If you’re a customer of Xcel Energy in Colorado and you’ve successfully installed solar panels on your roof, don’t expect a pat on the back from Xcel – even if you’re feeding electricity back into the grid.

The company says solar customers aren’t paying their fair share, because their use of the power grid isn’t included in the $6 to $7 per month charged for meter reading and billing. The grid, however aged and inefficient, is costly to maintain and the more customers go solar, the less cash Xcel Enegy will have in its coffers for these expenses. Currently, customers are only charged transmission and generation fees when they draw power from the grid.

“These customers are connected to the grid and yet they’re not paying for the infrastructure,” says Xcel spokesman Tom Henley.

Not so fast, say solar industry advocates – it’s actually Xcel that benefits from having solar energy-producing customers hooked up to their grid, because they help the company meet peak summer afternoon demand without having to buy extra energy at a high cost. They’re also helping Xcel meet a state requirement that 20 percent of its power come from renewable sources by 2020.

Solar industry experts are also worried that the new fee, which will affect all customers who install solar systems after April 2010, will discourage some homeowners from giving renewable energy a try.

While some states have laws forbidding such supplemental fees, Colorado doesn’t – at least, not yet. The Colorado Public Utilities Commission will hold a public hearing on the fee proposal next week, but the decision, slated to come next year, may not arrive in time to keep solar customers from having to shell out.