Solar Panel Questions

[Kevin H]

I am putting together a solar system for my van.  Considering 400 watts.  Looking at solar panels and looking for ideas.

Is it better to have a single large panel or multiple smaller panels?

One thing I am not clear on:  Shade - why does shading a small portion of a panel compromise so much of the entire panel's output?

[Daveh]

One panel would be the most cost-effective and easier to install if you are just dealing with a single open space. However, shading anywhere on that single panel will decrease the output of the entire panel.  The installation of one panel is generally easier since there are fewer mounting points and number of wires. 

Multiple smaller panels may allow you to position them so that you can get more total wattage on the roof and shading of one panel will not reduce all of the panels (if they are wired in parallel) as you would experience with a single large panel. Smaller panels are generally more expensive on a per watt basis and require additional wiring and connections for install. 

As to shading very generally think of a panel as a series of cells working together to collect the suns energy. Each cell collects the energy and passes it on to the next cell and together their output equals the total wattage output of the panel. However, the strength of this collective system of cells is limited to it's weakest link. Even if some cells are getting the full amount they can only pass on an amount equal to the weakest cell in the link so the cumulative total will be substantially lower even if a small amount of shading occurs.

The best way to get into this is to read Jack Mayer's tutorial on solar systems for Rvs.  Reading through this a few times will get you in the position to ask the right questions AND actually understand the answers.    http://www.jackdanmayer.com/rv_electrical_and_solar.htm

 

Dave H

[oldjohnt]

10 hours ago, Kevin H said:

Considering 400 watts.  Looking at solar panels and looking for ideas.

Is it better to have a single large panel or multiple smaller panels?

 Kevin, good questions I pretty much agree with Dave's good response, here's my own take:

1) A 400 watt SINGLE panel would be one fairly big unit. My 245 Watt panels are 39 x 64. If you cant find a single 400 watt panel to suit your needs and fit your roof ????  you may be left with the use of MULTIPLE PANELS like it or not.

2) A SINGLE panel (if you can get a single 400 watt that fits on your roof) means less wiring connections and less mounting problems. 

3) Multiple panels wired in parallel may (subject to location) reduce some shading problems..

4) Without any idea of your available roof space and what if any roof restrictions you may have (AC units and vents etc etc) the use of a couple say 200 + Watt 24 Volt panels wired in parallel may be an easy straight forward approach versus a single huge panel. I CANT SAY WITHOUT KNOWING YOUR ROOF.

5) I would shop around to see if you can get a single 400 watt that will fit correctly ???? but if not consider two 200+ watt units which Id prefer versus say FOUR 100 watt units JUST TOO MANY WIRES AND CONNECTIONS. EITHER WAY WILL WORK Id say the answer depends on your roof space 

John T Long retired electrical engineer and NOT a solar expert so do as they say not me

Edited February 21, 2018 by oldjohnt
add

[hemsteadc]

15 hours ago, Kevin H said:

one thing I am not clear on:  Shade - why does shading a small portion of a panel compromise so much of the entire panel's output?

Because, as mentioned, all the cells are in series.  This can be mitigated by buying panels with bypass diodes.

[Yarome]

All good points raised thus far. A couple additional to consider:

1. Localized weight. A single large panel requires more structural support and will, therefore, generally weight more than the combined weight of 4-100 watt panels. Not necessarily a major consideration, but something to be aware of... If you are using heavier mounts and larger screws as a result then in the "unlikely" event that your panel get's snagged by a branch... subsequent damage to the roof itself may increase. Idealy, I would like to see a lightweight panel shred and leave the mounts intact.

2. Heat. A large single will generate more internal heat than 4-singles. As temps increase, production decreases.

3. Maintanance. Dismounting a large heavy panel for under roof maintanence is more difficult and increases the likelihood of damage to the roof or other components.

A bit on shading. It's not difficult these days to find single larger panels with internal cell "cluster" bypass diodes (which I would consider just about necessary in a single panel array like that). Especially in higher voltage panels. Much like a single shaded panel out of a 4 panel array will be by-passed to prevent a massive drop in the array's combined output, a larger panel may have interal "zones" so equipped so as not to affect the output of the entire panel. So, basically the same 'nanimal.

