Manual vs Automatic control
This depends more on who you talk to, and who you purchase your system from. Some solar pool heating system retailers sell 85% of their systems with a manual valve. Others sell 85% with an automatic valve. The difference lies with volume purchasing. The answer to this question may tell you more than you bargained for. In fact this question may tell you who you will purchase you solar system from. Let me explain.
Solar system installations coincide with pool openings and pool installations. Retaillers who specialize in pool sales are often far too busy to manage solar heating installations in the Spring. They would much rather see you install your own system, therefore limiting their sales of solar systems to the very few who can handle such a project. Because these retailers sell so few systems, they also purchase very few automatic control valves. Their bargaining power vis-à-vis the suppliers is next to none. They will explain to you that the valves come with a non-sense warranty that states that the owner will have to deal with the manufacturer, and ship the defective valve to New Jersey, Florida or California (during pool season!), at the owner's expense, in order to get warranty service. On the other hand, one Canadian distributor (Patrick Murray Solar Installations, who sells 85% automated) benefits from lower wholesale prices due to volume purchasing, and transfers its saving to you by offering an extended warranty, free of charge, and makes house calls as a courtesy.
So which control valve should I get? A manual valve costs from $30 to $90, is easier to install and cheaper than buying three large (and ugly) faucet valves. An automated valve costs $489 to $600, and one model (Goldline) allows you to convert from manual to automated in three easy steps. The automated valve will monitor the available heat, compare it to pool water temp, and shut down the heating system when heat is no longer available (when it rains, and overnight). It will allow you to collect 100% of the available heat, and you won't get caught with your pants down (cooling the pool when it starts to rain, or in the evening when there is nobody home). Compared to the manual valve, it will collect about 40% more heat than the same system under manual control. It would be wiser to purchase fewer collectors, and to keep the automated valve, if you wanted to save money.