Questions & Answers

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The Stirling engine is a thermal engine whose basic principle revolves around taking a difference in temperature and converting it into mechanical action. To achieve this, gas is kept in a closed canister. Various parts of the canister are heated or cooled, resulting in the gas in the respective parts either expanding or contracting. The change in volume is used to force a piston back and forth, which in turn can power a wheel or something else, such as a power generator in our case. The technology was invented in 1816 by Irish priest, Robert Stirling.

A number of characteristics make the Stirling engine particularly well-suited to the development of climate-positive and cost-effective power generation solutions. Qualities that other engines and solutions lack completely or are significantly less well-positioned to offer. Among other things, the Stirling engine can be operated using basically any heat source at all. It is quiet and virtually vibration-free. The combustion that drives the engine takes place externally – i.e. outside of the engine itself. Above all though, the Stirling engine possesses an outstanding ability to convert thermal energy to kinetic energy.

Swedish Stirling’s engine is unique in that it is both highly effective and highly efficient. It is not particularly complicated to manufacture a smaller Stirling engine that is highly efficient. But to build one that is highly effective whilst maintaining its efficiency is complicated. The underlying technology in Swedish Stirling’s engine is built on Saab Kockums renowned Stirling engine that was developed over the course of decades and has been used in Swedish submarines since 1988. Swedish Stirling has since further developed the technology with a primary focus on adapting it for mass production. Aside from its high levels of both effectivity and efficiency, the company’s Stirling engine can now boast low maintenance costs, and the unit costs per engine drop off dramatically with mass production.

There only really needs to be a few degrees’ difference to be able to run a small Stirling engine. But the larger the temperature difference, the greater the output. In the PWR BLOK we apply a difference of almost 700 degrees between the “warm” and the “cold” sides of the Stirling engines.

The Stirling engines that are contained in the PWR BLOK have an actual output of 40 KW per engine. In order to reduce the need for maintenance and to achieve a longer technical product life, we do however run these at a maximum of 30 KW per engine. The efficiency levels of the engines (the ability to convert thermal energy to kinetic energy) is approximately 30%. Swedish Stirling’s engines are unique in that they are both highly effective and highly efficient. The effectivity of the products of most commercial manufacturers is considerably lower.

We do not have a formal ongoing collaboration with Saab Kockums. We do have a manufacturing license and a support agreement that have been in place since 2008. The agreement gives Swedish Stirling the perpetual, worldwide license for the development, marketing, sales and manufacturing of Stirling engines (with the exception of defence applications). License fees are based on delivery volumes.

The PWR BLOK 400-F is a container-based solution developed by Swedish Stirling in which the company’s Stirling engines are used to recycle energy from residual and flare gases in industrial applications, by converting it to electricity. This allows for significant energy and cost savings, and also reduces global CO2 emissions through energy recycling.

Each PWR BLOK consists of 14 engines and has a nominal output of 400 kW.

The PWR BLOK solves a problem that metal producers, for example, all over the world, have been trying to solve for decades. Basically, the PWR BLOK recycles energy from residual gases that are the by-product of metal production, and converts it to electricity. This allows for huge cost savings, thanks to the reduced need for metal producers to buy electricity, and thereby greatly reduces their carbon dioxide emissions.

Each PWR BLOK has a nominal output of 400 kW.  As an example, for a ferrochrome producer with residual gas that typically consists of a mix of: CO (65 %) – H₂ (13 %) – CO₂ (8 %) – O₂ (1 %) – N₂ (13 %) and with an estimated energy content of approx. 9.05 MJ/NM³, the PWR BLOK produces approx. 3,480 MWh per year. Fuel consumption averages approx. 560 NM³/h. The temperature in the Stirling engines’ fuel chambers is around 720 degrees, whilst the cooling temperature is about the same as the surrounding air temperature plus 5 degrees.

The PWR BLOK is designed to basically run 24 hours a day, 365 days a year. A degree of service and maintenance is required after approx. 6000 hours of uptime. Estimated annual uptime, including service and maintenance downtime, is thereby about 93 – 95 percent.

This can vary from case to case. The PWR BLOK has two very significant advantages that cause the price to be very low compared to other energy types. Firstly, the fuel is often “free of charge” as it is currently classed as a type of waste that must be flared (burnt off) for environmental reasons. Secondly, the PWR BLOK is basically running every hour of every day of the year. Many energy types – such as wind or solar power – are naturally limited in their number of operational hours. The factor that affects the electricity price from the PWR BLOK is primarily capital – i.e. the investment and the customer’s costs of financing it. When Lloyd’s evaluated the PWR BLOK in May 2019, the price of electricity generated by the PWR BLOK was found to be 19.5 EURO/MWh, which is considerably lower than any other energy source.

