Mother Nature is bullish on solar:

Over the past several years, FedEx, Staples, the Timberland Co., Johnson & Johnson, Microsoft, Macy's, Tiffany & Co, Toyota, Target, Lowe's, corporatebehemoth Wal-Mart and even the U.S. Department of Defense have begun installing solar panels at their facilities.
Now listen, I don't want you to be disillusioned. These companies aren't installing solar panels because they've suddenly become concerned about global warming.
No, they've installed solar panels because it'll reduce their electric bills by as much as 90% each month. 

Cap and Trade:

As society focuses on tackling the challenges of greenhouse gas emissions, market-based solutions have emerged as a means for reducing emissions in the most economically efficient manner, i.e. at the lowest possible cost. Cap-and-trade programs cap the levels of emissions for a particular sector of the economy, but provide compliance flexibility to capped facilities in order to contain costs. Two main products are often used in these programs – allowances and offsets.

Allowances (or permits) are tradable units that represent the right to emit a specific volume of a particular pollutant. They represent the currency of a cap-and-trade program. Initially, a quantity of allowances equal to the size of the cap is distributed by a regulatory body into the market either through allocation, by auction or a combination of both. Subsequently, allowances can be bought and sold under the cap-and-trade program. Facilities need to ensure they have sufficient allowances to submit for every compliance period.

Many cap-and-trade programs include the use of offsets (to varying extents), sometimes known as Certified Emission Reductions (CERs) or Verified Emission Reductions (VERs). Offsets represent project-based reductions of emissions that are undertaken outside of the capped sector(s) and that are above and beyond any legal requirement to do so. These emission reductions are used to offset a like amount of the buyer’s own emissions. They are particularly common in cap-and-trade programs that regulate greenhouse gases.

Renewable Energy Credits;

Many governments mandate that a certain percentage of electricity is to be generated by renewable resources. In addition, many individuals and corporations are promoting the development of renewable resources through the acquisition of Renewable Energy Credits (RECs). RECs are tradable instruments that reflect the environmental attributes of electricity generated from renewable sources, such as wind, biomass, solar or hydro. RECs are an important revenue stream for many renewable projects – by purchasing a REC, the buyer is directly supporting that project’s development.

 "Few power-generation technologies have as little impact on the environment as photovoltaics. As it quietly generates electricity from light, PV produces no air pollution or hazardous waste. It doesn't require liquid or gaseous fuels to be transported or combusted. And because its energy source--sunlight--is free and abundant, PV systems can guarantee access to electric power." --U.S. Department of Energy