Solar panel types and sizes, looking for input

[neoneddy]

I'm looking to add some PV solar to the bus, I was almost set on some 190 watts monocrystaline panels, but they are no longer sold.

Then I dug into the differences more.

Monocrystaline - better in perfect conditions, more efficient.

Polycrystaline - better in shade and cloudy days , less efficient.

With this in mind I'm actually leaning more towards polycrystaline.

I was also considering sizing, at first I gravitated to larger panels, but now I'm leaning toward smaller 100w panels that I can arrange with a walkway down the center for maintenance on the panels and ACs.

Overall array size is 1-2kw , might start with a 1/2 of it and go from there.


Thoughts?


Sent from my iPhone using Tapatalk

[solardude]

neoneddy, I certainly don't want to discourage you from any well thought out plan. My wife often plays the part of cynical critic, so I am well versed in having my bright ideas popped. That being said, I have some questions that may help you make educated decisions.
Here are a few recent posts that touch on your topic:"How many Watts of Solar is enoughhttp://www.busconversions.com/bbs/index.php?topic=32650.0"Add more House Batteries or add Solar?"http://www.busconversions.com/bbs/index.php?topic=32649.0

Inaddition: Your post mentioned low wattage panels <100W, and mentioned 1-2kW total, it would be difficult to have a walking path and A/C and vents and 10-20 100W panels on my bus roof, perhaps your bus is much longer than mine. It would be pretty easy to get 1-2kW with >350W panels though. However, after reading through the above posts you see why that may not be practical either.

Whatever you decide, take pictures and post.

PS, Partial shading will usually cause problems on any array, even with MPPT, so research, research, research.


SolarDude.

[Iceni John]

The best bang for your buck is with standard grid-tie panels, either 60-cell or larger.   When you buy little panels you'll end up paying a lot more overall.

1kW is about the largest array for a 12 volt system that a single charge controller can handle.   If you eventually want more power you will need two CCs for a 12 volt system.   If however you have a 24 volt system you can use a single CC for up to about 2kW of panels.   CCs' outputs are rated by current, regardless whether they are charging 12 volt or 24 volt batteries;  if my system were 24 volt I could use a single 60 amp CC, but because it's 12 volt I need two CCs.   (FYI, I have eight Sharp 255W polycrystalline panels wired in parallel in two separate tiltable arrays, feeding two Morningstar TS-MPPT-60 charge controllers that will eventually charge eight golfcart or L16 batteries in two separate 12 volt banks of four each;  both battery banks feed through 250 amp Schottky diodes to the DC main busbar that powers the DC breakers and Magnum inverter.)

John

[neoneddy]

@solardude :  Thank you for the reply and info.  For most part I'm settled on sizing as far as wattage, it was just on panel sizes . I'll need to refresh myself on those posts. 

I did some layouts and got 1.5kw on by running the panels lengthwise along the sides of the top and then 3 across the back.  I have 4 or 5 layouts using those littles ones all the way up to 330 watt panels.   I'm still up in the air on the physical size of panels, I do know I want Solar.   My way of doing things is to have a 70% plan, start small, adapt as needed. Maybe I put 400-600w up there and it serves me just fine for everything. Except AC usage of course.

@john I'm on 24 volt banks, seems the best way to go is 48-100v panel voltage into a CC . Last thing I want to do is burn power on line resistance.


I guess my main question still remains - mono or poly? Is it worth worrying about for our application?


Sent from my iPhone using Tapatalk

[Iceni John]

@john I'm on 24 volt banks, seems the best way to go is 48-100v panel voltage into a CC . Last thing I want to do is burn power on line resistance.


I guess my main question still remains - mono or poly? Is it worth worrying about for our application?


Sent from my iPhone using Tapatalk

MPPT charge controllers work most efficiently (i.e. produce least heat) when their voltage stepdown is as little as possible.   If your PV array's voltage is no more than twice the batteries' voltage, the CC's efficiency will be in the high 90s percent; but if you have a much higher voltage array the CC will run much warmer because its efficiency will drop to the low 90s percent.   72-cell panels will work well for a 24 volt system if they're wired in parallel.   Because RV and bus PV installations are not large, compared to some fixed installations where the panels can be some distance from the CCs, it's really not necessary to connect panels in series to avoid voltage losses through long runs of cable.   I use 10 AWG cables to bring each panel's power to the combiner box in which each group of four panels is paralleled, then 4 AWG welding cable for each group's downfeed to the CC;  the downfeed cables are only 12 feet long, and the 2 AWG and 2/0 AWG cables from the CCs to the batteries are only a few feet long, so there are no real voltage losses to be concerned with, even at full charging.

And as for the eternal mono-versus-poly debate, don't sweat it, it doesn't really matter too much.   If you can get a deal on either, then that's what you'll buy!   The question of which works better in cloudy or dull conditions is largely moot  -  in such conditions both panels' output is lower anyway, so who cares if it's at 40%, 45% or 50%?   Keeping the panels clean of dust, bird poop, leaves etc will gain you more power than the difference between mono and poly.   That's why I have two water quick-connect outlets up on the roof, so I can easily and safely wash down my panels without needing to drag hoses or carry heavy buckets of water up onto the roof  -  I just climb through the front roof hatch with my washdown brush, plug it into a water outlet, and wash the panel while safely standing on the catwalk between my two roof hatches.   Easy!

John  

[neoneddy]

@john I was fixated on getting the most power for space that I had and I figured smaller panels would allow for more coverage and then monocrystaline would deliver the most power per sqft.  Thanks for providing some real world reality to it.  There is also extra cost in general, extra mounting hardware, wiring,  as well as lost square footage to frames and bezels.

I've been talking with a rep from  SEP batteries  looking at this panel maybe doing an order of 6. http://sepbatteries.com/yingli-solar-yl315p-35b-315w-solar-panel

John, I've also attached  a graphic how I'm thinking of configuring it.  My ACs and Hatches are in place now, so those aren't really movable.   I'd be interested to see shots of yours and how it's configured.  Also @solarDude's as well.  Or anyone else for that matter.

[richard5933]

More a question than a comment here...

Would the long length of these panels make them more susceptible to flexing/damage from being on a moving vehicle?

[Iceni John]

More a question than a comment here...

Would the long length of these panels make them more susceptible to flexing/damage from being on a moving vehicle?

That's exactly why I went to the trouble of making support frames for each panel.   Each panel itself sits inside a rectangular frame made from a 16' length of 1.75" 6063 angle, with an extra 2' piece riveted on to bridge the gap (the total length is about 17.5'), with a half inch gap inside all round just in case I ever had to replace a panel and the only replacement was up to 1" larger.   The panel is secured into the support frame with four stainless bolts bearing against the top of panel's own frame, so no holes are drilled into the panel at all.   Each support frame is hinged to the roof walkway with two stainless hinges, and is supported at its outer edge with two stainless telescoping/sliding/pivoting/hinged struts that can raise it up to 45 degrees above horizontal for winter insolation.   Bear in mind that my Crown's roof is more curved than most buses' roofs, so when the panels are down against the roof they are actually at 21 degrees below horizontal;  in summer I can raise the side opposite the sun to 21 degrees up, and in other seasons higher than that.   This creates maximum practical solar harvest throughout the year, and there is absolutely zero shading ever on the panels (even the slightest partial shading will hugely cut output).   When driving, all panels are stowed against the roof at 21 degrees down, secured with latches to prevent any movement, and the airflow under them doesn't cause any noise.   All I need is a 6' stepladder to easily raise or lower the panels entirely by hand, no tools needed.   Keeping the panels above the roof itself, even when they're all the way down, also helps cool them by allowing air to circulate under them  -  I see RV solar installations where the panels are flat against the roof, and when they heat up in the sun their output will drop significantly.

John

[windtrader]

John,

You've thought alot about getting the panels secured and oriented for optimal performance and durability for a bus rooftop which represents a fair investment in hardware, time, energy, and labor on this project. It works great under optimal conditions. When parked in a shady spot or one oriented north/south, not so well.

Having gone down the same paths, after weighing it all out, I'm going KISS and simply securing them to the roof. No muss, no fuss, cheap, fast. If I'm short of watts, I'll add another panel to compensate for the loss from laying flat. I don't trust myself anywhere near 100% of the time I'll faithfully stow the tilted panels before driving off, then end up with panels twisted or banged up or some other such incident by improper storing.

Remember, once "boondock optimized", the coach will not draw much watts, so it won't take many panels to keep the bank charged up. A rough calc is something like 3 x 320 = 960 watts; say 720 watts usable (max).  6 hours generating average 500 is about 3000 watt. If the house bank can store just 2000 watts, it seems plenty based on our use profile.  AC is not included in any of this calculation and generator is needed while running AC.

[lostagain]

The solar panels filling the space between wind mills near Palm Springs are fixed, oriented at an average angle. They used to be mobile and follow the sun, but the tour guide last year explained that it was too much maintenance and trouble. The utility companies that operate them find it more efficient to have them non movable.

JC

[bobofthenorth]

............ Remember, once "boondock optimized", the coach will not draw much watts, so it won't take many panels to keep the bank charged up. ..................

