by +Cesar Anton
Fresnel lenses are pretty cool, they are big, flat and you can melt some metals if you have a large enough one and a sunny day... But they are hard to manufacture (and therefore expensive) especially the large, powerful ones that are need by most electric and industrial needs
There are many ways to use the principle behind Fresnel lenses, once of them is the Compact Linear Fresnel Reflector which uses an array of large and flat hori by distributing the light in many long areas (as long as the flat mirrors used) it puts less stress on the absorbers (usually up to 300 °C, allowing to use cheaper materials and a less exotic transfer fluid if needed, it can produce Steam, Saturated Steam or transfer the heat using a synthetic oil to power some heat exchange machine. It is also a modular approach so it can grow as needed so long one has enough space (and budget).
This diagram shows how the light is reflected in the absorbers in a CLFR, in this case the is one absorber at each side of the mirror array.
Here is a video that demonstrates the use of CLFR technology in creating solar power:
You can use CLFR's as a heat source for a Stirling Engine which is particularly efficient (and ecological) into transforming heat into mechanical work which can be used for machinery, generate electricity, or both, this works best if you have a cold source, like ice, a lot of fresh water or even warming cool air in very cold places, this is because stirling engines gathers energy from the thermal transference between the hot and cold zone, so the bigger the difference, the more power it can generate in less space.
If efficiency is crucial and cost its not a problem, multiple layers of smaller stirling engines can be used to transform most of the heat into work, every layer significantly improves efficiency (and cost) by gathering the transferred heat from the previous layer of engines and passing it into another (colder) reservoir. Stirling engines can be adjusted to work even with the heat of the palm of your hand! You can see an example on this video,
Another great thing about using Stirling Engines is that you can leverage costs by producing solar energy day and night! This might sound impossible, but if you gather a lot of energy during the day and store it in a thermally insulated reservoir, you can use stirling engines to extract it slowly (and efficiently) working for as long as there is some heat remaining, so if large enough it could make engine keep running on rainy days, it will even have a little extra performance on those first cold and rainy days since the outside temperature will be even colder than it was the day it was collected, that means even more "free" thermal difference. Also, stirling engines can get expensive, so one can leverage both technologies to provide a very reliable source of power in some places, like developing countries located in places with a lot of sun like tropical places, deserts or even places permanently covered by Snow (this places require deeper heat storage and/or better thermal isolation.
Here is an animation that shows the internal work of the Alpha type Stirling engine, it is important to notice that there is no engine exhaust or combustion at all, all the work come from the temperature difference between the hot and cold sides.
Also, a very small scale demonstration of a Beta type Stirling engine running around 5,000 rpm using the sun and fresnel lens as a heat source can be seen on this video.
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