Need Help, I am a little confused.

Lets hope you have not bought all the panels yet.. you can save $ by using 250W grid tie panels, and let the MPPT controller, down convert the panel voltage to battery voltage.

So, in winter, you have a cloudy day, followed by a sunny day. and need to both recharge batteries AND run your normal daytime loads
easiest to count in watt hours, if you burned 3600wh on the cloudy day, and plan on another 3600 of loads, and recharging
that's 7200wh x (about 30% losses) or 9360wh you have to harvest in your 4.5 hours (you sure are optimistic) - you would need about 3Kw of panels, and that's cutting it close (remember panels only give you 80% of nameplate under normal conditions)

Thanks for the reply Mike. I want to ensure I understood your response. Are you saying I need enough panels to cover little over the full capacity of the batteries? In my case, 100 watt panels were all I could get to Puerto Rico at no additional cost.

Can you look at my specific case again, I think the way you calculated consumption in my case was broad and I explain. My four 6v batteries can only hold a maximum of 5280wh. Of which I can only use a maximum of 2640wh. On my original post, I did not mention consumption, I will do that now in order to provide a clear picture. The main load will be a refrigerator, It is small and uses 100w when running. Led television utilizes 70w, a dish network DVR 12w. Other than that it will be lights "they are all LED" 13w each. Fan 100w.

So we have.

TV 70w x 5 hours = 350wh
dishnetwork 12w x 5 hours = 70wh
Refrigerator used .8KWH or 800wh in 24 hour period. = 800wh
Lights 2 of them (13x2) = 26 * 6 hours = 156wh
Fan 100w x 10 hours = 1000wh

The only load that must be running ideally is the refrigerator. Taking those numbers into consideration, how many 100 watt panels should I shoot for? 10 of them will be a total of 5000wh in a 5 hour period. that exceeds the maximum daily allowable usage by almost double. That should give me extra power on sunny days, minimizing my overall needs from the battery bank.

How much more of a savings is 250w panels? I paid approx one dollar per watt with free shipping.

from sunelc.com - half the price/watt you paid.
Astronergy 250 Watts
Location: Miami
Model: ASM 6610P-250
Qty: 22
Pallet Price/W: 0.48
Single Price/W: 0.55
Modules/Pallet: 22
specs sunelec.com/ASM6610P_250_260.PDF 30v panels

Assume any panel will only produce 70-80% of nameplate
Assume batteries need 1.3 x what was taken out, use 100Ah, recharge with 130Ah
Inverters have loss, figure 20%
Charge Controllers have loss -MPPT stage 95% eff

Mornings and Afternoons, sun angles are bad and you may only get 50% of nameplate +- 1 hour of solar noon is the peak production time.

I suspect your 800wh fridge usage is, over a year, going to be low, few fridges can run below 360Kwh / year

Using your daily need of 2300 wh's and using 4.3 as the total hours of sun exposure with 1 day autonomy , at 100 watts per panel I am seeing you need 700 watts per day from the array to recharge the batteries. Everything more than that is gravy or excess power that could be used to run stuff in the day . I am getting this from the Alte Store Off grid calculator that you could search for on the web and mess with the numbers yourself.

Thanks for the advice guys, truly appreciate it. I live in Florida, but the reason I did not buy from a local supplier is that they the few I contacted wanted 700 plus dollar to ship to Puerto Rico. I am installing this system for my mother, she is without power and expects to be for another six months due to the hurricane. I will give them a call tomorrow, to see if they ship to PR. I remember a while back they had opened an office in Puerto Rico, but I think that is no longer open. I am flying at the end of the week to do the install, I will take pictures, just waiting for some parts as I plan on installing internet while I am there to my mother's house via wifi, that will be an excellent experiment as I must shoot the signal 8 kilometers to a mountain and then shoot it down to her lol

So I am going to shoot for 10 panels to have a little extra juice for unexpected stuff.

Bonus question The 30-volt panels are they intended for 24 volt battery systems?

They are 60 cell grid tie panels. A single panel, by itself doesn't have high enough voltage for 24 volt battery charging. These are considered 20 volt nominal panels. A 72 cell panel is considered a 24 volt nominal panel. Two or more series wired 60 cell panels and a MPPT charge controller will allow you to charge a 24 volt bank.

Thanks for the reply, the 100-watt panels I have are made by renogy. Again price of getting them to Puerto Rico was the main contributing factor in the purchase. the specs are as follows.

• Maximum Power: 100W
• Maximum System Voltage: 600V DC (UL)
• Optimum Operating Voltage (Vmp): 18.9V
• Optimum Operating Current (Imp): 5.29A
• Open-Circuit Voltage (Voc): 22.5V
• Short-Circuit Current (Isc): 5.75A
• Output Cables: 4.0 mm2 (0.006 in2), 800mm (31.5 in)
• Connectors: MC4 Connectors
• Dimensions: 47 X 21.3 X 1.4 In
• Weight: 16.5lbs

I am planning on wiring 5 pairs. in Serial to make them 24 volts. Then I was going to use a combiner box. Does that sound about right? Just want to ensure that this panels wired in pairs will deliver enough power to charge the bank.


Thanks

Yes this will give you 24 volt nominal voltage, BUT,
If you're running a 24 volt system then you would want to wire your panels either 3, or 4 in series with a MPPT controller. Your best bet with that controller would be 3s3p. 9 panels will be right about the comfortable limit for that controller @ 24 volts.

10 panels would be properly wired as you've suggested... put two in series, and then each of those 5 pairs in parallel. I think you will be happier using all 10 than dropping down to 9 panels. The next increment you could consider would be 12 panels, 4 strings in parallel each with 3 panels in series.

For any of these options, you will have more than two strings, so each string needs overcurrent protection. You will need to think about where to combine them in a way that balances wire costs with transmission loss.

Thanks again for the prompt responses.

Littleharbor,
if I was to wire three cables in series would that then make the power sent to to the controller far higher than the 24 volts needed by the battery bank? I think the controller will step down the current to the correct charging power, however, does that mean that if I send 36volts and the ban4 is a 24v bank the extra power is wasted by the controller? I am certain that is not the case, I would just appreciate a response to understand what happens to the extra energy in the case of 3 panels wired together.

Sensij,
Overcurrent protection, are you referring to fuses?


Thanks all

Yes, mppt controllers very efficiently (>90%) convert the higher PV voltage to the battery voltage.

Overcurrent protection is usually fuses or circuit breakers, either can be appropriate for PV.

I'm stepping out of this conversation due to conflicting suggestions on inputting power into a MPPT controller. Only other comment is watch out for the wattage limit for your 40 amp controller.

Thank you all for the sound advice, I understand that with solar there is always more than one way to skin a cat. I for one appreciate different approaches, it gives me more options, and that is always good.

Thanks

Generally, MPPT controllers work well with PV array voltage twice that of the battery voltage. For a 24V bank, you want the array wired for 48V. That lets the MPPT down-convert the power most efficiently (around 95-99%) Higher voltages work, but become less efficient, so you need to do a trade off study between wire run gauge and length, vs conversion loss. Generally not more than a couple %, but you can save a bundle on wire cost for long lengths of copper wire..