Use Solar Preheating to liquify oils before filtering and processing. There three methods that are in use by homebrewers.
1. Paint a 55-gallon drum black and sit it in the sun. This works really well in the summer. This calls for moving drums full of oil, which can be a problem for some. Methods of moving full drums of vegetable oil include tilt and roll, using a drum truck ($150 and up) or a drum dolly ($30 and up). A drum dolly is inexpensive but requires an even surface and is difficult to move from drum to drum. A drum truck is expensive, but does not need an even surface and can quickly be moved from drum to drum.
2. Build a solar bucket or drum box. This works year round.
5 gallon solar box.
110 gal cone bottom solar box.
Both can be found at http://www.localaction.biz
3) Use a solar water heating panels. This method seems to be used mostly to heat clean oil for processing and can be used to get oils up to reaction temp.
http://biodiesel.infopop.cc/ discussion using solar panel to heat WVO.
http://biodiesel.infopop.cc/ another thread on using solar panels
$25 Solar Box that holds 2 55-gallon drums:
2 sheets 4x 8 x ½ Styrofoam insulation
1 clear plastic sheet 60 x 48
1 roll duct tape
1 can black paint
1) Cut one Styrofoam sheet in half one half will be the bottom and the other half the back
2) Cut the second sheet in quarters 2 x 4
3) Cut one of the 2 x 4 panels from corner to corner making 2 equal sized triangle shaped pieces.
4) Tape the pieces together using duct tape. Leaving the back piece taped only on the top to act as a door for the box. see attachment
5) Paint the inside black
6) Cover the opening with clear plastic.