I have a question regarding the solar radiation results in DIVA for GH. The following result is generated for a plaze in Seattle with a legend between 1-400 kWh/m2/day. (Summer months only: Jun through Aug)
However, the mean global horizontal radiation for Seatte area in these three months are around 5000-6000 Wh/m2/day (1500-2000 Btu/ft2/day) according to USA_WA_Seattle-Tacoma.Intl.AP.727930_TMY3.epw data. (see attached file)
So here I have an unobstructed horizontal surface receiving 5-6 kWh/m2/day from the epw data, while a partially shaded plaza is getting 200+ kWh/m2/day according to the DIVA simulation. I can't really make sense of the result and I'd really appreciate some clarification.
Hi Wei Yan,
I have two comments:
1. It looks like your context actually does a significant amount of shading, just based on the gradation of results from front to back.
2. The weather data you show is the mean hourly rate of energy incident upon a horizontal surface. If I simply sum up the mean values for July, I get 6230 Wh/m2 per day on average for July (or 6.23 kWh/m2-day). We're on the same page so far with your 5-6 kWh/m2-day assertion above. Since the simulation is for 3 months, roughly 5.5kWh/m2-day * 90 days = 495 kWh/m2. That's for a completely unobstructed surface (and a hand-wavey calculation). Also, if a value is above the 400 kWh/m2 on your scale, it will still just show as red, so there may be more there than you see. Even if 400 kWh/m2 is the max result in DIVA (which I don't think it is), 400kWh/m2 / 90 days = 4.4 kWh/m2-day.
I think you're misinterpreting the results. DIVA shows the gross accumulation of irradiation over your entire time period, not the daily average.
I can't remember where I got the impression that DIVA results are daily averages but it makes sense to be the total radiation over the test period. Thanks a lot for the explanation Alstan!