They hope to reach zero emissions by 2050. Trials with various fuel blends are underway including in cold weather sites like Pennsylvania in winter.
Waste oil as from deep fryers are probably most economical but supplies are likely insufficient. Rendered fats from dead animals or meat packing scraps or fats from industrial meat processing (frozen precooked meat dishes) etc may help. Processing top quality oils like soybean oil or canola oil are likely to be costly.
They are making progress.