Building my solar system for "The T@Bin In The Woods"

ColoradoJon

rfuss928 said:

Jellybones11 said:

 I am in market to find a MPPT controller right now and am looking at the Renogy but the one you have looks quite competent. 

MPPT controllers are a technology that is able to help capture the excess voltage at a panels Maximum Power Point.  This MPP only occurs under near perfect conditions including low temperatures, ideal alignment and crystal clear atmosphere.  Think Denver on a blue winter day at noon.  A condition that rarely exists with our small portable systems.   The technology can not and will not capture any additional energy in less than optimum conditions and is actually less efficient than a standard PWM controller under most conditions.
IMO...The extra cost of the MPPT controller is better spent on additional panel wattage which will always produce more energy. 

This!  Even in perfect conditions you will see very little gain in these small systems.

phulishcat

Ok, so there are many people who will say the mppt controllers are a waste of money. However, pwm cannot take extra voltage and convert it into amperage. with a pwm controller in place my 200 watts of panels took on average 5.6 hours to fully recharge our battery bank. With the mppt controller we are back at full power within 2 to 3 hours of sunrise. This has held true at lakes in the forest and on overcast days. I wont say that there is no truth to the near perfect conditions theory, however as they say the proof is in the pudding. (honest disclosure i pretty much only camp in AZ)

dsatwork

@phulishcat not sure how you pull that off in forest. I pretty much have the same setup and was dry camping in Idyllwild last fall in a campground that had pretty good cover of trees and I couldn't get much charging going at all. I assume there had to be some exposure to the sun? Idyllwild is in the mountains we couldn't really see the sun until about 10am and there weren't many hours where we got a direct hit on the panels.

ColoradoJon

@phulishcat - You still need to be careful about the type/size/specs of the controller that you buy.  You need to make sure that the one you get can push the proper amount of voltage to the batteries.  If you are not getting 14.4v or higher at the batteries you will not charge as fast or as full.  Voltage is just as important as amps.  Of course this is just a rule of thumb and really depends on your needs/battery capacity/length of runs/wire gauge (voltage loss over distance).  You need at least 14.4V *at the battery*, and some batteries require even more voltage.  The Trojan 105 6V golf cart battery recommends at least 14.8V for optimal charging, and some AGM batteries require even more.

You may certainly be seeing a difference between the mppt controller and the pwm controller, but I doubt that the difference its due to the mppt function.  More likely the mppt controller that is giving you better performance is due to a higher voltage output.

rfuss928

phulishcat said:

with a pwm controller in place my 200 watts of panels took on average 5.6 hours to fully recharge our battery bank. With the mppt controller we are back at full power within 2 to 3 hours

You describe a 100% increase in charging rate!!
Even the most optimistic advertisements for MPPT controllers only claim a 30% increase.  The reality is 5-10% at optimum solar conditions with a deeply depleted battery.
Clearly something else is effecting your observations.

dsatwork

@phulishcat Just to be clear, I wasn't saying that you can't do what you say you're doing. I was more asking for clarification of the conditions and explaining my less impressive results. We both have 100 watt panels placed in the the same positions and we both have mppt controllers, I have 2 100 watt AGM and you're running with 6v flooded, so I should have the advantage on charging speed. I supose the wild cards are the controllers, have a Victron BlueSolar 75/15 MPPT charge controller.

I want to learn how to get better results. My primary purpose for fixed solar is for recharging the batteries with the fridge set to dc. We maximize our time off by driving long days as we run up and down the west coast and travelling in the South West. So far it has worked great for that. I would like to get better results when I'm dry camping, but I suspect that is where the portable panels, have an advantage over permanently mounted panels. We do have a 60 watt portable that has been a great help while dry camping when we can't get in the perfect placement to make the most of the panels we have installed.

Also, I find it very hard to really know how much the battery has really charged until evening and everything is turned off. During the day there is a constant charge on the battery that shows up as 13.4 or so on the Seelevel monitor. At night when you're using lights and such it shows lower than it really is.

Sharon_is_SAM

ColoradoJohn- I recently read Handi Bob’s Solar annual update.  Interestingly, he recommends charging AGMs at no more than 14.4 V.  It sounds like he had premature battery failure.  I know the conditions he uses Solar are much different from most Tabbers travels, but he has real world experience and I believe very insightful info.  He questioned a battery corporations recommendation for charging.  Check it out.

phulishcat

@rfuss928 , I too was confused about the massive increase in charging however I chalked it up to a cheap pwm (you get what you pay for) and the 30% increase. However I assure you that multiple people have seen the results in person.  Honestly I would need an electrical engineer to help figure out what exactly is going on. 

