Up here in the mountains looks isn't a problem and our house is already passive-solar with the entire south-facing side of the house nothing but windows...and we already have a solar hotwater heater installed by the previous owner.
This plan almost sounds too good to be true.
The only downside I see is that you are locked into rates for 25 years. Then if there were a significant breakthrough in energy development and electrical costs actually dropped significantly. Big deal - you're out $500 bucks after saving money on your bill for a number of years.
The other downfall is if the rates went so high that the company was losing money buying off grid power for your back up that they went out of business.
Both scenarios seem unlikely.
Another thing this company is counting on are much more efficient appliances and lighting in the future. If a customer is locked in at a fixed $$ per month, there isn't much incentive to upgrade to the higher efficiency appliances.
Your house sounds like it is very cool!
This plan is too good to be true. In exchange for not having to put up the upfront cost, you are giving all of the cost savings to this company instead of capturing them yourself. Right now, electricity prices are at a relative high. You are going to lock in that price for the next 25 years. Meanhwile, as solar comes down in price, you are stuck, and you don't get to benefit.