QUESTION:

I want to calculate the total gain on a solar collector (photovoltaic). Which calculation should I use, Solar Exposure, Cumulative Insolation or Resource Consumption (Daily Load Matching) ?

ANSWER:

Firstly using the solar collector element type allows you to use the Resource Consumption functions instead of the regular solar calcs. These will do all the hard work of multiplying collection etc. for you and accumulating it for the whole year. In addition if you place appliances/equipment that use energy in your model you can also plot usage against collection -- kinda neat.

So to do this, go to the Calculate menu and choose the Resource Consumption item towards the bottom of the list. Either choose Hourly Solar Collection or Daily Load Matching (to compare collection vs. usage) from the Resource Data pull-down list, then click the Calculate button. You should get a graph for the whole year with red and or yellow lines. This calc is considering both direct and diffuse solar values for the entire surface area of the collector, as well as incident angle etc. as explained next...

The resource consumption calc. uses surface area only not exposed area of the object. The calc. assumes that the object tagged as a solar collector is not overlapped by any other object -- whereas the solar exposure and the cumulative insolation calcs cant make that assumption as you can choose any object in your model to do these on... for example a wall that is 50% overlapped by another zone, this would have a surface area of say 20m but an exposed surface area of only 10m -- the calcs you did must work this out themselves, thus the warning about no exposed area and thus only direct values being considered. In using the solar collector object the assumption is that you wont place it such that it is permanently overlapped by another object -- this would be a waste of an expensive solar collector, don’t you think

The reason this assumption was made is because a lot of people place the solar collector directly on the surface of a roof object (i.e. same plane), which if the exposed value was used would always result in a 0 solar collection value -- i.e. 2 objects in the same plane overlap each other.

The resource consumption calc. does one more step than the other two calcs. you tried. That is it also works out the effect of the refractive index of the glass/plastic cover on the solar collector (as specified in material properties). Thus it considers the reduced collection when the suns angle is at grazing with the surface of the collector.