Design upgrade suggestions

DarkstormNH Registered Users Posts: 48 ✭✭

Gents please read and feedback please


I’m planning a new system in port au prince Haiti.

The load 12 led light bulbs 5 watts each, maximum usage a day 6 hours however not all would be on at the same time.

Projected max 400 watts

A small fridge 1kw day

A small freezer .900k a day

55’ television 75 watts, 5 -6 hours per day

2 phone chargers, and kurig coffee maker (the one cup version) 2-4 cups per day. 

Fan 40 watts 6 hours per night.

I’m thinking the standard 3.3kw I see the usage a day would do

The system

4 panels 


325 Wp Open circuit voltage Voc 47.0 V Maximum power point voltage Vmpp 

37.7 V Short circuit current Isc 9.28 A Maximum power point current 

Impp 8.68

First question do I connect two in series and parallel them?

Later on I would add another two units 

The Charge controller



Nominal System Voltage 12, 24, or 48 VDC (Auto detection)

 Maximum Battery Current 60 Amps Maximum Solar Input Voltage 145V PV Array

MPPT Voltage Range 60~115VDC

Maximum Input Power 12 Volt--800 Watts

24 Volt--1600 Watts

48 Volt--3200 Watts


Question 2 can this unit handle the panels now and adding 2 more later for 6

Would that make sense?



Magnum 4024



The batteries I have 8 t105 now, but I was thinking on buying 4 Trojan l16


Or 4 s-550 surrette




Waiting on feedbacks


  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Even 6 PV panels will not manage those loads well.
    3 Red flags:
    _ Fridge
    _ Freezer
    _ Kurig Coffee maker (unless you put it on a timer for just 2 hours a day ON)

    You need a large enough inverter to handle one of the 3 above loads being already ON, and a 2nd one turning on, with some of your other loads being ON too.

    This needs to be a 48V system, maybe possible with well engineered 24V, but really should be 48V.

    You have not mentioned a back-up generator, or how it will charge the batteries, many 48V inverters also have an integral charger, verify that before purchase.

    Do you have a water pump (well pump)  Any 240V appliances ?
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • BB.
    BB. Super Moderators, Administrators Posts: 33,442 admin
    You also need to add up your loads in Watt*Hours per day (many are just guesses... Things like fridge and freezer may be on the low side of estimates):

    12 bulbs * 5 watts * 1/2 on at a time * 6 hours per day = 30 WH per day
    1 fridge * 1,000 WH per day = 1,000 WH per day
    1 freezer * 900 WH per day = 900 WH per day
    1 TV * 75 Watts * 6 hours = 450 WH per day
    2 phones * 10 WH per day = 20 WH per day
    1 coffee maker * 900 WH = 900 WH per day
    1 fan 40 watts * 6 hours = 240 WH per day
    2,810 WH per day

    Your 3.3 kWH (3,300 WH per day) estimate seems to work... You would have to watch your loads and cut off/reduce some of them during less than sunny weather...

    A good battery bank would supply 2 days of no sun and 50% minimum discharge. Using 3.3 kWH per day for system design:
    • 3,300 WH * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max discharge * 1/24 volt battery bank = 647 AH @ 24 volt battery bank
    Calculating the solar panel sizing, you have two things to watch for. First is optimum charging current of 5% to 13% or so--With 10%+ recommended for a full time off grid home/cabin:
    • 647 AH * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,218 Watt array minimum
    • 647 AH * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 2,437 Watt array nominal
    • 647 AH * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 2,168 Watt array "cost effective" maximum
    And then there is based on the amount of sun you get in your region by season. A fixed array would see somewhere in New Hampshire:

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 47° angle from vertical:
    (For best year-round performance)
    Jan Feb Mar Apr May Jun
    Jul Aug Sep Oct Nov Dec
    Toss the bottom three months (assume you would use a genset), we get the "break even" month as October with an average of 3.79 Hours of unobstructed sun per day (trees/mountains/etc. can reduce amount of sun):
    • 3,300 WH per day * 1/0.52 average AC off grid system efficiency * 1/3.79 hours of sun per day = 1,674 Watt array minimum
    So--The first question is do you have enough panels in your plans? Do you use less power in winter (no fans, fridge/freezers in cold rooms/outside use less power)? Do you plan on using a genset a fair amount in the winter? Will your system be shut down in winter? Should you tilt the array to near vertical in winter to shed snow better (usually full/snow free array not needed if not occupied during winter)?

    Don't know about this specific EBay MPPT controller... But, in general, for a 24 volt system you would want ~Vmp-array of ~38 volts minimum. Placing two panels in series would probably be better overall (smaller diameter copper cables from array to battery shed).

    I suggest the larger 10% charging system (2,437 Watt array) if you will be using power during the day (fridge/freezer/TV) as this will mean you will not have to monitor your daily power usage/battery charging as closely (day time loads reduce charging current to battery bank). And, over all, less genset use in the winter.

    Realistically, the largest suggested AC inverter (and solar array) is ~500 Watts per 100 AH of battery bank (at 24 volts). So, for a 647 AH battery bank, that would be ~3,200 Watts of AC inverter / Solar.

    The Surrette S550 batteries are ~428 AH per 6 volt cell... So your 24 volt battery bank will be either 24 volts @ 428 AH or 856 AH (4x or 8x batteries).

    The Trojans are somewhere between 370 to 420 AH @ 6 volts, depending on which model you get.

    Flooded cells batteries are typically cheaper and more forgiving vs AGM. And you can check the cells with a hydrometer for state of charge (AGM/Sealed batteries you cannot). AGM are cleaner, less maintenance (no water to check/add), and can supply higher surge current (if you have a well pump/power tools--And a larger inverter per AH of battery bank).

    If you are looking for an >800 AH @ 24 volt battery bank, I too would suggest looking at 48 volt battery bank. Note that larger battery bank would very much like larger solar arrays to support 10% minimum rate of charge--If you do not need such a large bank (or do not want so many solar panels), a smaller battery bank (and a bit more conservation/monitoring power usage) may be a better choice for you.

    Note that cold climates run battery charging voltages higher than "normal" in mild climates. And Rolls/Surrette batteries seem to need higher voltages too (24 Volts ~ 32+ volts?). Check your AC inverter--Many will shutdown around 30 volts DC input--That can be a pain if you are there running the system in winter.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset