Stirling Work

The closest thing to free energy

Jamil Shariff is one of the world’s leading researchers into the ancient technology of Stirling Engines – he reveals why they are about to undergo a revival:

Local governments in the US are starting to develop their own strategies for energy-independence, or micro-grids. One little-known technology, the Stirling Engine, is being revived because it can make use of waste heat from other energy sources.

In Helena, MT, city commissioners are designing a project to cut utility bills by generating electricity at the wastewater treatment plant, the city government’s biggest energy user. Camp, Dresser & McKee Inc. are drafting plans for a Stirling engine and generator, which will use excess methane gas at the plant to generate electricity.

The technology likely will cost several hundred thousand dollars but could pay for itself in as few as five years. So what is a Stirling engine exactly, and why are they not more widely used? If the explanation below is too technical, try Building a Stirling Hot Air Engine (2 Video Set). Click “more” for the rest of the story

The engine has two compartments with a temperature difference between them, and a sealed gas inside. The gas is moved from one compartment to the other cyclically, so that it heats up and cools down and  according to the laws of thermodynamics  expands and contracts, respectively. As it expands it creates a greater pressure on the piston and is able to push it out, producing what is known as a power stroke. When the gas is cooled the pressure drops, which means less work needs to be done by the piston to recompress the gas on the return stroke, giving a net gain in power.

The hot heat exchanger of the engine can be a chamber in thermal contact with an external heat source, for example, a fuel burner, and the cold heat exchanger a chamber in thermal contact with an external heat sink, like air fins.

The engine boasts no exhaust gas (as the gas is sealed inside), and is most efficient when the temperature difference between the compartments is greatest. Small demonstration engines have been built which will run on a temperature difference of around 15 �C, e.g. between the palm of a hand and the surrounding air, or between room temperature and melting water ice.

The engine boasts a long history, starting from around 1699 when devices known as �air engines� have been recorded to exist, though the English inventor Sir George Cayley is credited with having devised air engines around 1807.

The engines name comes from Robert Stirling, who introduced an important innovation to air engines known as the ‘Economiser’ in 1816. It is now called the regenerator, and it stores heat from the hot portion of the engine as the air passes to the cold side, and releases heat to the cooled air as it returns to the hot side. The Economiser improved the efficiency of Stirling’s engine enough to make it commercially successful in particular applications, and has since been a component of every air engine that is called a Stirling engine.

The Stirling engine was used widely during the nineteenth century but was eventually replaced by the electric motor at the century’s end.

But the Stirling’s design has endured and some novel ways to use its design have since surfaced cryocoolers are Stirling engines in reverse.

Stirling engines have even been known to power submarines. Kokum, the Swedish shipbuilder, built at least 10 commercially successful Stirling powered submarines during the 1980s. As of 2005, they have started to carry compressed oxygen with them.

2005 has also seen the Southern California Edison announcing an agreement to purchase solar powered Stirling engines from Stirling Energy Systems over a twenty year period and in quantity (20,000 units) sufficient to generate 500 megawatts of electricity. These systems, on a 4,500 acre (19 km) solar farm, will use mirrors to direct and concentrate sunlight onto the engines which will in turn drive generators.

Sunmachine in Germany is planning to commence full scale commercial production of solar-powered Stirling engines this year. A large concave mirror automatically traces the path of the sun, and the concentrated energy gets the Stirling engine up to speed at an output of 2.5 kW. They claim 80,000 hours without any maintenance whatsoever!

WhisperGen, a New Zealand firm with offices in Christchurch, has developed both AC and DC Micro Combined Heat and Power Stirling cycle engine-based systems, gas-fired central heating boilers which sell power back into the electricity grid. A 20 unit trial has started in Germany, and a further 80,000 units are being produced for the residential market in the UK.

A UK supplier of the WhisperGen, is quoting around 10K for a DC system. It’s designed to be used as an electricity generator that also produces heat, and can be used to charge batteries for off-grid locations. The WhisperGen also claims over 90% efficiency.

Of course, you could always try to make your own – check out these links…and good luck!



2 Responses


    In order to insure energy and economic independence as well as better economic growth without being blackmailed by foreign countries, our country, the United States of America’s Utilization of Energy Sources must change.
    “Energy drives our entire economy.” We must protect it. “Let’s face it, without energy the whole economy and economic society we have set up would come to a halt. So you want to have control over such an important resource that you need for your society and your economy.” The American way of life is not negotiable.
    Our continued dependence on fossil fuels could and will lead to catastrophic consequences.