Touching on your question as to "why?". Trying to keep it simple... a shaded cell doesn't just sit there idly by and simply not contribute to output. If it's not "pushing" it's "pulling"... basically becoming a heat sink within the cell cluster/panel capable of "absorbing" massive amounts of current from the surrounding "cells". Typically, a shaded cell is compared to a weak battery in a string. For all intents and purposes that's generally an apt example everyone can relate to, however, a batteries capacity is "fixed". A shaded solar wafers ability to "absorb" energy is dynamic and unlimited.

To think of it in another way... if you have a water pipe with passive pressurized water moving through... say... like rain water moving through a pipe. Call it "energy production". A shaded cell would not just "not" contribute to raise the water flow/pressure... or be similar to a leak in your pipe... but the equivelant of an active back flow pressure. With "passive" water pressure it doesn't take much of any backflow pressure at all to stem the overall flow by a highly significant degree.

That's why I'm often heard to say that all panels are not created equal. Wafers are not just "poly" or "mono". They will have different conductivity characteristics, resistivity, O2 and carbon concentrations, thichnesses, and on that affect not just their ability to produce energy, but how they will react within a cluster. It's not really talked about much, but how well a panel deals with shading can have long term affects. I think everyone is well aware that heat is the enemy of any electronics. A wafer is no different.

I digress. 

All the above is just academic and in no way meant to discourage you from your current plan of attack. None of us know your particular situation, roof-top real estate layout or what your future plans may be for solar. Just points to ponder and likely TMI as is.  

[jcussen]

 

You would probably need a mppt controller to use the higher wattage panels.

https://www.solarelectricsupply.com/solaria-powerxt-400c-wx-solar-panel-wholesale-price

Edited February 21, 2018 by jcussen

[hemsteadc]

1 hour ago, jcussen said:

You would probably need a mppt controller to use the higher wattage panels.

Yes,  larger-wattage panels are rarely, if ever, 12v

[OldMan]

I've looked around and there are very few 400-watt panels around. Can you possibly get by with 375??

Edit: If you're willing to go direct, here is a good buy.

Edited February 22, 2018 by OldMan

[Yarome]

32 minutes ago, OldMan said:

Can you possibly get by with 375??

You're aware, of course, that the one linked has a minimum order of 24 panels and won't ship until late 2018, correct?  Otherwise... not a bad panel with LG's NeON2 tech and just a shade over 19% efficiency.

Edited February 22, 2018 by Yarome
Typo

[OldMan]

Oops. My bad. And of course, you like that.

[oldjohnt]

I found

4 hours ago, OldMan said:

I've looked around and there are very few 400-watt panels around

That's the same thing I found (NOT saying there aren't some out there) which is why for ease and availability and price and possibly less shading concerns subject to roof real estate and possibly less heat problems and less weight per panel, if I had to have 400 watts Id at least consider using TWO 200 Watt probably 24 volt probably wired in parallel Panels. They are so readily available at less then a dollar per watt. I'm running three of the 24 volt 235's in parallel now on my small 29 foot Class C and have room for even one more.

 Study your roof layout shop around and do your homework and I'm sure you will do fine

John T

[OldMan]

12 hours ago, oldjohnt said:

I found

That's the same thing I found (NOT saying there aren't some out there) which is why for ease and availability and price and possibly less shading concerns subject to roof real estate and possibly less heat problems and less weight per panel, if I had to have 400 watts Id at least consider using TWO 200 Watt probably 24 volt probably wired in parallel Panels. They are so readily available at less then a dollar per watt. I'm running three of the 24 volt 235's in parallel now on my small 29 foot Class C and have room for even one more.

 Study your roof layout shop around and do your homework and I'm sure you will do fine

John T

I'm not looking for  them, the OP was. I'm not even doing a roof mount.

I'm getting three 250s but it will be for a class A. OP will do fine with a 360, I believe. But to take advantage of it, he has to use lithium-iron batteries. Lead-acid batteries cannot provide the amp hours he seeks, and that type of battery cannot become a thing of the past, fast enough. You can even get lithium-iron starter batteries, as in starting your car.

Edited February 23, 2018 by OldMan

[Daveh]

I think we lost our OP but it was a great discussion. His loss!

[chirakawa]

6 minutes ago, OldMan said:

I'm not looking for  them, the OP was. I'm not even doing a roof mount.

I'm getting three 250s but it will be for a class A. OP will do fine with a 360, I believe. But to take advantage of it, he has to use lithium-iron batteries. Lead-acid batteries cannot provide the amp hours he seeks, and that type of battery cannot become a thing of the past, fast enough. You can even get lithium-iron starter batteries, as in starting your car.

