• Since 2010, generation of solar thermal electricity  (STE) from concentrating solar power (CSP) plants has grown strongly worldwide, though more  slowly than  expected in the first IEA CSP roadmap (IEA, 2010). The first commercial plants were  deployed in California in the 1980s. A resurgence of solar power in Spain was limited  to 2.3 gigawatts (GW) by the government in the context of the financial and economic crisis. Deployment in the United  States was slow until 2013  because of long  lead times and  competition from cheap unconventional gas and  from photovoltaic (PV ) energy, whose costs decreased rapidly.1  Deployment in other places took of f only recently.

• Global deployment of STE, about 4 GW at the time of publication, pales  in comparison with PV (150 GW). Costs of CSP plants have dropped but  less than  those of PV. However, new  CSP components and  systems are coming to commercial maturity, holding the promise of increased efficiency, declining costs and higher value through increased dispatchability. New markets are emerging on most  continents where the sun is strong and  skies clear enough, including the Americas, Australia, the People’s Republic of China,  India, the Middle East, North Africa and  South  Africa.

• This roadmap envisions STE’s share  of global electricity  to reach  11% by 2050  – almost unchanged from the goal in the 2010  roadmap. This shows that  the goal for PV in the companion roadmap (IEA, 2014a) is not  increased at the detriment of STE in the long  term. Adding STE to PV, solar power could  provide up to 27% of global electricity  by 2050, and  become the leading source of electricity  globally  as early as 2040. Achieving this roadmap’s vision of 1 000 GW of installed CSP capacity by 2050  would avoid the emissions of up to 2.1 gigatonnes (Gt) of carbon dioxide (CO2) annually.

• From a system  perspective, STE offers significant advantages over PV, mostly  because of its built-in thermal storage capabilities. STE is firm and  can be dispatched at the request of power grid operators, in particular when demand peaks in the late afternoon, in the evening or early morning, while PV generation is at its best in the middle of the day. Both technologies, while being competitors on some  projects, are ultimately complementary.

• The value of STE will increase further as PV is deployed in large amounts, which  shaves  mid-day peaks  and  creating or beefing up evening and early morning peaks.  STE companies have begun marketing hybrid  projects associating PV and  STE to offer fully dispatchable power at lower  costs to some  customers.

• Combined with long  lead times,  this dynamic explains  why deployment of CSP plants would remain slow in the next ten years compared with previous expectations. Deployment would increase rapidly  after 2020  when STE becomes competitive for peak and  mid-merit power in a carbon-constrained world, ranging from 30 GW to 40 GW of new-built plants per year after 2030.

• Appropriate regulatory frameworks – and  well- designed electricity  markets, in particular – will be critical to achieve  the vision in this roadmap. Most STE costs are incurred up-front, when the power plant is built. Once  built, CSP plants generate electricity  almost for free. This means that  investors need to be able to rely on future revenue streams so that  they can recover  their initial capital  investments. Market structures and regulatory frameworks that  fail to provide robust long-term price signals  beyond a few months or years are thus  unlikely to attract sufficient investment to achieve  this roadmap’s vision in particular and  timely decarbonisation of the global  energy system in general.

The Global Solar Thermal Electricity Outlook scenarios shows the range of possible outcomes depending on the choices we make now for managing demand and encouraging growth of the STE market. In the next five years, we could see as little as 941 MW of STE installed each year under the Reference scenario, to as much as 11,950 MW annually under the Advanced scenario.

Even under the Moderate scenario of fully achievable measures, the world would have a combined STE capacity of over 22 GW by 2020 and 781 GW by 2050, with an annual deployment of up to 61 GW. This would generate 54 TWh in 2020, by 2050 this would increase to 2054 TWh or around 5% of global demand. This scenario would require over €16 billion in investment by 2020, increasing raising to €162 billion by 2050. In the Moderate scenario, 935,000 jobs would be created in 2050.

In the Moderate scenario, 32 million tonnes of CO₂ emissions would be avoided annually in 2020, increasing to 1.2 billion tonnes in 2050. The CO₂ savings under the moderate scenario would be comparable to 3.5% of today’s global CO₂ emissions.

Under an Advanced scenario, with high levels of energy efficiency, STE could meet up to 12% of the world’s power needs in 2050.

The Reference scenario is derived from the IEA’s2014 World Energy Outlook. It starts off with an assumed annual new capacity additions of 1.5 GW of STE increasing to 3 GW/yr by 2020. Growth rates continue at around 10% per year until 2035, and then decrease to around 5% by 2040. After 2040, the scenario assumes no significant further growth of STE. As a result, the scenario foresees the following:

• By the end of this decade, cumulative global STE capacity would have reached 11 GWs, producing 28 TWh per year, and providing 0.1% of the world’s electricity demand.

• By 2030, cumulative global STE capacity would be 21GW, producing around 54 TWh, and providing 0.2%-0.25% of the world’s electricity demand, depending on whether low or high levels of energy efficiency measures are introduced.

• By 2050, cumulative global STE capacity would be 42 GW but the penetration of solar power would be no higher than 0.3 % glob- ally.

Under the Moderate scenario, growth rates are expected to be substantially higher than in the Reference scenario. The assumed cumulative annual growth rate starts at 26% for 2016, and increases to 28% by 2020. By 2030, the growth rate falls gradually to 17% until it reaches 8% in 2040 and 6% after 2050. As a result, the scenario foresees the following:

• By the end of this decade, cumulative global STE capacity would reach 22 GW, with annual additions of 4.8 GW.

• By 2030, cumulative global STE capacity would be as high as 131 GW with annual additions of 18.8 GW. By 2050, the world would have a cumulative global STE capacity of over 781 GW, with the annual market running close to 62 GW.

In terms of generated electricity, the Moderate scenario would mean over 344 TWh of electricity produced by STE in 2030. De- pending on demand side development, this would account for 1.1%-1.3% of global demand in 2030 and 5%-5.9% in 2050.

Under the Advanced scenario, the assumed growth rate starts at 29% in 2016. By 2030, it has decreased to around 20%, and decreases further to 10% per year by 2035.Thereafter, the annual growth rate levels out at around a 5%. As a result, the scenario foresees the following:

• By 2020, cumulative global STE capacity would have reached 42 GW, with annual additions of around 11.9 GW.

• By 2030, cumulative global STE capacity would be over 350 GW, with annual additions of around 50 GW. This would lead to STE capacity of almost 940 GW by 2040, with an annual market volume of 75 GW.

• By 2050, the word’s total fleet of STE plants would have a capacity of 1,600 GW.

• In terms of generated electricity, the Advanced scenario would mean 103 TWh produced by STE in 2020, 920 TWh in 2030 and over 4,300 TWh by 2050. Depending how much demand has been curbed by energy efficiency, solar power would cover 3%-3.4 % of global electricity demand in 2030 and as much as 10.6%-12.6% by 2050

Under an Advanced scenario, with high shares of solar electricity from STE plants, 2.6 Gt of CO2 could be avoided by 2050, making a significant contribution to protect the world´s climate whilst providing a substantial share of electricity to the world’s power needs.