As world leaders prepared to discuss a major climate change treaty in Paris last week, Germany had a couple of especially windy days, which drove the share of wind energy in the German grid above 50 percent and the spot price of electricity to zero, or so close to it as to make no difference.

All that’s missing to make 100 percent renewable energy feasible is cheap and ample storage that would help to smooth supply. That requirement no longer looks impossible.

Few countries have the political will and resources for something like Germany’s ambitious, painful and expensive energy transition program, known as Energiewende. Yet by going through with it, Germany has helped to spur the development of technology that may work for others without massive subsidies soon.

On Sunday night, Germany’s wind farms produced 35.25 gigawatts of energy, an all-time record; for most of the weekend, more than half of Germany’s electricity came from wind, and it was so cheap as to be almost free:

Germany is depressing in late November: The sky is a cloud factory in overdrive. Little solar energy is produced. In sunnier July, though, solar can combine with wind for more than three-quarters of Germany’s power. On July 25, a new record was set: A combined 78 percent of consumption for all renewables, including hydro and biomass.

These are, of course, only temporary peaks. There are quiet, gray days when very little wind and solar energy is produced. For the year, however, Germany was on track for a 33 percent renewable share even before last weekend’s wind surge. The jump from 27.4 percent last year shows that Germany’s 2020 goal of 40 percent may be achieved earlier than planned.

Only a year ago, critics of Energiewende said it had failed, claiming that Chancellor Angela Merkel had derailed it by pledging to give up nuclear power in the wake of the Fukushima disaster. Phasing out “clean” nuclear energy drove up the use of Germany’s primary source of traditional energy — the dirtiest one, coal — and for a few years, the country’s carbon emissions actually increased. The trend ended last year, however, as emissions dropped almost to the 2009 level, the lowest since 1990. Constantly increasing solar and wind installations — Germany now has about 45 percent of Europe’s total wind generation — were the main reason for that.

That growth was fueled by massive subsidies. Last year, German households paid €23 billion ($24.3 billion), about €572 per family, in feed-in tariffs, or surcharges on energy bills that guarantee “clean power” producers can cover their costs. The results were, in the skeptics’ eyes, less than optimal. Though solar generation accounts for 19 percent of Germany’s total capacity, it produces just 5 percent of the country’s electricity. For wind, these shares are 18 percent and 8 percent, respectively. By contrast, lignite (so-called brown coal, which has high CO2 emissions when burned) accounts for 12 percent of installed capacity but 25 percent of electricity output.

Cost and the unreliable supply are Energiewende skeptics’ biggest problems with wind and solar as replacements for coal- and gas-fueled power plants. In Italy and Spain, the development of wind and solar has almost completely stopped after reaching about 25 percent of total supply: These countries cannot afford to subsidize further expansion and power companies cannot see these sources replacing efficient, reliable traditional production. The United Kingdom, too, appears poised to curb wind and solar with subsidy cuts.

In Germany, however, there’s continued public and political support for the subsidies. They were slightly reduced in 2015, but they will increase next year as wholesale energy prices fall (the total energy bill for the typical family will thus remain the same). There’s a good reason why the German government feels confident about pushing on with renewables development. Energy storage may soon be able to level out the weather-related supply jumps at prices that will make it attractive to energy companies.

Europe’s first commercial battery storage system went online in Germany a little over a year ago and more projects have since joined it. It’s a hot market. Earlier this month, the investment bank Lazard published its first analysis of the costs of various storage technologies, and it showed that for some of them, costs were rapidly declining. The bank said the energy storage industry was at an “inflection point” similar to the one renewable energy saw eight years ago:

“Even without subsidies, certain storage technologies are already cost-competitive with certain conventional alternatives (for example, lithium-ion batteries for certain power grid support applications). Other storage technologies are close to being cost-competitive in other applications, and costs are expected to decline in coming years.”

Germany has an incentive scheme for households that wanted to install storage systems combined with solar panels (millions of German homes have them). The government planned to scrap the support starting next year, but has apparently decided against it. There’s also a research and development initiative for energy storage.

Energiewende has been a brave move: The German government started out with a lot of unknowns, and the decision to close down nuclear plants reshuffled the deck in unpredictable ways. Energy companies have suffered; last year, E.ON, the country’s biggest power supplier, posted a net loss of €3.2 billion, the biggest in its history, and decided to split in two, one part focusing on renewables and the other on fossil fuels. Yet it’s clear now that the program has been a success and that as long as there is a well-defined goal and a determined effort to reach it, the necessary technology will present itself.

The most heated arguments at the COP21 climate change conference in Paris, which got under way on Monday, will be about how to split the cost of reducing emissions among richer and poorer countries. Germans have already answered the question by unilaterally shouldering the energy transition burden. It’s a matter of resolve, and the degree of resolve required goes down each year as technological advances make renewable energy an economically viable alternative to fossil fuel.

Leonid Bershidsky is a Bloomberg View columnist and the author of five books.

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