But much more needs to be done. Ratcheting up solar to produce approximately 1 percent of global electricity has required a lot of technology and investment. Making solar big enough to matter environmentally would be an even more colossal undertaking. It would require plastering the ground and roofs with billions of solar panels. It would require significantly increasing energy storage, because solar panels crank out electricity only when the sun shines, which is why, today, solar often needs to be backed up by fossil fuels. And it would require adding more transmission lines, because often the places where the sun shines best aren’t where most people live.

The scale of this challenge makes economic efficiency crucial, as we argue in a report, “The New Solar System,” released on Tuesday. The policies that have goosed solar have been often unsustainable and sometimes contradictory. One glaring example: With one hand, the United States is trying to make solar cheaper, through tax breaks, and with the other hand it’s making solar more expensive, through tariffs it has imposed on solar products imported from China, the world’s largest maker and installer of solar panels.

The tariffs are prompting Chinese solar manufacturers to set up factories not in the United States, but in low-cost countries that aren’t subject to the levies. And the Chinese government has responded with its own tariffs against American-made solar goods. Those tariffs have eroded the United States share in the one part of solar manufacturing — polysilicon, the raw material for solar cells — in which America once had a significant role.

That solar is now involved in a trade war is a sign of how far it has come. The United States developed the first solar cells in the 1950s and put them into space in the 1960s. Japan and Germany began putting big numbers of solar panels on rooftops in the 1990s. But solar power didn’t really advance into a real industry until a decade ago, when China stepped in.

In the mid-2000s, stimulated by hefty solar subsidies in Europe, a handful of entrepreneurs in China started producing inexpensive solar panels, much as had been done in China before with T-shirts and televisions. These entrepreneurs bought equipment from manufacturers in Europe and the United States, built big factories with government subsidies, and got down to business cranking out millions of solar panels for export.