You are thinking one dimensionally on this. I have a 4.5 kW system. It sends surplus power to the grid in summer, and I receive credit toward power in winter months when I have a deficit.
My monthly bill from the utility company is $10 dollars, and I used a home equity loan to finance the panels. My old bill was $130 per month, going up every year as they tack on more charges for things like decommissioning nuclear plants and carbon taxes. My gross cost out of pocket is now fixed at $100 per month, and my net after tax deductions is about $75 per month.
We’ve had the panels for 18 months with no hiccups or issues financially or technically. The grid is my power bank, and my cost of acquisition and maintenance is only about $10/month. A bargain in my book. No way you can ever get that level of benefit for that price from a DIY approach.
I understand that solution you describe completely and have looked into it, but I am mainly interested in a backup if the grid goes down.
I am thinking of building a wheeled approach that can be unplugged and moved instead of a fixed approach on top of my roof.
The vendors that I have talked to are only interested in installing a system that sells back to the grid, and I think that is great, but not what I am interested in.
The only reason your economics are so good for you personally is federal and state laws make it so. Your little power plant needs backup power to get you through the night and times of little solar production. You are not paying for that backup power...the rest,of,us are. You are not paying for your share of the transmission and distribution infrastructure you use...the rest,of us are. Without laws distorting markets, you would NEVER pay what your system fully costs.