PHOTOVOLTAIC POWER WITHOUT BATTERIES
FOR CONTINUOUS CATHODIC PROTECTION

W. W. Muehl, Sr.
Department of the Navy, Coastal Systems Station (COASTSYSTA)
Dahlgren Division, Panama City, FL 32407-7001

The COASTSYSTA designed, installed, and started up on 20 January 1990, a
state-of-the-art stand alone photovoltaic powered impressed current cathodic
protection system (PVCPSYS) not requiring any auxiliary/battery backup power
for steel and iron submerged structures. The PVCPSYS installed on 775' of
steel sheet piling of a Navy bulkhead is continuing to provide complete,
continuous corrosion protection. This has been well documented by COASTSYSTA
and verified on-site by the U.S. Army Civil Engineering Research Laboratory,
Champaign, Illinois and the Navy Energy Program Office-Photovoltaic Programs,
China Lake, California. 

The Department of Defense (DoD) Photovoltaic Review Committee and Sandia
National Laboratories consider this successful and cost effective system a
major advance in the application of photovoltaic power. The PVCPSYS uses only
renewable energy and is environmentally clean. A patent is pending on the new
technology. Other possible PVCPSYS applications are mothballed ships, docks,
dams, locks, bridges, marinas, offshore structures, and pipelines. The initial
cost savings by installing a PVCPSYS vs a conventional CP system was in excess
of $46,000.00.


The objective of the initial project was to successfully demonstrate that
renewable energy can efficiently and economically replace or be used instead
of continuous non-renewable power sources. An opportunity to clearly show that
photovoltaic power is practical and reliable was the result of a
recommendation to provide cathodic protection to the Naval Diving and Salvage
Training Center bulkhead.

The COASTSYSTA in Panama City, Florida, has broken new ground in the
application of solar energy for cathodic protection. Photovoltaic arrays
without battery backup have been connected to the 775 foot-long steel sheet
piling of a dock bulkhead via a cathodic protection system, to prevent
corrosion on that steel structure in a salt water environment.

Cathodic protection, as the name signifies, is the process by which, in the
COASTSYSTA impressed current type application, the entire steel sheet piling
is transformed into a cathode via a series of anodes mounted in PVC standoff
racks, in the water, next to the piling. When direct current (DC) energy is
applied to the anodes and sufficient electrical potential is attained by
current flow from the anodes via an electrolyte (seawater) to the piling, the
corrosion is transferred to the anodes, preventing piling corrosion.

Mr. Wally Muehl, Electrical/Mechanical Engineer at the Coastal Systems
Station, was evaluating power sources to protect the Naval Diving and Salvage
Training Center bulkhead when he focused on photovoltaics. Although there were
10 other impressed current cathodic protection systems installed on the docks,
all were powered by a continuous power source with the current rectified to
DC. Of these l0 systems, eight were down from 1 to l 1/2 years due to
rectifier failures and/or the power source secured due to construction and as
a result no corrosion protection was provided. PVCPSYS's would have continued
to provide power and corrosion protection and would not have been affected by
these type power outages.

The Naval Diving and Salvage Training Center is in a separate location from
these docks, and it was determined that power was not readily available and
would be expensive to provide rectifiers on the dock due to the dock
configuration. Rectifiers would also pose a safety hazard on the dock that is
regularly used for diver and salvage training. This bulkhead was 12-years old
and other than the initial coating, received no corrosion protection.

Mr. Muehl developed a state-of-the-art solar powered impressed current
cathodic protection system for submerged steel and iron type structures
without requiring any battery backup power. Innovations in design and method
of operation permits the photovoltaic arrays to easily provide and maintain
complete continuous corrosion protection without the necessity of DC power
backup such as batteries. Battery backup power is considered costly and an
environmental problem. To date, all impressed current systems require a
continuous DC power supply in order to provide cathodic protection.

The COASTSYSTA photovoltaic power system is a fixed-axis system which is
suitable for the Panama City latitude of 30*10'N, 85*22'W. The tilt of the
adjustable arrays were set at latitude instead of +15 degrees in January 1990,
and have not been changed. This is a good indication that other areas with
good distribution, but lower insolation levels, would be excellent prospects
for a similar type of photovoltaic powered system. For higher latitudes, there
are several other options to improve system performance without battery
backup. These include one-axis East-West tracking, two-axis North-South,
East-West tracking, or simply adding a module or two to meet the additional
current requirements.

As engineer in charge, Mr. Muehl, who designed, prepared the specifications,
and monitored the installation, also had two other problems that had to be
considered and resolved in order to install a impressed current cathodic
protection system. The first problem was ensuring that the steel piling had
electrical continuity. Another problem was providing sufficient impression of
current "carry over" to overcome a 155-foot section of piling that had to be
bypassed, and provide cathodic protection, without anode placement in the area
having a water depth of 27 feet, where diving takes place. Both problems were
overcome in the design.

To facilitate the use of a photovoltaic powered cathodic protection systems
without battery backup, the steel sheet pilings were provided an initial
one-time only preconditioning polarization for a predetermined continuous time
period to the extent that these pilings were initially polarized to a
relatively high negative potential by a temporary DC power source. The
photovoltaic power system was provided with blocking diodes to prevent any
possibility of current reversal. 

