National Public Radio: The nation’s electricity grid is facing some huge challenges — it’s outdated and unprepared for increasing demand and a future that includes more renewable sources of energy. In a weeklong series, NPR is examining the state of the nation’s electricity infrastructure. The economic stimulus bill passed in February includes $11 billion to upgrade the country’s power grid, but that’s just a down payment on a massive undertaking. That’s because when it comes to electricity, not much has …