The National Renewable Energy Laboratory (NREL) just released a report (Cost-Reduction Roadmap for Residential Solar Photovoltaics, 2017–2030) suggesting that residential rooftop solar could reach a very affordable and unsubsidized $0.05/kWh LCOE (Levelized Cost of Energy) by 2030. The study begins with the premise that annually, 3.3 million homes will either be built or re-roofed – the optimal time to consider adding PV to the rooftop. If every one of those houses added a 9 kW solar array, that would increase the generating capacity by 30 GigaWatts every year. What will it take to get there? Ingenuity. Good thing “engineering” and “ingenuity” are derived from the same Latin word: ingeniare.
The report highlights four notable trends that point to inexpensive energy from rooftop solar:
economies of scale
business model integration
The first point, market maturation, is pretty obvious. Like most technology, solar products will become better and less expensive over time. The second point, economies of scale, refers specifically to new construction situations where entire subdivisions are being built, allowing a roofing/solar company to consolidate travel time for workers and materials.
NREL lists the remaining two factors separately, but I’m going to suggest that they’re very closely related. First, the report discusses business model integration, citing recent partnerships between roofers and solar installers as well as alliances between PV manufacturers and battery makers. Next, the study addresses product innovation, mentioning companies that make PV-integrated roofing materials, like CertainTeed, GAF, and … what’s that other company? … oh, yeah, Tesla.
The United States’ national motto suggests that there is strength in unity; it’s time to apply that to residential rooftop solar. Why? Because as long as we have multiple products, we’ll have expense involved in putting them together. So if I were a young, energetic, entrepreneurial type, I’d be looking to design a roof that combines everything and can be installed easily. In fact, there are companies headed in that direction, but none that do it all. To me, the solution is an aggregate of a few product ideas that I’ve reported on in the past.
Prefabricated housing has become popular over the past few decades, largely due to decreased construction costs and improved quality. Materials are manufactured and cut to size in a factory – a controlled environment – which produces tighter tolerances, better fit, and fewer air leaks. In many cases, a prefab house can be built by someone with little to no construction experience. So let’s apply the same principle to a roof: prefab roofing panels that combine solar, storage, insulation, and balance-of-system components (i.e., cabling, racking, and electronics).
Forward Labs has a modular product that integrates PV with galvanized metal roofing panels. And the name Forward Labs reflects some very forward thinking: someday most of our homes will use DC wiring, with AC provided only for specific appliances. (That’s a bit beyond the scope of this discussion, so I’ll leave that for a later article.) Its racking system and cabling are concealed for better aesthetics and weather protection, but it still needs an electrician’s time and skill to complete the wiring, and it doesn’t build in the storage or electronics.
SunCulture Solar makes an innovative panel – SolPad – that integrates solar, storage, and electronics, but it still needs to be mounted on an existing roof with external racking. The snap-together feature keeps all cabling hidden and makes installation – quite literally – a snap. One issue: because a battery is integrated into each panel, rooftop temperatures could limit its application to certain climates.
What if the panels were insulated, with the electronics and batteries under the insulation? That’s the idea behind 3-in-1 Roof. This upstart company patented a PV-integrated roofing panel that’s insulated, allowing an external battery bank and all associated electronics to be located in the attic, closer to the solar panels, which reduces both labor and materials cost and decreases power loss from long wires. It doesn’t include the onboard storage, integrated electronics, or snap-together electrical connectors like the SolPad.
Unlike solar panels, which typically come with a 25-year warranty, inverters, charge controllers, and batteries only last ten years or so. The module itself will need to be made of swappable components, allowing easy replacement from inside the attic.
Speaking of swappable components, the integrated storage could create a secondary market for used electric vehicle batteries. EV manufacturers normally guarantee their batteries for ten years, but that doesn’t mean the batteries die after a decade, just that they’ve lost about 20% of their total capacity. Obviously, we want full capacity in EVs, where range and weight are significant issues, but in a grid-tied house, it’s not such a big deal. Purchasing used batteries keeps them out of the waste stream and decreases the cost of behind-the-meter storage.
Source: NREL Report Challenges Engineers to Design Better Solar Products .