The world needs a new source of energy, an unspillable source.

at what level of the oil price do alternative sources of energy (ie solar, wind etc) become viable?

what is the cost of energy production per therm for the different methods of production? ie oil, biofuels, solar, wind etc. i understand that oil is the cheapest way of energy production at the moment, but at what level of the oil price would other methods become economically viable?