Questions about solar power - Page 4 - Fiberglass RV


Reply
 
Thread Tools Search this Thread Display Modes
 
Old 03-08-2014, 01:05 PM   #43
Senior Member
 
blodn1's Avatar
 
Name: Deborah
Trailer: Prius camping - want an Oliver
Virginia
Posts: 351
Maybe I could have stated it better - that you should BUY higher voltage panels, because you won't get 16-20 out of a 17 volt panel.
__________________

__________________
I don't get lost, I go on interesting side trips.
blodn1 is offline   Reply With Quote
Old 03-08-2014, 02:16 PM   #44
Senior Member
 
Jon Vermilye's Avatar
 
Name: Jon
Trailer: 2017 Escape 21
Oswego, NY
Posts: 1,407
Registry
The GoPower 30 amp PWM controller is a 4 stage unit. It does equalization when ever the battery voltage drops below 12.1 volts and every 28 days.
__________________

Jon Vermilye is offline   Reply With Quote
Old 03-08-2014, 05:19 PM   #45
Senior Member
 
Mike Magee's Avatar
 
Name: Michael
Trailer: Li'l Hauley
Oklahoma
Posts: 5,142
Peter, thanks. I had somehow gotten the mistaken idea that the MPPT controller would act like a transformer during bulk charge, converting excess voltage into more current (keeping wattage the same). Probably read that on the internet!
__________________
How much time do we have left? 2 Chr. 7:14
Mike Magee is offline   Reply With Quote
Old 03-08-2014, 05:28 PM   #46
Senior Member
 
Carol H's Avatar
 
Name: Carol
Trailer: 22' Airstream Formerly 16' Scamp
British Columbia
Posts: 11,731
Registry
Although interesting the discussion of PWM vs MPPT solar controllers is staring to sound a lot like the big debate on whats the best type of converter to use to get a the elusive fully charged battery we hear so often
Carol H is offline   Reply With Quote
Old 03-08-2014, 08:43 PM   #47
Senior Member
 
Briantb's Avatar
 
Name: Brian
Trailer: 2015 Scamp 13 Front Washroom, Little Guy Teardrop
Ontario
Posts: 372
For a small RV system use an inexpensive controller and save your money for the new battery you're eventually going to need.
__________________
Briantb is offline   Reply With Quote
Old 03-08-2014, 08:52 PM   #48
Senior Member
 
peterh's Avatar
 
Name: Peter
Trailer: 2005 19 ft Scamp 19 ft 5th Wheel
Oregon
Posts: 1,519
Registry
There have been a lot of innovations in the solar market. Affordable PWM controllers were a nice step forward, and is what I have on my Scamp. Only recently, however, have MPPT controllers come down in price to where they're not more expensive than the solar panels they support.

MPTT controllers are like many tools. They are very good at what they do. The question, as always, is, "Are they the right tool for the job?"

The answer to that can be yes or no, depending on things like money, the size of your solar panels and battery, and how you use the power your batteries store and panels make. What follows here is a long-ish, boring-ish discussion you can skip (just head down to the "=========" line below the boring stuff) explaining what scenarios an MPPT controller makes a lot of sense in.

==========

First off, a good MPPT controller will charge your batteries at least as well as a good PWM unit. It may not do it better, but it will do at least the same job. Whether you get more out of an MPPT controller has a lot to do with the size of your solar panels, the size of your batteries, and the amount of electricity you use from your solar system and batteries.

MPPT controllers make sense when your solar panel output is just adequite to getting your battery fully charged. So, let's say you have a 100w panel and get the equivalent of four hours of full sunlight. After doing the math, that means your solar system can optimally provide about 16 Amp-Hours (AH) of battery power each day. If you have a fully-charged 50 AH battery that you discharge down to 12 volts or so by the next morning (30AH used) you will never use the features of your MPPT charge controller, and your battery will go dead over time.

Double the size of your battery, to 100 amps and use the same amount of power, and you'll get some small benefit from an MPPT controller on the first day or two, but your battery will still go dead, and in slightly less than double the time compared to using a 50 AH battery.

If, on the other hand, you discharge that same 50 AH battery to 12.4 volts by the next morning (20AH used) you will use the MPPT features for the first several days while it trys to keep your battery charged. Your battery will still eventually go dead, but it'll take longer, so you do get some value out of your MPPT controller. Bump your battery size up to 100AH, and it'll still discharge in slightly less than half the time, but will again use the MPPT features a lot during those first several days.

Let's say your daily usage is right at 16 AH, the amount of power your solar panels can produce. Because more energy is lost during the absorbtion and float phases of battery charging, your solar system won't quite keep up for the first several days running on solar, but then you'll get back from a day in the great outdoors and discover your battery voltage is about 12.5 volts (80% charged), same as the day before, and same as the day before that. This is the break-even point where an MPPT charger makes the most sense, when your solar panel power production and daily consumption are just about in-balance, regardless of the size of your battery.

