Solar Panel Arrangement

Moxie96

Hi - I'm new to the website and I'm hoping to get some help on an exisitng camp solar system. I'm a electrical engineer with a PE in the state of Maine and I do P&C design on substations/transmission lines at the 115000v and up level so my solar experience is limited. I have installed solar power in 3 camps so far.

A good friend of mine wants to upgrade his camp solar system. Currently he has 2 - 110 watt solar panels on opposite sides of the roof peak. He wants to add a 3rd solar panel (200 + watts) on the front part of his roof. This will result in 3 solar panels facing different directions but all 3 will get direct sunlight at different times thru out day.

I have verified the charge controller can handle the additional panel. I have 2 questions:

-The solar panels with be connected in parallel so I don't see any problems adding the larger panel - correct?

-Does having the panels in different locations and each one receiving peak sun at different times cause any problems? I've heard that one can absorb power from another if they are not operating nearly the same wattage but that really doesn't make sense to me.

That's all I have for now. Thanks in advance for any responses.

Jim45D

Re: Solar Panel Arrangement

Moxie96 wrote: »

I have verified the charge controller can handle the additional panel. I have 2 questions:

-The solar panels with be connected in parallel so I don't see any problems adding the larger panel - correct?

-Does having the panels in different locations and each one receiving peak sun at different times cause any problems? I've heard that one can absorb power from another if they are not operating nearly the same wattage but that really doesn't make sense to me.

My three cents worth: I have done the same thing in the past, and I referred to it as "Stationary Tracking", that being that the panel itself doesn't move, instead the sun obviously does. It will work, but I discovered that you lose effeciency, and perhaps it creates some confusion with the controller. Is the controller MPPT? At any rate to achieve full efficiency.....a controller for each panel was the way I went. Quite an improvement.

icarus

Re: Solar Panel Arrangement

You must use an MPPT controller, or 3 separate controllers, or you will lose a HUGE percentage of you out put.

Welcome to the forum and keep in touch,

Tony,

BB.

Re: Solar Panel Arrangement

Slowing down a minute--If the three panels have Vmp~17.5 to 18.5 volts and you are using a PWM-Pulse Width Modulated (not MPPT-Maximum Power Point Tracking) type charge controller, then paralleling panels with different orientation is not an issue at all... Their Vmp voltage will be >~15 VDC and their output current will be proportional to the amount of sun hitting each panel.

If the panels are connected to a MPPT type charge controller--You may have problems with the controller trying to find the local peak for Pmax=Vmp*Imp where Vmp varies with temperature--So you could have two or three local peaks, varying across the day, which would probably confuse the MPPT software/function (MPPT algorithms typically are not designed to find the highest peak--and in any case, you cannot get optimum power with a single MPPT controller if there are two or more peaks).

If this was a MPPT charge controller--You would need to monitor its current output during the day and make sure that it is outputting what you would expect.

-Bill

Cariboocoot

Re: Solar Panel Arrangement

The larger panel will in all likelihood have a Vmp that is too far off to be used with the existing panels. Small panels around 110 Watts usually have a Vmp of about 17.5, whereas the 200 or so Watt panels tend to be in the neighbourhood of Vmp 30.

Putting panels that point in different directions, even if they are the same, can mess up MPPT controllers. PWM type don't much care as they simply pass whatever current is available.

On the whole it's not the most ideal situation. I'd be getting a handle on loads and re-evaluate the system as a whole. Stationary tracking with a system that small usually doesn't make much sense. 220 Watts existing panel is only good for a 140 Amp hour 12 Volt battery, and it should be receiving full charge from both panels at the same time in order to maximize the charge current and bring the battery up quickly.

When you do a stationary tracking system, the "East array" is usually largest to bring the batteries up fast, the "South array" sized to maintain Absorb and Float, and the "West array" big enough to keep the system in Float as long as possible.

For a small system such as you describe, one array of the right size aimed in the right direction will function better and be less of a problem to put together.

BB.

Re: Solar Panel Arrangement

Yea--I missed the 200+ watt panel... Other than Evergreen (now out of business), there are few >100 watt panels with Vmp~17.5 volts (for 12 volt battery bank). So, depending on what panel is purchased (Vmp>~18.5 volts), you will need a MPPT charge controller for that one panel (or group of similar Vmp/Imp panels).

If you use a ~30 volt panel on a 12 volt PWM controller, the losses would be, roughly:

17.5 Vmp ideal / ~30 volt Vmp for large wattage panels = 0.58 = 58%

Unless a MPPT controller is used... Some controllers you might look at:

Morningstar SunSaver 15 Amp MPPT Solar Charge Controller
MPT-3024 MPPT PV Charge Controller 30A - 12V/24V
Morningstar TriStar 45 amp MPPT solar charge controller

The above range from ~$225 to ~$400 and are all good quality product. If you go larger output current, there are more options available (upwards of $500-$600 each).

-Bill

Moxie96

Re: Solar Panel Arrangement

Thanks for the replies. I waited to respond because I wanted to find out what charge controller is being used. It's the Solar Boost 2000E 12V/25A MPPT.

Based on what I'm gathering here, there's a possibility that we are losing efficiency with the panels being on opposite sides on the roof peak with this charge controller.

My friend doesn't want to relocate the panels to a different location as the holes and mounting is already there. He says one side gets peak sun in the AM and the other gets peak sun in the PM.

Would the following changes work depending on his budget?

-Put the 2 existing panels on same side and run thru existing controller
-Add 2 similar panels to other side and add separate controller

He wants to add more charging - I want to help him get the best set up he can with what he has. Any advice will be appreciated.

Thanks. Tim

Cariboocoot

Re: Solar Panel Arrangement

Yes, if that's within his budget:
Adding more panels will add more charging power. Putting arrays that face in different directions on separate controllers will improve the efficiency.

westbranch

Re: Solar Panel Arrangement

you can not connect 3 panels with more than 20 amps

Section 4. of the SB 2000e manual:
h) Do not connect to a PV array capable of producing greater than 20 amperes of short circuit current (ISC) or 24V of open circuit voltage (VOC) @ STC.

HTH