Lower Power or Higher Power panels?


#1

I am planning a PV solar system for my off-grid home in the Philippines. As a solar newbie I need some expert opinion(s) on a recent exchange I had with a solar panel provider in China. I had requested a quote on some different models of panels and they quoted 275 watt panels, even though they offer higher power panels. Their reply to my question as to why they did not quote the higher power panels follows:

  1. Why recommending 270W/275W: Please see below:

Panel Working Voltage Off grid voltage Conversion Rate

270W 31.1V 24V 24V/31.1V=77%

275W 31.3V 24V 24V/31.3V=76.6%

300W 32.8V 24V 24V/32.8V=73%

325W 37.5V 24V 24V/37.5V=64%

370W 39.4V 24V 24V/39.4V=61%

The principle is that no matter what solar panel voltage, it could only charge a 24V system ( if you need 48V system, you need 2pcs, the principle is same), so the system voltage is fixed, it is 24V or 48V, then the total watt you get is 24V multiply by the current, so the voltage is wasted, no need to use high voltage. So I recommend 270W or 275W, it is enough. Or you can also choose PERC mono 300w, but price is expensive than poly.

I’m a little confused by their explanation as it is my understanding from reading other solar blogs that the output higher power panels would not be wasted but would in fact charge my battery bank more efficiently?


#2

Hi chewface

That doesn’t make a lot of sense to me. I guess it depends somewhat on how the system is setup. Do you know if you are planning a DC coupled or AC coupled system? Or what type of inverter/charger you’ll use?

See our page here on Battery Systems for more info https://www.cleanenergyreviews.info/energy-storage/.

Cheers
Marty


#3

Hi chewface (haha great name)

The information they supplied is for old PWM solar charge controllers. With the modern efficient MPPT solar charge controllers the panel voltage does not matter at all. Who is the solar panel provider? If they are giving you this bad advice I would not purchase from them.

How many panels are you purchasing? What type of solar charge controller are you using? I would recommend the Victron MPPT controllers if they are available in your area.


#4

Hi Jason;
Thanks for your reply and insights. This China company is an Alibaba solar distribution company that sells a range of products from Canadian Solar, Trina, Jinko, etc. I don’t think the sales rep that I am speaking with is an ‘expert’ on solar system design, which is why I’m asking for input from experienced solar gurus like yourself.

FYI, I’m planning a ‘near off-grid’ PV set-up i.e. the PV system/batteries will be my primary power source with the (very unreliable) grid used strictly as a back-up to charge the batterybankj in case my panels fail for whatever reason and with a generator as a emergency 2nd back-up.

My current monthly electricity usage (in Singapore) is approx 500kWH monthly but as I will be living in a rural environment (in the Philippines), will need to add the power needs for a water pump, security cams and a workshop :slight_smile: . Therefore, am planning on 30 PV panels feeding a 600AH LifePo battery bank.

As for the charge controller, I’m completely undecided. A local solar installer in the Phils recommended “Axpert” MPPT controllers, which apparently are widely used in Australia. The Victron CC’s are very expensive in this part of the world.

Any advice or guidance you and other solar experts could offer would be much appreciated.

BTW, my nickname “chewface” was given to me, by my sister when we were kids…before FB was even invented!

Thanks for your help


#5

Marty;
Thanks for your reply.
Being a solar newbie I’m unclear by your reference to a “DC or AC-coupled system”. Do you mean grid-tied?

As explained in my reply to Jason, I am planning on the PV system as my primary source of power. I plan to connect the grid through a manual switch only as required in the event that my PV panels fail to charge my battery bank sufficiently.

As you recommended I will spend time reading through the materials on solar CC’s and inverters. Sure this will result in more questions!

Appreciate the support of solar-minded experts like yourself.

Brgds,
William (Singapore)