PV Revenue to Dec 2012

December was pretty grey here and my solar panel revenue reflect that, see below. However, note the difference between Dec 2010 and Dec 2012 - nearly half the production in '10 and I attribute this to snow cover. It is always hard to assess the impact of snow on panels because it is hard to have a "control" that is snow-free and a "normal" array of panels that are permitted to accumulate snow. It is ether too expensive to set up such a study for a home owner and heck - if you could clear off the snow easily and safely then you'd do it! It is not really a research question anyways, it is a curiosity that has financial implications  And perhaps design considerations too.
One interesting thing I was asked the other day was about the way snow slides off, safety, and panel layout. When I had my panels installed I spoke to my installer where the bottom panel should be placed:

• bottom of panel is above shingles - some rain will fall on a concentrated location on the shingles and could cause excessive wear. Snow can slide off and can cause ice damming.
• bottom of panel is above eavestrough - rain drops into eavestrough. Ice and snow can slide off and accumlate in eavestrough potentially causing high load on eavestrough and/or causing ice damming that may harm shingles.
• bottom of panel extends beyond the eavestrough - show and rain are shed directly below, potentially causing safety issues. 

I opted to have my panels end directly over my eavestrough. I can't say if ice damming has been a significant issue but I don't think so. Only under the most intense thunder storms has rain run off the panels and gone over the eavestrough. Some precip may shoot down the other two rows of panels down onto the lower row and caused a concentration of water on the lower panels, but the small gap between the panel rows is sufficient to minimise that. Overall, I don't think it is a huge issue. However, just like a metal roof on a shed or barn, one must be careful about the risks of snow and ice sliding off the structure and falling on people below.
Table 1. Sum of daily revenue by month.

Sum - Revenue, daily	Years
Date	2010	2011	2012	2013	Total Result
Jan		$136.10	$205.18	$67.37	$408.66
Feb		$220.57	$258.66		$479.22
Mar		$449.77	$456.57		$906.34
Apr		$395.30	$501.84		$897.14
May		$428.51	$607.72		$1,036.24
Jun		$567.19	$573.10		$1,140.30
Jul		$616.75	$611.45		$1,228.19
Aug	$131.53	$528.09	$577.23		$1,236.85
Sep	$351.28	$423.49	$480.85		$1,255.62
Oct	$360.90	$313.65	$270.70		$945.25
Nov	$285.03	$253.69	$229.61		$768.33
Dec	$62.74	$176.31	$115.73		$354.79
Total Result	$1,191.47	$4,509.43	$4,888.65	$67.37	$10,656.92
as of:	2013-01-13

Table 2. Sum of daily power generation by month.

Sum - Daily kWhr	Years
Date	2010	2011	2012	2013	Total Result
Jan		170	256	84	510
Feb		275	323		598
Mar		561	569		1130
Apr		493	626		1119
May		534	758		1292
Jun		707	715		1422
Jul		769	762		1531
Aug	164	658	720		1542
Sep	438	528	600		1566
Oct	450	391	338		1179
Nov	355	316	286		958
Dec	78	220	144		442
Total Result	1486	5623	6096	84	13288
as of:	2013-01-13

Note: August 2010 and January 2013 are partial months.
It is nice to see that we have 4 months now with 3 years of full data measurements. It shows the considerable variability between the months.