In our assessment, today there is no other technology that is capable of converting residual gases into electricity in such a way that it can compete with the PWR BLOK. In the metal industry, decades have been spent trying different types of combustion engines, and gas and steam turbines, but all efforts have failed. The reason tends to be that the gases are of such poor quality that most internal combustion engines don’t work. Or that the technical solution is extremely costly. We also know that a number of companies have researched the possibility of converting industrial residual gases into other fuel types. It’s likely that this is possible. But we have seen clear indications that these attempts have also been extremely costly, making it very difficult to compete financially with the PWR BLOK.

The PWR BLOK 400-F in itself is specially developed to handle residual gases from the metal industry. But the underlying technology has enormous potential as a future cost-effective and environmentally-friendly source of energy. Any type of liquid or gas-based fuels can in principle be used to run a Stirling motor, such as natural gases, LNG, biogas, ethanol and so on.

The PWR BLOK is better for the environment simply because it reduces the customers’ need to buy electricity. By burning residual gases in the PWR BLOK, thermal energy can be harnessed and converted to electricity. In other words, heat that would normally be wasted, is being recycled. From an environmental point of view, this is extremely valuable. In South Africa – our primary market – the metal industry, by using the PWR BLOK, could reduce the need for bought electricity by about 15%. And because about 87% of all electricity used in the country is produced using fossil fuels – mainly coal – the PWR BLOK allows for an enormous reduction in CO2 emissions. When compared with solar panels for example, a PWR BLOK is four times more effective at reducing emissions in South Africa, as it is a technology that can run around the clock.

We protect our technology through a combination of patents and by keeping parts of our production process classified. Thus far we have submitted two patent applications for the PWR BLOK and are in the process of submitting more, primarily within areas where patent infringements are easily discovered. In areas where potential infringements on patent protection are harder to keep in check, such as the packing or sealing of the engines, we will instead try to keep details and production methods classified. 

Our long-term strategy and ambition is to develop a strong and comprehensive intellectual protection for our technology. We are the first on the market with a new, proprietary technology that opens up an entirely new market with considerably more potential than what most people realise today. A sound and wide-ranging patent protection will secure this and ensure that Swedish Stirling can also reap the rewards of the developmental work that has been put in. And it will make it a highly costly endeavour for any larger industrial parties to copy the technology the day they do realise how real and substantial the potential market for the PWR BLOK is.


Residual (or flare) gases are combustible by-products that result from various types of operations and industry. These gases are often extremely toxic and/or harmful to the environment. Methane, which is a common residual gas from farming and treatment plants for example, has a potential for global warming that is 34 times greater than that of carbon dioxide. Because residual gases are so harmful to the environment, these are always burnt off through flaring before being released into the atmosphere. Awareness that large amounts of residual gases are flared annually without the thermal energy being harnessed all over the world, is remarkably low, considering the discussions on climate change in recent decades.

Combustible residual gases are a by-product in very many and varied industries and operations. But from what we have gathered, there is no reliable collection of data on the total amounts produced globally per annum. Within the ferrochrome industry, where Swedish Stirling has chosen to focus initially, approximately 6 billion Nm3 per year is flared, but this is just a small proportion of the entire metal industry’s residual gases. In all metal production of non-precious metals, such as steel, nickel, titanium and so on, residual gases are produced and are usually burnt off without being recycled. Residual gases are also present in the petroleum industry, at treatment plants, in farming and landfills, just to name a few areas. When it comes to the petroleum industry, the World Bank put together a report a number of years ago (OPEC Bulletin 2015/5) on how much residual gas is burnt off annually. According to the report, the petroleum industry flares an astonishing 140 billion Nm3 of residual gases per year, without harnessing the energy content. This is roughly equivalent to the energy needs for the whole of Africa for a year.

Initially, we have decided to focus on the South African ferrochrome industry. The priority for Swedish Stirling now is to establish the PWR BLOK commercially. Once this is done, it will enable larger projects, higher volumes of production and a broader focus. We identified the South African ferrochrome industry as an appropriate start market at an early stage. There are several reasons for this. We have had a presence in the region since 2012, and have good contact with representatives of all of the larger producers from the country’s ferrochrome industry. 

The production is extremely electricity-intensive, while the market price for electricity in the country is high. So the PWR BLOK imparts massive energy cost savings to the customers. The market potential for the PWR BLOK is great within the country’s ferrochrome industry, at an estimated 220 MW, or 500 PWR BLOK units. As South Africa makes up a third of the world’s production of ferrochrome, the global market is about three times this size.


The reason that we chose to start by prioritising the metal industry is simply because that’s where the greatest customer benefit from our technology is to be had. The PWR BLOK is a fantastically good deal for metal producers as they have residual gases and a large need for electricity. All metal production uses large amounts of electricity. It’s not unusual for this to constitute a third of metal producers’ total costs. Half of all the energy that goes into the process is then converted to chemical energy (residual gases) that are flared (burnt off) due to a lack of a decent method of recycling this energy. With the PWR BLOK, metal producers can recycle energy from their own residual gases and thus produce 15% of the electricity required for themselves. The PWR BLOK thereby solves the problem that metal producers around the world have been deliberating over for decades. 

