We used LaPlante Electric this summer. They installed 18 Silfab panels on our barn roof. We financed it ourselves and got the federal tax rebate. They were so very professional and pleasant to work with. One panel had a connection issue which they detected remotely ( we had no idea) and they came right out to fix it. They also installed our heat pumps and a generator too. Solar cost was 19K after the rebate. LaPlante is a little more expensive I think, but their service is impeccable and they guarantee everything. Regarding your older windows, instead of replacing them, good honeycomb insulating window shades will make a big difference at a fraction of the cost of replacing windows. I believe some of the Hunter Douglas shades qualify for a rebate now.