Finally a design that could work on flat roofs that combines an efficient heat collection plumbing with 2-axis motion for the concentrators. Heliotron Energy from Greece has a design that puts an array of single-axis concentrators onto a rotating turntable, which gives the concentrators 2-axis capability.
Each concentrator is about one square foot in size, and they each rotate up and down with their base parallel to the surface of the turntable, and each has 90 degrees of mobility, from vertical – to face due east at sunrise, or due west at sunset, to horizontal – to face straight up at noon. The turntable rotates 180 degrees from east to west each day to ensure the concentrators constantly face the sun.
Because the up-down axis of each concentrator requires an axle parallel to the suface of the turntable, within the each axle is a highly efficient heat exchanger to heat water flowing through it. The pipes from all the collectors are consolidated and connected to heat storage system – because the turntable holding the collectors only rotates 180 degrees each day, slowly rotating to keep the collectors facing the sun – there are a variety of options to cost-effectively connect pipes from the heat exchangers to a storage system.
With a website http://www.heliotron.gr that won’t load here, this company is stealthy, but Heliotron’s Managing Director, Alex Papadopoulos, claims the optical design of Heliotron’s system is inexpensive to manufacture. Each collector is shaped almost like a clamshell. The entire collector is translucent. The upper portion of the collector fans out and turns inward, and the entire collector consists of parallel tubes extending from a tight row along the axle to become somewhat thicker as the collector fans outwards.
The intent of this design is to channel sunlight downwards to galium arsenide photovoltaics located at the bottom of the tubes above the axle, and it is claimed the quality of this light is superior because of the light is channeled down the seemingly fiberoptic tubes into the photovoltaic material. And simultaneously, heat is also efficiently harvested. It seems this design could work with parabolic trough arrays. In fact, a parabolic trough array on a turntable is a good design alternative.
If Heliotron’s clamshell fiberoptic solar magnification design inexpensively delivers superior concentrated sunlight to the photovoltaics, then their innovation could have legs. And using the turntable not only simplifies the mechanics of 2-axis collector motion, but makes heat extraction far more feasible.
Heliotrope’s innovations are exciting, but also exciting is what they suggest. Practical rooftop arrays that generate electricity at the same time as they heat water are almost here. Mini-troughs on turntables could gain photovoltaic efficiencies as well as improved heat exchangers. A very high watt output per area can be achieved, allowing less rooftop to support more solar harvesting.