Our solar production

[mwalsh]

So mwalsh, what was your result? I had a peak production of 31 kWh vs my high in May of 33 kWh. I think that May is likely our peak month, as others have said.

40.73kWh. Best day ever was 40.93kWh on April 30th. Before the cleaning, I hadn't been able to do better than 39kWh since the end of June.

 

[SanDust]

My guess is that production drops in AZ during the summer because of increased heat. I cleaned my PV panels last year on the theory that they were dirty. Production jumped during the cleaning as the water cooled the panels but then dropped down to its baseline. Obviously dirty panels can be a problem but the dirt didn't make a difference whereas the heat did.

The roof pitch also matters. Flatter in the summer is better and more of an angle is better in the winter. The means that for fixed installations there is a trade-off between summer and winter production and that, while you're not going to get more production in December than June, the exact month of peak production will vary depending on your location and the location of the panels.

AFAIK microinverters aren't more efficient than a central inverter. It's just that as a distributed system they're more robust. Claims of greater efficiency usually refer to the life of the system and situations where there are shading or other issues with one panel in a string, which brings down the production of the entire string.

 

[Boomer23]

So mwalsh, what was your result? I had a peak production of 31 kWh vs my high in May of 33 kWh. I think that May is likely our peak month, as others have said.

40.73kWh. Best day ever was 40.93kWh on April 30th. Before the cleaning, I hadn't been able to do better than 39kWh since the end of June.

Dang, that means that I have to climb up and do my own annual cleaning soon. My panels are looking a bit dusty. Not looking forward to it.

 

[mwalsh]

Dang, that means that I have to climb up and do my own annual cleaning soon. My panels are looking a bit dusty. Not looking forward to it.

LOL! I hear you there. Never been very big on the heights thing my own self. But since I've been messing around with the solar, I've been getting better.

 

[TonyWilliams]

For the cleaning, I installed a ladder to my attic access, then hinged the 24"x30" vent on the roof so that I can open it up and walk right onto the roof. My roof is way too far off the ground for outside ladders (that I'm going on!).

Also, my production has stabilized a bit, and my original numbers were a bit off, it seems:

Date/Time

Energy Produced (kWh)
07/09/2011 47.4
07/10/2011 53.8
07/11/2011 47.3
07/12/2011 52.2
07/13/2011 47.5
07/14/2011 40.5
07/15/2011 52.1
07/16/2011 43.9
07/17/2011 48.3

 

[tbleakne]

My guess is that production drops in AZ during the summer because of increased heat. I cleaned my PV panels last year on the theory that they were dirty. Production jumped during the cleaning as the water cooled the panels but then dropped down to its baseline. >>>>>>>>>

AFAIK microinverters aren't more efficient than a central inverter. It's just that as a distributed system they're more robust. Claims of greater efficiency usually refer to the life of the system and situations where there are shading or other issues with one panel in a string, which brings down the production of the entire string.

Temperature makes a substantial difference. I like to hose down my panels at least once/week during the peak production of the day, to take maximum advantage of the temporary cooling you mention. Today before/after my hose-down, production went from 2465 -> 2740 watts, a gain of 11%. Within 20 min or so production returns almost to its previous level, showing that there was only a modest amount of dust degradation.

I have had my array operational 7 months, including one Winter and one Summer solstice. The maximum production of 17 KWhrs has occurred 4-5 times in that interval, always on a cooler, clear day. Once such day was in July, the rest in May.

Shading loss is more significant for me. I am unwilling to cut down the trees whose shade starts to reach some of the panels after 3:30 PM this time of year. Each string of a solar array has all of its panels wired in series. I have a single-string system, so full shade on even one cell of one panel can shutdown the full array. However, the by-pass diodes in my panels usually mitigate this problem by passing the current around the shaded sections. I chose a single-string system to take maximum advantage of this effect. My panels are divided into 3 sections, with one diode by-passing each section. Small changes in shade pattern can make a big difference.

You can see whether your by-pass diodes are effective under a particular partial shade condition by looking at your inverter's output as the shade moves in. If the the total voltage goes up while the current drops precipitously, the panels still in sunlight are under-loaded and the diodes are not activated. If the total voltage drops while the current level is maintained, this means that the diodes are active, passing the current from the illuminated panels around the shaded panels. In this case the inverter has been able to track the voltage down to a new local optimum.

Since I am driving the Leaf more than I projected, I am considering adding a few more panels. Shade in the new location is again an issue, so I may go with micro-inverters this time.

 

[wsbca]

Also, my production has stabilized a bit, and my original numbers were a bit off, it seems:

[ average of 48kWH/day, or almost exactly "6 solar hours X raw DC panel rating"]

That does sound more realistic than the 120kWH in two days, which would be pretty incredible.

Over that same 9 day span we averaged 6.4 solar hours x DC rating, or 7.4 solar hours X our AC rating , also on Sunpower panels (16x215, also installed by Baker) but with a single inverter. I'm going to speculate that you might be a little closer to the coast than we are with more marine layer to deal with on the shoulders of the day, but other differences could be panel orientation or whether you have any shading at all - which may be why you have microinverters? But no matter how you slice it, you're making a bunch of electricity! I reckon on a year-round basis you're cranking out about 43,000 Leaf Miles worth - excellent.

