A Solar Tale

Remember “The Long Tail”? Maybe not. Unless you were up to your eyeballs in the nuances of search engines and niche marketing around the turn of the century, you wouldn’t. The phrase originated with a Wired article by Chris Anderson, but more generally Marziah Karch describes it like this; traditionally records, books, movies, and other items were geared towards creating “hits.” Stores could only afford to carry the most popular items because they needed enough people in an area to buy their goods in order to recoup their overhead expenses. The Internet changes that. It allows people to find less popular items and subjects. It turns out that there’s profit in those “misses,” too. Amazon can sell obscure books, Netflix can rent obscure movies, and iTunes can sell obscure songs. That’s all possible because the Internet, search engines and search advertising provide easy access to these niches out on the long tail of the demand curve, allowing them to compete with the head of the curve where the big hits and brick and mortar stores reside.

What does this have to do with solar energy? Plenty as it turns out. Demand for solar has traditionally been met by large, centralized solar farms that generate many megawatts of energy per system, per day, like the big-box retail stores of yore selling blockbuster records, books and movies, the hits at the head of the solar demand curve.

These centralized solar farms are comprised of rows and rows of identically mounted flat crystalline solar modules tilted at the ideal angle for the latitude. With their economies of scale they deliver the lowest installed system costs, in the $2 per watt range according to Greentechsolar, if you ignore the typical transmission infrastructure additions and upgrades required to deliver this energy to market. String inverters are a key ingredient in delivering such favorable economics. Large strings of solar modules, devoid of shading and other sources of performance differences between modules, can be connected to a single, rather expensive string inverter. The number of solar modules per string inverter, and therefore the number of watts by which the cost of the string inverter gets divided, is large, rendering favorable dollars per watt.

Centralized solar farms also fit neatly into the existing utility-driven paradigm and business model. Energy is generated centrally, delivered over wide area networks of transmission and distribution lines to paying customer loads and then paid for and recouped by regulated returns over long time horizons. These are the big hits.

Like the big box retail stores with search advertising, though, this centralized utility-scale model is being disrupted. Land acquisition and permitting for new solar farms combined with the challenges of adding net new or even upgrading existing transmission and distribution lines is constraining big solar. At the same time the cost of crystalline solar modules and supporting electronics has plummeted, opening up the first wave of distributed solar, known more commonly as rooftop solar. Rooftops are smaller than the acres devoted to centralized solar farms, by a lot, so the fixed costs of a rooftop solar generating system – e.g., solar modules, inverters, mounting infrastructure – are divided by fewer watts. As a result, the dollars per watt for rooftop solar initially suffered by comparison, but continues to get rosier and rosier as these costs continue their precipitous decline, sitting just under $4 per watt according to the same Greentechmedia study.

Rooftop solar is more distributed than a centralized solar farm, and more varied. A single rooftop may have several different pitches and possibly even directions these pitches face. Since economics will always drive towards maximizing the number of watts installed per rooftop, these variations become more and more common. Plus, shading plays a role. Rooftops are not pristine like single-purpose solar sites. Trees, neighbor houses, nearby foothills and the like can cause seasonal shading during times of the day, emphasizing the point that a rooftop is first and foremost, a rooftop. Fortunately for the rise of distributed solar, a Module-Level Power Electronics (MLPE) market has emerged to assuage the technical ramifications. Microinverters and power optimizers are examples of MLPEs. Each optimizes a single solar module’s output, an important innovation when adjacent solar modules may perform very differently due to shading or even their orientation relative to the sun. Mating a microinverter or power optimizer with every solar module costs more in dollars per watt, but as the distributed solar market grows and gains economies of scale for MLPE manufacturers, costs are coming down rapidly as they have with solar modules, while overall system generation across varied solar modules increases.

 Many Facet Rooftop Solar

Rooftop solar is filling out the inflection point between the head of the solar demand curve and the tail, but it cannot fuel the long tail all on its own. As of the third quarter of 2014, nearly 600,000 home and business owners already generate their own solar electricity from rooftop systems. Unfortunately, only as many as 20% of rooftops are suitable to host solar generation. Plus socially, rooftop solar contributes to the electrical divide, the increasing cost of energy low-income families will face as part of the utility death spiral – i.e., the concept where falling barriers to distributed generation coupled with rising electric bills will cause consumers to defect from the grid, leaving a smaller population to pay for the costs of maintaining the electrical infrastructure. This smaller population is filled with low-income families, families without the means or often even the rooftops to participate in the benefits of rooftop solar.

What will fuel the long tail? What is at least as distributed and local as rooftop solar, more egalitarian and offers unlimited surface area to cover and generate solar energy? Infrastructure Solar! Imagine the ability to economically cover all shapes and sizes of existing infrastructure out in the wild with solar generation, like light and utility poles of all heights and diameters, traffic intersection poles and arms and supports, bus and rail stops, wind turbine towers, water towers, floating bridge barricades, the list goes on and on. Each system is small in terms of nameplate generation – a 75 kilowatt lighting system, a 4.5 kilowatt traffic intersection – but like the Long Tail of the Internet, the sum of all installed Infrastructure Solar kilowatts will eventually dwarf the centralized and rooftop kilowatts being installed today because, well, the tail is really, really long.

