Help w/ Panel choices in a shady area

System

Hello all, first off I'd like to thank all of you for making a really neat and informative forum here for all & us new guys to find the ropes and not throw our money off the bridge!!

I'm getting ready to buy some solar stuff to make emergency back up power for our small home. My goal is to have a little power to run a few CFL's and charge our cell phones + run my ham radio in case of a power outage.

I have done some research from this site that is great. However I'm still confused over what "kind" of panels to buy per my situation. I found some inexpensive panels on eBay that fit my current budget. The first problem is my shady back yard - I have an open area to the south that gives me 4+ hours of almost full sun . These next few pics show my s. east - south & finally s. west. When these trees get leaves or when the sun goes lower thru the sky in winter I'm worried I might be out of luck.

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I have my eye on some 80 watt Mono panels on eBay that seem decent & have Ce cert & satisfied buyers. But after doing more digging the Mono panels are not shade tolerant. I have found amorphous panels online that are and "they say" better at catching the sun from sun up to sun down as opposed to direct sunlight only. These "amorphous" are 40 watt panels x 2 = 80 watt same cost as the Mono's I have been looking at per watt.

Would you advise to just go all mono or mix and match amorphous w/ mono's?

My charge controller will probably be a Xantrex c40 or c60 with the front display. 160 to 200 watts pv to start and hope to get to 400 watts pv down the road. I'm planning on a 4 bank of marine deep cycle batteries because I have them.

Any ideas or thoughts would be greatly appreciated!! Thanks!!

BB.

Re: Help w/ Panel choices in a shady area

STS,

Welcome to the forum...

Basically, there is really no such thing as a shade tolerant Solar PV system... At the very least, you will loose 10% power if 10% of your panel is shaded... At the worst, you can have 25% shading and loose 100% of your power--depending on how your panels are oriented, how shade falls on the panel, and your Series/Parallel connection setup, and PWM (your CXX series controllers) vs MPPT (those that cost 2-3x as much).

Remember you are charging a battery to ~15 volts (12 volt system) with a Vmp=17.5 volt array... which is ~36x 1/2 volt solar cells in series. Each point of shade blocks 1/2 volt of "solar battery"... Get Vmp below 15 volts, and you are not pushing current into the battery. Also, solar PV cells go "high resistance" in "dark"--so they not only reduce voltage output, they block series current too.

Panels typically have a bypass diode every 12 cells to prevent electrical damage to the solar PV cells, but the bypass diodes can allow current to go around a shaded string of cells (say you have 4 panels in series connected to a MPPT charge controller for Vmp=5x17.5v=87.5v--so you have some "headroom" for a bit of shading).

Personally, I am not fond of thin film panels... They typically require 2x the square footage for the same amount of power (physically larger panels, more panels, more electrical wiring, more mounts to hold the larger array, etc.).

I have seen some test results that indicate that thin film panels may output something like 5-10+% better (not sure of numbers) better than crystalline panels in poor conditions (such as overcast days, or very hot days)--But the few links I followed were quite ambiguous regarding these test results. Part of my "confusion" is that Thin Film panels are actually rated to output ~120% more power out of the box, because they tend to "age" about 20% in the first 6-12 months to a stable output. I.e., a 100 watt panel will output around 120 watts out of the box in full sun, and ~100 watts in the same sun 12 months later. So--a new thin film panel will, initially have very good output in this tests... Just adds to the confusion.

Certainly, $1 per watt for Thin Film panels looks very appealing--but once you add the additional cost for racking and wiring out the system, plus the larger physical area needed to support rated power output compared with crystalline panels--many people find the overall cost savings to be near zero at the system level.

I cannot help you with figuring out if you are getting good panels from Ebay (or anywhere else) or not... I thought I got good panels and they failed 5 years later--fortunately, my manufacturer did honor the warranty and I have a brand new 3,500 watt array now. Direct sun and weather is a killer for solar panels--And a vendor with good history can be helpful (assuming they stay in businesses for the next 25 years, etc.).

In the end, location is critical for solar PV... If you do not have enough shade free sun, solar PV is not going to work for you.

Do you want to cut some trees? Are the trees on your property? Will local government let you cut those trees? Those look like pretty fast growing trees--Is the situation going to get worse 5-10 years down the road?

Ignoring weather, a Solar Pathfinder (don't know price) is the tool to use to evaluate shading.

You might also try looking through the links on this site... Perhaps you can do the equivalent of the Solar Pathfinder by printing a chart out and plotting the horizon obstacles.

-Bill

I should add that solar thermal systems (hot water, hot air) are more shade tolerant because they just collect heat (no current/voltage issues)... But, obviously, they still require sun to collect the heat.

