How to connect 16 solar panels for best performance

I have 11 panels (size 120x300 cm) on my roof connected in one big parallel group. I just got 5 more. The question is how to connect them for best performance (I live in Denmark so I need to get the most out of them). You can see a picture here:
https://dl.dropboxusercontent.com/u/...8/solardur.jpg

I read somewhere that it is better to divide a large number of panels into groups. But should the groups be connected in parallel or serial? Or combined? My friend (who knows a lot about pools and solar heating) suggested this setup:
https://dl.dropboxusercontent.com/u/...08/diagram.JPG

I thought 3 or 4 groups in parallel were better but my friend pointed out that it would be the same as one big group in parallel.

Any ideas are most welcome

You're greatest thermal efficiency will come if the panels are in parallel, since that arrangement reduces heat loss, as the panel temps rise.

Provided you use a header (large main pipe -- which your panels have) you'll ALSO get a reduced head loss (pressure loss) with the panels in parallel.

You'd get the highest out put temperature with a serial layout, but since your concern is to warm the pool, not provide hot water for a shower, that's of no benefit to you.

thanks for the quick reply.

So if I choose parallel, would I not benefit from dividing the flow/panels into 3 groups?

Don't you think that with 16 panels it would okay to have a seriel connected group?

You'll get the most heat in the pool from a parallel configuration. It looks easy to do from the picture.

Three parallel groups might have some advantage if the headers (top and bottom) of the panels are smaller than the pool plumbing.

Putting any of them in serial will give a higher change in temperature of the water through the array of panels but lower total collected calories.

Thanks for all the input.
So 3 groups in parallel makes no difference because running all panels in one group is also parallel and shouldn't be a problem when the manifolds are 40mm (only slightly smaller than my 50mm piping)?

Also, 3 groups requires al lot more piping and thus possible leaks. So is it really worth having 3 parallel groups compared to one parallel group?

I would ask this:

Are they ALL always in the sun at the same time? My solar panels vary. (I have two groups, all in serial, but the two groups are parallel).
My NW group gets lots of morning sun, but little to no late afternoon sun.
My SE group gets the late afternoon sun. Both get mid-day sun.

So frequently I'll turn on just the NW panels in the morning, turn on the SE panels when the sun hits them, and turn the NW panels off as the sun leaves them.

yes they are all in the sun at the same time. A whole group in serial seems like it would give a lot of pressure. How many do you have in a group?