What, you might ask, gives you the most bang for the buck if your solar panels make more electric power each day than you use? Say your 100w panel makes 16AH each day but you use just 12AH. In that case, it doesn't matter whether you have an MPPT controller or a PWM controller. Both will bring your battery up to full charge each day.

==========

In the end, MPPT charge controllers make a lot of sense if your solar panel generating capacity more or less matches your average daily consumption, say plus or minus 25%.

If you have an abundance of solar compared to your daily demand, your solar system is already beefier than you need, so why spend more on an MPPT controller? If your solar panel capacity is less than 75% of your daily demand, you won't get much out of those fancy MPPT features, and perhaps your money would be better spent buying a larger solar panel, a second panel, or buying a larger battery.

Yes, it gets complicated. And, rather than working all the details out I can really see the logic of saying "Screw it. I'm spending the extra $50 and getting an MPPT controller."

Which is, in the end, what I decided to do for our Surfside project trailer.
__________________
peterh is offline   Reply With Quote
Old 03-08-2014, 09:56 PM   #49
Senior Member
 
Name: Drew
Trailer: Trillium Outback - 2004
Alberta
Posts: 106
Registry
This white paper makes more sense. I use the mppt controller mentioned and it works. Not for everyone though.

https://s3.amazonaws.com/Morningstar...Whitepaper.pdf
__________________
Where we’re going, we don’t need a plug-in.
multi-task is offline   Reply With Quote
Old 03-09-2014, 11:15 AM   #50
Senior Member
 
Mike Magee's Avatar
 
Name: Michael
Trailer: Li'l Hauley
Oklahoma
Posts: 5,142
Quote:
Originally Posted by multi-task View Post
This white paper makes more sense. I use the mppt controller mentioned and it works. Not for everyone though.

https://s3.amazonaws.com/Morningstar...Whitepaper.pdf
That's a very good document. Well worth reading. I see that MPPT can indeed convert excess voltage into current. But there is no easy way to quantify the charging advantage of MPPT over PWM because it depends on several factors that are in flux throughout the charging day. Thus they summarize with some 'rules of thumb' based on assumptions that will usually be valid.

Carol H, I would say there's no debate here... just discussion and learning.
__________________
How much time do we have left? 2 Chr. 7:14
Mike Magee is offline   Reply With Quote
Old 03-09-2014, 11:49 AM   #51
Senior Member
 
Name: Darwin
Trailer: 2002 19 ft Scamp 19 ft 5th Wheel
Posts: 3,029
Send a message via Yahoo to Darwin Maring
It's beginning to look like this site is turning into a Fiberglassrv Science Forum.
__________________
Darwin Maring is offline   Reply With Quote
Old 03-09-2014, 12:49 PM   #52
Senior Member
 
Name: Paul
Trailer: Escape 19 ft (sold) Escape 21 May 2014
Wisconsin
Posts: 258
Registry
Nice. The discussion of the different controller types is causing me to rethink my selection process. I was set on this controller, Blue Sky Sun Charger 30, but now I will review that choice.

The biggest difficulty seems to be measuring different usages and discharge rates. For that reason it seems hard to hit the "sweet spot".

Mike, Peter and Jon. Thank you for the discussion and the informative links you provided. Carol, I have to admit I am one of those junkies who loves getting into all of the intricacies of battery charging and getting the battery fully charged.
__________________
Paul Braun is offline   Reply With Quote
Old 03-09-2014, 04:15 PM   #53
Senior Member
 
peterh's Avatar
 
Name: Peter
Trailer: 2005 19 ft Scamp 19 ft 5th Wheel
Oregon
Posts: 1,519
Registry
Quote:
Originally Posted by Mike Magee View Post
. . . I had somehow gotten the mistaken idea that the MPPT controller would act like a transformer during bulk charge . . .
That's a yes and no kind of thing. When you have a higher-voltage set of solar panels, say a "24" or "48" volt system (with actual panel output in the 35 and 70 volt range), MPPT controllers will transform and down-convert the output voltage to match the voltage of your batteries. This is great for fixed installations in homes because, counter-intuitively, running higher voltage systems allows you to use less-expensive, lighter-guage wire to connect the panels to the charge controller and other elements. MPPT controllers are practically required in applications like these because you don't want to charge a lead-acid battery at voltages more than around 1.75 times the voltage they hold when fully charged. (Above this number the current overcomes the resistance of the battery, causing a short circuit that is dangerous to the battery and any people nearby.)

You can chain solar panels on a trailer, connecting two panels in series (e.g. two 60-watt panels with the negative output of one connected to the positive output of the other) one after the other to create a "24 volt" panel set, and making the system more house-like. The problem with this approach is that, if one panel winds up in the shade, it'll draw the output of the second panel down, and you won't get as much power. Connect them in parallel (positive to positive, negative to negative), and shade on one panel won't steal power from the other.

On the Morningstar "White Paper."