The PWR BLOK is of course of interest for the petroleum industry. But there, their own need for the electricity produced by the PWR BLOK is not likely to be as high. So the financial incentives for investment in the recycling of the energy from their residual gases are not as strong as they obviously are for metal producers. There are most certainly exceptions to this within the petroleum industry today. And circumstances are also sure to change with the continued increase in the global demand for electricity and tougher environmental requirements. 


Yes. Any operations and industries where residual gases are produced constitute potential markets for the PWR BLOK. The price we can offer is record-low for climate-positively produced electricity and very interesting for all types of electricity-intensive industries with access to residual gases. We are currently however completely focused on the South African ferrochrome industry.

In the coming years, our continued focus will be on the global metal industry in general, and the South African ferrochrome industry in particular. Within the South African ferrochrome industry alone we have the potential of at least 550 PWR BLOK units. Within the global production of ferroalloys, we have a potential market of at least 6,500 PWR BLOK units.

We have. We have for example got the specs for residual gases from a South African titanium producer. When we analysed these, we were able to see that the energy content was higher than in residual gases from ferrochrome production, and that it would work excellently as a fuel in the PWR BLOK without any modifications to the equipment. We also know from our analyses that the PWR BLOK will function perfectly on residual gases from all types of production of ferroalloys. The PWR BLOK has a very wide range of future use cases when it comes to recycling the energy from residual gases and converting it to carbon-neutral electricity from various industrial operations globally. Because practically any fuel in liquid or gas form can be used in Stirling engines, it also becomes possible to develop and adapt the PWR BLOK for other types of fuel. But our focus is, and will remain, on the metal industry.

Launching and introducing new technology always takes time. The concept for the PWR BLOK was presented for the metal industry in South Africa in the autumn of 2017. The first complete, full-scale prototype (PWR BLOK generation 1) was installed and deployed in the spring of 2019. And the first commercial unit (PWR BLOK generation 2) was deployed in the autumn of 2020, approximately three years after the concept was presented to the market. In the South African mining industry alone, there have been attempts to find technical solutions and methods for recycling the energy from residual gases for 40 – 50 years! Massive amounts of time and resources have been spent on the search, and yet no sustainable solution has been found. Based on this time frame, the introduction of the PWR BLOK has gone extremely quickly. Don’t forget that the PWR BLOK is an entirely new solution to an old problem, in a fairly conservative sector. The feedback that we have received, without exception, from potential customers, banks and other parties, is not that the launch has gone slowly, but rather quite the opposite.

Yes. Swedish Stirling has been listed in Sweden on the NGM Nordic SME market since November 2016.

We develop, manufacture and sell the PWR BLOK. Initially, our focus is on the South African ferrochrome industry. Although for our first two deals with the South African ferrochrome producers Glencore and Samancor, we have chosen to sell a conversion service, whereby we own and finance the PWR BLOK and charge the customers for the actual conversion. We consciously chose this method in order to be able to quickly get large renowned companies to use the technology on a large scale. Future deals will be solely based on sales of the technology. Not financing the plants. This may mean that it can take a little longer to build substantial volumes, but we’re convinced that this is a better business model for the future.

We try to regularly communicate what’s happening at the company, and to be as open, transparent and available as we can be. As we are alone in providing a new technology that solves a wide-ranging industrial and ecological problem, we are still quite selective in spreading detailed information about the technology itself. There may also be situations in which we are contractually bound to not communicating details and which we of course respect. Otherwise, it is naturally in our own interest to share and disseminate information about our technology. 

When it comes to financial information or other information that can affect the share price, we follow the legislation and regulations in place. A lot of the information on the company is also available on our website, where we also regularly publish news and events from the market and elsewhere that are or can be of importance to the company. Since autumn 2019, we have also retained a large Nordic bank and a British research firm to publish quarterly analyses on the company. These are published at: Furthermore, we publish our financial reports on a quarterly basis as well. When it comes to meeting us, we try to visit various investment fairs and events across the country. You can find these here:

No, we’re not. The solar energy project was entirely phased out in 2019, and our full focus is on the PWR BLOK.

Swedish Stirling is a small company with limited resources. For the moment, we are 100% focused on our own product, the PWR BLOK, and on a large-scale commercial launch of the product within the metal industry in general, and the South African ferrochrome industry in particular. We don’t currently have the possibility to put resources into other types of project or fields. Commercial success for Swedish Stirling will also bring about a substantial reduction in global carbon dioxide emissions.

We don’t sell single Stirling engines. Our production of engines is solely for our product, the PWR BLOK.