The trend is clear: solar installations, based on existing silicon photovoltaic (PV) technology, should expand their market penetration over the next decade. But beyond then, their growth could hit a ceiling.

This is the premise of Georgetown Professor Varun Sivaram’s book, Taming the Sun: Innovations to Harness Solar Energy and Power to the Planet.

He warns of three reasons that could limit solar’s growth. One economic, and two technology-related arguments:

• The economic value of solar will decline as the technology scales: as more solar comes onto the grid, the less valuable it becomes. This is because the more solar is installed, the less of the electricity that it produces in the middle of the day is needed. As a result, solar begins to compete with itself, driving down the price that utilities are willing to pay generators. On top of this, higher levels of solar power strain the rest of the electricity system, imposing additional costs that lowers the value of solar. At some point – if for example, solar PV met 30% of electricity demand – it may not make sense to install another solar project because the electricity that it would generate would be worth less than the cost to deploy the project in the first place.
• Under-investment in solar technology innovation will limit solar energy’s future: Silicon technologies manufactured by Chinese companies dominate the panel market today. The industry spends on average a measly 1 percent of its annual revenues on R&D. And most of these firms’ R&D expenses remain targeted at incrementally improving existing silicon technology. Technology disruption is simply not the aspiration for most Chinese firms. But breakthroughs in other solar materials and systems is direly needed to exponentially lower costs and widen Solar’s applications. It is essential to accelerate innovations in perovskite, organic and quantum dot solar cells, solar fuels, and possibly orbital solar power satellites. The current dearth of innovation should be deeply worrying to anyone hoping for a solar-powered future.
• The grid could become unreliable with high solar penetration: the current electric grid will be limited in its capability to accommodate high levels of renewable energy. A common view is that solar power will come into its own once batteries and other storage technologies make steady improvements. Yet Sivaram notes that lithium-ion batteries are not well-designed for storage across days, weeks and months – which is a discouraging sign for the notion that solar energy storage is on a satisfactory track.

These are medium and long-term problems that we need to prepare for right now if we want solar energy to really work.