Solar-powered Valve Actuation: An Update

In the early days, solar power was used in noncritical applications that required low power consumption, primarily to supply monitoring of valve-related and process data at remote locations. As solar power technology evolved, applications expanded along with the sophistication of the technology.

Today, the most extensive use of solar power in valve actuator applications is found in remote parts of the world that have vast stretches of jungle, desert or mountainous terrain—environments without reliable utility power. For example, South and Latin American oil-producing nations pioneered extensive use of solar and telemetry mostly for use on critical oil and gas pipelines.

In the U.S., fewer off-grid applications present themselves; however, recently some energy pipelines and governmental water agencies have come to rely on solar even for critical applications. The decision to go with solar in these cases is usually based on the comparative costs of bringing the grid to the job site or keeping the site off the grid. Furthermore, the current boom in unconventional extraction methods for oil and natural gas is driving more interest in solar power for valve-actuator applications.

ENERGY CONSUMPTION

A key factor of whether or not to consider solar power for an application relates to available energy and consumption. Two examples would be a 36-inch valve or gate operating at 1,000 psi on a crude oil pipeline and a 96-inch sluice gate in 25 feet of head water at a remote dam site. The two would require about the same force and amount of energy to operate. In both these cases, users would find bringing utility power to the sites cost prohibitive, which triggers the process to consider solar power.

In these scenarios, the pipeline company needs to be able to close the valve in an emergency in response to environmental and safety concerns. The water utility needs to maintain an appropriate level in its reservoir through the winter, which means changing the outlet gate position as the lake level rises or falls. Both applications need to sense process conditions, transmit information, move a load and do it all off grid. Solar power can be more cost effective in such cases and requires less maintenance than gas or diesel generation systems if the loads can be managed.

One of the ways technology has improved in the solar industry is that, in the last 10 years, panels have become much more efficient and reliable. A case in point is an energy company in Wyoming that had a solar panel riddled with bullet holes. In earlier times, that panel would not have functioned. Yet, in this case, they did not need to replace the panel until a significant portion of its surface area was damaged because of the latest generation of solar panels, which employs self-healing technology.

Today, battery racks can be as simple as a pair of marine-grade gel cells wired to deliver 24 volts direct current (VDC), or racks of batteries wired to deliver 48, 96 or 110 VDC. A typical electric motor operator would reach the limits of battery storage and energy transfer capacity very quickly. But if speed is not an issue, then trading horsepower for gear reduction would allow some very large valves and gates to be operated this way.

Most importantly today, however, is that users don’t have to be in the sun-belt to make solar work. Canada has many successful remote solar sites.

HIGH SPEED AND FORCE, CRITICAL CONTROL

High speed, high force and critical control, which are all necessary requirements for dependable valve actuator operation, can be accomplished with an appropriate hydraulic operating system. By combining solar electric battery storage with hydraulic accumulator storage, very high operating forces and flexible speed control are possible. Full pipeline and station diagnostics are available as well.

Only a few years ago, communication options in remote areas were very limited. Satellite receivers were expensive and required a license; cellular towers had not yet spanned the country; and data capacity was limited. Radio systems were complicated and required intensive maintenance. Today, however, wireless technology covers even the most remote parts of the country, and most new pipelines are built with fiber-optics for supervisory control and data acquisition (SCADA) along their full length. This allows the same level of data acquisition and control at remote sites as in a plant connected to the grid, including both power and control redundancies for critical operations.

In addition, significant improvements in energy efficiency of instrumentation have been made, so continuous load on the battery system is minimized.

CONTROLLING HYDRAULIC SYSTEM LEAKS

An important factor when considering solar power for valve actuation applications is the potential for leaks. If the equipment is not properly designed for the environment, operating conditions, and pressure and temperature cycling, hydraulic systems can leak. In addition, the fluid itself needs attention. So-called “food-grade” hydraulic oils are readily available, and many can be rated for arctic or tropical conditions.

Hydraulic systems also are capable of great pressure and very high forces. More than a few pipeline gates with bent stems have been the unfortunate result of a lack of understanding about valve operation.

This is where a specialist engineering company with experience in remote solar-power applications comes into play. A valve automation center or even a company that specializes in general hydraulic equipment may not suffice in a remote situation.

Another potential pitfall is a segregated scope of supply. Buying an actuator from one vendor, a solar power supply from another and then having yet another company perform instrumentation could spell trouble. An integrated scope of supply from a source that maintains disciplines in-house and has years of field experience can stand up to the rigors of remote isolated duty.

EXAMPLES OF SUCCESS

In northern Argentina, 39 solar-powered actuators were field installed on an existing 24-inch product pipeline’s through-conduit gate valves. The actuators were installed along with a new pipeline SCADA system, which allows the pipeline dispatcher to monitor pressures and flow at each valve site and close sectional block valves if needed.

A large steel cabinet holds an M-drive, bi-directional fluid drive system and the SCADA remote terminal unit (RTU) equipment. Batteries are provided for the RTU and satellite communication system. Electronic controls provide slow-cycle closing of each valve (over 10 minutes) so that normal shutdown of the pipeline will not cause pressure shock to the 25-year-old pipeline. (A much faster time of operation is available for emergency shutdown.)

At each valve site, hydraulic linear actuators were field mounted on the existing through-conduit gate valves.

Another example of a solar power application closer to home can be found in Oklahoma. There, a solar-powered emergency shut-down actuator protects an Oklahoma products pipeline at a navigable river channel where commercial power is unavailable.

In this application, a solar-powered spring return rotary actuator permits remote shutoff of a critical products pipeline if damage occurs from barge traffic or heavy rains. Solar electrical energy is used to generate hydraulic pressure. The hydraulic pressure is used to hold the valve open and compress a powerful, self-contained spring. If valve closure is required, hydraulic pressure is released and the spring quickly closes the valve, preventing further loss of product.

These are just two examples of the hundreds of viable applications for solar-powered valve actuators. As technology continues to evolve, more and more users will explore solar power actuation for their particular applications.

Tom DeGaetano is general manager of Flow-Quip Inc., Tulsa, OK (www.flowquip.com). Reach him at tdegaetano@flowquip.com.