How Solar Thermal Power is Losing Ground to PV

How Solar Thermal Power is Losing Ground to PV

Solar power generation comes in two main forms – solar photovoltaic (PV) and solar thermal. For years, solar thermal power was considered the more promising technology, but PV has staged an incredible comeback and is now clearly the dominant solar energy source.

The Basics of Solar Thermal Power

Solar thermal power uses mirrors or lenses to concentrate sunlight and convert it into high temperature heat. This heat is then used to spin a turbine to generate electricity.

The main types of solar thermal power plants are:

  • Parabolic trough systems use long, curved mirrors to focus sunlight onto a tube filled with fluid. The heated fluid is used to make steam to power a turbine.

  • Power tower systems use a large field of flat mirrors (heliostats) to concentrate sunlight onto a central receiver tower. The tower heats molten salt that is used to generate steam.

  • Dish/engine systems use dish-shaped mirrors to focus sunlight onto a receiver, heating a fluid that powers a Stirling engine to generate electricity.

Solar thermal plants have certain advantages over PV:

  • They can store heat energy to continue generating electricity even when the sun isn’t shining.

  • They can reach higher efficiencies than PV panels.

  • The steam generation process allows solar thermal to easily integrate with existing turbine technology.

The Rise and Fall of Solar Thermal

Solar thermal power saw substantial growth in the late 2000s, led by investments in the American Southwest and government incentives. The capacity of concentrated solar power (CSP) plants grew over 10 times from 2004 to 2011.

Spain built many parabolic trough plants and led the world in solar thermal capacity. The United States experienced a boom in power tower facilities. Enthusiasm was high that solar thermal could contribute significantly to the global clean energy mix.

However, adoption stalled in the early 2010s due to several challenges:

  • PV costs plummeted dramatically, making solar thermal less competitive.

  • Natural gas prices fell thanks to the fracking boom, challenging solar thermal’s cost advantage.

  • Government support dried up. Tax credits and incentives that favored solar thermal expired or were cut.

  • Water use became a concern, especially in arid regions suitable for concentrating solar power.

Since 2014, global solar thermal capacity has been virtually flat, while PV capacity has soared.

The Shocking Growth of Photovoltaics

In contrast to the struggles of solar thermal, adoption of photovoltaic solar has grown exponentially due to both improving economics and supportive policies.

Some key factors behind PV’s rise:

  • Costs have plunged over 90% in the last decade, driven by economies of scale, manufacturing innovations, and Chinese market dominance.

  • Efficiency has increased steadily, with top lab cell efficiences now over 47%. Commercial panels are typically 15-22% efficient.

  • Government support has accelerated, including renewable energy mandates and programs like net metering.

  • Rooftop solar has surged in popularity as costs made PV affordable for homes and businesses.

Cumulative Capacity

The divide between PV and CSP is stark when comparing cumulative installed capacity:

  • Global PV capacity reached over 500 gigawatts (GW) in 2018, over 100 times higher than cumulative solar thermal capacity.

  • China is the clear PV leader with over 175 GW, more than the entire world’s solar thermal capacity.

  • The United States has over 62 GW of PV capacity, second only to China.

Annual Additions

Looking at annual capacity additions shows PV’s dominance:

  • In 2018, over 100 GW of PV capacity was added globally, a new record. Solar thermal added just 0.9 GW.

  • Since 2015, PV has represented 95-99% of annual solar capacity additions. This percentage continues to grow.

  • The top country for new PV capacity is again China, which installed over 44 GW in 2018.

It’s clear that PV growth is exponential while solar thermal stalls. Thermal technology has been left completely behind in solar power generation.

Why PV Has Overtaken Solar Thermal

There are a few key reasons why photovoltaics have surpassed concentrating solar power so decisively:

1. Cost

  • As mentioned above, PV module costs have dropped at astonishing rates, far faster than anyone predicted. This has made rooftop and utility-scale PV very affordable.

  • In contrast, solar thermal costs haven’t fallen nearly as quickly. While PV is now under $1 per watt, solar thermal remains over $6 per watt.

2. Scalability

  • PV systems are highly modular and scalable, with panels typically under a meter square. Systems can be tiny or huge.

  • In contrast, scaling solar thermal requires large, complex installations and major capital spending. This limits flexibility.

3. Installation

  • Rooftop PV is now simple and quick to install. It can slot in easily on existing buildings or open space.

  • Solar thermal plants require substantial land, grading, mirrors or lenses, and civil works. Installation is complex and site-specific.

4. Policies

  • Government policies like renewable portfolio standards and net metering have specifically spurred PV adoption, especially rooftop solar.

  • Thermal power has received less policy support. Without subsidies, it struggles to compete.

In summary, PV’s dramatic cost declines, greater scalability, easier installation, and supportive policies have enabled it to pull far ahead of solar thermal generation.

Does Solar Thermal Power Have a Future?

Solar thermal technology clearly faces huge challenges going forward. Does it have any future role in our energy mix?

  • Existing plants should provide reliable, low-cost power for decades but few new facilities are being built.

  • Without major cost reductions, solar thermal will likely continue to stagnate. Breakthroughs in materials or designs could help drive down prices.

  • Hybrid solar PV + thermal plants hold some promise, benefiting from both technologies. But growth will be limited.

  • Developing countries with abundant sun and land may adopt more solar thermal, but PV cost reductions apply everywhere.

In summary, while solar thermal power will not disappear entirely, its role is set to keep declining. It has lost the battle for the future of solar energy to the incredible rise of photovoltaics. The age of cheap PV is here, and concentrating solar plants are collateral damage. The consistent exponential growth of PV shows no sign of slowing down, while solar thermal drifts further into irrelevance.