Oil prices dropped by more than 50% from December 2014 to February 2015. Large variations in oil prices have been common. The causes have been both political and economic, but the current situation has been caused by having an excess supply of oil and not enough demand.
If the current price drop is short, investment in renewables will most likely not be affected, but if it is longer lasting then more government support will be needed to keep the transition from fossil to renewable energy on path. Long-term commitments to cut greenhouse gas emissions will work as a counterweight to low oil prices, and keep up investments and technology development of biofuels.
If international agreements to cut emissions are reached, renewable energy costs will be much less linked to the price of oil and thus follow a different financial scheme.