This is the second post in a series about rooftop solar technology (view the first post here). The first post reviewed roofing costs because they affect the overall solar cost of a home. In 2016, Fortune recognized the trend towards less expensive solar power installations that could drop another 60% in cost from where they are today. Fortune points out that up until the 1990’s much of the cost reductions were due to technology and manufacturing improvements. They believe the future cost drops will be due to non-technical factors such as financing. I believe there are still technology improvements on the way. This post focuses on the variety of panels that are available for installation and the technology they contain.

It is amazing to look back and see how far the solar panel technology has progressed since Edmond Becquerel first observed the ability of light to generate electricity in 1839. Many in our industry worry about what disruptive developments will come from “kids in their garages”, so it is important to remember that Becqueral was only 19 at the time and he was working in his father’s laboratory. I can imagine that laboratories in 1839 are similar to basements, garages or other workspaces today.

Solar cells took over 110 years to become practical and we have Calvin Fuller and Gerald Pearson from Bell Laboratories to thank for their modern form. They were working on the Bell Solar Battery and in 1954 had created a working prototype. Within four years, solar batteries were powering The Navy’s Vanguard space satellite. These cells had an efficiency of around 14%. No meaningful improvement was made in efficiency until the appearance of thin film technology in the 1990’s. The next big jump occurred over the last three years as manufacturing and design improvements pushed efficiency over 20%.

Solar cells are commonly classified by generations:

• First Generation (or Wafer) – Wafer solar cells are created with crystalline silicon (c-Si). They are efficient, but expensive to produce and contain toxic metals like cadmium and lead. Wafer panels are easy to find but are not eco-friendly and easily identified because of their hexagonal shape.
• Second Generation (or Thin Film)– Thin film amorphous silicon (a-Si) is cheaper and cleaner to produce but is less efficient than first generation wafers. Thin film first made its consumer appearance in the 1970’s as the power source for pocket calculators.
• Third Generation (or Organic) – Organic solar cells are still not practical because of their low efficiency. They are cheap to produce but only have 1/3 of the efficiency of Wafer

An exciting development in thin film panels was achieved by Panasonic’s SANYO brand in the 1990’s. They are now producing thin film solar cells with nearly 20% efficiency (in the real world not the lab). Their technology is a real tongue twister, Heterojunction with Intrinsic Thin layer. I prefer the consumer friendly label “HIT”. Panasonic technology is being used in the Tesla Solar Panels scheduled to hit the market in California this year. Tesla will produce the products in both their Fremont, CA and Buffalo, NY plants.

HIT solar panels are examples of thin film technology so a deeper dive is required to understand who why they perform so well. The answer is due to the clever design of the product. They have a sandwiched design that reduces efficiency loss when heated while capturing more sunlight. This approach makes HIT “bifacial” or able to capture direct and reflected sunlight. This approach increases efficiency in the range of 2-3%.

Tesla’s solar roof is not the only product using of bifacial cells; they have been used for some time in space and in multi-positional configurations. A multi-positional configuration could be used to expose two sides of an array at different times of the day. When used in a vertical arrangement, instead of maximizing generation at high noon, two small peaks can be created; one in the morning and one in the afternoon. If the sum is at a low angle, it is possible to increase the angle of a horizontal panel to capture the reflection off of a light colored roof.

The energysage website provides a comparison of solar cell manufacturers. Their Economy, Standard and Premium categories do not match up with the solar cell generations above because energysage is a consumer-friendly guide not a science website. Also on the energysage website, you will find a regional cost comparison information. All of their information is presented using easy to understand graphics.

The next post will address the regulatory and legislative issues technologies associated with solar energy collection. Can government keep up the changes in the technology? Up until now, the answer has been a resounding “Yes”.