phase transfer catalysis (PTC) in water work nicely and yield is excellent

Microwave irradiation is also used

did you try solar irradiation. 

No, Since the solar Light might destroy the starting materials or the formed Products,

I think the best method for Knovenagel is 

1- Microwave irradiation

2- Ultrasound wave

3- Some Heavy metal catalysis 

4- Conventional Method

reactions are usually catalyzed by bases such as ammonia, ethylenediamine,

guanidine, dimethylamino pyridine, piperidine or corresponding piperidine salt, Lewis acids in organic solvents and ionic liquids have also been added to the existing list of substances that assisted Knoevenagel condensation in organic synthesis. a grinding method under solvent free conditions used in Knoevenagel condensation has rapidly increased. Many catalysts have been used in the synthetic procedure, for example , K2O-Al2O3, CaO, ZnCl2, NH4OAC and triethyl benzyl ammonium chloride (TEBA). Knoevenagel reaction under solvent - free conditions carried out by microwave irradiation and by grinding has rapidly  increased.But microwave irradiation processis difficult to apply in the industrial process until now and the grinding reaction is only suitable to some active solid reactants

http://www.e-journals.in/PDF/V2N1/197-207.pdf

there are a lot of "new" methods, using mild reaction conditions, sonication...

have a look at:

- Ultrason. Sonochem 1999, 6 p199 / 2002, 9 p159

- JOC, 1984, 49 p 5195

- Tet Let, 1987, 28 p4541.....

good luck