Cariboocoot

Re: Help w/ Panel choices in a shady area

A couple of observations from my POV.

Amorphous panels have a "scattered" pick-up pattern, grabbing light from whatever direction it comes from, so to speak. As such, the light can never be directly on all of the panel's PV. In other words in direct sunlight they produce considerably less than a polycrystaline or monocrystaline panel (about 7% efficiency vs. 18%) They tend to be much larger as a result.

If you've got four hours good sun per day, go for that. Although the general guidelines say "aim panels at solar South" the real world says "point them to where they'll produce the most during the day". Sometimes this is South-East or South-West, depending on local conditions.

Also check the difference in angle for your site between Summer and Winter. Some info on this and its effects on output here: http://www.macslab.com/optsolar.html

One suggestion: aim your camera in the other direction and take pictures of the spot you intend to mount the panels on throughout the day (1 hour intervals). This will give you a visual comparison of how much shadow will actually fall, if the leaves are out (Spring? It snowed today!)

It sounds as though you will have to settle for less than ideal conditions, which is far from uncommon.

May I ask what is your purpose for putting up the panels? That may influence opinions and suggestions on how to solve the problem.

icarus

Re: Help w/ Panel choices in a shady area

It should also be note that simply for emergencies, a Honda EU1000 generator will provide 800 watts of continuous power,using about one quart if fuel every four or fine hours at full load. It is, a much cheaper alternative.

That said, if you are looking to get your feet wet, building a small system for hobby, go for it.

Tony

Ps Welcome to the forum and keep in touch.

T

System2

Re: Help w/ Panel choices in a shady area

Thanks for your replies & clarification on shade tolerance - less $$ off the bridge already :-)) If I move forward I will definitely choose a mono/poly crystalline panel.

The trees - I can cut some of the trees in picture 1 (which will cause a direct shading ) - the trees in pic 2 & 3 are 150- 200 ft away and could be cut down also if absolutely necessary.

Well I guess my next step is to do some plotting - and take some 1 hr pictures, great ideas. This has got me thinking about instead of buying all kinds of panels & other stuff maybe I should just get 1 panel and a controller and check the incoming numbers and go from there.

No more snow!! I don't want to see that anytime soon. The purpose for this project has a lot to do with my interest in solar electricity as a hobby and potentially to make back up power that doesn't use gasoline. Of course If things go well and I can get enough sun, landscape wise I could expand and take a few things off the grid to save a little in electric.

I will check out that estimation radiation site you put up. In the mean time I have to figure out why 48 volts would be better than 12v, series vs parallel, lol - I digress - lots to learn. All good things in all good time. Thank you very much for this info!!!

Also thanks for the honda gen recommendation that seems like a little miser!!

BB.

Re: Help w/ Panel choices in a shady area

More or less, the more peak power (watts) you want to use and/or the longer distance you want to send the power, then moving to a higher voltage bank will help.

More or less, 1,200 watts or less can work OK with 12 volts. 2,400 watts or less then 24 volts, and over 2,400-3,600 watts, look at 48 volts.

It is all about power=V*I and if you double the voltage, then the current is reduced by 1/2...

Basically, 1,200 watts at 12 volts is around 100 amps already... For a 1,200 watt inverter:

• 1,200 watts * 1/10.5 cutoff voltage * 1/0.85 eff * 1.25 NEC safety factor = 168 amp fuse/breaker/wiring

You can get 3kW and even 5-10kW 12 volt inverters--but the amount of copper and the 1.0 volt maximum voltage drop that a typical 12 volt battery bank+wiring can support makes it almost impossible to have enough copper to operate those inverters at their rated capacity (yes, it can be done, but why?).

Your other decision is do you have native 12/24/48 volt DC devices (HAM, boat electronics, truck stuff at 24 volt, etc.)...

Usually, I think it is worth buying a nice True Sine Wave (TSW) inverter and running the rest of the stuff off of 120 VAC... Simple wiring (120watts= 10 amps at 12 volts or 1.0 amps at 120 volts), small gauge wire, and the inverter losses at 85-90% efficiency are not that bad.

In the end, we recommend starting with conservation (almost always cheaper than generating your own power), then measure you loads, then design the system. Lastly, then break out the wallet.

-Bill

Slappy

Re: Help w/ Panel choices in a shady area

also "in a nut shell" 1) The higher wattage panels are cheaper per watt. 2) you have a short "sunny window" time frame (4 hrs). so the higher wattage panels, will get your batteries up to par quicker. 3) it will take up less real estate space. (than a bunch of smaller panels). 4)less hardware involved as in racking, nuts, bolts, washers, (stainless steal??). wire connectors.....etc........just added this just as a thought. or to help on the thought process?