超大型太陽能？
（接續前篇2/3）根據IEA的STEPS情境，到2020年代中期，再生能源將取代煤炭成為最大的電力來源。到2040年，低碳能源將滿足全世界一半以上的電力需求，在SDS情境中甚至達到85％。
（不過，值得重申的是，今日電力僅佔總能源消耗的1/5，到2040年，這個數字在STEPS中將上升到24％，在SDS中將上升到31％。這是僅靠再生能源無法解決氣候挑戰的諸多原因之一。）
值得注意的是，今年的STEPS中，再生能源的前景大幅提高，2040年的太陽能總量提高了23％，風能提高了11％。非水電再生能源的增加了8％（下圖中的紅線），在2030年代後期超過了煤炭。
再生能源產量的成長大部分被增加的需求用掉，表示其他來源的發電相對不受影響。Carbon Brief的分析顯示，相對於去年的展望報告，2040年需求成長主要來自於2018基準年的需求增加，年複合成長率為2％。
WEO解釋：
由於成本持續降低，太陽光電成為2020年中國和印度最具競爭力的電力來源。到2030年，太陽能在歐盟和美國與其他能源的差距將大大縮小。在STEPS之下，2018年到2030年全球太陽光電的平均成本（均化成本）下降了約50％。
此外WEO強調，風能和太陽能的成本下降使「直接從煤炭轉往再生能源有更堅強的經濟理由」，而不是將天然氣當作通往低碳能源的過渡能源。
它還提到，美國新公布的海上風電競標，歐盟各地的競標價格低於預期，中國再生能源零補貼的趨勢也有所減弱。
IEA最近發表了一份關於海上風電前景的深度探討報告。IEA認為海上風電的技術潛力可滿足當今電力需求的好幾倍，成本更將在十年內與化石燃料相當。
IEA表示，隨著風能和太陽能在電力領域的發展，將面臨越來越多的挑戰：「政策制定者和監管機構必須迅速採取行動，以跟上技術變革的步伐和不斷成長的需求，以確保電力系統的靈活運作。」
太陽能傳說
儘管如前所述，今年的STEPS大幅上修2040年太陽能產出，但與其他預測相比，IEA對該技術的展望相對保守。
IEA對太陽能前景的預測受到許多批評。如下一個圖表的藍色色塊，IEA連續好幾個版本的前景報告上修太陽能容量成長。
（請注意，圖表顯示的是扣除退役後的淨增加。由於絕大多數太陽能容量的增加發生在近期，因此最初期可以忽略不計。IEA假設到2040年將有298GW的太陽能容量退役，也就是說在2030年代和之後，實際增加量會增加，而不是像下面的淨增加量表所示的那樣相對平穩。）
IEA將這些連續上修歸因於政府政策隨時間變化，尤其是中國的變化，中國是世界上最大的太陽能市場。
IEA解釋，繼2018年太陽能增長略顯疲軟後，「重新加速年度太陽能佈署，並加大力道確保將太陽能所發電力穩定進入電力系統，對於實現氣候目標和其他永續發展目標至關重要」 。
IEA相對保守的太陽能前景預測似乎部分取決於其對各種發電技術的標準加權平均資本成本的計算，視每個國家的發展階段，設定在7%到8％。
正如IEA對海上風電所做的估算，這可能對特定計畫的均化電力成本（LCOE）產生非常大的影響。 （歐洲海上風電的實際資本成本已接近4％，足以將其LCOE從每千度（MWh）140美元左右降低到100美元。）
另一個因素可能是IEA將重點放在系統「價值」上，而不是前期成本。IEA在WEO 2018發展出的「VALCOE」指標是這麼說明的。
IEA表示，降低成本並不保證能維持競爭力，「因為隨著其發電比例的增加，太陽能的系統價值相對於系統平均值而言往往會下降」。
因為太陽能輸出集中在每天中午時段，容量增加使供電增加，也部分影響了既有太陽能板創造的電價。
有些預測報告同樣考慮了這些因素，卻看好太陽能發電量的增長。到2040年，IEA的STEPS之下每年新增的太陽能不足140GW，而彭博新能源基金會（BloombergNEF）的新能源展望報告則認為，屆時新增的太陽能將超過300GW。這個數字與IEA的SDS中的佈署相同。
彭博新能源基金會還更看好風電容量的增長，預測到2050年，煤炭的電力輸出將下降一半，而非像IEA STEPS所預測的保持穩定。（系列專文3/3）
Supersized solar?
Elsewhere in the electricity sector, the IEA's central STEPS sees renewables surging and overtaking coal as the largest source of power by the mid-2020s. By 2040, low-carbon sources would be supplying more than half of the world's electricity needs – rising to 85% in the SDS.
(It is worth reiterating, however, that electricity accounts for only a fifth of final energy consumption today, a figure that rises to 24% by 2040 in the STEPS or 31% in the SDS. This is one of the many reasons why renewables alone cannot solve the climate challenge.)
