Heat, Electricity, Storage, and Four Times the Energy

The FourFold photovoltaic-thermal module captures four times the energy of a standard PV module, and it’s easy to manufacture.

Photovoltaic thermal (PVT) panels – hybrid systems that generate electricity and extract heat – aren’t new, but a company called Focused Sun has developed a unique PVT panel that’s inexpensive to manufacture and easy to install. Recognizing that 95% of the world pays considerably more for energy than the US does, the company hopes to produce energy systems for developing nations.

Focused Sun’s FourFold module consists of four sun-tracking mirrors that reflect light onto an absorber, where the light shines on a thin strip of photovoltaic cells. A tube carrying coolant sits behind the PV cells; it cools the cells, improving their efficiency, and transfers the heat to the storage shed where it heats 30 gallons of water to temperatures around 180oF (71oC). The electricity generated by the PV cells is stored in a battery bank in the storage shed. They don’t specify the size of the battery bank, but I calculated that about four deep-cycle lead acid batteries would store an entire day’s worth of electricity from one FourFold unit.

The mirrors, whose tracking motors are manipulated by a microcontroller, cover an area of 2.8m2. In full sun about 2700 watts of solar power hits the surface. A conventional PV panel of that size would generate 500 watts of power. The Fourfold generates that much electricity, and also captures over 1500 watts of heat, bringing the module’s overall efficiency up to 75%. 

Taking a cue from Mother Nature, the mirrors are made using the same technique that gives bones and succulent leaves their strength: sandwich fabrication. A lightweight foam core is flanked by two outer layers of galvanized steel, providing a solid strength-to-material ratio. The mirrors can withstand 150 mph winds. (That’s a Category Four hurricane, by the way.) In extreme wind or hail conditions, the on-board microcontrollers will rotate the mirrors to a safe position, lowering the wind profile and protecting the mirrors from damage. When it rains, the mirrors face up so the rain will wash them. If it snows, the mirrors will rotate so that the snow falls off, or they’ll use heat to melt the snow.

The FourFold has been in the works for several years, undergoing numerous changes in absorber design, software control, electronics, and plumbing. But more than the design of the product, the real innovation is in the manufacturing processes. Focused Sun has developed an inexpensive way to make the modules, which allows them to be manufactured in small towns, even in developing countries, using primarily local materials. For the most part, low-tech and low-skilled manufacturing techniques are used. Focused Sun says that as few as five people could run a factory that produces these units. In order to reduce installation costs, the modular unit can be assembled in just a few minutes.

Focused Sun was founded by Dr. Shawn Buckley, retired professor of mechanical engineering at MIT. He holds 26 US patents, six of which are related to solar power. The company is running a crowdsourcing campaign, hoping to raise money for an intense wave of testing and certification. Major companies and investors don’t seem to be interested because Focused Sun plans to keep a low profit margin and allow the units to be manufactured by licensees, rather than making the FourFold at its own factory and selling only the finished product. Their plan is to create market penetration through low pricing.

The primary goal of the FourFold is to create inexpensive clean energy for developing nations, but its design can easily be adapted to any off-grid or grid-tied location.  

Images courtesy of Focused Sun