Do solar lights work in colder cloudy climates?

Residential Solar Power Question

I purchased a few solar powered garden lights and they have not worked very well for me so far. Is there anything I can do to make them work more effectively?

Does it matter whether they are in direct sunlight or slightly shaded for some of the day?

I am also wondering if altitude would affect the garden lights I bought, we do get sunshine but as we are quite high up it doesn't always get very warm where we are.

I am wondering whether I bought dud lights or else there is some trick to making them work that I am unaware of. I like the idea of solar powered garden lights as they allow me to enjoy my garden in the dusk and at night without having to run power cords round my yard.