A major challenge facing research and development of renewable energy technologies is securing funding for risky new ventures.

Solar, wind, biofuels, and other firms have been turning to increasingly innovative financial mechanisms to raise funds from persistently risk-averse lenders. While some of these efforts have borne fruit, not all companies have managed to convince the market that financing their projects is worthwhile.

But some lucky firms and forward-looking ventures have attracted the attention of major oil companies which, armed with multi-billion dollar capital budgets, can provide them with the financial backing required to push their schemes forward.

All segments of the renewables sector continue to evolve, and it is impossible to say which companies and technologies will survive over the long term. But major oil company support is giving the following initiatives a strong financial advantage in moving to the next phase of market evolution.

Breaking Energy has been running a series of top fives throughout this week and last, which can all be found with the image (top) and the ‘Top5′ tag. Read the other Top Fives: Top Five DOE Recovery Act Loans, Top Five Electric Vehicle Partnerships, Top Five Clean Energy VCs And Principals, Top Five International Energy Partnerships, Top Five Energy Regulators, and Top Five Energy Law Firms.