Production Update to March 2016

Time for me to post a new update of the production from my solar array. In October 2013 I installed some new equipment, including Tigo Energy optimisers [www.tigoenergy.com]. I was not anticipating a significant increase in the overall array efficiency because the array is not facing any shading. It should increase the output and efficiency during the winter when there is partial coverage due to snow and ice.
Table below shows the production to date as well as the efficiencies for each month.

Updated:	04/02/16
		Years
Date	Data	2010	2011	2012	2013	2014	2015	2016	Total Result
Jan	Sum - Daily kWhr		170	256	243	216	281	210	1374
	Average - Efficiency [kWhr/kW]		0.9	1.3	1.2	1.1	1.4	1.1	1.2
Feb	Sum - Daily kWhr		275	323	214	197	333	312	1652
	Average - Efficiency [kWhr/kW]		1.5	1.7	1.2	1.1	1.9	1.7	1.5
Mar	Sum - Daily kWhr		561	569	499	577	663	483	3352
	Average - Efficiency [kWhr/kW]		2.8	2.9	2.5	2.9	3.3	2.4	2.8
Apr	Sum - Daily kWhr		493	626	574	615	656		2962
	Average - Efficiency [kWhr/kW]		2.6	3.3	3.0	3.2	3.4		3.1
May	Sum - Daily kWhr		534	758	768	699	745		3504
	Average - Efficiency [kWhr/kW]		2.7	3.8	3.9	3.5	3.8		3.5
Jun	Sum - Daily kWhr		707	715	633	757	687		3499
	Average - Efficiency [kWhr/kW]		3.7	3.7	3.3	3.9	3.6		3.6
Jul	Sum - Daily kWhr		769	762	693	735	821		3780
	Average - Efficiency [kWhr/kW]		3.9	3.8	3.5	3.7	4.1		3.8
Aug	Sum - Daily kWhr	164	658	720	711	694	693		3640
	Average - Efficiency [kWhr/kW]	3.2	3.3	3.6	3.7	3.5	3.5		3.5
Sep	Sum - Daily kWhr	438	528	600		626	625		2817
	Average - Efficiency [kWhr/kW]	2.3	2.8	3.1		3.3	3.3		2.9
Oct	Sum - Daily kWhr	450	391	338	79	381	455		2093
	Average - Efficiency [kWhr/kW]	2.3	1.9	1.7	1.8	1.9	2.3		2.0
Nov	Sum - Daily kWhr	355	316	286	296	177	334		1765
	Average - Efficiency [kWhr/kW]	1.9	1.6	1.5	1.5	0.9	1.7		1.5
Dec	Sum - Daily kWhr	78	220	144	119	169	148		877
	Average - Efficiency [kWhr/kW]	0.4	1.1	0.7	0.6	0.8	0.7		0.7
Total Sum - Daily kWhr		1486	5623	6096	4828	5841	6439	1005	31317
Total Average - Efficiency [kWhr/kW]		1.8	2.4	2.6	2.4	2.5	2.8	1.7	2.5

You'll see that of course the efficiency is different for each month from winter to summer to winter again - there is much less sun energy coming in so the panels generate less. The same pattern for total energy output. The summation in the right column doesn't mean too much given that part way through October 2013 the equipment changed. The sum and averages at the bottom are interesting. Disregard 2013 again due to partial data and a change in the equipment. 

Comparing 2011 and 2012 with 2014 and 2015 we see the following:

• lowest output was 2011 [range between 2014-2011 = 218 kWhr]
• highest was 2015 [range between 2015-2012 = 343 kWhr]
• average efficiency 2011-2012 = 2.5, post upgrade = 2.65]

These statistics, if anything, show that there is quite a lot of annual and intra-annual variability in energy production. There was 600 kWhr difference between 2014 and 2015, or about 10%. 

So? Was the equipment upgrades worth it? Let's look at more statistics.

Variables kWhr Dollars

Mean 15.90 $13.03

Mean post upgrade 15.50 $12.43

Per 1 kW 3.24 $2.66

Per 1 kW post upgrade 2.42 $1.94

Min 0.05 $0.04

Min post upgrade 0.08 $0.07

Max 35.44 $28.42

Max post upgrade 36.49 $29.26

Pre and post upgrade, the data show an underwhelming result despite an extra 1.5 kW of capacity:

• mean kWhr was actually higher before the upgrade
• efficiency was lower by 0.8 kWhr/kW installed post upgrade
• maximum daily output on the best day pre and post upgrade increased from 35.4 to 36.5 kWhr

The maximum daily output and other values of course can vary by year, but really, the max daily output should be at least 1.5 kW x 3 hours = 4.5 kWhr. I'll state this because I think that over any given 2 year period, there will be at least one amazing, sunny, clear, long, cold day.

I shall investigate this much more indepth using RETScreen soon and share these results with you.

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.

Some Basic Parameters of the PV System to Date

There are some handy parameters that can be used to estimate the power or revenue generation of a PV system. Often people will take the kW of the system and multiply it by the expected parameter to get expected value such as kW hours per year or dollars per year. These numbers are relatively easy to calculate. Ideally people are using the most realistic values possible if they want to estimate their expected outcome.

An example is, how many kilowatt hours should I generate from my 5 kW system on my roof?

First, here are my parameters for our 4.9 kW DC system [5 kW string inverter]:

Variables	kW	Dollars
Mean [4.9 kW]	15.81	$12.68
Per [1 kW]	3.23	$2.59
Min [4.9 kW]	0.05	$0.04
Max [4.9 kW]	35.13	$28.17

In this case, applying my parameters to a hypothetical 5 kW DC system, we could estimate mean daily kW production over the year to be 5 kW * 3.23 kW per kW = 16.15 kW per day. Multiply that your FIT contract price and this would be your daily income averaged over the year. 

You can use the values above to estimate your highest and lowest income as $28.17 / 4.9 * your DC kW.

Oh, and you can see that you'll have some bad days too - $0.04 / 4.9 kW will give you $0.01/kW on dark snowy, snow-covered panel days. 

March 2012 Power Yield and How RETScreen is Doing

I've downloaded the data up to 13 April and I've put it in my spreadsheet to calculate the power yield for March 2012 (table below). It was marginally better than 2011. I am looking forward to the rest of April because so far the bright, cool days have been good energy producers. March 2012 was just 9 kWhr over last year. However, RETScreen calculations show that my system should have yielded 584 kW, so, two years in a row RETScreen is overestimating the system. Two years of data is not enough to say RETScreen is not accurate, but the overall trend with my system is underestimation. RETScreen calculated that my system should have produced 9128 kWhr to the end of March whereas my system did 8256 kWhr (10.6% under estimation). Most of the deviation came from the winter of 2010-2011 where snow substantially reduced the panel output. So, with this limited dataset, it points to people being conservative when estimating their payback expectations.

Sum - Daily kWhr	Years
Date	2010	2011	2012	Total Result
Jan		169.7	255.8	425.5
Feb		275.0	322.5	597.5
Mar		560.8	569.3	1130.1
Apr		492.9	313.5	806.4
May		534.3		534.3
Jun		707.2		707.2
Jul		769.0		769.0
Aug	164.0	658.5		822.5
Sep	438.0	528.0		966.0
Oct	450.0	391.1		841.1
Nov	355.4	316.3		671.7
Dec	78.2	219.8		298.1
Total Result	1485.62	5622.72	1461.16	8569.52