Cleaning Solar Panels

Tripp,

Most new fridges will use ~ 1kwh/day. I think we use about .75kwh/day with ours. As for the dryer,,,Why wait until spring. In the N.W we use the dryer perhaps one load per week in the winter, never in the summer. That one load per week cost us about 10% of our total monthly use. Your 264kwh/month is about 8.8 kwh/day,,, pretty darn good, trade the fridge and you be laughing!

Icarus

 

Unfortunately, it can swell up to ~500 kWh/mo in the summer. Our avg over two years is 380 kWh/mo.

In the winter here it is often REALLY windy and cold. Some days a clothesline would be great, others not so much. In the main, it'll be about convincing the missus since she does the bulk of the laundry. I do my own, but she does her's and the kids' too. In the spring/summer a line would be mint.

The other one for us is the radiant range. Not much we can do there except use it as efficiently as possible.

 

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Convince her that each load through the dryer cost ~$2.50. Offer to buy her a night out every month for a couple if she'll try hanging it out. Cold and windy is great for drying, especially in your dry Colorado climate. Stuff will dry in a matter of minutes. Even hanging laundry INSIDE is a viable alternative in a dry climate. The humidity gained from drying the clothes would be welcome in the room.

When people can see and feel the effects of their actions, both positive and negative it is easier to change behavior. That's why a "Kill-a-watt" is a great invention.


Icarus

 

We've got one, that's how I know what a pig the fridge is.

Perhaps we can rig up something inside. Taking laundry out when it's 10F isn't going to work too well. I imagine that the clothes would freeze rather than dry out.

My answer to the drying thing is to buy synthetic kit, which dries out quite quickly in our climate.

 

While hanging laundry out at -10 may be no fun, in fact it dries very quickly. With low humidity and perhaps aided by wind, the water in the laundry sublimates to vapor very quickly. It may freeze first, but then the moisture gets sucked right out.

Icarus

 

a small shadow over a single panel hooked in series making such a difference is alarming.

 

Alarming but true. Think of it as a series of batteries,,put a (partial) insulator between two cells, and the output of the entire string drops off. Some manufacturers build in series/parallel arrays within each panel to reduce this effect.

When laying out a array, consider all possible shading events, and plan accordingly. For example, if one section of the array gets a wire across it at some specific time, wire that section into it's own sub array, to mitigate the shading effect on the whole.

Grid tied systems run a comparatively high voltages, with panels arrayed in series/ parallel arrays to make up the working voltage from lower voltage panels. In other words, a working voltage of ~500 vdc, made up of panels of 12 or 24vdc individual panels.


The best bet is to keep all shading off the panels for obvious reasons.

Icarus

 

Hey Pat, you've heard that new installs as of Jan. '09 get a 30% credit from the feds? I see yours went on line in August. Ouch. Our install is 90% complete, but we're turning in a new app with edison. That won't happen though until Friday, January 2, so we can (in essence) save about $18K on our near 8KW system. It's worth the $550 or so we'll loose not generating power in the interum. Thanks for the advice on cleaning. The installer was somewhat nonchalant about cleaning, saying once or twice a year was all that's necessary. Sheesh. Gary ~ w4abj

Even bigger than the dryer? We switched to a front load washer. WoW! what difference. And as Pat said in another post, a higher seer rating on the AC compresser is a huge one.

 

what is the surface area of a single cell?

typically what is the voltage and current output of a cell,

how many are in series together?



why a cell receiving no power acts like an open short instead of a dead battery is simply beyond me. i dont know enough to understand the most efficient way of creating the best series-parallel array, but seems to me that i have to be misunderstanding something here

 

