HARRISBURG - Solar energy. Ethanol plants. Biodiesel fuel. Smart meters. For Gov. Rendell, these things have become a passion, if not a part of his potential legacy.

But as the legislature prepares to convene a special fall session tomorrow on Rendell's sweeping plan for alternative-energy projects across Pennsylvania, serious questions remain about how much the governor can get past lawmakers who already have fought him on it once - to the brink of a government shutdown.

Many issues still divide the two sides, with the central disagreement remaining: how much to spend and where to get the money.

The Rendell administration is optimistic an agreement can be reached, especially since the state is staring down a 2010 deadline. That is when electric-rate caps imposed after deregulation in 1996 expire, and electric bills are expected to skyrocket.

"The bottom line is, we have an economic train wreck heading our way with respect to soaring electricity rates," said Kathleen A. McGinty, state secretary of environmental protection.

At the heart of Rendell's energy plan is an $850 million Energy Independence Fund. Senate Republicans are pushing a $530 million alternative. Both plans seek the same result, but would get there different ways.

The largest portion of Rendell's fund, $500 million, would be invested in clean-energy projects such as biofuel plants and solar and advanced coal technologies. In addition, $100 million would be made available to help Pennsylvania firms interested in expanding clean-energy production to attract private-sector investors.

The fund would also be used to help residents cut energy costs. For instance, it would provide grants to reimburse homeowners and small businesses for up to half the cost of installing solar panels, pay for $100 rebates on residential purchases of energy-efficient air conditioners and refrigerators, and allow homeowners to install smart meters - high-tech devices to help them target electricity use to times when the cost is lowest.

Rendell says the overall goals are to break dependence on foreign oil and cut electricity bills through new conservation techniques.

"These policies . . . will not only grow our competitive edge in clean energy even further, but move us dramatically closer to energy independence," he has said.

The proceeds of a bond issue would generate the $850 million fund, and the bonds would be paid off over 30 years with a new fee added to electric bills. Although Rendell in July indicated a willingness to back off the fee, his administration is now maintaining it is still part of the plan.

That per-kilowatt-hour fee would cost residential customers an average of $5 a year, according to the administration. For large customers, the fee would cost no more than $10,000.

Rendell says a small fee now would produce a larger, long-term reduction in high-cost energy use. The administration believes its proposal would cut Pennsylvania's energy bills by $10 billion over the next 10 years.

Rendell's plan has been more than a year in the making. He has said in interviews that alternative energy is a key interest for him. He has also said he would be interested in serving as energy secretary if a Democrat won the White House next year.

It is no surprise, then, that the issue has become a staple of many of his speeches - including one scheduled for Sept. 24 before a joint session of the legislature.

"He's always been very good at finding issues that elevate his profile," said Larry Ceisler, a media consultant from Philadelphia who works mostly for Democrats.

"Having said that," Ceisler added, "with this governor you know when he's calling it in and when he's passionate. And when he talks about energy, he's being real. He gets it."

Given rumblings from the Republican corner, getting all Rendell wants may prove difficult.

The GOP plan, sponsored by Sens. Robert M. Tomlinson (R., Bucks) and Mary Jo White (R., Venango), calls for borrowing $250 million up-front, and spending an additional $40 million annually for seven years for alternative-energy projects and home-energy conservation.

The money would come from existing revenue rather than a new fee on electric bills.

Said Senate Majority Leader Dominic Pileggi (R., Delaware): "I don't see any support in our caucus for a new electricity tax - or a need for it."

House Republicans are sounding similar warnings. At a news conference tomorrow, they are scheduled to announce their own energy plan - one more conservative than the Senate's.

Rep. Stanley Saylor (R., York) said the proposal would require no new borrowing or new fees. It would use grants and tax credits to promote alternative-energy production.

Saylor, too, said the governor's plan had little backing among his colleagues.

"He knows his plan is dead, and that he should be working on trying to get a plan B," Saylor contended.

Despite the tough talk, Rendell administration officials said they believed lawmakers had little option but to act - and act aggressively.

"The legislature is getting the message that doing nothing is not an option," McGinty said.