Solar Cells and Modules

Standing between today and the explosion of Infrastructure Solar are a few innovations. Traditional flat crystalline solar modules can be added to existing infrastructure such as rooftops using mounting rails and attach points that depend on the type of roof material and structure. These flat solar modules work well on rooftops with large, flat, generally south-facing surfaces. When mated with MLPEs like a microinverter, each flat solar module’s generation is optimized. Localized shading only affects the generation of the shaded module, unlike string inverters where the performance of shaded solar modules can affect the performance of other solar modules sharing the same string inverter. Or when rooftops have multiple flat surfaces with different slopes and orientations, flat crystalline solar modules with microinverters per module perform optimally as well. However, these flat crystalline solar modules are big. A typical 60-cell solar module is in the 65 by 40 inch range, and getting bigger. Sunpower is now producing a 128-cell, 435 watt solar module that is a whopping 82 by 41 inches and over 20 percent efficient!

While bigger and more efficient is better for solar farms and most rooftops because the dollars per watt decrease, bigger is worse when the goal is to cover existing infrastructure. Curvature is the problem. Flat crystalline solar modules are, well, flat and rigid. They do not bend, so the bigger the flat crystalline solar module the less curvature it can effectively cover. Much less existing infrastructure can be transformed into solar energy generating devices with big, efficient crystalline solar modules.

Flexible Solar Modules

Flexible amorphous-silicon and CIGS solar modules can more easily attach to and cover existing curved infrastructures like poles and arms, but the cell efficiencies are less than crystalline cells and the orientation of bypass diodes between cells may or may not align optimally for the infrastructure being wrapped or the position of the sun throughout the day. When not ideally oriented, module generation performance suffers. For example, wrapping an amorphous silicon solar module designed to lay flat between spars on a metal roof, around a vertically oriented cylinder like an aluminum light pole, yields less than optimized generation because the cells were not wired with this geometry in mind.

The first innovation needed to unlock Infrastructure Solar combines the best of both crystalline and flexible solar cells into an articulating solar module; a solar module designed to transform existing infrastructure into optimized solar energy generating devices by attaching to and covering with articulating facets comprised of crystalline solar cells. This new class of solar module is comprised of two or more facets that articulate relative to one another, while each facet is comprised of one or more solar cells whose size and shape is determined by the geometry of the existing infrastructure being transformed and whose orientation relative to the sun is the same.  The size and shape of a facet’s crystalline solar cells need not be square or rectangular, but instead should be determined by the infrastructure being transformed and its curvature. These cells may take on the shape of all kinds of polygons such as triangles, pentagons, hexagons, octagons and the like, all to facilitate covering arbitrarily curved, already standing infrastructures.

Facets

Second, like the optimization benefits gained from mating microinverters with today’s solar modules, MLPEs must be applied more granularly than a single 60 or 70 or 128-cell solar module. Each articulating crystalline cell, or each group of crystalline cells that articulate together (i.e., facet), must be mated with an MLPE to optimize its performance regardless of orientation relative to the sun. Generalizing this notion and extending it across years of technological advancements, the logical result is the incorporation of a direct-current, solid state, Maximum Power Point Tracking (MPPT) power optimizer directly into each facet, and then sharing a single, separate, grid-tied inverter across numerous so-equipped facets to create an articulating solar module. An Infrastructure Solar system is then constructed from as many articulating solar modules as are necessary to cover the existing infrastructure being transformed.

Power Optimization

Obviously economics plays a big part in Infrastructure Solar too. The previous two technical innovations open up the market, but the dollars per watt must also be compelling. Balance of system costs should be less for most types of Infrastructure Solar because the infrastructure already exists and the cost is already sunk. However, a new type of articulating solar module employing more granular MLPEs will drive up system cost, initially.  Fortunately, if we have learned anything from the solar boom these past several years it’s the fact that solid state technologies and manufacturing processes consistently outperform predictions about economies of scale, solar modules and MLPEs included.

Data Center

The final innovation that will unlock the potential of Infrastructure Solar involves big data. Microsoft and Google both have truly massive geocoded data sets along with ecosystems seeded with platform development tools and services to extend these data sets. Think about the mapping app on your mobile device and all the supporting data overlays you see when following directions, like restaurants with their menus and star ratings, gas stations with their gas prices, etc. Now what if this same machinery were used to geocode existing infrastructure like street lights, traffic signals, water towers, and so on, and then overlay these locational data with ever more detail like height and diameter of street and traffic poles, easement ownership information for the land on which these poles reside, specifics about the below-ground power available to the poles like voltage and the nearest circuit panel, and so on? This level of detail would dramatically reduce the cost of standing up the first wave of Infrastructure Solar. Infrastructure will need to be cherry picked initially because economies of scale will not have kicked in, so easily and cost effectively identifying these cherries will be crucial initially. Yet even after this first wave helps to drive down system costs, the data will remain invaluable as a tool to reduce balance of system costs, perpetuating the economies of scale cycle.

Eleven years ago it was The Long Tail of the Internet. Eleven years from now it may very well be The Long Tail of Solar, with every size and shape of existing infrastructure transformed into solar energy generating devices. When summed, all these small, niche, solar generating systems will dwarf the kilowatt-hour capacity of the big solar farms just like Internet search advertising did for niche products relative to big product hits. Maybe then we will finally be able to put the 1 kilowatt of direct sunlight that hits every square meter of the Earth’s surface to good use.

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