Should I add a solar water heater to my house?

Solar Water Heater Question

We are doing some remodeling on our home, we recently moved here and fully intend to be here for a long long time, at least 20 years.

One of the things we are considering doing is installing a solar water heater, heating water uses a lot of electricity so using a solar water heater should save us money straight away.

I am wondering why they aren't more popular though, do they provide enough hot water for a family?

If we get a solar water heater is it possible to also keep some sort of emergency water heater for when our kids all come home to visit and take showers one after the other?