    The federal, state and local government should implement a mandatory renewable energy installation program for residential and commercial property on new construction and remodeling projects with the use of energy efficient material, mechanical systems, appliances, lighting, etc. The source of energy must be by renewable energy such as Solar-Photovoltaic, Geothermal, Wind, Biofuels, Ocean-Tidal, Hydrogen-Fuel Cell etc. This includes the utilizing of water from lakes, rivers and oceans to circulate in cooling towers to produce air conditioning and the utilization of proper landscaping to reduce energy consumption. (Sales tax on renewable energy products and energy efficiency should be reduced or eliminated)

    The implementation of mandatory renewable energy could be done on a gradual scale over the next 10 years. At the end of the 10 year period all construction and energy use in the structures throughout the United States must be 100% powered by renewable energy. (This can be done by amending building code)

    In addition, the governments must impose laws, rules and regulations whereby the utility companies must comply with a fair “NET METERING” (the buying of excess generation from the consumer at market price), including the promotion of research and production of “renewable energy technology” with various long term incentives and grants. The various foundations in existence should be used to contribute to this cause.

    A mandatory time table should also be established for the automobile industry to gradually produce an automobile powered by renewable energy. The American automobile industry is surely capable of accomplishing this task. As an inducement to buy hybrid automobiles (sales tax should be reduced or eliminated on American manufactured automobiles).

    This is a way to expedite our energy independence and economic growth. (This will also create a substantial amount of new jobs). It will take maximum effort and a relentless pursuit of the private, commercial and industrial government sectors’ commitment to renewable energy – energy generation (wind, solar, hydro, biofuels, geothermal, energy storage (fuel cells, advance batteries), energy infrastructure (management, transmission) and energy efficiency (lighting, sensors, automation, conservation) (rainwater harvesting, water conservation) (energy and natural resources conservation) in order to achieve our energy independence.

    “To succeed, you have to believe in something with such a passion that it becomes a reality.”

    Jay Draiman, Energy Consultant
    Northridge, CA. 91325
    Feb. 12, 2007

    P.S. I have a very deep belief in America’s capabilities. Within the next 10 years we can accomplish our energy independence, if we as a nation truly set our goals to accomplish this.
    I happen to believe that we can do it. In another crisis–the one in 1942–President Franklin D. Roosevelt said this country would build 60,000 [50,000] military aircraft. By 1943, production in that program had reached 125,000 aircraft annually. They did it then. We can do it now.
    The American people resilience and determination to retain the way of life is unconquerable and we as a nation will succeed in this endeavor of Energy Independence.

    The Oil Companies should be required to invest a substantial percentage of their profit in renewable energy R&D and implementation. Those who do not will be panelized by the public at large by boy cutting their products.

    Solar energy is the source of all energy on the earth (excepting volcanic geothermal). Wind, wave and fossil fuels all get their energy from the sun. Fossil fuels are only a battery which will eventually run out. The sooner we can exploit all forms of Solar energy (cost effectively or not against dubiously cheap FFs) the better off we will all be. If the battery runs out first, the survivors will all be living like in the 18th century again.

    Every new home built should come with a solar package. A 1.5 kW per bedroom is a good rule of thumb. The formula 1.5 X’s 5 hrs per day X’s 30 days will produce about 225 kWh per bedroom monthly. This peak production period will offset 17 to 2

    4 cents per kWh with a potential of $160 per month or about $60,000 over the 30-year mortgage period for a three-bedroom home. It is economically feasible at the current energy price and the interest portion of the loan is deductible. Why not?

    Title 24 has been mandated forcing developers to build energy efficient homes. Their bull-headedness put them in that position and now they see that Title 24 works with little added cost. Solar should also be mandated and if the developer designs a home that solar is impossible to do then they should pay an equivalent mitigation fee allowing others to put solar on in place of their negligence. (Installation should be paid “performance based”).

    Installation of renewable energy and its performance should be paid to the installer and manufacturer based on “performance based” (that means they are held accountable for the performance of the product – that includes the automobile industry). This will gain the trust and confidence of the end-user to proceed with such a project; it will also prove to the public that it is a viable avenue of energy conservation.

    Installing a renewable energy system on your home or business increases the value of the property and provides a marketing advantage.

    Nations of the world should unite and join together in a cohesive effort to develop and implement MANDATORY RENEWABLE ENERGY for the sake of humankind and future generations.
    The head of the U.S. government’s renewable energy lab said Monday (Feb. 5) that the federal government is doing “embarrassingly few things” to foster renewable energy, leaving leadership to the states at a time of opportunity to change the nation’s energy future. “I see little happening at the federal level. Much more needs to happen.” What’s needed, he said, is a change of our national mind set. Instead of viewing the hurdles that still face renewable sources and setting national energy goals with those hurdles in mind, we should set ambitious national renewable energy goals and set about overcoming the hurdles to meet them. We have an opportunity, an opportunity we can take advantage of or an opportunity we can squander and let go,”
    solar energy – the direct conversion of sunlight with solar cells, either into electricity or hydrogen, faces cost hurdles independent of their intrinsic efficiency. Ways must be found to lower production costs and design better conversion and storage systems.

    Jay Draiman
    Northridge, CA 91325
    Email: renewableenergy2@msn.com

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