Looking for advice on using Solar powered heating in Greenhouse

I have finally given in to temptation and ordered my first greenhouse - was an offer on 6x8 with toughened glass! Due to be delivered in mid March when hopefully the weather will be better, so it can be erected!

One of the things i would like to do is use solar power to operate a heat sink - saw it on "it's not easy being green" years ago and thought has always stuck in my head for when i eventually got my own greenhouse! I also thought i could then divert the solar power in the winter for a small electric greenhouse heater - i have a lemon and a lime tree that need some winter heat, and as i'm in Central Scotland i don't think just insulating the greenhouse would be enough (they are currently overwintered in a garage with a natural light source and some heat).

I have thought about gas/paraffin heaters but i work away from home sometimes so wanted something that in effect managed itself!

I've seen a few articles about how to build a heat sink, etc - but not many about peoples experiences of using them and if they are worth the investments of the solar panel, battery, converters, etc.

I was just wondering if anyone in the forum had tried this approach and if they thought it worthwhile?

Thanks