Multiple different panel size connection

bgu1982

New question..im in now unsatisfied with the length of time my two 135 ah batteries last on full charge. Is it as easy as adding another two batteries? Provided the the panels can charge the of course. And i know they were fully charged because i double checked them with multimeter

bgu1982

I have another possible important question. I got a new mppt controller and have not hook it up yet because i know i have to rewire all the panels. My question is can i hook it up as the panels are already arranged.which would be only temporary. The are 4 25  watt18 v so that would be 72v. 1 more set of those 4 and the 2 100 watt 18 v in parallel. All connected on parallel. I know i have to rewire them but its still works on the old pwm controller. Can i hook that set up as is to the new mppt controller or wait till i rewire them the way they should be?

BB.

In the "olden days", yes, folks simply added more batteries to their system to "increase power". Batteries were cheap, and solar panels expensive.

The real answer is batteries "store energy" and solar panels "generate energy". Adding batteries will help you over 2-3 days of "no sun"--But they will not help if your daily loads (on average) exceed the solar harvest.

So, now we are at the "add panels" option. More panels, more energy harvest, and batteries are kept at higher states of charge (discharging below 50%--Roughly--Reduces cycle life. Letting batteries sit for days/weeks/months at below 75% sulfates them and pretty quickly they permanently lose capacity).

Today, solar panels are (relatively) cheap (15+ years ago, $10 per Watt, today around $0.50 to $1.00 per Watt)--And batteries are relatively expensive. So more panels is both technically and cost effective to give you more energy.

Yes, you can keep the panels all in series for the present for your PWM controller (12 volt battery bank = Vmp~18 volt array; if 24 volt battery bank then Vmp-array~35-40 volts for a PWM controller). (I got lost regarding if you have a 12 volt or 24 volt battery bank)

Yes, you can (usually) wire up a new MPPT controller to a PWM wired array. You probably will harvest a bit less energy--And you don't get the advantages of a "high voltage" solar array (using higher voltage array, use smaller diameter copper wiring and/or the ability to put the array farther from your home in a more sunny location). You will not hurt anything.

With off grid solar--Knowing your daily loads is critical towards designing a cost effective solar power system. And with off grid solar, you will always have a larger array to carry you through winter / a few days of stormy weather--And have a buffer when you need more power (guests, etc.).

More or less, your array/predicted harvest should be ~2x larger than your planned daily energy needs. Of course, part of the equation is how much generator runtime you want (or don't)--Larger array, less genset runtime. It is just the nature of the beast.

There are some things that solar alone cannot resolve--Typically far north (dark winters) and shading you have no control over (tree cover, buildings, even deep valleys).

-Bill

bgu1982

bgu1982

Picture of my new mppt contoller..its a monster compared to that tiny one the harbour frieght cc came with. Cant wait to see what this bad boy will do. Getting two more 135ah batteries and two more 100 watt monocrystaline panels.

BB.

What is your battery bank voltage? 12 or 24 volts? That will affect what the "optimum" solar array voltage will be (and the number of panels in series for Vmp-array).

-Bill

bgu1982

Its is 12v ..let me know any adjustments that need to made

BB.

2x Vmp~18 volt panels in series for Vmp-array~36 volts on an MPPT charge controller @ 12 volt battery bank.

So, that is fine.

The other question is sizing the solar array (total Watts)--Either 5%/10%/13% rate of charge and/or your daily loads (loads vs hours of sun per day)...

Rates of charge (10%+ rate of charge recommended for full time off grid):

• 540 AH battery bank * 14.4 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 505 Watt array minimum
• 540 AH battery bank * 14.4 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 1,010 Watt array nominal
• 540 AH battery bank * 14.4 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 1,313 Watt array "typical" cost effective maximum

And then there is calculating the solar array based on hours of sun and Watt*Hours of loads per day (by season).

For example... Say you use 25% of the battery capacity per day:

• 540 AH * 12 volt bank * 0.85 AC inverter eff * 1/2 days storage * 0.50 max discharge = 1,377 WH per day (over night) load

If you have a 1,377 WH per day load, and 4.85 Hours of sun per day (October--See previous post for details):

• 1,377 WH per day * 1/0.52 off grid system AC efficiency * 1/4.85 Hours of sun per day (October) = 546 Watt array for October

Questions include, what is your average daily load (vary by season)--Do you want to run a genset in the winter? And you should up size the array by almost 2x if you want to reduce genset usage and you need to support loads every day (vs only use when sunny weather).

The maximum array for your 40 Amp MPPT charge controller (typical cost effective maximum--check manual, it may be less) for a 40 Amp MPPT charge controller on a 12 volt battery bank:

• 40 amps * 14.4 volts charging * 1/0.77 panel+controller deratings = 748 Watt array "typical cost effective" maximum

You need to review the manual to ensure that you meet all of the electrical requirements for the array.

And you need to mount the panels, electrically connect them (series fuse per parallel string connection) and such...

-Bill