It is to be noted that evolution of a protective hydrogen film is merely a
by-product of the preconditioning polarization at the higher negative
potentials. Additionally, depending upon the environment and if higher (more
negative) polarized potentials could be maintained other than required to
provide basic complete cathodic protection, formation of thicker calcareous
deposits having protective value over a period of time could occur. The
initial DC power for polarization can be provided by a DC power source such as
a portable motor driven DC generator or a portable motor driven DC welder.

The COASTSYSTA photovoltaic powered cathodic protection system tests performed
and other data obtained, provide a further explanation that the
anode-seawater-cathode piling structure acts like a battery and when allowed
to rest, the polarity level recovers and is electrochemical in nature. An
electrochemical lead-acid battery, for example, can recover charge if allowed
to rest after serving a load. The electrochemical reaction reverses slightly
when the load is disconnected, however, a capacitor without an external
current source cannot recover by simply removing the load. 

It is believed that the one-time only initial preconditioning polarization
(controlled conditions) of the structure embeds single hydrogen atoms in the
steel sheet piling that can also migrate and diffuse in the structure. This
system delays the decay of the negative potential and permits the photovoltaic
arrays to supply sufficient power allowing the system to easily provide
complete continuous cathodic corrosion protection including cloudy, overcast,
rainy and nighttime conditions without the necessity for DC power backup such
as batteries.

In summary, the foregoing novel method and system of a one-time-only
preconditioning or prepolarizing the structure prior to energizing the PV
solar array on-line with the system, provides a relatively higher negative
potential that has a slow rate of decay. This permits the use of regulated PV
solar energy with excess available power, and without any backup power, to
easily provide complete continuous corrosion protection, including cloudy,
overcast, rainy and nighttime conditions, with excellent polarization levels
and improving with time. An analogy may be that the steel structure becomes
very effectively polarized, and will remain so by the variable DC charge
effect provided by the simple solar array system, much like a piece of steel
or iron can become magnetized by the application of a DC electrical current.

The installation, start up, and continuing operation, including underwater
inspections, are well documented to date by the Coastal Systems Station and
verified on site, during the day and at nighttime by the U. S. Army Corps of
Engineers, Construction Engineering Research Laboratory, Naval Energy Program
Office and members of the Department of Defense (DoD) Photovoltaic Review
Committee. The average amount of available sunshine for the three weeks prior
to these organizations visit, per data provided by the National Weather
Service, averaged 24%.

This system has been in operation almost 3 3/4 years without requiring any
maintenance or adjustment. A patent is pending on the new technology. Other
possible applications are mothballed ships, docks, dams, locks, bridges,
marinas, offshore structures and pipelines.

The estimated cost in 1985 of a conventional Cathodic Protection (CP) system
requiring continuous DC power was $75,000.00 and the estimated cost in 1990
was $108,000.00. The PVCPSYS cost at contract completion was $61,816.00,
complete and ready for use. The initial cost savings by installing a PVCPSYS
was in excess of $46,000.00.

The Department of Defense Photovoltaic Review Committee and Sandia National
Laboratories consider this successful and cost effective system a major
advance for the application of photovoltaics.

A photovoltaic power system without any backup power has been installed on
another 800 foot bulkhead. The two previous 400 foot conventional rectifier
powered impressed current cathodic protection systems were modified to allow
this conversion. This PVCP system successfully started operation on 21 May
1993, without any backup power and is providing complete continuous corrosion
protection. A state-of-the-art data collection systems is provided that among
other capabilities, will monitor, report, analyze and record simultaneously
the solar energy output DC Volts, DC Amps and the DC negative potential
voltage of the steel sheet piling on a personal computer that is MS-DOS
compatible located about 1/2 mile away from the site.

With reference to this manuscript, it is with pleasure that I acknowledge the
"helpful cooperation and information" received from the following personnel:

* Dr. Michael G. Thomas and Mr. Terry Schuyler - Senior Members, Technical
Staff,
 Photovoltaic Research Dept., Sandia National Laboratories, Albuquerque, NM

* Mr. James F. Jenkins, P.E., Corrosion & Metallurgical Engineer, Naval Civil
Engineering
 Laboratory, Port Hueneme, CA

* Mr. L. E. Humble, Photovoltaic Programs, Energy Program Office, Naval
Weapons Center,
 China Lake, CA

* Mr. Roch A. Ducey, Principal Investigator and Ms. Jearaldine I. Northrup,
Research Engineer,
 U.S. Army Construction Engineering Research Laboratory, Champaign, IL

* Mr. Thomas F. Lewicki, P.E., Facilities Corrosion Program Manager, HQ Air
Force Civil
 Engineering Support Agency, Tyndall Air Force Base, FL

* Dr. Thomas M. Cawthon, Hydrogen Program Manager and H. Dana Moran, Manager,
 Research and Technology Applications, National Renewable Energy Laboratory,
Golden, CO

* Navy Divers & Dive Locker, Coastal Systems Station, Panama City, FL

* Members of the DOD Photovoltaic Review Committee

***Reproduced from a Technology 2003 white paper
Sponsored by Tech Utilization Foundation, NASA Tech Briefs and NASA