+1^ Glenn, but PSU is correct too. Where do you live? The desert Southwest might be completely different from where I live in the mid-Atlantic.
My RSM250 gets some fall/winter sunlight and I have not noticed a problem with algae or heat gain. First it doesn't last too long - not enough to make a difference. Plus it's shining through modern windows with "Low-E" glass (reduces solar radiation), then goes through the RSM glass and my theory is that much of the light energy gets filtered out. And in my case it's late day sun which is more diffused than mid day sun anyway.
Any algae issues I had earlier on were surely caused by my newbie mistakes like over feeding etc. Those 6 T5 lamps will put out much more energy than a sprinkling of diffused sunlight. Plus if it turns out to be a factor for you, I'm thinking you could always compensate by shortening your light cycle by an hour or two.
Plus keep in mind how the eliptic (sun's path) changes over the year...it may or may not be a problem during other times of the year. And mid day sun is much stronger than afternoon sun. If worse comes to worse, maybe you could block the light w/ curtains/shades, tinted film etc.
If you do live in an exceptionally sunny, clear sky area like say Southern Arizona for example, the only thing I'd be concerned with is possible heat gain. This could be checked by letting a glass jar of tap water sit @ room temp in the shade. Then put it in the sunny spot all day. Take a before/after temp reading and see what you have. Even IF you have a significant gain, (I doubt it though) that could be dealt with with a chiller.
