System design question Philippines - more panels vs bigger batteries

Hi Everyone,
I’m now in the late stages of finalizing a system design for an off-grid PV system for my retirement home in the rural Philippines. The public power grid here is notoriously unreliable with at least one of more brown-outs every week, some lasting 24+ hours. To boot, grid power is very expensive.

However, while the cost of PV panels have fallen a lot, the cost of batteries, esp LifePo, remain quite expensive. Therefore, before soliciting supplier bids for a system, I would appreciate the advice of more experienced solar experts, on whether it makes sense to buy more PV panels as a way to reduce the size and cost of a battery bank.

My thoughts are that with enough PV panels, even on a cloudy day, the system could generate sufficient power to serve most of our essential household needs, or at least extend the capacity of our batteries.

Not sure how the charger controller would handle the ‘excess’ power being generated by panels on a sunny day though…

Would be grateful for any guidance.


Hi @chewface

The issue is that you will have stormy periods (as I know there are many of in the Philippines) where there simply isn’t sun, and all the panels in the world won’t help you with that. Either way you will need a backup generator, I trust you are considering that in the mix, or perhaps you already have one?

You’ll need a proper system design by an off grid expert designer to size your system correctly. It will save you enormously in the long run. There are already a number of threads on this forum regarding systems in the Philippines that aren’t working well due to lack of design. Assuming there is no one with the expertise locally, perhaps there are off-grid experts elsewhere in the Philippines that could work with someone locally?

You can find similar threads regarding off-grid systems in the Philippines here, perhaps some of these posters could help.

I hope that helps.


@chewface oversizing solar is quite common these day and isn’t generally an issue when using DC-coupled MPPT solar charge controllers. When the batteries are full on a sunny day the MPPT charge controllers just reduce the power output to a minimum amount. When oversizing solar, just be careful you don’t put too much current into the batteries during charging. LiFePO4 batteries have a maximum charge rate.

Also, as @Marty suggested you should get someone experienced with off-grid solar to help or you could end up wasting a lot of time and money.


Hi, We are here in PH as well. Our primary system has, right now 4 60amp charge controllers with 32 360 watt panels for a 10kw inverter. We have perfect Azimuth Alignment and have the panels adjustable for 3 seasons. We are going to add lifepo4 batteries soon, 4 sets of 16 280ah, we have been planning the design for 20-30 hours without any sun. We are also adding another 9 360 watt panels and another charge controller to boost the system a bit more. Right now, when the inverter actually works we make enough power on a cloudy day to maintain the battery charge, but when the rain is really bad, we don’t make enough. You need an inverter that uses separate charge controllers so you can use additional panels without overloading. Make sure the charge controllers can talk to each other and have settings for LifePO4 batteries so they will work correctly, our do and maintain perfect charge just clipping the excess. I have an Ames 10kw split phase inverter, (we have Meralco split phase utility system) but it has given trouble from day 1, no one can figure out what’s wrong with it and Ames is useless and hasn’t honored the warranty, don’t buy one!. We have found someone who can do the electrical repairs to the inverters boards, but ours still won’t carry a normal load. Be very careful here, many of the “Experts” don’t even know enough to crimp the connectors on the solar panels let alone design and match components. No one I’ve talked to here knows what azimuth, true south (Northern Hemisphere) proper angle for the latitude, correct wire sizing, nor anything else commonly accepted as basic knowledge is. My suggestion is ask here about everything, Svarky and Marty have helped me tremendously so listen to them. If you have the single phase 230 volt system as many rural areas here have, don’t use a split phase inverter as they cost more and won’t do anything for you unless you want 110 volt as well. Most electricians here don’t understand proper ground and neutral installation and watch out for splicing, they love to do that here and many inverters don’t like it. Good luck! Watch your workers closely to eliminate shortcuts, if you’re not from here, most of them won’t listen to you and as soon as you turn your back will shortcut things and splice and tape things. That’s about it. the dog

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