If you collect data (V,A) and sample every second and multiply the two and save the result and add it to the previous result, at the end of an hour you will have a single result. Would that not be the average Watt/hours for that hour ? if you then save that result as hour_1, and do this for all 24 hours and add them all together would that not be the average output for one day ? If you divide that by 24 would that not be the average Watt/hour output for one day ? Couldn't you use nested FOR loops fir seconds, hours , and days ?
I don't know but that's my guess...