Angle of solar collector
I have installed solar collectors, in addition to my wood stove to heat our home. The answer to the angle issue depends on what you want to do with the collector, heat, hot water, winter, summer.
In general collectors for year round use, typically hot water, would use your latitude. Just checking, for central North Carolina, that would be about 36 degrees from horizontal. If you want to optimize the collector for winter use, say space heat, you can drop this by up to 10 degrees, but usually not less than 30 degrees. Collectors need some vertical for the hot air/water to rise, they don't do well when lying flat and horizontal.
The collector can be mounted in the vertical angle, latitude plus or minus 10 degrees. The the direction angle, (aspect) is plus or minus five degrees.
The biggest problem is often dumping heat off them in the summer. The collectors need to be covered, or have a pump pushing fluid through them at all times into a heat dump, basically a finned radiator outside of the dwelling. Evacuated tube collectors are safer in this situation than flat panel, are slightly more efficient but more expensive.
I have an Apricus system (apricus.com). From our limited experience, I anticipate that it will my house during the day for half the year, during the day, late September through middle November, and February through May. It heats hot water year round. Only in December and January, when the solar energy is low, do I have to use some oil (backup) during the day when I am not home to keep a wood stove going.
The drawback is the high initial cost and the need of a clear southern exposure. The cost is presently partially offset by the 30 percent tax credit. My system was planned to have a 8 year payback, but is more effective than anticipated. (It was planned as a domestic hot water system, but when the demand for hot water is satisfied (110 gallons (storage) of 130 degree water per day), it puts the rest of the heat into my heating ducts through a hot water coil, direct from the collectors. Basically, it heats hot water in the morning and the house in the afternoon. In the evening, we use the wood stove. Wood of course, is another variant of solar heat.
Hope this helps,I have discovered that every install is different.