Is exponential growth of solar PV the obvious conclusion?

Solar PV has experienced exponential growth in recent years, with global installed capacity increasing ten-fold from 2010 to 2017 – annual capacity additions rose from less than 20 GW in 2010 to 40 GW in 2014 and a record-breaking 97 GW in 2017. At the same time, wind power has continued to expand, adding about 50 GW annually over the past five years.

Together, solar PV and wind have the potential to transform electricity worldwide, with significant impacts on the operations of whole systems and the economics of all sources of electricity. But to what degree can we reasonably expect such exponential growth to continue?

China has been the driving force behind the exponential growth of solar PV, accounting for 75% of global growth in solar PV deployment over the five years leading up to 2017 (though official data indicates that additions declined in China in 2018).

China’s success in this sector has been thanks to a virtuous cycle of strong policy support and falling technology costs. For example, China’s 2020 targets for solar PV have been ratcheted up several times, rising from an initial target of 1.8 GW set in 2008, to 105 GW in the 13^th Five-Year Plan set at the end of 2016. Recent discussions are looking to 210 GW or beyond.

Support policies have also played a determining role in other world leaders of solar PV. In the United States, the extension of tax credits in late 2016 gave a significant boost to both solar PV and wind power markets, complementing state-level renewable energy goals that continue to evolve. In the European Union, the renewables target of 27% for 2030 set in 2016 was recently revised up to 32%. In India, implementation measures have been expanding, including in 2016 doubling the amount of land set aside for solar PV deployment.

Driven in part by these strong policies, the solar PV market has grown dramatically, at a rate of 27% annually over the past five years. However continuing at this pace would mean a doubling of annual deployment every three years, passing 200 GW in 2020 and exceeding 2 100 GW in 2030. This would represent a massive scaling up that would go beyond any level of construction seen in the past, at more than 6-times the capacity of all technologies built in 2015. It would also require mobilising a dramatic level of investment.

For now, policy has been the key driver in accelerating deployment, but maintaining this growth rate would far outpace established policy goals. For example, combining the policy ambitions of the US, EU, Japan, China and India would require only about 70 GW of solar PV per year. Even in the case where actions to mitigate climate change and reduce air pollution accelerate, as defined in the IEA’s Sustainable Development Scenario (SDS), solar PV deployment in these leading regions would rise to about 120 GW per year to 2030, a level well below what is implied by continued exponential growth.

In addition to support policies, solar PV growth has been driven by impressive cost reductions, falling by about two-thirds over the past five years with all indications pointing to further reductions in the future. New utility-scale solar PV projects completed in 2017 had average levelised costs of electricity (LCOE) of just over $100 per megawatt-hour (MWh), based on standard financing over 20 years. Best-in-class projects with preferential financing can costs as much as 60% less today and recent auction bids indicate that next wave of leading projects could cost $30 per MWh or less.

However, low costs do not guarantee accelerated deployment, as they are only part the story. In this light, to better assess the relative competitiveness of technologies WEO2018 included a new metric of competitiveness that has been developed over several years, called value-adjusted LCOE (or VALCOE).

VALCOE builds on the foundation of LCOE that incorporates all cost elements, but also adds three categories of value in power systems: energy, flexibility and capacity. Combining these elements provides a stronger basis for comparisons between variable renewables like solar PV and dispatchable.

From this perspective, hourly simulations of electricity demand, supply and electricity prices in China, India, the United States and European Union all point to a more complex picture for the competitiveness for several technologies, including solar PV.

In India for example, the LCOE of new solar PV is projected to drop below that of coal-fired power plants by 2025. But the story is different using VALCOE. As the share of solar PV surpasses 10% in 2030, the value of daytime production drops and the value of flexibility increases. After 2030, even with further cost reductions, solar PV becomes less competitive.

Ultimately, the ability of market forces to drive exponential growth will depend on the profitability of solar PV without government intervention. This calls for a healthy return on investment in the face of market risk, a challenging prospect for solar PV or any power generation technology today, as current market designs rarely monetise all the services provided. Exponential growth also calls for solar PV to outcompete not only alternatives for new investment but also the existing power plants based on costs and value. 

For example, recent deployment of onshore wind highlights that falling costs alone may not lead to ever-increasing deployment. In 2017, the LCOE of onshore wind power continued to decline to about $75 per MWh globally, some 30% lower than utility-scale solar PV. However, global capacity additions fell for the second year in a row to 44 GW in 2017, well below the record of 65 GW set in 2015.

The future of solar PV, like so many parts of the energy system, will continue to depend largely on decisions made by governments. With pressing global and local environmental concerns, governments should look to ratchet up ambitions related to all low carbon options, including solar PV and wind power, but also nuclear, carbon capture utilisation and storage, hydro, bioenergy and renewables for heat and transport. Without this boost, the annual market for solar PV may stagnate or decline, an unfortunate fate that has happened to many other promising technologies.