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nilsinside AB proudly presents
the Green Revolution Energy Converter - the GREC

nilsinside green revolution
nilsinside green revolution


The technology behind the GREC

Simple concept, amazing potential

The technology behind the GREC has a simple concept yet so innovative and powerful. The GREC is a Carnot engine using an electric motor to move its "Work Generating Volume" between a hot and a cold reservoir. This generates pressure pulses that in turn generate work (connecting to a piston, a turbine, a pump, an electricity generator…).
- The larger the volume of air, the more energy.
- The greater the temperature difference, the more energy.
In thermodynamic terms, the GREC acts as “a closed system with a moving boundary” that transforms an existing given temperature difference into movement (kinetic energy).

Today's external heat engines are very limited in power due to limited (small) cylinder volumes but not the GREC. The GREC uses very large sliced heat transfer areas allowing a very large cylinder volume (Work Generating Volume - WGV) which can benefit even from lower temperature differences and be built for much higher power output.

Technical Explanation

The GREC is a closed system that heats up and cools down a large sliced volume "WGV" efficiently, fast and repetitively, resulting in internal pressure changes.
The illustration below shows a cross-sectional view of the GREC and its internal parts.

An inside view of the GREC with the hot and cold blocks and their respectively conducting fins in red and blue, and the electric operated "Revolving Shutter - RS" in brown with its quarter openings which contain the slices of the Work Generating Volume - WGV. The hot and the cold blocks are separated by two insulating nil blocks in transparent beige. The nil block with insulating nil-fins situated closest to the viewer has been removed in order to see the RS quarter opening.

The closed GREC uses an internal “Revolving Shutter” (RS), a pack of discs, to move the sliced gaseous volume column which is held within a quarter of an opening called the Work Generating Volume (WGV). The RS rotates the WGV between the conductive fins of a hot and a cold block where they heat up/cool down quickly. This results in internal pressure changes. Note that these are thin slices with large area as they heat up and cool down faster than thick volumes.
- The more revolutions per minute, the more energy.

To prevent unwanted efficiency leaks, the GREC contains two “nil blocks” with insulating fins placed in-between the hot and the cold blocks. These insulating blocks prevent the simultaneous heating up and cooling down of the Work Generation Volume allowing a perfect Carnot cycle for every revolution.

The RS is not in contact with the fins and is free wheel turned by a controller with logics and an electric stepper motor. Although the purpose of the RS is only to move around gas, its revolution is constantly controlled. This is done by the “Revolution Dynamic Link” (RDL). The RDL software continuously adjusts the RS speed according to input from the running application. It’s designed for variable speed as well as a varying work load.

Here’s how the GREC works, step by step:

1. The Revolution Dynamic Link (RDL) positions the opening of the RS (the WGV) to overlap with the hot block (red) of the GREC.

2. Conductive heat-transfer from the hot fins into the slices of the moving gaseous volume (WGV) takes place.

3. The internal pressure of the GREC increases to actuate a connected device. Like for example to force a piston to move a certain distance.

4. The RDL turns the gaseous slices of the Work Generating Volume over to the fins of the cold block (blue), where the WGV will dump its heat.

5. The internal pressure drops and in the case of a connected piston, it returns to its original position, i.e., pushed back the traveled distance.

6. To conclude a full Carnot cycle, the revolving process continues to the hot block where it restarts from step 1.

Still a bit of a blur?

Check out the video animation of the GREC cycle:

The enclosed Work Generating Volume (WGV) is formed between the fins and the open quarters in the Revolving Shutter (RS). All the open RS segments, the WGV, is part of the total volume. The pressure distribution of the total volume is used to generate power - in the example in the video above this is done by connecting a piston or a membrane. The GREC may also be used in series to generate more power output.

What makes it so much better than conventional engines?

Theoretically the GREC can be compared to a Stirling engine (which alternately heats and cools a closed working volume and convert the pressure / volume changes to work) but the GREC is NOT limited in power.
Important differences between the GREC and conventional heat engines are:

  • it delivers ready made 2-way alternating pressure pulses opposed to one-way pressure

  • it delivers pressure pulses of a desired exact frequency

  • it’s not limited to steam and can benefit from lower temperature differences allowing the recovery of £millions worth of waste heat on a large scale that no other technique is able to acheive,

  • its power range is significantly higher and varies from a few kW to several MW – a Stirling engine’s max output is generally less than 100kW!

  • It’s more cost efficient due to the simple dessign and much lower manufacturing cost,

  • it scales from small to very large engines, and has a very wide power range compared to other heat engines that very often are limited in size,

  • it has a unique ability to change the thermodynamic cycle on the go,

  • it has a Revolving Shutter with a unique ability to change the convective heat transfer coefficient (htc) to optimal ratio. The convective htc for a turbulent flow is relatively high compared to a low coefficient of a laminar flow!

  • Its design even allows for partial phase-change from gas to fluid and fluid to gas. These are conditions where a fairly low temperature gradient may generate a high change in pressure for certain gases.


Nilsinside’s technology innovation is unique and the Intellectual Property associated with the GREC model has been registered. Currently the IP has been approved in Sweden, China, USA and several European countries.

Click this link to read: The Green Revolution Energy Converter Explained

Link to the GREC Explained in pdf format: RevolutionEnergyConverterExplained.pdf

Link to frequent protyotype questions in pdf format: QuestionsAndAnswers.pdf

updated by KITS