Solar Hot Water Model - Commercial - Cannot explain drop

Attached is a commercial hot water system modeled. The output drops suddenly after the first 7 hours of simulation.
I cannot explain the behaviour. Looks like a bug in SAM 2013.9.20

Here is how the Hourly Energy and Q delivered look in the simulation. Steep drop after hr 7 and stays that way rest of the way. Looks like a bug. Should be getting about 17% capacity utilization and 0.4 solar fraction.

Hourly Energy (kWh) Q delivered (kWh)
71.7983 93.7972
41.0276 53.5499
46.156 60.1885
56.4129 73.4957
102.569 133.503
225.652 293.421
456.432 592.878
0.616632 0.649087
0.49534 0.521411
0.375786 0.395564
0.311782 0.328192
0.246098 0.25905
0.250038 0.263198
0.245113 0.258014
0.25246 0.265747
0.21945 0.231
0.361399 0.38042
0.414035 0.435826
0.445218 0.468651
0.404604 0.425899
0.367733 0.387087
0.349161 0.367538
0.331162 0.348591

I did some more investigations into sizing large hot water systems. Rule of thumb for the system to perform well in SAM is to have 0.02 kg/s flow rate PER m^2 of collector area. Tank size is 0.08 m3/m2 of collector area.

I tried this in the SAM model. There seems to be a BUG in the model for tank volume. The input seems to be in litres but modeled as m^3. See revised model that seems to make a lot more sense in terms of Solar Fraction.

Can someone at NREL check this out?