A few weeks ago, someone asked me if we had a dev blog. I said we had one ‘of sorts’, because, in contrast to most dev blogs I’ve seen, such as this one, you won’t find html codes, software algorithms, or physics principles expounded here. Our approach has been to make the technology accessible to technical and non-technical audiences alike.
That said, I realize that some people are genuinely interested in this stuff. And, while IP protection and some degree of secrecy are facts of life for any early-stage technology company, we try to be open and transparent – as much as is possible without compromising our or our partners’ ability to operate. For anyone interested, technical background or not, here are some recent, fairly techy developments for our first product to market, the Sun Simba – a lot of this coming from a poster presentation made at CPV-7 by Dr. Stefan Myrskog, our Director of Science. I’ve also written out the answers to common questions asked to Stefan during his poster pres below.
The main development is that the market-ready version of the Sun Simba has evolved from a square shape to a hexagonal shape. We’ve mentioned the new hex design in some places before, but here will outline some of the considerations that went into the decision, its benefits, as well as other advancements.
1. Increased active area.
The optic’s corners have the longest path length to the optic’s centre, so contribute less to performance. Moving from a square to hex shape reduced the maximum and average path lengths, improving angular performance and increasing the overall proportion of photons sent to the III-V cell per optic.
Not central to the hex shape, but key to increasing efficency, we eliminated the mirror that had deflected light down at the centre of the optic in the Gen 2 version. The result is that the centre of the Gen 3 optic is now a light-collecting surface.
Importantly, since no outer frame is required, no dead space is created when tiling the hexagonal optics together.
2. Increased acceptance angle.
By getting rid of the square’s corners, and via other design optimizations, we increased the acceptance angle of the optic from 0.75 degrees half angle to 0.9 degree half angle.
3. Less material costs.
The Gen 2 square optic was 200 mm by 200 mm, whereas the Gen 3 is a hex is 200 mm across when measured between parallel faces. This means that Gen 3 has roughly 90% of the surface area of Gen 2 but, surprisingly, produces slightly more power. Gen 3 is also thinner, making it even lighter. So a lighter, smaller part, producing more energy.
The Sun Simba was designed to be made of low cost commodity materials. The Gen 3 represents a further advancement: reducing the materials and weight of the module.
FAQs from CPV-7
Q1. How does acrylic, which makes up most of our optic by weight, last in the field over time?
A1. There are many grades of acrylic, a material that was originally developed in the late 1920s as a shatter-resistant alternative to glass during World War II. Some grades degrade considerably when exposed to the elements. We chose the grade we did because of its superior weathering properties; a UV-resistant optical-grade PMMA for which the vendor had over 20 years of outdoor performance and degradation data. Transmission changes over time are marginal in this type of PMMA.
Q2. How do the small concentric ridges on the optic’s surface weather dirt and dust when compared with flat plate panels?
A2. We’ve had a test site outside of our facility in Toronto for over a year. Despite being next to a major highway (the Gardiner Expressway), our scientists have not observed significantly more sullying of our optics when compared with a reference flat piece of glass.
We extensively studied dirt capture during the development phase of our products. Research into how materials soil, and how surface energy influences dust accumulation, gave us guidance on the angle at which acrylic can be molded and still have dirt or dust blown or blasted out of its crevices by air currents/ pressure, or water.
The basic physical principles that inform the Sun Simba design have stayed constant since the beginning: a wave-guided optic that eliminates the need for focal distance, and that is extremely durable in the field over time. We have refined this concept to the current, market-ready iteration, which has increased efficiency, increased acceptance angle, and lowered costs as compared to the Gen 2 Sun Simba.