@dsatwork, totally understand the need to figure out less than stellar performance.  Also i believe location of where i camp has much to do with the effectiveness because if I am in Forest and cloud-cover both there is a quite noticeable drop in power production. Also the forest in norther AZ almost always lets a fair amount of sun through. 

@SAM is this Handi bob's solar online somewhere if so link please?

lastly anyone who wants to check out my setup I will be at T@bazona and would love feedback.

Sharon_is_SAM

http://handybobsolar.wordpress.com/

ColoradoJon

@SAM - yes, I am very familiar with Handi Bob!  His observations are spot on.  Notice that I said *some* AGM batteries, not all of them

Always check the charging specifications on the particular batteries that you have.  They vary quite a bit.

Sharon_is_SAM

Yes, I need to check our specs.  

laetulos

One suggestion, we did this without drilling any holes by putting the cables through the roof vent. Well, we did need to drill a whole in the vent on the inside, but that is easy, invisible, and harmless when plugged with plumber's putty.

jkjenn

I like this configuration, a lot and have been thinking about doing something very similar. Yes, I know you cannot park in the shade, but it might be worth keeping my portables for that purpose and utilizing this configuration for shorter stops and when I am parked in the sun.

phulishcat

@laetulos, we did not go through the roof vent we went under the T@B and used the holes for the propane lines. unless you want to mount the remote monitor you don't have to drill any holes.

@jkjenn, with my system i can get full charge in only a few hours in partial shade.

jkjenn

phulishcat said:

@jkjenn, with my system i can get full charge in only a few hours in partial shade.

I usually can, too. MPPT controller was a good decision, for me.

laetulos

@phulishcat Good thinking. We had considered that but then we looked at that vent and saw how easy it would be to run the cables through it, looked more difficult to pull off the trim. Just to clarify, the vent we used is the black vent for the plumbing.

About production: I put on 1 100w panel because on my previous pop-up a 50 watt panel was adequate to never worry about it again. Panel placement is same as everyone else. Several thoughts: 1) in the winter if facing south, I max out at just under 80 watts, seems acceptable. 2) If it is parked facing north no shade, (I got a ticket for parking the wrong direction on my residential street???) I get a max of 24 watts from the panel. 3) The fridge seems to draw a LOT of power, with the fridge set on 1 and the panel moderately well placed, the power is low enough after 2 days that the heater stops working, with the fridge off and sun we get up to a full charge during the day. 4) I'm thinking about adding 2 panels so I don't have to worry about it.

phulishcat

@laetulos, what voltage are your panels? pwm doesn't get any advantage from voltage while mppt does.  also it is said that you really do need to match your panels...i have a matched pair from the same manufacturing run sequential serial numbers.  but i have read multiple places that you don't want to add 80w to 100w etc.

pthomas745

And the reason for not matching panels is what, exactly?

laetulos

Sorry, been out a while. Well, they rate the panels at 12volts, BUT, my MPPT controller typically reads somewhere between 12 and 18 coming in, really depends on how much they are generating. There is a lot of information on matching panels, most of what I've read indicates that it denends on the charge controller you are using. An MPPT controller should be able to handle panels with different watt ratings and different volts, it just adds up. My controller can handle up to 300 watts total with a 12 volt battery (twice as much I think with a 24volt battery), so adding 2 more 100 watt panels SHOULD I think, scale pretty much perfectly and perhaps keep the fridge running in the summer... cold beer!

rtolan

More good info. Thank you. Just met with my solar installer and this info was so helpful. ALMOST know what I'm talking about. Can't wait to get out.

morey000

rfuss928 said:

Jellybones11 said:

 I am in market to find a MPPT controller right now and am looking at the Renogy but the one you have looks quite competent. 

MPPT controllers are a technology that is able to help capture the excess voltage at a panels Maximum Power Point.  This MPP only occurs under near perfect conditions including low temperatures, ideal alignment and crystal clear atmosphere.  Think Denver on a blue winter day at noon.  A condition that rarely exists with our small portable systems.   The technology can not and will not capture any additional energy in less than optimum conditions and is actually less efficient than a standard PWM controller under most conditions.
IMO...The extra cost of the MPPT controller is better spent on additional panel wattage which will always produce more energy. 

