Legislation for establishing a federal renewable portfolio standard (RPS) could ride that momentum and become law by year's end.

The Senate is likely to end debate on the bill and call for a vote on its version Tuesday, according to Reuters. The bill will likely pass thanks to support from three republican senators, and will then move to be reconciled with the House's version. While all of that's happening on Tuesday, the Senate Committee on Energy and Natural Resources will hold a hearing on a proposal for an RPS. The standard would mandate that starting in 2011, a minimum of 4 percent of electricity sold to retail consumers come from renewable resources other than hydropower, ramping up to 20 percent by 2021.

Meanwhile, the House has its own bipartisan proposal for an RPS that goes further, asking for 25 percent of electricity from renewables by 2025.

While half of the states already have their own RPS, many are not as aggressive as these federal proposals. Those states with higher goals would take precedent over any federal plans, according to analysis by the law firm of Stoel Rives.

One question sure to come up during debate is, how can utilities afford to pay for adding renewable resources when the economy is in shambles? Federal loan guarantees provided in the final stimulus package that President Obama signs could address at least part of those concerns.

According to analysis by the Apollo Alliance, the house bill calls for about $10 billion in loan guarantees for renewable and transmission projects, while the senate version calls for about $8 billion. Both bills provide extension to the wind and solar production tax credit, another incentive that makes these projects more affordable for utilities.

If utilities themselves aren't so motivated to operate wind and solar farm, then independent power producers, or even large customers, could take advantage of the loans and sell the power or the renewable energy credits (RECs) to the utilities.

However, the cost of even a relatively small RPS will be much bigger than the stimulus money alone can provide. According to a new report by a group of regional organizations involved in power production and distribution, incorporating 5% wind energy into the eastern U.S. grid will "require the addition of approximately 10,000 miles of new extra-high voltage transmission at a cost of approximately $50 billion, in addition to nearly $700 billion in total generation capital costs by 2024." The total cost for 20 percent wind (which in many cases is cheaper than solar) would be more than the entire stimulus package -- $1.1 trillion.

The enactment of the stimulus package will increase the likelihood that an RPS could win passage by the end of the year. However, congress has a lot on its plate this year, and unless more republicans are brought on board, it could be challenging to bring the legislation to a vote.