I use the same technique for cleaning polycarbonate roofs as for cleaning gutters. The only difference is the brush I use.
1 - dip your brush (on a Harris pole) in a bucket of (weak) TFR solution and scrub the roof with it. Be generous with the amount you use and scrub well. Get into the roof spars and under the ridge cappings. Be careful with the ridge cappings. They might need a good scrubbing. My technique is to rest the pole on the edge of the roof and move the brush side-to-side or use a twisting motion. Whatever you do, don't push on them to scrub hard. They might come off!!!
To get under the ridge capping, you might need to take the brush off the pole and wrap a microfibre cloth round the end. You can then use this to poke out most of the odd bits and pieces that get caught up there.
2 - rinse off with a hose pipe before the TFR dries. Use a strong jet.
Dirt is only loosely bound to the surfaces. You may need to scrub long to get off baked-on algae, but you'll never need to scrub hard. (An exception to this is where there is moss - that's a nightmare scenario.
First time might take ages. You'll get quicker the more you do.