# Solar engines using highly expandable gases **URL:** \ **Category:** Factual Questions\ **Created:** [July 26, 2021, 1:37pm UTC](https://boards.straightdope.com/t/solar-engines-using-highly-expandable-gases/947332 "2021-07-26T13:37:39Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [July 26, 2021, 1:37pm UTC](https://boards.straightdope.com/t/solar-engines-using-highly-expandable-gases/947332/1 "2021-07-26T13:37:39Z")
Has there been any work done in this area past or present? A simple example would be freon gas heated by the sun and then the pressure used to lift weights that would drive generators as it came back down. No intake or exhaust valves so they would rely on natural cooling to cycle. Possibly use a water source to cool the coils for more cycles. I don’t know how they could be configured but basically have highly expandable gasses been used in solar energy experiments? ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [July 26, 2021, 1:48pm UTC](https://boards.straightdope.com/t/solar-engines-using-highly-expandable-gases/947332/2 "2021-07-26T13:48:02Z")
Are you thinking about something different than a Stirling Engine? [A study on two-phase, two-component Stirling engine - NASA/ADS](https://ui.adsabs.harvard.edu/abs/1982iece.conf.2169I/abstract) And if so, what are the benefits you perceive over a Stirling design? ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [July 26, 2021, 1:53pm UTC](https://boards.straightdope.com/t/solar-engines-using-highly-expandable-gases/947332/3 "2021-07-26T13:53:07Z")
To be honest with you I don’t know anything about this at all. It just seems naturally heated gasses could be an effective way to produce energy however they could find ways to harness it. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [July 26, 2021, 1:57pm UTC](https://boards.straightdope.com/t/solar-engines-using-highly-expandable-gases/947332/4 "2021-07-26T13:57:56Z")
Then the answer to your question is yes. Freon can make Stirling engines more effective, and the way to utilize expanding gases to produce energy is to use a Stirling engine. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [July 26, 2021, 2:11pm UTC](https://boards.straightdope.com/t/solar-engines-using-highly-expandable-gases/947332/5 "2021-07-26T14:11:40Z")
> [@HoneyBadgerDC](#): > > To be honest with you I don’t know anything about this at all. It just seems naturally heated gasses could be an effective way to produce energy however they could find ways to harness it. This is what solar power towers do. They use solar power to heat water, generating steam that drives turbines to produce electrical power. > **[Solar power tower](https://en.wikipedia.org/wiki/Solar_power_tower)** > > A solar power tower, also known as 'central tower' power plant or 'heliostat' power plant, is a type of solar furnace using a tower to receive focused sunlight. It uses an array of flat, movable mirrors (called heliostats) to focus the sun's rays upon a collector tower (the target). Concentrating Solar Power (CSP) systems are seen as one viable solution for renewable, pollution-free energy. > Early designs used these focused rays to heat water and used the resulting steam to power a turbine. Newer... There are variations that allow for energy storage so the energy supply can be time-shifted to meet nocturnal power demand - but in the end, they’re generating steam to produce mechanical power (and then electrical power). ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [July 26, 2021, 2:17pm UTC](https://boards.straightdope.com/t/solar-engines-using-highly-expandable-gases/947332/6 "2021-07-26T14:17:55Z")
> [@Machine\_Elf](#): > > [Solar power tower - Wikipedia](https://en.wikipedia.org/wiki/Solar_power_tower) > > There are variations that allow for energy storage so the energy supply can be time-shifted to meet nocturnal power demand - but in the end, they’re generating steam to produce mechanical power (and then electrical power). I was thinking more in terms of no exhaust type engines. Something where cooling had to take place for a cycle to complete itself. So the primary challenge I would imagine would be in how rapidly we could cool the gasses. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [July 26, 2021, 2:30pm UTC](https://boards.straightdope.com/t/solar-engines-using-highly-expandable-gases/947332/7 "2021-07-26T14:30:21Z")
> [@HoneyBadgerDC](#): > > I was thinking more in terms of no exhaust type engines. Something where cooling had to take place for a cycle to complete itself. So the primary challenge I would imagine would be in how rapidly we could cool the gasses. ? Not following. No exhaust gases here: heat water, generate steam, run through turbine, cool/condense steam into liquid water, send water back to solar furnace tower. What am I missing? _(rereads OP)_ OK, I see you don’t want any flow. Not seeing the value of such a restriction. If you want to dump heat from your working fluid, it makes sense to send it to a device that specializes in cooling, rather than leaving it in a place where you have to alternate between heating and cooling. ---
