Complete rookie needs help with first project

[SunEagle]

Tell you what. I am feeling generous today. I will cut you in for 30% ownership of the company. Send a check of $10,000 good faith deposit and then we will talk.

ya got my interest. how about 6% interest for $2000?

[Jokeaccount]

Except from the previous question (which I'm still looking for an answer) I also have a new one:

It seems that I'm gonna need a 45W panel. Now I went and checked the store and they sell 20 and 25 W panels (no 45 ones). Can I connect a 20 and a 25 to make 45 with a single battery? I have the feeling that the output voltages will be different thus making it impossible but wouldn't that be the same even if I connected two 25s to make a total of 50W panel? Maybe they have the same specs but different positions and other factors could make them have slightly different output voltages right?

[mega man]

just connect 2x 25watt panels in parallel, you'll maintain the same voltage but increase the wattage, and if its 45w you need i'd suggest u getting say 65-70watts of panels, a 45w panel will operate at 25w so you need more to acquire a specific target

[Jokeaccount]

just connect 2x 25watt panels in parallel, you'll maintain the same voltage but increase the wattage, and if its 45w you need i'd suggest u getting say 65-70watts of panels, a 45w panel will operate at 25w so you need more to acquire a specific target

1) I asked a fellow student about connecting 2 panels in parallel or in series and he said that such a connection wouldn't net the 45W required. Also, connecting them separately would require 2 controllers which is definitely not cost effective. But what is this about the 45W panel not operating at full capacity? I know that in the calculations of Wh required for the load we increase by a 50% (fudge factor), is that it?

[Naptown]

Two identical panels wired in parallel will give you 50 watts from the panels
Now if you are using a pwm controller it will only be about 35 watts
Since your panels will put out 17 volts approx that is all the amps you will get.

[mega man]

1) I asked a fellow student about connecting 2 panels in parallel or in series and he said that such a connection wouldn't net the 45W required. Also, connecting them separately would require 2 controllers which is definitely not cost effective. But what is this about the 45W panel not operating at full capacity? I know that in the calculations of Wh required for the load we increase by a 50% (fudge factor), is that it?

the fellow student your asking is also still learning, i have 1000watts of panels(1kw) comprised of more than 1 panels which are wired parallel and i get about 750watts when it reads on my mppt controller, i don't have a sun issue as most of you do as i live in Jamaica where its always sunny(we do have rain sometimes lol), as the day breaks i begin to charge and have sun all the way until 5 in the evening(sometimes even longer), and with all these panels i use a single 60amp controller so him telling you about 2 controllers is incorrect, and fudge factor is an added amount used when calculating expected needs, panels operating at less than what they say they are has nothing to do with that, if a panel says its 280watts your most likely to get 220watts or say 240watts, to see a max reading you'd have to be exposed to extreme circumstances.

cheers.

[Jokeaccount]

What he actually told me is that I have two options:

1) Connect each panel to a different controller (not cost effective)
2) Connect each panel in parallel into a single controller but the panels will output less Wattage than expected (just like your connection instead of 1k gives 750W)

Anyways, let me give you a run down of what I have so far to make sure I haven't made a huge mistake somewhere:

Load is a 12V 15W LED. 8 hours/day -> 15*8=120Wh. With fudge factor 1.5 that gives 180Wh required per day
The place the system will be installed has 3 sun hours in december (worst case). That means the panel will have to be a 60W one.
The battery has to have a 5 day self reliance which means it requires at least 120*5=600Wh of energy. Assuming it will output a voltage of 12V that means it needs to have 50Ah
The controller will have to process 60W of power which means it will have to be a 5 Amps one.

Have I missed anything?

[Sunking]

Load is a 12V 15W LED. 8 hours/day -> 15*8=120Wh. With fudge factor 1.5 that gives 180Wh required per day
The place the system will be installed has 3 sun hours in december (worst case). That means the panel will have to be a 60W one.
The battery has to have a 5 day self reliance which means it requires at least 120*5=600Wh of energy. Assuming it will output a voltage of 12V that means it needs to have 50Ah
The controller will have to process 60W of power which means it will have to be a 5 Amps one.

Have I missed anything?

If you are using PWM controller Fudge Factor is 2. For MPPT 1.5. However 60 watt panel will work as minimum required with PWM is 50 watts.