportional to the amount of solar radiation. In practical terms, more chlorine is
produced using the PV system in summer than in winter. This feature is quite advantageous to compensate for the loss
of chlorine due to ultra-violet radiation and by evaporation. In addition, people usually use the swimming pool more
often when there’s sun. If PV system is to be used, oversizing may be necessary to compensate for cloudy periods.
Alternatively, a backup source of chlorine may be more cost effective.
Economic analysis was undertaken and showed that the PV system offers a payback period generally under five years
(Khouzam 2000). The result is more evident if the pool pump (in-line) normally operates during sunlight hours.
4
DEMONSTRATION SYSTEMS
At the time of writing, four installations were completed; of which two are in public pools owned by city councils
(Logan and Maroochy). Table 1 gives a listing of three PV chlorinator installations in Queensland. All systems are
performing well and are providing valuable feedback.
Figure 1 shows a schematic control diagram of a PV chlorinator installation in a public swimming pool at Palmwoods,
Maroochy Council, in the Sunshine Coast. A photograph of the system is shown in Fig. 2. As can be seen, the system
is supplied with dc volt from six 80 W PV panels (on top), which in turn supplies the electrolytic cell. Water is taken
through the inlet by the pool pump and is filtered. Chlorine is produced in the cell, and returns to the pool via the
pipe. A data acquisition system was installed to monitor the system. (The heater unit is optional).
Proceedings of Solar 2002 - Australian and New Zealand Solar Energy Society
Paper
3
Field Testing of Photovoltaic Electro-Chlorination Application in Salt Water Swimming Pools
K.Khouzam
Table 1. Summary listing of PV chlorinator installations in Queensland.
Pool Data
Owner /
Operator
Pool Type
Pool
Volume
Pool
Chemistry
Prior
Operation
Water
temperature
Ave. Usage
in Winter/
Summer
Changes to
operation
Date of
installation
Number of
PV panels
SX80
Panel tilt
angle
Panel
structure
Taringa
Private
Palmwoods
Maroochy Shire Council
Pallara
Private
Logan Central
Logan City Council
Inground painted
cement
55,000 L
Inground painted
cement
32,000 L
Inground painted
cement
57,000 L
Inground painted
cement
97,000 L
pH at 7.0-7.2
Chlorine at 2 - 3 ppm
Salt at 5 - 5.5 kpm
Power pack 20 A
pH at 7.0-7.2
Chlorine 1.5 - 2.5 ppm
Salt at 5.5 - 6 kpm
Power pack 50 A
pH at 7.0-7.2
Chlorine 2 - 3.5 ppm
Salt at 6.5 - 7 kpm
Power pack 20 A
Not heated
Heated 26 Deg
totally enclosed
Not heated
Partially shaded
pH at 7.0-7.2
Chlorine 2 - 2.5 ppm
Salt at 5.5 - 6 kpm
2 Power packs
100 A*14 V (7+7) each
Heated 27 Deg
fully enclosed
W: 0-2 people, 1-2 hrs
S: 3-4 people, 3-4 hrs
W: 10-50 people, 6 hrs
S: 50-100 people, 8 hrs
learn to swim pool
Power pack is used for
backup
W: 0-1 people, 1-2 hrs
S: 4-5 people, 3-4 hrs
PV: April 2001
D/Acquisition: July 01
4 * 80 W but 1 was
disconnected due to
excess chlorine level
PV: August 2001
D/A: September 2001
6 * 80 W in 6 V
configuration
PV: September 2001
D/A: September 2001
3 * 80 W for
chlorination and
1 x 80 W for pumping
15 Deg
19 Deg
25 Deg
W: 10-30 people, 8 hrs
S: 40-90 people, 8 hrs
learn to swim classes
One pack was
disconnected
2nd Pack was set to low
PV: March 2002
D/A: May 2002
8 * 80 W in 12 V
configuration connected
to two electrodes wired
in series
27 Deg
Standard panel frame
on pool shed roof
Standard panel frame
on roof over equipment
Power pack was
disconnected
On carport roof with
aluminium brackets
Pipe / Alum structure
forming roof over
equipment
Nil
Roughly 10% up to 9:45
Shading
am caused by trees
during winter
As normal by owner.