This is the key if you are serious about "living" solar.  We met a guy one winter on the desert north of Quartzsite. He had completely committed to solar living - he had modded his computer power supply so it didn't need 110V input, he didn't watch TV, he went to bed when the sun went down (I assume to read but I didn't pursue that level of intelligence), he cooked on a BBQ.  IOW he completely altered his lifestyle to match the available power.  It wasn't a lifestyle I would ever choose but it is an option if you seriously want to live solar.  Most of us start from what we want to do - watch TV, stay up late, use computers, tablets and phones, boil water, run AC, etc etc.  If we turn that around and start from the available power (number of panels X real output in watts) and then decide what we can do its absolutely possible.  For the way we live that calculation always comes up with a massive power deficit which we solve by burning dinosaur juice.  YMMV

[ccbmster]

I just got a couple of additional panels for mine from Wellspring Components in Shipshewana, IN.

140 Watt Panels for $135.00 each.   Very happy with them and good guys to deal with.

[Iceni John]

The solar panels filling the space between wind mills near Palm Springs are fixed, oriented at an average angle. They used to be mobile and follow the sun, but the tour guide last year explained that it was too much maintenance and trouble. The utility companies that operate them find it more efficient to have them non movable.

JC

Because PV is so cheap these days it is simply not cost-effective to have 1-axis or 2-axis trackers for them any more.   It's now much cheaper to just have an extra panel or two to make up the difference that tracking could have gained.   I've driven past the wind farm near the Banning Pass and noticed that some of the PV panels seem to be in the windmills' shade for some of the day.   I wonder if that's deliberate  -  maybe it's assumed that full production will only happen at zenith!

John

[Geom]

Just a few comments,

Based on your diagram, pay close attention to where shade might be thrown on those panels from the ACs and vents.
Even a tiny bit of shade will significantly reduce your panel output.

You absolutely want an MPPT controller. It is much more tolerant of voltage and output variances and dynamically adjusts its algorithms to better account for some of the losses associated with that. Plus with a PV array as large as you're considering it's probably not optional anyway

You want to be careful with how you run those panels in terms of parallel vs series. Panels run in series will suffer (power loss) greatly, if any of the other panels in the series are even partially shaded. But series runs allow you to push more power over thinner wires (by using higher voltage).
Parallel connected panels are much more tolerant of that. So while the affected panel may drop its output, the others will continue to produce. But depending on output, you'll need thicker (and more) wiring with parallel runs.

As far as mono vs poly, I'd definitely choose mono. They're significantly more power dense, lighter, and run cooler.
However, you don't have to choose either/or. The Panasonic HIT panels I've been looking at feature a mono primary layer with a poly-like sub-layer that takes advantage of both technologies' advantages. They're big-honking monsters and are 330W each. But they're more tolerant of angle variances, shading, and cloudy days. And are actually a smaller panel per watt, overall, than a smaller <200W panel.

And finally, you can produce all the power in the world, but if it has nowhere to go, you're just burning money and wasting energy.
So your battery storage is perhaps as important, if not more important, than the PV size (unless you plan on being grid-tied).
While lithium, at first, seems costly; it is by far the desirable target for all that solar.
Of the many advantages lithium has, it can take a high rate of charge fully from 0% to 99% of capacity. Any lead-based technology can only take a marginal charge up to 80% or capacity, and then for the remaining "20%" you're pumping/wasting a whole lot of power to trickle in there; to get it full.
And lead can be damaged and degraded over time if you don't charge it to that full 100% state. As where lithium could care less.
Plus you can discharge from lithium considerably faster, with zero voltage lag/drop, than you can with any lead based technology - and you can essentially half the size of your bank for the same amount of usable output.

Although I wouldn't discharge a lithium array by more than about 70%-80% of its stated capacity, they can be discharged to near 100%.
Granted that will lower their life-expectancy. But with lead, discharging them below 50% is significantly damaging to them, and a full discharge can be lethal.

[windtrader]

Is it possible for Lithium and LA batteries to coexist is some workable configuration? That would be ideal for those who want transition over time to new batteries. The one time $$ outlay, even for a smallish bank, is pretty spendy.

Totally agree that lithium is much better for charging mobile solar, especially given the much greater ability to charge faster. On patchy sunny days, the lithiums can uptake much more energy quicker, plus the 100% charging to full, that you'll surely get more stored energy than over LA under same conditions.


These looked interesting until I read the back story about Stion. Also, mentions the reason for rising panel prices this year. I guess for consumers, it's better that Trump does not impose any import tariffs - back to cheap panels.

https://sfbay.craigslist.org/sby/for/d/new-1000w-of-solar-panels/6444715512.html
http://www.realclearenergy.org/articles/2017/12/18/president_trump_say_no_to_solar_tariffs.html

https://www.solarpowerworldonline.com/2017/10/u-s-thin-film-solar-panel-manufacturer-stion-discontinue-operations/
https://www.greentechmedia.com/articles/read/american-solar-manufacturer-stion-discontinue-operations-layoffs