Perhaps we are getting confused as to the definition of a "cell" In the vernacular a solar "cell" might also be called a "solar Panel" A solar panel is (usually) made up of a number of "solar cells" in series/parallel array such that the output voltage of the "panel" is what is called for. IE 12vdc, 24vdc 36vdc etc. These are 'nominal' voltages, the panel design voltage will be significantly higher, ~18vdc for a 12 volt panel. (The reason for this in some fashion is to provide enough over voltage to charge a 12 volt battery for example). A typical solar cell might me 1" square, like those on you hand held calculator, putting out something like ~1.5 vdc. Wired into a panel in series would take 8 cells to make 12 vdc, but more like 12 wired to make ~18vdc, these in turn would be paralleled with others to make a 18vdc (12vdc nom) panel. If each series put out say 1 amp, and you had 10 strings in the panel, you would have a 10 amp panel, or ~120 watts (depending on the voltage you measured the output at) parallel 10 of these panels together and you would have 100amps of 12vdc output or 1200 watts. Put the same string together in series and you would have 120 vdc at 10 amps,,,or the same 1200 watts! There are of course significant advantages of using higher voltages because of the line loss in low voltages. So you can see that you can string this panel array in any number of ways. You always get the same 1200 watts (gross) but what you might net into your grid, or into your battery bank might be better one way over another depending on your situation. If for example, part of your array went dark an hour earlier than the others, and you couldn't change it, wiring the dark string into it's own sub array might make sense.

I don't believe there is a way to build the "best" series/parallel array. That answer lies in the design criterion for the panel designer. For the panel array designer the criterion lies in the ultimate desired output voltage, coupled with the desired amperage output, taking into account things like solar insolation, shading, time of day etc.

As to why a series array output will drop to almost zero is a question for a Electrical Engineer, of which I certainly am not. It has been explained to me that a darkened solar cell with "go high resistance" such that not only will it stop generating, it will, in effect, add a giant resistor to the series. What I don't know is, why there is not considerable heat generated in the high resistance area,,perhaps there is, but if for example you had a 1000 watt string "shut down by one dark section, why wouldn't that 1kw of power show up a a huge hot spot like a toaster? Part of the answer lies in blocking and bypass diodes that allow some of the current to bypass either a series of cells, or an entire panel. It is not a question of acting like a "open short" (I think that is a misnomer,, you can have an open circuit, or a short circuit but not an open short,,someone correct me if I am wrong), but more a question of acting like a high resistance that drops the output to near zero IN THAT SERIES.

I confess I know just enough about all this stuff to be dangerous. I'm sure I have written just enough to confuse everyone.

Icarus

 

We've got an evaporative cooler, no AC. That's a big reason why in the last two years our highest consumption month was 533 kWh in July of '07.

I'll have to take a look at our washer. It's not a front loader, but we do adjust the load size to save on water. We also vary the run time accordingly (I rarely go more than 8 minutes on the wash cycle). It really doesn't run that much so compared to the dino-fridge I'm sure it's peanuts. Worth a look though.

In the winter, I think one of our big ones is the furnace blower.

 

Actually that was August, 2004!!!!

But hey over 65000kWh generated to this date so far!!

I am already getting my payback!!

Pat KK6PD

 

That's WAY killer!
Hey, So. Cal. just got their 1st day of real rain today. I thought I'd go up on the roof to 'check out' the 97+ % completed-install, since they'll be shiny clean now. I haven't even seen what they look like except from a tiny view from the other side of the street. Here's a few pic's up close & personal, as well as one of our two sun power inverters inside the garage:

I can' wait to turn these puppies on! Only four more week 'till January 2nd.
You know, the economy really went 'toes up' since the install happened, roughly 5 weeks ago. We really could have used the $40K sitting in the bank, rather than sitting there up on the roof. We go through $6K-$7K a month, and things are going to get tight for at least another 6-12 months. What an irony it'd be if we had to sell our home of 5 1/2 years. What to do, what to do ... keep a house for free power, or move to preserve our $400 in equity we put in as a down payment (it's already lost $500K that it went up {then down} over the last 5 1/2 years.

 

Hill,

I don't mean to be critical, but it looks like a significant number of your PV panels are on the back side of the roof. Is this correct? If so you are going to have a huge loss of production as a result of the panels not being properly oriented.

