Replacing vented HW/CH cylinder, move to unvented a good idea?

I have a Navitron based solar system, been installed for 4 years so far (and generated 8.5MWh so far).

I would suggest:

• Get the 30 tube panel instead of the 20. Not much more purchase cost, same labour cost, 50% more output.
• Fit the biggest cylinder you can in the available space. I had one custom-made to fit a space, wide and short so I could put a counter top over it.
• If custom-made, go for the thickest insulation you can.
• Consider building a heat dump into the system, to get rid of excess heat when the cylinder is at max temp. Cleverly plumbed towel radiator(s) with relay switched wiring can do this on the DHW circuit. (ask me for further info if needed).
• Get a decent solar controller, like Resol - more configurable than some of the cheapies.
• Add a data-logger - useful for trending and understanding what the system has been doing over time. I have the Resol DL1, about to upgrade to the DL2 for the web interface and larger memory.

Alan.