Further Solar energy capture increases, can be achieved by using larger curved reflectors to intercept larger areas af sunshine and redirect that solar energy to a smaller "focus" At the focus, a smaller more intense" image" of the Sun is formed at the focus.

The Cylindrical Trough and the Parabolic Trough solar collectors
are examples of so called "Imaging Solar Concentrators" that
attempt to produce a smaller but more intense "image" of Sol's energy
at the focal plane or focal line. Due to their" Imaging Optics"
geometry, (essentially adapted from telescope designs), the
aperture of the collector, must directly face the sun, to avoid loss of
collection efficiency, and to maintain the co-location, of the "solar Image,"
with the solar energy receiver, or absorber. These types of solar
trough collectors, require complex, and expensive mechanical tracking devices, just to keep them pointed always at the sun!

A more sophisticated parabolic collector trough can be
Designed, that avoids the need to track the sun altogether, by
combining two parabolas together, to form the "Compound
Parabolic Trough Solar Collector."

Patents are not forever. They are a bargain struck to give an inventor, like Roland Winston, some market protection, but only for a limited time, in exchange for the inventor, giving a wonderful new idea to the world!
Winston's 1977 patent has now expired, and thus his idea for a Non-Tracking Compound Parabola Solar Concentrating Collector is now in the "Public Domain." That means than anyone and everyone, is now free, and legally entitled, to make use of, or even market and sell the invention, without any need to pay royalties to the inventor.

Non-Imaging Optical Outward facing Compound parabolas are useful for Non-Tracking, Concentrating Solar Energy Collectors that redirect Solar Insolation onto a flat plane at the rear of the solar energy collector.
These can increase the output of simple solar cells several times over!
Properly Designed Inward-Facing, Non-Imaging, Non-tracking Compound Parabola Solar Concentrators, Can Redirect Solar Insolation Energy, from many different Sun angles, throughout the day, to a stationary Co-Focal point!

Compound Parabola Solar Energy Concentrators can also be designed as a trough shaped solar energy collector.
When this is done, the co-focal point then becomes a co-focal line.
If a coolant filled pipe solar energy absorber pipe, or a tubular evacuated tube solar energy absorber tube is co-located at the co-focal line, there will then be a maximum of concentrated Solar energy delivered and transferred to the energy absorber tube!

By using Non-Imaging Optics that do not require telescope-like aiming to preserve a distortion free image of the sun, we can also avoid the need to keep the collector pointed directly at the sun. We can thus still concentrate the sun's energy with out needing to keep the solar energy collector reflector mirror pointed directly at the sun. We need only to collect and concentrate the Sol's total energy, irrespective of any need to create or preserve a precise optical solar image. By selecting non-imaging optics we can thus avoid the need to keep the collector aperture pointed at the sun. Instead, we can collect and concentrate Solar Energy from multiple directions separately or at once. So while the sun moves across the sky, we can still accept and concentrate the Solar Thermal Energy all day using a properly designed compound Parabolic Trough Concentrating Solar Collector coupled with Evacuated (vacuum) tube Solar energy Capture Tubes. Using this type of collector, the output energy if a Solar Energy Capture Tube can be increased by a factor of 4- 6 times using a stationary solar collector. Concentration ratio is similar to the ratio between the area of the Solar Capture tube, and the size of the larger collector aperture area. The upper limit of the power output will be the glass softening temperature and the maximum allowable thermal expansion and contraction permitted by the vacuum seal glass-to glass weld seals.
Such solar collectors do not need tracking, and require only occasional season angle adjustments (several times a year) are required to keep the aperture perpendicular to the noonday sun, to the maintain maximum power output!

An array of such Compound Parabolic concentrators has the co-focal lines running East -to-West. The seasonal tilt required, just points the array to face more to the southern horizon, when the sun is lowest, at the winter solstice. As the sun rises higher in the spring and summer, the tilt is reduced, to make the array point more generally toward the zenith. The correct angle is simple to determine, just make the seasonal adjustment at least six times a year, no more than two months apart, and do it at noon, by simply pointing at the noonday sun.
Then, no daily tracking at all is required!
Thick thermal foam blocks can be hot-template-sculpted to create the compound parabola shape and then covered with aluminized Mylar to create very inexpensive Solar energy reflector mirrors!

Ideally, the fixed Non-Tracking Concentrator Collector Array should be covered with a glass plate to keep out rain, snow, dirt, leaves, and wind blown debris, which can dirty the reflectors, and reduce Solar energy output.
A cheaper alternative is to omit the glass and regularly clean the mirrors every two weeks or so.
A slight chevron tilt as shown above can be used to provide low cost rain-water drainage as well as assist thermo-siphon flow, in systems without circulation pumps or, in systems that utilize gravity return, of the colder, denser coolant fluids to the lowest levels in the Solar Energy capture Tubes.