Hello to all,
New kid on the block here. I have been trying to educate myself by reading threads on this forum and one other. I have a couple of areas that I am unsure about and hope the members here can help.
I have a small RV ( 24 feet ). Iam putting together a system for it.
I have decided on a Morningstar Sun Saver MPPT controller. I am limited to a maximum width of 22 inches for the panel.
Especially if I add a second panel later on. Battery Amp hours are 160 at present ( AGM ). Will possible increase to around 260 in the future.
Now the questions. I really wanted to start with a 130 watt panel but spac does not allow it. That leaves me at a typical 80 watt panel as they are about perfect in physical size. However there is another panel that is also perfect in size rated at 100 watts. I know that everyone here is familiar with it. As it has 44 cells it produces Approx. 121.5V. The Morningstar controler will handle plenty of voltage. Is ther an advantage to increase the V to a MPPT controller? If there is something to be gained by using the 100W/21.5V panel? I would feel better paying the premium price they ask for it if there is an advantage as it is the dimension that I need.
If more voltage is desirable, would it be advisable to wire a future panel in series with the firss panel? This would require less wire and allow for less line loss as well. Correct?
Last question ( for now ). I may want to make the panel easily removed for travel. Is there a quick connect/disconnect that I could use in the line? Would I get much loss here.
Thank you,
Lee

> I know that everyone here is familiar with it. As it has 44 cells it

I have no idea what panel it is !

As to the voltage, in cold weather, your panels will produce higher voltages. (maybe 4 volts more at 32F) If you have panels in series, that can start to add up. I don't know off the top of my head, what the sunsaver MPPT limit is.
Running a higher PV voltage IS desirable, as you have less voltage drop( IR Loss) in the wire.
A higher voltage system will also help insure on a hot day (when panels produce LESS voltage) you will be able to achieve a full charge.

A 160A battery, will barely be able to to be recharged with 100W of panel. 2 panels would be better, as you will seldom see 100W of output.

> Is there a quick connect/disconnect that I could use in the line?
> Would I get much loss here.

If your panels come with the new MC connectors, you can use them as a disconnect, but you may need the unlock tool, if you have the locking MC connectors. You must shade or cover the panels when connecting or disconnecting, to have zero current flow, so you don't arc or fry the connectors.

Thats my free nickel worth.

Thanks for the reply Mike.
I was beginning to despair a little waiting for some replies.
The 100 watt panels are marketed by AMsolar. They claim that they are made for them by BP Solar. I have seen some disussion about them on the other Solar forum that most of this forums members also frequent. That is why I thought folks would be familiar with them. I believe that the Morningstar sunsaver MPPT controller would be able to handle the voltage of two of these in series. If increased voltage is good then I will feel better about paying the price for them. My only other choice would be to use 180 watt panels wich are about the same width as the 100 watt/21.5V panels. I guess it would be a no brainer, 80X2=160 compared to 100X2=200.
Would draping the panels with a dark fabric suffice for the connect/disconnect procedure?

I would think so. Just don't forget to drive off, with loose panels on the roof!

Maybe each time you set up the panels, you attach the ignition key to them, forcing you to get on the roof, to get the key.

mike,
i bet thieves love you right now. i would say try to come up with better way to discourage driving off with unsecured pvs than leaving your keys up there.

different drummer,
you could place 2 of those pvs in series, assuming it is the am100 you refer to, but no more than 2 as the sunsaver mppt has a maximum pv open circuit voltage limit of 75v. the 27v open circuit voltage from the pvs will be additive to now be 54v with 2 in series and is not allowing more room for a 3rd pv in series. the only alternative would then be to parallel more of those series strings watching that the current limit of the controller, also allowing for about 10% mppt, is not exceeded as this would waste your precious and expensive pv power seeing as how the controller will hold the output current from exceeding 15a.

Thats what I do with the TV antenna. Hang the keys on the crank.
Actually I plan on hanging the panels on the side of the MH.

Maybe each time you set up the panels, you attach the ignition key to them, forcing you to get on the roof, to get the key.[/quote]

how about something like the club and put the keys to it up there? at least you can take a small walk this way and not worry too much.

