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Energy Blog Turning Waste Heat Into Electricity

Turning Waste Heat Into Electricity

Chris Hurcombe
by Chris Hurcombe November 24, 2016
Diesel farm

A new energy efficient engine has been invented, that generates electricity from waste hot water. This new machine has the potential to reduce energy consumption and carbon emissions for thousands of businesses, ranging from cargo shipping companies through to data centers.

This solution comes from a firm based in Dublin, Ireland called Exergyn, who intends to run the first industrial trials of this new technology early next year. The firm’s CEO, Alan Healy, stated that there’s an ample supply of waste hot water in the world, and in most cases, companies are spending excess energy to cool it back down.

Shrinking Carbon Emissions

For example, normally cargo ships pump wasted hot water from the engine around the vessel to be cooled, whereas in data centers energy hungry fans are used to dissipate the heat generated by rows of servers.  Finding an efficient way to utilize this wasted energy has the potential to reduce costs and cut carbon emissions.

The new engine created by Exergyn harnesses the unique properties of nitinol to power its machine and meet this need.

Nitinol is an alloy of nickel and titanium, that has the ability to revert back to its original crystal lattice structure when heated, regardless of how much you bend it. This memory shaping property makes nitinol very useful in a wide range of applications, including unbreakable sunglasses, medical devices, and NASA’s Mars rovers.

The alloy has another unusual quality: nitinol expands when cooled, akin to how water does when it is frozen (or like cans of pop that explode when left in the freezer by mistake).

Very few materials in the universe are able to do that, Exergyn’s head of product management, Mike Langan said.

These two properties are fully utilized in the Exergyn Drive. Within the engine, a bundle of metre-long nitinol wires is attached to a piston, where cold and hot water are alternatively flushed over the wires every 10 seconds. This causes rapid expansion and contraction of about 4 centimeters, which is used to drive the piston up and down. A hydraulic system then converts the forceful linear motion into a rotary one, that in turn drives a generator.

On average, the engine produces 10 kilowatts of electricity from about 200 kW of thermal energy.

Using Free Energy

The electricity generated by the Exergyn device may not be extremely efficient, however, it is free energy that would normally be discarded. In addition, the engine also provides a relatively less expensive way to cool down the waste hot water.

Exergyn has spent three years perfecting the design and modifying the material to assure that it has the capacity to keep working for millions of cycles.

Last year, the European Commission’s Horizon 2020 awarded 2.5 million euros to help bring the firm’s technology to market. Exergyn plans to utilise these funds by testing their new engine at Dublin Airport and two landfill sites in 2017.

The industrial tests conducted will use 90°C or colder water generated from a gas engine at the airport and biogas generators at the landfill sites to produce electricity on-site.

Exergyn hopes that their engine will help expand the geothermal energy market, as well as harness the energy lost from the waste hot water.

Currently, generating electricity from geothermal sources in a cost-effective manner requires very hot water at high flow rates.  Typically this requires the expensive drilling of deep wells with a wide diameter.  Langan says that the Exergyn Drive makes a broader range of geothermal sites viable, due to its ability to work with water at a lower temperature and flow.

A past president of the Institution of Diesel and Gas Turbine Engineers has remarked that the technology has a massive range of applications. John Blowes went on to say that only a small percentage of these will be viable unless the company can produce the technology at a reasonable price.

It comes down to the commercial viability, Mr. Blowes concluded.

The Exergyn Drive’s combination of mechanical simplicity and no fuel costs will be able to keep expenses down, Langan declared. He went on to say that the engine can generate electricity at £40 per MWhr, which is currently cheaper than gas and coal.