Cloudy weather is also our winter-growing problem. Add to that, the low angle and few hours of winter sunlight.
When I first looked into having a backyard greenhouse, I really planned on supplemental lighting. I just couldn't justify all the gas and electricity that it was going to take to grow most things through the winter.
After several years, I tried Asian greens. Carried out the 18' bench, cultivated the ground beneath, and put in both seeds and transplants. No heating. It worked! ... except for January, after the transplants had been harvested and the seedlings were still to small. I had to cover the bed with a plastic tunnel and use a tarp over that during the coldest weather.
It was all quite a bit of bother for such a small growing space. I couldn't even make more use of the full 9'x20' greenhouse, first of all because I had to walk in there. Also, because the plants couldn't be too close to the plastic film south wall - too cold! It was worth the effort but I was left with a 3'x18' bed.
Now, the greenhouse is over 20 years old. At some point in the next few years, the south wall will have to be taken out and replaced. That isn't a very big job but it needs to happen when the weather is cooperative, when I don't need it for the growing season plant starts, and when I'm not busy through the summer. Hmmm, or, I could hire it done.
Steve