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [July 26, 2021, 3:41pm UTC](https://boards.straightdope.com/t/solar-engines-using-highly-expandable-gases/947332/8 "2021-07-26T15:41:29Z")
You can design a heat engine that will operate anywhere you have a hot and cold source close together. One location that has been proposed in on the arctic ice. That seems unlikely at first but you have 32 degree water underneath (the hot source) and -20 to -50 above the ice as the cold source. That’s a substantial temperature difference. You need to tailor the working fluid for each application. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [July 26, 2021, 6:37pm UTC](https://boards.straightdope.com/t/solar-engines-using-highly-expandable-gases/947332/9 "2021-07-26T18:37:29Z")
The earliest practical steam engines, Newcomen engines, cooled the steam inside the cylinder. However, they were extremely inefficient because you end up cooling the entire cylinder as well, instead of just the gas. And then on the next cycle it heats up again. It’s also just plain difficult to cool, because there’s not much surface area between the gas and outside. The Newcomen engine sprayed water inside the cylinder to cool the steam because simply cooling the cylinder would have made for too slow an engine. The solution is to keep the hot and cold cylinders separate, with the gases flowing between them. You can increase efficiency even further by putting a heat exchanger and heat store between the cylinders. That heat exchanger can do its job properly because there’s no cylinder there, and you can give it a lot of surface area like a typical heat exchanger. And that’s just a Stirling engine, as **naita** mentioned. It’s really about the simplest heat engine you can imagine that’s not horribly inefficient. It’s closed, as you wanted, and can work with just about any working fluid you want. Small ones can run on the heat difference between your hand and the ambient air. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [July 27, 2021, 5:00am UTC](https://boards.straightdope.com/t/solar-engines-using-highly-expandable-gases/947332/10 "2021-07-27T05:00:33Z")
> [@mixdenny](#): > > You can design a heat engine that will operate anywhere you have a hot and cold source close together. One location that has been proposed in on the arctic ice. This can even be done in oceans without ice. I think I’ve read of a project in the Caribbean Sea. The plan is to find regions with a large-ish difference between surface water temperature and deeper water temperature, and build a heat transfer engine to take advantage of that. > **[Ocean thermal energy conversion](https://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion)** > > Ocean thermal energy conversion (OTEC) is a renewable energy technology that harnesses the temperature difference between the warm surface waters of the ocean and the cold depths to produce electricity. It is a unique form of clean energy generation that has the potential to provide a consistent and sustainable source of power. Although it has challenges to overcome, OTEC has the potential to provide a consistent and sustainable source of clean energy, particularly in tropical regions with acce... ---
**Author:** ![Ruken](https://avatars.discourse-cdn.com/v4/letter/r/f475e1/32.png) [@Ruken](https://boards.straightdope.com/u/Ruken)\ **Post date:** [July 27, 2021, 11:43am UTC](https://boards.straightdope.com/t/solar-engines-using-highly-expandable-gases/947332/11 "2021-07-27T11:43:24Z")
Keep in mind that your efficiency is limited by the hot and cold temperatures (see Carnot wiki below), so for a given surface area, one needs to consider whether more power can be generated with solar panels. But yes, solar Stirling engines are a thing. > **[Solar-powered Stirling engine](https://en.m.wikipedia.org/wiki/Solar-powered_Stirling_engine)** > > Pages for logged out editors learn more > > A solar powered Stirling engine is a heat engine powered by a temperature gradient generated by the sun. Even though Stirling engines can run with a small temperature gradient, it is more efficient to use Concentrated solar power. > The mechanical output can be used directly (e.g. pumps) or be used to create electricity. > NASA patented a type of solar-powered Stirling engine on August 3, 1976. It used solar energy to pump water from a river, lake, ... > **[Carnot cycle](https://en.m.wikipedia.org/wiki/Carnot_cycle)** > > Pages for logged out editors learn more > > > A Carnot cycle is an ideal thermodynamic cycle proposed by French physicist Sadi Carnot in 1824 and expanded upon by others in the 1830s and 1840s. By Carnot's theorem, it provides an upper limit on the efficiency of any classical thermodynamic engine during the conversion of heat into work, or conversely, the efficiency of a refrigeration system in creating a temperature difference through the application of work to the system. > In a Carnot cyc...