There is some truth to that, as in many conditions, a PWM controller will be just about as good as an MPPT.  An MPPT controller is never worse- but for a low cost system, it may or may not be worth it.
Here is a terrific white paper from Victron on the performance difference.  https://www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf

Lemme' summarize:   Firstly:  Power = Voltage (V) x Current (I).  (important to know)

If it's sunny, a PWM controller will spit out current AT your battery's voltage.  So, if your battery is low, let's say 12V... you get 12V x your panel's current output (Ip).  Even if your panel voltage is higher. Whereas For a MPPT controller- it's a DC to DC converter.  If your panels are at 17V and batteries are at 12V, it's using all 17V x Ip, instead of 12V x Ip.

The other common case when MPPT is better is if your panels are putting out low voltage (below battery voltage).  Either due to partial shade or very low irradiance.  With a PWM controller- if panel voltage is lower than battery voltage.... you get nothing.  Whereas, the MPPT can turn 10V into 14V for charging.  

The great equalizer: HEAT  It reduces panel voltage- so, wipes out a lot of the benefit of having the voltage difference.  your 17V panels may only be getting 14V to the controller... so, it kills most of the benefit.

So- rfuss928 may be right.  A PWM controller might be $20 vs $100 for an MPPT, saving you $80.  You can probably get 50 more watts of panel for that price difference, which would be a more cost effective option.

I saw another post when reading through solar stuff on this forum, where people are putting insulating material behind their flex panels.  While it will reduce the temp of your ceiling- your panels won't have any way to dispense with the heat, and will get quite a bit hotter, reducing their performance.  

jkjenn

A couple thoughts.....

Many MPPT controllers allow you charge at a higher voltage and then convert down to 12v. This results in faster charging, which is convenient for mid-check outs or the summer afternoon monsoons.

Those near perfect conditions are pretty common for folks who camp in the Southwest. After 3 months in Colorado, I only had 1 day where I was unable to recharge to 100% and that was with heavy use and 225ah battery capacity.

The Victron MPPT controllers use algorithms to help you get the most out of lower voltage outputs from changing light conditions and new solar technology prevents partial shading from shutting down charging  (as in the case of the new factory panels.)

rfuss928

morey000 said:

The other common case when MPPT is better is if your panels are putting out low voltage (below battery voltage).  Either due to partial shade or very low irradiance.  With a PWM controller- if panel voltage is lower than battery voltage.... you get nothing.  Whereas, the MPPT can turn 10V into 14V for charging.  

This is a common misconception.

To my knowledge there are no charge controllers that can boost output voltage.  All I am aware of trade excess voltage for higher current at lower voltage.  Many units now can handle input voltages as high as 75 -100 volts and still control outputs in the 12-15 volt range.  This allows running panels in series for higher output voltages at low insolation conditions still having enough output voltage to overcome battery potential.  In this manner the MPPT controllers can provide a big advantage in poor conditions.

morey000

rfuss928 said:

morey000 said:

The other common case when MPPT is better is if your panels are putting out low voltage (below battery voltage).  Either due to partial shade or very low irradiance.  With a PWM controller- if panel voltage is lower than battery voltage.... you get nothing.  Whereas, the MPPT can turn 10V into 14V for charging.  

This is a common misconception.

To my knowledge there are no charge controllers that can boost output voltage.  ...

you're right. Engineers (me) are people who think they know how things work.  And I was imagining a DC-DC converter using a transformer.  Re-reading the white paper:
"Most MPPT controllers cannot transform a lower voltage to a higher voltage... If the MPPT voltage Vm becomes lower than Vbat, they will therefore operate like a PWM controller, connecting the panel directly to the battery."

However... two things:
1.  Panels, even if irradiated at only 100 w/m^2  ( a 1/10th of direct sun)  Still put out near full voltage... they just don't put out much current.  So- if you've got enough light to provide useful energy, you probably have the voltage.
2.  With an MPPT you wire up two panels in series and feed it double voltage.  Gives you two benefits- firstly that if you've got any sun, you'll have plenty of voltage.  Secondly, you'll have half the current of running panels in parallel that you'd need to do with a PWM, so less voltage drop through your cables.  might buy you 0.5-1% efficiency.  granted- not much.

jkjenn

The MPPT controller takes advantage if running panels in series to yield a higher voltage. So, by running 2 12v panels in series, I can send 24v to the controller to be converted to 12v, thus charging more quickly.

The Victron controllers prioritize battery life when charging. This if the voltage is too low, it shuts off. While it might seem that this means a PWM controller is better, because it may not shut off, it is not necessarily better for your batteries.