Despite these auspicious trends, not all the news was good, however. The U.K. slashed its feed-in tariff, which is expected to decimate the British solar industry. Solar stock prices collapsed mid-year, and have not recovered. Finally, battery storage is starting to emerge not as a future hope, but a real market.
COP21 boosts solar prospects
From the perspective of previous global agreements, the resolution hammered out in Paris in early December was weak, as it is based on national contributions that are voluntarily determined by each nation, and are not legally binding. However, many observers have stressed the importance of reading between the lines of the Paris Agreement.
In particular, in the lead-up to the agreement at the 21st Conference of the Parties (COP21) a number of nations, provinces and even cities made pledges and unveiled programs to reduce carbon emissions, including goals for increased adoption of renewable energy.
Additionally, the text of the COP agreement echoes statements that are increasingly being made by various financial and energy experts: that global dominance of fossil fuels, particularly coal, is over, and that the world is inevitably moving towards a transition to renewable energy.
Finally, the Paris Agreement was accompanied by a voluntary global agreement to increase clean energy research and development (R&D) funding, initiated by Microsoft Founder Bill Gates. While this R&D funding is expected to include more nuclear R&D and despite the global track record showing that policies to spur deployment are more effective than additional R&D spending, such support was nonetheless welcomed by the solar industry.
An unexpected gift: US ITC extension
In terms of concrete impacts on the global solar industry, the Paris Agreement and the sum of all the national commitments leading up to it were not the most important development in 2015. The U.S. and global solar industries got a Christmas surprise, in the form of an unexpected three-plus year extension to the U.S. Investment Tax Credit (ITC) which passed the U.S. Senate as part of a budget bill on December 22.
The ITC extension includes a multi-year phase-down, which solar industry legend Jigar Shah notes is especially important for avoiding a cliff and allowing investors to plan with certainty.
Overall, the policy is expected to allow the U.S. solar market to continue to grow through 2017 and beyond. According to IHS, it will also avert the first annual drop in the volume of global solar installations in over a decade and a potential crisis for suppliers along the PV value chain.
The Tories ax the feed-in tariff
But while there was good Christmas tidings from the United States, on the other side of the pond policy news was decidedly more grim. The ruling Conservative Party in the U.K. again showed its penchant for rapid policy sabotage and hostility to solar, by sharply reducing feed-in tariff levels effective February 2016.
This is expected to have a dramatic impact on the U.K. solar market, and even during consultation on the cuts the nation's solar industry was reporting layoffs.
Solar costs keep coming down
When the smoke clears from all the big policy stories of the last few months, other trends that continued throughout 2015 can be seen. In particular, solar costs have continued their historic fall, and utility-scale solar is becoming competitive with wholesale electricity in an increasing number of areas.
In Texas, municipal utility Austin Energy signed power purchase agreements (PPAs) with First Solar, Hanwha Q Cells and other developers for hundreds of megawatts of solar, at prices under five U.S. cents per kilowatt-hour. These PPAs are only the beginning, as low prices in Texas have led the state's grid operator to predict that the state will install 13 GW of solar PV by 2030 before new federal policies are even factored in.
However, it was not just the United States that saw record low prices. Saudi Arabia's ACWA Power and Spanish Engineering firm TSK put in a successful bid to build a large solar project in Dubai for under six U.S. cents per kilowatt-hour, raising speculation that six cents could be the new normal for large-scale power contracts for solar.
Even Germany, which has far inferior solar resource to either Texas or Dubai, is recording record low prices. Contracts at under 0.08 per kilowatt-hour (kWh) were awarded in the nation's latest solicitation. In August, around 150 MW of solar PV installations were built at a feed-in tariff price of 0.09/kWh.
Bear market: Solar stocks crash
Falling costs and good policy news were not enough to save prevent a crash in the price of solar stocks, brought on by a combination of larger stock market problems and a decline in oil prices which has broadly effected energy stocks.
Investors have particularly expressed skepticism over yieldcos, with concerns about over-leveraging leading to falling valuations. SunEdison and its yeildco TerraForm Power performed particularly poorly, as investors voted with their wallets against the company's pending purchase of Vivint Solar, leading to a shift in strategy and layoffs.
This is not to mention Hanergy, where a stock price bubble spurred by over-enthusiasm turned into a severe crash following an annual meeting gone wrong, which has wiped billions off the valuation of the company and led to concerns about the company's viability.
In short, at the beginning of 2016 it is a buyer's market for solar stocks.
Energy storage on the rise
In retrospect, 2015 may also be seen as the year where energy storage went from a niche market to a main current of the renewable energy revolution. Spurred by new policies mandating energy storage in California, the ongoing use of incentives in Germany and falling costs, a nascent solar plus storage market is emerging.
By the end of the third quarter the United States had added more than 100 MW of energy storage capacity in 2015, already setting a new annual record. GTM predicted at the time that the nation could reach 192 MW of new storage capacity by the end of the year, and 60 MW was added in the third quarter alone.
German figures are harder to come by, however during the first two years of Germany's residential energy storage subsidy, from March 2013 to March 2015, an estimated 17,000 energy storage systems totaling 120 megawatt-hours were connected to the low-voltage grid.
And while this year saw the unveiling of Tesla's new PowerWall battery system, at the end of the year Sonnenbatterie beat Elon Musk's company to the punch by rolling out their energy storage solution on the U.S. market first.