inexpensive panels

Final analysis/thoughts: If you ONLY want/need a 200-250w system....

The 250w MPPT package SunTan Solar offered for $165 includes just about everything including 2 fuses. That does not include shipping. I put in my shipping info to Central California (the company is in Gilbert Arizona near Phoenix). The shipping cost was between $180-$300! So it looks like having it shipped would be a deal breaker. BUT...if you can pick it up locally in Gilbert, Az (...which I might be within 10 miles during an upcoming family visit :)), picking up this package for $165 seems like a good deal.

One alternative would be to buy a 200w PMW system from Amazon (ie. WindyNation, etc) and pay ~$280 shipped.

I have two RVs. I already did purchase a 200w WindyNation kit for one of my RVs (still need to install). I think what I will do is pick up one of these SunTan Solar 250w systems and put it on my other RV. Then (if I ever get around to it) I can do a test between the two and provide you all with a comparison/update just for fun. I have an Aili battery monitor on both and I can see exactly how many amps are flowing into or out of the batteries. Will be interesting to see how a New 200w panel (2x100) on PMW does compared to a Used 250w panel with MPPT.

As long as the 250w used panel puts out as much charging capacity as the 200w new panels (which seems like it should easily accomplished) I will be happy as it cost 70% more for a New WindyNation 200w system compared to a Used 250w SunTan Solar system. I assume that will be the case. In fact, I think I'll even pick up an extra SunTan Solar 250w used system as long as I'm there (...I'll likely be adding a 3rd RV to my "fleet" in the spring).

Thanks all for the knowledgeable discussion/info.

-Chris

One last question: Have any of you purchased and installed one of these SunTan Solar systems? If so, it would be great to hear from you...

Boon Docker,

For equal wattage panels, MPPT may, under some conditions, harvest about 10% more. But it has to be a quality MPPT. Research heliotrope controllers for an example of a lousy mppt.

So with 12 volt panels, given current low costs--it may be better to do an extra panel.

On the other hand, if you want every erg of power--populate the entire roof, use electronic actuators for tilting, and use a top of the line MPPT controller.

If you go that far, then consider jumping to a 48 volt battery bank, with SiO2 batteries for storage.

Gdetrailer wrote:

MPPT does not always "equal" "more power" or "longer charging" either, there are limitations on how much energy the panel can actually efficiently garner from the given strength and duration of the sun that falls on it. MPPT attempts to maximize what can be harvested but in many cases you will only be talking in fractions of Ahrs per day over a PWM controller with a single 24V panel. Not uncommon for home panel arrays to be wired for 48V and higher..

Could you possibly show how many fractions of AHrs harvested: Using PWM and MPPT controllers using the panels below with all conditions being the same.
- 250 watt 24V panel (VOC 37 V - Imp 8 A)
- 250 watt 12V panel (VOC 20 V - Imp 12 A)

Hi Gde,

The $165 kit includes a controller, hardware, and panel. It is not expandable.

They offer other kits as well--which come with a 50 amp MPPT. That seems to me to be an 'odd ball' size.

I'm glad solar prices have dropped. Perhaps it is time for me to expand the system and get a 1000 watts (or more) on the roof.

What has held me back in the past is the cost of a large MPPT controller that will function with a 12 volt output. My current mppt works well, but is pretty much maxed out for solar input, so if I add panels it is an "ouch".

There is no question in my mind that new panels are preferable to used ones. On the other hand I have champagne tastes and a beer budget.

pianotuna wrote:
Gde,

The company sells a 250 watt with 20 amp mppt controller for $165. Considering my system was $1700.00 in 2005 it is a heck of a deal.

They also have some larger 50 amp mppt controllers sold in a kit for a few dollars more. That is what I'd advise, as they can add some panels that way.

Goodness knows whether the controller or panels are great, poor, or bad.

Sadly, with pretty much anything electronic, you cannot "compare" cost of something that was "cutting edge" 15 yrs ago.

Cost of panels back then was well above $5 per watt and MPPT was pretty much in its "infant" stage of life.

Like I have mentioned, you can buy two new "12V" 100W panels and even get a 30A PWM charge controller for $200 now days..

Kind of takes the starch out of the savings that one lonely $50 24V 250W panel is going to cost once you buy the proper MPPT controller which you mentioned from the same vendor is $165..

From my math, that used panel setup is $215 (with your MPPT price quote) and that doesn't include shipping.. And you still have a used panel, while they do have relatively long life, it won't be as good as a new one starts out or the used panel may have a few dud cells rendering it with less voltage and capacity..

