It was a rough week for most solar stocks, although there wasn't any real bad news driving the industry lower. Mor likely, investors are beginning to take 2013 profits off the table, causing some unusual movements in stocks this week.

SCTY Total Return Price Chart

SCTY Total Return Price data by YCharts.

As we close in on the end of the year, stocks that have increased, as solar stocks have, can sometimes act erratically in the short term, but remember to keep an eye on long-term trends that will see your favorite solar company either emerge an industry leader or fall behind.

SolarCity energy storage
Speaking of industry leaders, SolarCity (NASDAQ:SCTY) announced an energy storage product this week, a long-anticipated advance in the industry. The system is called DemandLogic and will be marketed to businesses installing solar and looking for ways to reduce peak load and have backup power during emergencies. Batteries will be supplied by SolarCity's sister company Tesla Motors.

I don't think DemandLogic won't be a big profit generator or a great investment for businesses early on, but the goal is to develop technology that will make battery backup cost-competitive in five or 10 years. That's when the industry will demand energy storage, and companies that have it figured out will be in a good position.

SolarCity is on the leading edge of solar, with the first residential securitization deal and now a battery backup product. That should keep the company growing and offering the kind of products customers around the country want.

Falling behind
One company that isn't emerging as a solar leader is ReneSola (NYSE:SOL), which wrote off a major plant upgrade in the third quarter. ReneSola isn't the worst operator from a margin or balance sheet standpoint, but it made a huge blunder in a polysilicon upgrade gone wrong. It has also decided to put less focus on project development, which has helped many solar companies become profitable in 2013.

Unforced errors are hampering ReneSola more than anything. ReneSola has a chance to return to profits next year, but it'll need continued improvement in the solar market. It's a laggard in the industry, and I just think there are better options for investors, like Canadian Solar or Trina Solar.

News and notes
Here are some of the other notable developments this week that didn't get big headlines.

  • SunEdison (NASDAQOTH:SUNEQ) doubled its distributed solar fund with De Lange Landen Financial Services to more than $100 million. These funds will help expand the company's footprint in the fastest-growing portion of the U.S. market.  
  • New York is also partnering with SunEdison to build the biggest solar system within the city's limits. SunEdison will build a 10 MW project on a site that was once the Freshkills landfill and will soon be one of the city's largest parks. This will also double the amount of solar in New York City.  
  • Hanwha SolarOne signed a memorandum of understanding with Jiangsu Zhongtian Technology that could lead to it supplying panels to the 150 MW pipeline Zhongtian has. It's expected that a definitive agreement will be reached within 90 days, and this is a huge opportunity for Hanwha SolarOne.  

Check back to fool.com for the latest on solar stocks, and I'll be back next week to update you on the latest in solar.

Fool contributor Travis Hoium has no position in any stocks mentioned. The Motley Fool recommends and owns shares of SolarCity. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.