greenhouse positioning help

[seneca]

I have a greenhouse which I am positioning next to a fence in the line of which it will get a reasonable amount of sun. It is the most suitable spot in the garden, though sunlight will be blocked for half of the day because as the sun moves about the greenhouse will be obscured by trees. It will probably have the sun shining directly at it for 4 hours. Is there anyway of increasing the warmth inside of it, by not heating it. As one side is against the fence could I put something reflective there to bounce the sun off? if so what? I was thinking of fixing an aluminium sheet against the fence or posibily putting a mirror inside it. Will these reflect heat or light to an amount that would make a difference. Or are they a waste of time.