Not to mention a 250W panel is huge and may pose difficulties on some RVs with other things on the roof..

MPPT does not always "equal" "more power" or "longer charging" either, there are limitations on how much energy the panel can actually efficiently garner from the given strength and duration of the sun that falls on it. MPPT attempts to maximize what can be harvested but in many cases you will only be talking in fractions of Ahrs per day over a PWM controller with a single 24V panel. Not uncommon for home panel arrays to be wired for 48V and higher..

You roll the dice and take your chances, but to me this panel is really more suited for folks setting up a 24V or higher battery system which opens a whole nuther can-o-worms..

In other words, you would have to REALLY "want" these panels to go through the trouble of making incompatible voltages work together.

It looks like you got your answer, you will have to up your controller.

I really just want to comment on your WindyNation system. I bought the 100watt system and added a second 100watt panel. It is doing well we have camped twice since I installed the system and in the 20 days we have been camping we have not needed to run the genny. We have two interstate GC1 batteries from costco that are about 2 years old.

We are moderate in power usage and run the 32 inch tv and the BluRay about 3.5 hours a night. The system is really worth it and I am very happy.b

SJ-Chris wrote:

Tom_M wrote:
That controller is a PWM. You need an MPPT controller.

Is it truly REQUIRED? Or is it just a preference?

I understand that the MPPT controllers might be a little more efficient. But the system I'm creating is probably an overkill anyways for my needs so I'm not worried too much about squeezing out every bit of efficiency.

-Chris

Chris it is truly required--either that or move to a 24 volt battery bank--I would not advise doing that at this stage.

Gde,

The company sells a 250 watt with 20 amp mppt controller for $165. Considering my system was $1700.00 in 2005 it is a heck of a deal.

They also have some larger 50 amp mppt controllers sold in a kit for a few dollars more. That is what I'd advise, as they can add some panels that way.

Goodness knows whether the controller or panels are great, poor, or bad.

Output for a 12v battery system is 14.+ volts
Or the batteries will not get fully charged,
PWM will supply nearly the same output amps as
The panel produces, but at a reduced 14v , meaning less actual watts charge into the battery,
MPPT "maximum power point tracking" makes sure the battery is supplied with nearly everything the panel is putting out, it reduces the voltage from the panel, but increases the amps going to the battery so nearly all the watts of power goto the battery, the MPPT controller is a DC to DC voltage converter,
Example 30v at 6amps from a panel is 180w
15v at 6 amps PWM is 90w to battery
The MPPT controller will supply most of the 180w solar power for charging instead of cutting it in half, somewhere like 140 to 160 watts, control output amps would likely be around 10+ amps , there is some controller conversion loss, they are not 100% efficent, that's why they big finned heatsinks to disperse the heat produced in the conversion, just like chargers, converters, and inverters

SJ-Chris wrote:

Tom_M wrote:
That controller is a PWM. You need an MPPT controller.

Is it truly REQUIRED? Or is it just a preference?

I understand that the MPPT controllers might be a little more efficient. But the system I'm creating is probably an overkill anyways for my needs so I'm not worried too much about squeezing out every bit of efficiency.

-Chris

MPPT is required if you are planning to use any panel over 17V with a 12V battery system.

Pretty much every cheap or low cost solar controller is PWM (Pulse Width Modulated) which are not designed to drop that 30V output of the panel to 12V..

MPPT controllers are much more expensive that PWM and GOOD MPPT controllers are even more expensive yet.

Hence a lot of your savings on that 250W 30V panel goes right out the door..

HERE is a Amazon search of MPPT controllers.

And looks like entry level MPPT starts at the $100 level.

I noticed one that was insanely cheap price, yeah, that one IS NOT MPPT once you start reading the information and reviews.

You have to shovel through a lot of marketing double speak and sometimes the lies to figure out if it is MPPT or not.

If you can find the manuals, read them before purchasing, you will need to make sure that the controller is able to take a higher voltage like 30V or even 60V and output 12V for a 12V battery.

So the reality is you spend $50 on a that panel, $100 on MPPT and we haven't even discussed the shipping which will be most likely better than $50 and if you are lucky the panel arrives in tact and working..

You can buy 2 100W 12V panels plus PWM controller at Amazon for around $200 and if you have Prime, might even be eligible for free shipping on top of that.. Pretty much makes that used panel a lot less of a "deal".