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Assume you built a Solar Kiln that is 10 feet wide x 16 feet Long. You have roof vents to suck out the moist air. Ect, ect. How many board feet of lumber can you put in that Solar Kiln at one time, to properly dry each load ? Assuming it is in the Summer. This would be all 4/4 Hardwoods.
Depends on the kiln design and thickness of lumber in the load. My small kiln's outside dimensions are about 4' x 12' x 8' high and can hold around 600 bd ft.
That seems like a pretty wide kiln. Make sure your fan(s) will supply sufficient air movement through the stack. How will you load it? Mine is small enough that I can hand load it from the long north side. Some are loaded from the end with a cart on tracks. There are a number of designs documented by the Forest Products Lab.
Solar kilns are relatively forgiving, but you still want to pay attention to the rate of moisture loss to prevent degrade, especially if drying green lumber as opposed to partially air dried. Again, the FPL is a good source of kiln operation info.
Virginia Tech has good information on the design and construction of a solar kiln.
https://www.pubs.ext.vt.edu/420/420-030/420-030.html
The key with any design is to have the correct ratio of glazing to bf of lumber. The VT design has 1 Ft^2 of glazing for every 10 bf of lumber. My kiln is 12' x 8' wide with about 90 ft^2 of glazing at 45 deg on the South side. The peak is somewhere around 9 ft or so. I load it from the side and can put a 4 or 5 wide stack of lumber in it up as high as the bottom of the glazing which is around 40". It holds about 750 bf. I've never exceeded the maximum allowable drying rate for the lumber I've dried in it. If I were in danger of doing that I would cover over some of the glazing. These kilns are pretty simple affairs and require little effort to control. Best of all, they cost almost nothing to run. The downside is they are pretty useless in the northern part of the country for 5 to 6 months of the year.
John
For green 4/4 white oak, the ratio is 10:1 in terms of collector size to load size. So 100 square feet of collector is good for 1000 bd ft of green 4/4 oak. Green 8/4 oak load size can be increased by a factor of 3.5 with the vents left closed and part of the collector tarped off until the wood is dried below 25% MC.
For maximum drying speed, load sizes should be decreased for faster drying woods, or the vents should be left open.