Sunflower seeds

[Impret-Sir]

Last year I saved a lot of seeds from my giant single sunflowers to sow this year. Not one of them germinated. A friend of mine told me that he had the same experience and said that all his seed was 'sterile'.I had never heard of that in seeds, is it a known problem with sunflowers? Is there any way to spot seeds that will not germinate next season, as I am thinking about saving some more from this years plants, but wont bother if they are not going to germinate.