Notably, this year's STEPS has significantly increased the prospects for renewables, raising the solar total for 2040 by 23% and that for wind by 11%. This revision, adding 8% to the total for non-hydro renewables (red lines in the chart, below), sees them overtaking coal in the late 2030s.
The increase in expected renewable output is mostly absorbed by higher demand, meaning that generation from other sources is relatively unaffected. Carbon Brief analysis suggests the increase in 2040 demand relative to last year's outlook is mainly due to higher demand in the base year 2018, which gets compounded by 2% annual growth.
The WEO explains:
"As a result of continued cost reductions, solar PV becomes the most competitive source of electricity in 2020 in China and India, and largely closes the gap with other sources by 2030 in the European Union and United States. In the Stated Policies Scenario, the global average [levelised cost] of solar PV declines by about 50% from 2018 to 2030."
It adds that cost declines for wind and solar are "bolstering the economic case for switching directly from coal to renewables", rather than using gas as a "bridge" to low-carbon sources.
It also points to newly announced US auctions for offshore wind, lower-than-expected prices in auctions around the EU and a softening of China's shift towards subsidy-free renewables.
The IEA recently published an in-depth review of the prospects for offshore wind, which it says "has the technical potential to meet today's electricity demand many times over" at costs set to be competitive with fossil fuels within a decade.
THREAD
Offshore wind has "near limitless" potential & is "set to be competitive with fossil fuels within the next decade", as costs fall 60% by 2040.
Turbines will soon be as large as the Eiffel Tower.
Pretty amazing stuff from today's new @IEA report.https://t.co/U8tV2P695i pic.twitter.com/EMn9x6tpe6
— Simon Evans (@DrSimEvans) October 25, 2019
The IEA says there will be an increasing need to address challenges posed by variable wind and solar as they take hold of the electricity sector: "Policy makers and regulators will have to move fast to keep up with the pace of technological change and the rising need for flexible operation of power systems."
Solar saga
Despite the large upwards revision in solar output in 2040 under this year's STEPS, noted above, the IEA's outlook for the technology remains relatively conservative compared with some others.
The IEA's outlooks for solar have become something of a lightning rod for critics of the agency's work. It has made upwards revisions for solar capacity growth in each successive edition of the outlook, shown in shades of blue in the chart, below.
(Note that the chart shows additions net of retirements. These are initially negligible as the vast majority of solar capacity growth has been recent. The IEA assumes 298GW of solar retirements to 2040, suggesting it expects capacity to switch off after around 25 years. This means that actual additions rise in the 2030s and beyond, rather than apparently remaining relatively flat as in the net additions chart below.)
The IEA attributes these successive upwards revisions largely to shifts in government policy over time, in particular pointing to changes in China, which is the world's largest market for solar.
Myth 2: #WEO underestimates renewables growth.
-False. Additions of renewables lead all sources in all scenarios. Track back and China's policy changes accelerated global growth. Unfortunately, in the rest of the world, renewables are behind (!) the STEPS equivalent from WEO2009 pic.twitter.com/NAs2jyemFe— Brent Wanner (@WannerBrent) November 17, 2019
The IEA argues that following slightly weaker solar growth in 2018, "a renewed acceleration in annual solar PV deployment, alongside enhanced efforts to ensure smooth integration of the resulting solar generation into power systems, is essential to reach climate targets and other sustainable development goals".
The IEA's relatively conservative outlook for solar appears to rest partly on its use of a standard weighted average cost of capital for all electricity generation technologies, set at 7-8% depending on each country's stage of development.
This can have a very large impact on the levelised cost of electricity (LCOE) for a given project, as the IEA illustrates with reference to offshore wind. (Actual costs of capital for offshore wind in Europe have been closer to 4%, enough to cut its LCOE from around $140 per megawatt hour to $100/MWh.)
Another factor could be the IEA focus on system "value" rather than upfront costs, illustrated by the "VALCOE" metric it developed for the WEO 2018.
The agency says that cost reductions do not guarantee continued competitiveness "because the system value of solar PV tends to decline relative to the system average as its share of generation rises".
This is because solar output is concentrated in the middle of the day, with additional capacity adding to supply and so partially eroding the price commanded by already-built solar panels.
Despite also considering these sorts of issues, some other outlooks are much more bullish on solar capacity growth. Whereas the IEA's STEPS has solar additions of less than 140GW each year by 2040, the BloombergNEF new energy outlook sees solar additions topping 300GW by then. This higher figure is in line with deployment in the IEA's target-focused SDS.
BloombergNEF is also more bullish on wind capacity growth, with the result that its outlook has electricity output from coal falling by half in 2050, rather than holding steady as in the IEA's STEPS.
※ 全文及圖片詳見：Carbon Brief（CC BY-NC-ND 4.0）