To operator/owner
operation
System is running as
requirements from 7 am
of pool
convection system
to 6 pm
with PV
Excess chlorine in
Low chlorine in early
Problems
morning (7 am) owing
for further winter resulting in
to low solar/PV output.
considera- disconnecting the
system and/or one PV
Also, excess chlorine on
tions
panel at a time.
sunny days by mid day
which result in manual
disconnection of system.
works well but needs a
Seems to work well
Feedback
controller to limit
during sunshine and
to date
excess chlorine
partially cloudy days
ORP control and use
ORP control and export
Recomenergy or battery
mendations excess energy or battery
storage
storage
Power pack was kept
but on lowest setting
Partial in late afternoon
during winter
Mostly in morning
during winter months,
no shading for 5 hours
8 hours or as suggested
Operator required (8
from sunrise to sunset
hours) or as suggested
from sunrise to sunset
Nil, except for a
Frequent cleaning is
suggestion to use
required. Develop
reverse polarity system reverse polarity control,
to reduce the frequency although not yet
of cleaning the cell.
commercially available.
Nil, customer is very
satisfied with system
Install reverse polarity
electrode system for
chlorination
No apparent problem.
Customer require more
instrumentation
Develop reverse polarity
control
Figure 3 shows a photograph of an installation in Pallara, south west of Brisbane. This installation runs three 80 W
panels for chlorination and a 80 W panel for water pumping. Figure 4 is a photograph of a PV chlorinator in a public
swimming pool owned by Logan City Council, south of Brisbane. In this installation a 12 V system was implemented
with two electrodes connected in series.
4
Proceedings of Solar 2002 - Australian and New Zealand Solar Energy Society
Paper
Field Testing of Photovoltaic Electro-Chlorination Application in Salt Water Swimming Pools
K.Khouzam
Figure 1. Schematic diagram of PV chlorinator system.
Figure 2. PV chlorinator in public swimming pool at Palmwoods in the Sunshine Coast.
Figure 3. PV water pumping and chlorinator system in Pallara south of Brisbane.
Proceedings of Solar 2002 - Australian and New Zealand Solar Energy Society
Paper
5
Field Testing of Photovoltaic Electro-Chlorination Application in Salt Water Swimming Pools
K.Khouzam
Figure 4. PV chlorinator installation in Logan City Council public pool south of Brisbane.
Alternative chlorination systems are considered and some are being implemented. These include in-line, convection,
floating, and submersible. Work has also commenced to install an interactive inverter to export excess energy when
the chlorine level exceeds 2.5 ppm.
5
CONCLUSIONS
The project has demonstrated the use of PV in an electrochemical process such as in the electrolysis of salt water for
the production of liquid chlorine for sanitization of salt water swimming pools and spas. The combined characteristics
of solar radiation and PV makes an ideal source for salt water chlorination. Several PV based chlorinator systems have
been installed in Queensland and are providing valuable feedback. The use of PV to the well established technology of
water chlorination shows that the process is technically and economically viable, and has substantial market potential.
The application also offers customers savings in electricity bills as well as environmental and aesthetic benefits. The
PV based chlorinator can replace mains ac power or alternatively used as retrofit in existing pools.
Given appropriate investment, PV chlorinators promise to make a valuable contribution to the renewable energy
industry. The efficiencies of PV devices and associated interfaces have increased tremendously and this has been
accompanied by a decrease in cost, making PV the best source for a variety of energy needs.
6
ACKNOWLEDGMENTS
This project is supported under the Queensland Sustainable Energy Innovation Fund. Additional funding was provided
by QUT and Allchlor. Mr. Jeff Braithwaite provided technical expertise to the design of the electrodes. The author
acknowledges the expert advice provided by Dr. Martin Gellender, Environmental Protection Agency.
7
•
•
•
•
6
REFERENCES
J. Appelbaum (1987), “The Quality of Load Matching in a Direct-Coupling PV System”, IEEE Transactions on
Energy Conversion, EC-2, No. 5, December 1987, pp. 534-541.
K.Y. Khouzam (2000), “Demonstration of a Solar Electrochemical Plant in the Form of Salt-Water Chlorinator”,
Final Report prepared for Department of Mines and Energy, Office of Sustainable Energy, QSEIF, October 2000.
K.Y. Khouzam (2000), “Investigation into the Powering of a Salt-Water Pool Chlorination Unit with Solar Power
- Interim Report”, Prepared for Department of Mines and Energy, Office of Sustainable Energy, May 2000.
K.Y. Khouzam (1990), “Optimum Load Matching In Direct-Coupled PV Power Systems - Application to
Resistive Loads”, IEEE Transactions on Energy Conversion, EC-5, No. 2, June 1990, pp. 265-271.
Proceedings of Solar 2002 - Australian and New Zealand Solar Energy Society
Paper