It can be hard for manysolarcompanies to feel peppy these days. The economic meltdown has bred fears of lending and spending, leading to a depressing outlook for 2009.

But the year also passed with highlights for an industry that is riding the wave of public enthusiasm for clean energy. Investors placed huge bets to enable entrepreneurs to investigate promising technologies. Many solar companies experienced double-digit growth in sales and profits.

Companies that set out to challenge the market dominance of the crystalline silicon technology reached milestones by starting mass production and lining up customers.

Here is a look at the top solar trends of 2008:

Solar Tax Credit Gets Eight-year Extension: The U.S. Congress extended a tax credit and got rid of rules that previously prevent utilities from getting the tax credit. Consumers also will receive more tax benefits than before. Solar technologies remain expensive, so government support is crucial for the industry's growth and for turning the United States into an even larger solar market.

A Fistful of Venture Capital: Venture capitalists pumped nearly $1.6 billion into solar companies in the third quarter alone. That was out of the $2.9 billion total for greentech investments for that period, according to Greentech Media's Venture Power Report. The $1.6 billion was more than the $1.05 billion investors put into solar companies for the entire 2007.

Companies that develop thin-film panels using copper indium gallium and selenium or cadmium tellurium received some of the largest rounds. SoloPower and AVA Solar each raised more than $100 million this year, while Nanosolar took in $300 million.

Rise and Fall of the Spanish Empire: Spain was a hot market in 2008, thanks to its government's policy requiring utilities to buy solar power at premium prices set by the government. Then government decided to reduce those prices and cap the amount of solar power capacity that can be installed nationwide from late September through 2009. That move triggered a frenzy to install solar power plants before the September deadline. It also led to fraud allegations that many developers claimed to have completed their projects when in fact they didn't.

The government hasn't announced its calculations of how much solar power was added in 2008. Some analysts believe it's under 1 gigawatt while others said it's more. The new cap will limit the installations nationwide to 500 megawatts.

Follow Spain's Lead – Sort Of: Spain and Germany proved that government policies are critical to create a growing new solar market. So other countries that also want to encourage solar power use – and reduce greenhouse gas emissions in the process – have adopted similar measures to require utilities to sell renewable energy.

The United Kingdom passed an energy bill this year to create such an incentives program, which is typically called feed-in tariff. The French government expanded its feed-in tariff policy. Japan, meanwhile, is looking at re-introducing a feed-in tariff it gutted a few years back.

Cheaper Polysilicon Cometh: Throughout 2008, analysts have been predicting that the prices for polysilicon, the key raw material for most of the solar panels on the market today, will fall significantly in 2009. That's because a materials shortage has attracted new and existing polysilicon producers to build factories this year.

Market research firm New Energy Finance looked at long-term polysilicon contracts earlier this year and found that the medium for polysilicon delivery in 2009 will be as much as 43 percent lower than the medium delivery price for 2008.

Solar Panel Glut?:  Many analysts also believe that an oversupply of panels could happen in 2009. But evidence showed that it might already be happening. The solar industry produced way more panels this year than it installed, and that gap is likely to widen in 2009, reported iSuppli, a market research firm, this month.

The report echoed a similar take by another solar analyst, Paula Mints of Navigant Consulting, who said the rush to sell panels to the booming Spanish market has led to an oversupply of panels. Earlier this month, a Spanish newspaper ran an article describing Chinese ships loaded with solar panels that had to be resold.

Renewable Energy Mandates: A growing number of states now require their utilities to sell renewable power by certain deadlines. States such as Michigan passed such a mandate while California and Massachusetts strengthened their requirements during 2008.

In response, utilities have scrambled to sign power purchase agreements with solar energy developers or build their own solar power plants. The Pacific Gas and Electric Co. in California is due to receive its first delivery of solar power on Jan. 1, 2009.

Just Say No to Solar?: Solar energy is renewable, so why would anyone oppose it? The thing is, building large solar power plants and transmission lines to move solar electricity around is costly and can pit solar companies and utilities against environmental and consumer advocates.

The controversial project to build a $1.9 billion transmission line from California's inland desert to the coast provides a glimpse of the regulatory battles to come. Critics fought to prevent the line from running through a state park and contended that the project is too costly (the cost will be passed on to ratepayers). Supporters said it would bring more solar, geothermal and other renewable power to the masses.

Making Residential Solar Affordable: The potentially large residential solar market in the United States has lured many new installers. A growing number of state and local solar incentives has boosted business for these companies, which also offer leasing or other financing options to make a solar energy system more affordable. Just four months after launching its leasing program in 2008, two-year-old SolarCity said 90 percent of the company's sales were from the program.

More Thin Films: Thin-film solar companies, which use very little or no silicon in producing solar cells, have started to prove that their technologies aren't just nifty-sounding theories – thin-films advocates say they can produce cheaper solar cells and assemble them into panels than makers of conventional crystalline silicon cells and panels. But crystalline silicon cells are more efficient at converting sunlight into electricity

Fremont, Calif.-based Solyndra, which uses copper indium gallium and selenium (CIGS) as the key ingredients to convert sunlight to electricity, came out of the stealth mode earlier this year to announce it had begun mass production and lined up customers. Global Solar Energy, another CIGS player, also started running its first commercial factory in 2008. The first commercial solar energy system using Global Solar's cells also was installed – at the company's factory in Tucson, Ariz. Several companies that use amorphous silicon as the key ingredient also have begun mass production this year.

Surviving Financial Woes: The credit crunch brought on by the fall of a slew of investment banks darkened many solar companies' outlook for 2009. Companies such as Q-Cells, Renesola, Solon and Suntech Power Holdings have had to cut their sales and production estimates after their customers delayed deliveries or simply couldn't find loans to make the purchases.

The surge of the U.S. dollar against the euro also prompted SunPower and First Solar to warn of lower sales in the near future. At this point, it's difficult to predict when the economy will recover. Already, the Solar Energy Industry Association, which represents solar companies in the United States, is lobbying Congress to get more than $30 billion for companies developing solar power plants.