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The Ultra-Reliable, Free Piston Stirling Engine Harnessed for Today’s Oil and Gas Industry

  February 2018 / Vol 8 Issue 1

The Ultra-Reliable, Free Piston Stirling Engine Harnessed for Today’s Oil and Gas Industry
By: Isaac Garaway, PhD, Chief Technology Officer, Qnergy and Dan Midea, North American Sales Manager, Qnergy


The Oil and Gas Industry has unique power requirements: low maintenance, lowcost, low-emissions and high reliability. A Stirling-based approach offers a new, rock-solid solution.

Working in operations in the oil and gas industry is a non-stop challenge. You’re reviewing a grid permitting document for a remote site. You sometimes feel that paying for extending the electrical utility grid and the huge amount of redtape around it is a waste of time. The phone rings. Another malfunction at a remote well site due to a failed on-site power source. This was expected after two days of – 35° F at the site.  You have to send in a technician for a full day to fix the system. More downtime, more lost revenue. You reopen a month-old proposal from a remote power generation service company. You originally did the ROI calculation and rejected it. Maybe you should reconsider, but the rates are exorbitant. The complexities of such a decision are not lost on those of us who have had to face such challenges to get work done in some of the most remote parts of the country.

Regardless of your position, if you want to focus on optimizing oil and gas production, getting electrical power out to your site is an essential ingredient. No one wants to pour their limited resources into power sources that don’t work and ultimately lead to additional headaches and cost.

In addition, we’ve all recently found ourselves facing additional environmental concerns. These are making it more difficult to employ large, noisy and oversized (above 30 kilowatts) generators and microturbines for loads that are just a few kilowatts. The power mismatch leads to excessive greenhouse gas (GHG) emissions and does not look good on the corporate sustainability reports.

Systemic Inefficiency This situation is hardly unique. The U.S. has about 900,000 wells and 305,000 miles of interstate and intrastate transmission pipelines (source: EIA). Globally, the Oil and Gas Industry spends about $10B per year on electricity. About $1.5B is spent on solutions in the smaller than 10 kilowatt range. Many of the wellhead sites in the U.S. and Canada have a need for expanded electric power – either the sites are too far from the electric grid or too far from large centralized power generating stations.

The industry depends on reliable and predictable energy supply for pumping, conveying, surveillance, communication, cathodic protection and other critical applications. In the last few years, there is also pressure to reduce GHG emissions. However, today the industry relies on high-cost and high maintenance ‘remote power’ solutions, which distract resources from driving positive results in core KPIs. None of the existing remote power solutions seem to address the issues that concern the site operator.

An Unmet Need The necessity for a 500 watt to 15,000 watt power range is increasingly being felt by operators. Many sites have electrical loads greater than 500 Watts and are left in a predicament as they do not qualify for the installation and maintenance of large power platforms (gas turbines and multi cylinder diesel generators). Applications like this include SCADA (data communications) and wellhead controls. The upper range includes compression, cathodic protection, mainline valve operation and other critical loads. Unfortunately, the current solutions have proved to be too costly to purchase and operate. At the 500 watt level, most reliable remote power technologies cost in the vicinity of $50 USD/ watt or more. “Green”, renewable solutions have similar pricing per watt but can also prove to be unreliable in inclement weather. A remote power site, such as an impressed-current rectifier or multi-well natural gas pad requiring more than just a few hundred watts, can become very expensive to operate.

Going External Combustion Qnergy (Ogden, UT) is now revolutionizing the remote power market. Over 200 years ago Rev. Robert Stirling invented the original external combustion Stirling engine. The principal “Stirling advantage” is that it is a closed-cycle external combustion engine, meaning the heat source is outside the engine and the inside of the engine can be sealed. Stirling engines also make use of a regenerative heat exchanger that allows them to re-use their heat. This regeneration feature is what makes the Stirling Cycle efficient, while allowing it to be powered by virtually any fuel.

The main challenge in adapting the conventional Stirling engine to oil and gas remote power was; how to make it a virtually zero-maintenance engine. Qnergy addressed this challenge by applying a special and proprietary variant of the Free Piston Stirling Engine (FPSE). Through a hermetically sealed generator casing, with few moving parts and a novel heat exchanger design, the Qnergy PowerGen series of generators transform heat into electricity directly by using linear alternators. Qnergy’s design breakthroughs have resulted in extremely reliable, maintenance free generator platforms. Qnergy generators have demonstrated millions of cumulative operating hours in a broad range of applications, using many different types of fuel sources. Designed with extremely long-life components, early series generators have already successfully demonstrated over 100,000 cumulative hours of maintenance–free operation.

As a testament to the robustness of this solution, the Assets Integrity Manager of a Large Interstate Pipeline Company in North America recently noted “The Qnergy PowerGen operates seamlessly and maintenance free within our critical infrastructure. It has an extremely high level of reliability, is easy to operate and has remote-control capabilities. We don’t expect to use any other alternative power systems on our remote power sites throughout our Rocky Mountain, Appalachian and Gulf Coast Regions.”

The Qnergy PowerGen technology was initially developed for deep space exploration and tactical military applications, where it performed remarkably well, providing anywhere from just a few tens of watts to kilowatts. Over the last five years, the system has been modified to provide remote power generation solutions specifically for the power needs of the Oil and Gas Industry. The PowerGen system outputs grid-quality AC power. Thus, it can be used on any remote location to provide seamless and uninterrupted power, as if the site was connected directly to the electrical utility grid.

The PowerGen system is also able to provide thermal energy for heating. A simple glycol loop circulation system can be driven without the need to add costly equipment to an existing site. If the end user would rather have direct, radiated heat for a building or a remote instrumentation shed, the PowerGen has an HRU (Heat Rejection Unit) that can be installed remotely. The HRU will take the waste heat (up to 60,000 btu/hr) and blow it directly into the customer’s building or enclosure, thus eliminating the need for a catalytic or expensive gas driven heater.

Given that PowerGen technology can be installed at a fraction of the cost of other competing remote power solutions, there is an appreciable growth of this generating technology throughout the US Gas Operation and Transportation Networks. These generation platforms are particularly strong for automation, communication, control and cathodic protection applications. With automatic power modulation capabilities these systems have the ability to increase power output, as the need for additional current grows, without the need to add more expensive hardware. This provides a reliable and economic long-term solution for every aspect of Oil and Gas Operational Networks.

Where ROI Meets Sustainability The drive to reduce GHG emissions throughout North America has led the industry to carefully take notice of the PowerGen systems as well. Using a tightly controlled, air assisted combustion process, the PowerGen is highly efficient in eliminating GHG emissions, compared to other forms of remote power technologies.

Furthermore, at less than $6 per watt, the system has the shortest payback time for any remote power generator in the industry.

Energy Certainty As you tackle your daily remote power challenges, remember that Qnergy has your solution ready. The PowerGen systems are low maintenance, lowcost, low-emissions and high reliability.

For more info, please contact, Isaac Garaway, PhD, Chief Technology Officer, Qnergy and Dan Midea, North American Sales Manager, Qnergy at,, 801-752-0100