That's good for one season here but if you want a regular supply you need to be able to control your lighting 365 days a year.
Have you looked into light deprivation greenhouses? They're expensive! And running them in the winter means supplemental lighting, heating and insulation, all of which drive up the costs involved.
Add up the costs of all that and an efficiently designed indoor setup with LED lighting is surprisingly competitive.
Those are very different scales though.
Pound per pound, in most latitudes a climate controlled greenhouse will always be more efficient than indoor.
Whatever design and technology you apply to your grow room you can also apply to your greenhouse, and use it less than half the time.
What's more, to power every sq. foot of indoor grow space you will need roughly 5 sq.feet of solar panels, which mind you, like you say, half of the year your power output will be significantly reduced. It makes really no sense in most places.
I lived half of my life in the arctic circle, in winter time -25f was very common, and it was pitch black 20-24h/day.
On the other hand energy is nuclear or geothermic and is very cheap: 3 cents/Kwh.
Under these conditions, indoor growing is acceptable.