Niel,
Thanks for the input.
I will never be able to install more than two panels. So I am trying to get the most charging capability that I can from two panels. As I mentioned earlier I am limited in width. Length is not a problem. 60 inches would be fine. I am still a bit confused as to the volts/Amps thing. The AMsolar panels are capable of more V due to the 44 cell design. However the Amperage raing is considerably lower than other 36 cell panels. I do not have a clear understanding as to if V is more important than Amps. Whenevr I have charged batteries in the past ( not solar ) I was more concerned with Amps going in and in fact was careful to not over voltage the battery. ( especially my AGM's ) I have been reading the solar forums and other sources to try and educate myself, but I remain confused on whether V or A are more important when using the MPPT controler.
If we talk watts then the AMsolar panels are the most watts that I can get into the space I have available. However I guess I am looking for some reassurance that the 44 cell/21.5V panel is not just hype. At $550.00 plus $25.00 repackaging fee plus shipping they get a little pricey for two. There are a lot more options availabe in the 80 Watt market that will fit my space requirements. Not to mention that on my trip west this winter I can simply stop and buy in person. That would eliminate the repackaging and shipping charge. I will be wintering in South West AZ. There are many options of places to buy between upstate NY and AZ.
So I guess to sum thigs up I just do not want to py the premium for the AMsolar panels just because they fit my space needs.
I need to get the most I can from two panels that are no wider than 23 inches. They wll be running through the Morningstar MPPT controler. I appreciate any suggestions from those who know a whole lot more than I on the subject.


different drummer,
you could place 2 of those pvs in series, assuming it is the am100 you refer to, but no more than 2 as the sunsaver mppt has a maximum pv open circuit voltage limit of 75v. the 27v open circuit voltage from the pvs will be additive to now be 54v with 2 in series and is not allowing more room for a 3rd pv in series. the only alternative would then be to parallel more of those series strings watching that the current limit of the controller, also allowing for about 10% mppt, is not exceeded as this would waste your precious and expensive pv power seeing as how the controller will hold the output current from exceeding 15a.[/quote]

i can't speak for the pv or that company, but if it is as it says it will work fine. as to what is more important the answer is going to confuse you some because neither are more important than the other as you need both. you can't always just go by the wattage either (watts = volts and amps times each other) because if you have need of say 29v for an application and the pv is 26.5v then it just won't work no matter how much current there is. if the general voltage requirements are met is when you can turn your focus to the current. the current of 2 pvs like the am100 will not just be what the imp rating is because the current will be increased firstly due to downconversion (if for example on a 12v output for the cc from say a 24v input like from pvs this would equate to 1/2 the voltage out = x2 the current) and secondly the mppt action will add typically 10% more current. your input voltage will be much greater than 24v as you'll be at 54v. you can power either a 12v or 24v battery system with the sunsaver mppt with 2 of those am100s in series. 54v to 24v would be more than x2 the pv imp current and 54v to 12v will be more than x4 the pv imp current assuming they are aimed at the sun during the day or simply put properly illuminated. aren't mppt controllers really great!!! i'm not pushing that particular pv on you and you will have to decide what would be good for you to use, but i did use it for example purposes.
if the pvs you decide upon aren't going to be enough then consider a portable remote ground mount for more pvs that will enable you to pick them up and fold them flat to store in the rv. you can make such a thing as this from aluminum angle and stainless steel nuts and bolts. wing nuts are quicker too. it could also be made to be adjustable and not just portable. think erector set and right triangles.

OK Niel,
Lets see if I got this correct. I noticed that you used open circuit voltage in your calculation.
I will try three different scenarios. For simplicity Lets leave the gains obtained with the MPPT controller out of the calculation. Also when multiple panels are used assume they are in series.

1) 2 AMsolar100 panels, OCV 27 X 2= 54V, 54V/12V= 4.5 multiplying factor
4.5 X 4.54 Imp= 20.43 Amps into battery

2) 1 Kyocera 135 panels, OCV 22.1 X1= 22.1V, 22.1/12= 1.84 multiplying factor
1.84 X 7.63 Imp= 14.04 Amps into battery

3) 2 Kyocera 135 panels, OCV 22.1 X 2= 44.2V, 44.2/12= 3.68 multiplying factor
3.68 X 7.63 Imp= 28.08 Amps into battery

How did I do?
There is one other thing that I am curious about. I understaned the relationship between Volts, Amps and watts. (OHM's law) But, how is the rating of a solar panel arrived at? What came first, the Chicken or the egg? You must know two of the values to arrive at the third. I know that on average one cell in a panel produces 4.88V. Therefore we can calculate the Voltage output based on the number of cells in the panel. Thats one value out of three. We must have one more value to complete the equation. Are all panels tested under known conditions ( ideal ) and amperage output measured? Or perhaps it is theoretically arrived at using a value that represents the suns potential for a given surface area of panel?

I do appreciate the time you and Mike have taken to educate me. Thank you.
If there is anyone else else using this forum, Please chime in.