I hope I am wrong in the way I am seeing the pictures. If, as you said, you have spent $40k on this system it would be a shame not to maximize it's production.

Icarus

PS In any case, congrats on the new system. Pretty cool to see those kwhs rolling up!

PPS Seeing that your location is in NW MT, I was scared that the back side ones might not get any sun in the winter at all, but from the shadow cast by your self, it seems that the ridge of the house runs North/South. In that case ALL the panels will suffer reduced output. Ouch! I hope I am wrong n my analysis! Seeing the trees made me realize that you are in SoCAl as well.

 

yikes....

 

Critique away! Here's a satelite picture taken before the install began. Hey! There's our Prius in the Driveway! The picture is oriented due south. Thus, one gable (right side of the picture) faces south-west, while the other faces north east. The gables slope pretty gentle. They only have an angle of maybe 13 or 14 degrees ... or put in roofer's language, less than a 2 & 12 rise. You can see our houses are like dominos ... only 7' or so from each other ... long and narrow, like a mobile home shape.



Oriented properly? I don't know, what do you think? We had to rely on the expertise of the solar company. The framing on the north-east facing slope could have been built up above the ridge so both halves were facing south west. But wouldn't that simply mean that less of the early morning sun would be captured? Then, there's "the look". We want to stay away from the Rube Goldberg-esq look (giant framing not following the roof-line) and avoid becoming the neighborhood Peraiah.

We'll post results after we lite 'em up in January, & get our 1st months results in February, the least efficient PV time of the year.

 

Give me a orientation to due south,,,, I'd like to look at it further, quite frankly my initial reaction is I am a bit concerned.

Icarus

With your permission I would like to link your picture to my solar forum. Give me your latitude as well. And the size of your total array.

T

 

great pic but without knowing time of day, we need a compass here, can i assume that straight up on pic would be facing just northwest of west??

or maybe if looking upper left corner to lower right corner would be facing Dead East... i am guessing by the angle and weakness of the shadow makes time of day early morning?

 

Assuming that the ridge line runs north and south, (genericly) all the panels on both sides of the ridge would get similar insolation. None of them would be ideal, resulting in a significant loss compared to an expected harvest. If on the other hand with the ridge running north and south, the panels were tilted to the proper elevation relative to latitude the harvest would be maximized given a fixed panel array.

If, however the ridge runs some other direction than north/south, the degradation of performance would be even worse. My worry with this installation is that the sales people were over selling the performance of this system in this orientation. (I don't want to judge too harshly until I get the specs however). It just seems that if you are going to spend ~$40k, you might have ~4kw system. If that system only produces 60% of expected output, the net effect is that the system is 40% more expensive than it should be.


I am involved in the PV business, and it is unfortunate that there are people out there who put profit in front of performance (and people). A big part of RE is managing people's expectations. In the case where people are over sold, the effect on the whole industry is large. If we are told that we should get X amount of performance in order to sell a deal, but in reality, only get 60% it leave a sour taste.

Icarus

 

No, straight up on the picture is not West. The top of the pic is 180 degrees ... due south. Our main roof ridge runs about 40˚ off the north/south line.
We are at:
N 33˚38.791'
W 117˚42.262'
By the amount of flowering on the Jacoranda Trees, the picture was taken around April/May. The shadows are late after noon, maybe 3PM.

COULD the array be set more beneficial? No doubt. But at what cost, in terms of hideousness? Does the law allow us to say, "association beauty concerns be damned" ? Pretty much yes. Do we really WANT to shove the law in our neighbor's faces? ... as well as (aesthetically) have a HUGE amount of visual 'funk' factor? We hope to represent 'early adapters' in our association (so that they TOO will want to go solar), and a HUGE part of that is not looking 'out-of-place' in our community.

Sure, on our Montana house, we could put up a full blown tracking system and no one would care (well, we would ... it wouldn't go with the Colonial Revival archetecture ) but in a So Cal manicured community there are other competing factors.