QUESTION:

Why are the solar radiation values in the Weather Tool given as energy units rather than power units ? Is this cumulative during a day ?

ANSWER:

Because the measure of solar radiation is done each hour, thus it is assumed that the measured value was constant for the preceding hour period. Hence a measured value of 500 Watts really means, 500 Watts continuously for an hour = 500 Watt hours or 0.5 KW/h

In terms of collection these values are usually what is needed. That is, if you were a solar collector this is what you would receive in the hour.