Tell me more about these lithium-iron batteries.

[OldMan]

7 minutes ago, chirakawa said:

Tell me more about these lithium-iron batteries.

Not a helluva lot. This will explain more and in truth, I'm reading it myself.

What I know is the cell chemistry has somehow been re-formulated with the idea of making it more stable and not prone to catching fire, like lithium ION batteries have been prone to do (iPhones, laptop computers). That page I linked to will help you a great deal.

It should be known, the lithium batteries made for RV solar systems  now, are almost all lithium-iron.

Same great price, lower liability exposure!!!

Edited February 23, 2018 by OldMan

[chirakawa]

Thanks. I've been using lithium batteries in RC vehicles for years.  They can be very unstable.  This lithium iron battery seems to be the answer for that.

[OldMan]

37 minutes ago, chirakawa said:

Thanks. I've been using lithium batteries in RC vehicles for years.  They can be very unstable.  This lithium iron battery seems to be the answer for that.

Indeed. Glad I could help. Let me know how your project goes, OK?

[Yarome]

18 hours ago, OldMan said:

... you like that.

Not at all. I get no joy from someones discomfiture when they are just trying to be helpful.

[Yarome]

1 hour ago, OldMan said:

...to take advantage of it, he has to use lithium-iron batteries. Lead-acid batteries cannot provide the amp hours he seeks...

 

1 hour ago, OldMan said:

What I know is the cell chemistry has somehow been re-formulated...

It should be known, the lithium batteries made for RV solar systems  now, are almost all lithium-iron.

Same great price, lower liability exposure!!!

I wouldn't even know where to begin to reply to that. Do you truly believe that or are you just making stuff up to incite controversy? Like telling everyone you're a commie? 

There's really nothing new about LiFePO's (Lithium-iron). It's actually about half a decades old tech (if you note the tradmark date of 2015... that particular article hasn't been updated for years) and lithium chemistries have expanded and multiplied greatly since then. We are still in a condensed version of "betamax vs. VHS with DVD's being tested and blu-ray just on the horizon" phase, IMHO. Lithiums are viable in an RV, but yet to have a true "pack leader" chemistry that is truly stable, can provide the lifecycles promised in real world application and affordable in the mainstream.

Just as combustion engines will remain a mainstream modal over electric cars for the forseeable future... wet cells, in it's various forms, will persist as a highly cost effective and proven tech in RV applications... fully capable of supporting even the largest of solar arrays.

[OldMan]

Someone said something, but it went in one ear and out the other.

[Daveh]

Yes, just to remake the point already made "lithium iron" batteries are actually Lithium Iron Phosphate batteries or LiFePo batteries and we have had rather extended discussions about them previously (Not that we won't all over again).   If you want to know more than most humans alive read this thread--- http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069.html

[Yarome]

20 hours ago, OldMan said:

...GFY

How clever! 

Probably not framed the best, but it was a legitimate question. You've stated in other threads that you've said "this/that/or the other" just to get a reaction out of people.

Just reading a screen it's difficult to tell if some of the gross misinformation you state, the criticisms and name calling ("gomers) is actually out of truly being misinformed or simply your "tongue-in-cheek" way of illiciting reactions from folks.

At any rate... it's not a prerequisite of forum membership to believe anything anyone has to say... although... you may learn a thing or two from others experiences and expertise. Something to consider, but no skin off my nose one way or the other and won't comment further unless it pertains to the discussion or the OP.

Edited February 23, 2018 by Yarome
Typo

[hemsteadc]

What is lifepo4?

I like my 48v 100ah Lifepo4 battery pack.

 

Edited February 23, 2018 by hemsteadc

[Al F]

23 hours ago, chirakawa said:

Tell me more about these lithium-iron batteries.

I wish it would be an easy or simple thing to reply to "Tell me more about these lithium-iron batteries".   You will find volumes of info about Lithium batteries by doing a search on this forum for "LiFePo4".  I found 94 hits with the search.  Many of which I participated in.  At least 1 or 2 where I started the topic. 

There are links to very extensive information from people who have installed lithium, as well as info about the pros and cons about lithium.

We travel extensively, mostly dry camping and boondocking, 10 months in 2016. 7 months in 2017.   I love our lithium batteries which I installed in Jan 2016.  With our travel style I would not go back to lead acid batteries of any type.