I love my SWCG and I don't think it matters if the pool is open all year or not. it just a way to get chlorine in the pool without lugging bottles of bleach. as far as price goes, it all really kind of works out to be the same, at least on the initial upfront installation. it goes down when you are just talking about cost for replacing a cell.
you always want to go larger with the SWCG, so for your pool it would be a system rated at 40,000 gallon. the Hayward T-15 cell would be right. if you are able to do the install youself, not difficult, just some way to get power and then some PVC work, you can buy the controller and cell for about $900...maybe assume $500 for an electrician to install he unit if you aren't comfortable with that, so your total cost would be $1,400 that cell is rated to produce 580lbs of chlorine gas over its life.
assuming your pool needs 3ppm of FC per day, that works out to needing roughly 0.34 lbs of gas per day. theoretically that means the cell would last for 1700 days...but that's not gonna happen. lets assume half, or 850 days for calculations. so that's $1.64 per day.
if you are paying $3/gallon of bleach, you would be using 0.5 gallons per day for the same 3ppm rise...so that's $1.50 a day
so they are basically the same cost per day....BUT, when your cell goes out after a few years, you are buying a replacement cell for $400. now you factor that cost, and its $0.33 a day since you aren't factoring in the cost of the controller and install.
