want to buy SE62-80H-045S tank

James, I've answered some of your post in the past. If the tank is leaking and needs to be replaced, you might consider purchasing a heat exchanger tank, such as a Superstor, instead and get rid of the externatl Novan heat exchanger which has given you problems in the past. Having the heat exchanger inside the tank increases the efficiency by having the exchanger directly in contact with the water in the tank as well as having a greater surface area. It would also reduce the amount of electricity needed since you could eliminate one of the circulation pumps. 

James, your email address didn't work. Anyway, when installing a SHW system that needs electrical backup, I usually recommend installing two tanks, one with an internal heat exchanger and one conventional electric hot water tank. It may sound like it would be more expensive, but when you take into consideration purchasing a SHW tank with electric back up, it comes out to be around the same price. The thing I don't like about having the electric backup in the same tank as the solar is that the two compete with each other. At night when solar is not available,the electric kicks in and heats the water, then in the morning when the sun is available, the water in the tank is already hot and the solar does not turn on. I've seen too many systems that operate like this, and what happens is that the panels overheat and build up pressure which can make the system sieze up. Basically the pump cannot overcome the pressure.
  If you choose to keep the tank with electric backup, I would recommend a Vaughn tank. But these tanks are just as expensive, if not more than a Superstor. Also, they are stone lined and can weigh up to 500 lbs which makes installation a bit more difficult. Vaughn tanks come with 7 year warranty and Superstor's have a lifetime warranty since they are made with stainless steel.
  You can purchase a Superstor, 45 gallon tank, for around $800, 80 gallon for around 1300. An 80 gallon Vaugn tank will cost around 1400. A conventional 40 or 30 gallon electric tank will cost $3-400.
  Then you install the two tanks in series, along with a bypass, so that the solar tank preheats the water entering the electric tank. Then if the water is hot enough, it keeps the electric from turning on. The bypass will allow you to use either the solar or electric tank individually if you choose.
If you have any further questions, just send them along..