Something to keep in mind: Morningstar's "white paper" is marketing material. Hype. It's largely accurate, but over-values the role of adaptive voltage regulation during bulk charging.

Specifically, their claim that MPPT controllers offer 15% increase in efficiency is accurate, but only during later adaptive, equalization, float phases of operation and at the beginning of the bulk charging cycle when the battery is heavily discharged. During the majority of the bulk charging cycle it doesn't make one bit of difference.

This is because the ideal, maximumly efficient input voltage for charging a battery is around 1.25 to 1.5 times the discharged battery's voltage. Much below this value and the battery will resist accepting a charge (chemists will recognize this as the minimum "activation energy" required), much above and you lose some of the power you're pumping in as heat.

Solar panels pump out around 17-17.5 volts (depending on the panel). That means, right out of the box, a standard panel already puts out the optimal charging voltage for a discharged battery with a voltage of 11.3-11.7 volts (15-25% of its total capacity) or more. That means you would have to very heavily discharge your battery, discharge it to the point where you're damaging it, before the MPPT circuitry offers any real advantage during the bulk charging over simply dumping panel voltage directly to the battery.

That's a complicated concept for a marketing paper to explain, and it doesn't help them sell their expensive MPPT controllers, so they kinda left that little detail out.
__________________
peterh is offline   Reply With Quote
Old 03-09-2014, 04:32 PM   #54
Senior Member
 
peterh's Avatar
 
Name: Peter
Trailer: 2005 19 ft Scamp 19 ft 5th Wheel
Oregon
Posts: 1,519
Registry
Quote:
Originally Posted by Paul Braun View Post
The biggest difficulty seems to be measuring different usages and discharge rates. For that reason it seems hard to hit the "sweet spot".
Yea. As I said in earlier post, "It gets complicated. And, rather than working all the details out I can really see the logic of saying "Screw it. I'm spending the extra $50 and getting an MPPT controller . . . Which is, in the end, what I decided to do for our Surfside project trailer."

When it came time to choose a charge controller, I had two choices on my list, the Morningstar SunSaver 10 PWM controller (about $50) or a Tracer1210RN MPPT controller (about $90). Frankly, neither controller was a bad choice, but I opted for the MPPT controller because, on some days, it might make a difference.
__________________
peterh is offline   Reply With Quote
Old 03-09-2014, 05:28 PM   #55
Senior Member
 
MCDenny's Avatar
 
Name: Denny
Trailer: Lil Snoozy
Michigan
Posts: 551
Questions about solar power

I appreciate all the discussion too. Maybe the people who really know this stuff could comment on what I envision my scenario to be:

Start camping with a full battery. During the day my (didn't buy it yet) 100 w panel will put out about as much energy as I consume. Load is intermittent 4a draw from the fridge (maybe on 1/3 of the time) and (worst case) a couple of hours of 6a draw to charge the computers. Assuming a 12 hr day that's 28ah consumption. The panel should give me exactly that "on average" in S Fl in the winter. So I'm thinking I'll still have a full battery when the sun goes down. Night time use would be fridge on 1/4 of the time, 12ah and maybe another 2ah for lights. I'll get up in the morning with the battery at a soc of around 92%. Every day my soc will drop another 8%. After a week I'd still be at 44% and be thinking about plugging into shore power somewhere.

Does this sound right? Would PWM or MPPT make much difference?

Thanks.
__________________
MCDenny is offline   Reply With Quote
Old 03-09-2014, 05:43 PM   #56
Senior Member
 
MCDenny's Avatar
 
Name: Denny
Trailer: Lil Snoozy
Michigan
Posts: 551
Another question, I'm liking this

http://www.renogy-store.com/100watts.../rng-100db.htm

It's the same output and area as a regular 100 w panel but is only about 1/4" thick and weighs 4 lbs instead of 16.5 for their regular glass panel. I could store it under the bed and it's light weight would make it easy to carry outside and place in the sun.

It would seem ideal to stick to the roof too but I think the hassle of setting it up would not be worse than keeping the rooftop panel clean. Plus with the portable we would get more sun exposure.

Anybody have experience with these kind of panels?

Thanks.
__________________

__________________
MCDenny is offline   Reply With Quote
Reply

Tags
solar, solar power


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Solar power added to my scamp Joe N Modifications, Alterations and Updates 9 05-10-2010 10:29 AM
Getting started with Solar Power Anne3358 Problem Solving | Owners Helping Owners 7 02-19-2010 12:14 PM
Xantrex power pack with solar panel Daniel V. Modifications, Alterations and Updates 9 03-05-2008 09:26 AM
Residential Solar Power Mary F General Chat 13 10-22-2006 07:09 PM
Solar Power Andrew D Modifications, Alterations and Updates 9 08-20-2006 07:27 PM

» Upcoming Events
No events scheduled in
the next 465 days.
» Virginia Campgrounds

Reviews provided by


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 08:38 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.