 

[dpodoll]

AFAIK microinverters aren't more efficient than a central inverter. It's just that as a distributed system they're more robust. Claims of greater efficiency usually refer to the life of the system and situations where there are shading or other issues with one panel in a string, which brings down the production of the entire string.

Temperature makes a substantial difference. I like to hose down my panels at least once/week during the peak production of the day, to take maximum advantage of the temporary cooling you mention. Today before/after my hose-down, production went from 2465 -> 2740 watts, a gain of 11%. Within 20 min or so production returns almost to its previous level, showing that there was only a modest amount of dust degradation.[/quote]

Interesting...have you considered a lawn sprinkler to do a cool down of the panels on a regular basis? Seems like 11% might be worth it.

 

[91040]

Is there any issue putting relatively cool water on very hot panels?

Also, water is a limited resource in the Southwest!

 

[DaveEV]

Interesting...have you considered a lawn sprinkler to do a cool down of the panels on a regular basis? Seems like 11% might be worth it.

So after he hosed his panels down, he got ~90 Wh more power at most (200W * 20 minutes - and being generous here, probably only half that) or about 1-2c worth of electricity. I doubt that it covered the cost of water.

 

[wsbca]

about 1-2c worth of electricity. I doubt that it covered the cost of water.

Exactly - I noticed a similar temporary boost when I rinsed my panels on a hot day...so hot that after I thought about it for a minute I was worried about cracking the glass - it's neat to see the inverter ramp up fairly dramatically, but there's no way that external application of water is worth the cost of the water, or even just the energy it took to move the water to your house under enough pressure to spray it up there - TANSTAAFL. There is potential for a hybrid solar hot-water/PV system where the heat from the panels is extracted into the water, rendering the panels more efficient while saving energy on heating of the water, but such a system would, it seems to me, be quite a bit more complex than each technology on its own, and therefore somewhat costly. For now, the best friend your panels have to contend with heat is a nice breeze.



Edit - it did occur to me (setting aside the energy cost of getting the water to you under pressure) if you could magically capture all the runoff of the cooling water, and re-use it for irrigation that you'd otherwise be doing anyway, that might pencil out under certain circumstances...but I'm going to guess not, given the evaporation penalty that occurs when watering in sunny conditions vs. watering at night. The wasted water would still likely more than offset the production increase - it needs to be a closed system.

 

[TonyWilliams]

There is potential for a hybrid solar hot-water/PV system where the heat from the panels is extracted into the water, rendering the panels more efficient while saving energy on heating of the water, but such a system would, it seems to me, be quite a bit more complex than each technology on its own, and therefore somewhat costly.

Well, it does exist. The guy quoted me $12k, and I didn't see how that would every pay back.

SunDrum Solar
(978) 562-5152

 

[LEAFfan]

Is there any issue putting relatively cool water on very hot panels? Also, water is a limited resource in the Southwest!

Yes! People putting water on hot panels are going to damage them and that won't be covered under the warranty. If you do any research, it will tell you to NEVER put water on hot panels. If you don't want to damage them, wash them early morning or late evening after they've cooled.

 

[mwalsh]

40.1kWh today.....a bit lower today due to a slight hazy overcast early on this morning.

 

[ERG4ALL]

Another reason not to "water" your panels is that water from the tap is most likely hard water. Over time when you allow the water to evaporate off your panels the minerals will be left and perhaps fused to your panels which over time will permanently reduce the panel's output. Whereas rain water for the most part is distilled water that condensed from water vapor.

 

[mwalsh]

40.17kWh yesterday.

So since I'm adding something of such little value with this post, perhaps I can sweeten the pot somewhat....Google maps has updated imagery of my house that only dates back a few months (since that's my LEAF in the street):

 

[patrick0101]

since that's my LEAF in the street

sweet

 

[TNleaf]

....Google maps has updated imagery of my house that only dates back a few months (since that's my LEAF in the street):

Nice! Looks good even from the skies.

 

[HarryHouck]

Cooler panels produce more? Serpentine tubing glued to the back of panels could cool a pool or preheat tap water. Dump the heat into the air with a radiator. The panels should last longer, right?

 

[HighDesertDriver]

Cooler panels produce more? Serpentine tubing glued to the back of panels could cool a pool or preheat tap water. Dump the heat into the air with a radiator. The panels should last longer, right?

Cooled panels have been standard on several demonstration homes exhibited on the Wash D.C. mall in past years. (A competition by many universities) The heat goes for other uses. None on the systems are commercial, however.

Our system hits 41-42kWh/day a couple days per year, usually in late April/early June when it is both cold and windy. On hot, still days, even with clean panels, production drops to around 35. The PVWatts annual production estimate is quite close to actual, but hit-or-miss on a monthly basis.

As for initial production, most manufacturers expect a slight drop in efficiency as the new panels "burn in" their first 30-60 days. This was true for both us and our Sunpower'ed back neighbor. We have a friendly neck-in-neck annual completion with their appx 8000WDC west-facing array.