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Some steel T posts, or sturdy wooden stakes, will serve you well here. Five should suffice. On the winter solstice drive three of them. One at the center of where you expect the array to reside and align a second on a line toward the point the sun rises, and repeat with the setting point. Keeping the center post repeat this for the summer solstice. Dividing the distance between the rising and setting solstice points will provide the yearly average exposure maximums. This will give you more information than any other resource about your site. Of course this depends on the sun shining on those two days, or a few either side. In your region the winter event could be obscured for weeks. Perhaps another means to obtain these angles can be found.

RS