Solar panel not gives it's max power - please help

[alexevt]

Hello,

I have installed 100W solar panel on the roof.
The OC voltage is 15V, SC current is 6A (the max it 8A).
My batteries is small capacity (6AH), because I want to use it with sun only.

The problem is: When I connect a laptop (5A) to the system (solar controller + inverter) the batteries gives 3A and the panel 2A. So after short time the batteries discharged and the controller disconnect the circuit.
Why the panel doesn't gives it's full ability?
What should I do to use the sollar power directly (the battery only for backup for shading moments)?

Thanks for any help.

[billvon]

I have installed 100W solar panel on the roof.
The OC voltage is 15V, SC current is 6A (the max it 8A).

There's your problem. For a 12V battery you need an OC voltage of around 18 volts, to ensure you can get full current at 15 volts. You might be able to help a bit with thicker wires but you're likely going to need a better panel.

What should I do to use the sollar power directly (the battery only for backup for shading moments)?

If the LVD is disconnecting the battery after a while then the solar panel isn't giving you enough power to run the laptop.

[alexevt]

There's your problem. For a 12V battery you need an OC voltage of around 18 volts, to ensure you can get full current at 15 volts. You might be able to help a bit with thicker wires but you're likely going to need a better panel.

I can add some modules to make it 18V, but the batteries are fully charged with this panel too. Do I anyway need 18V?

If the LVD is disconnecting the battery after a while then the solar panel isn't giving you enough power to run the laptop.

To run the laptop I need about 5A. And the panel gives me 6A on SC. How can is be that the panel isn't giving me enough power?

[inetdog]

I can add some modules to make it 18V, but the batteries are fully charged with this panel too. Do I anyway need 18V?

To run the laptop I need about 5A. And the panel gives me 6A on SC. How can is be that the panel isn't giving me enough power?

The current from panel is related to the voltage! Your zero current (open circuit) voltage is 15 volts. That does no do you any good.
The short circuit current from the panel is 6 amps, but at zero volts. That does not do you any good either. At a reasonable voltage for maximum power from the cells, you might see 5 amps at 11 volts. Since that is lower than the battery voltage, some of the current needed by the computer is coming from the battery instead.
It looks like at 12+ volts the panel can only produce 2 amps.

That is the reason you need a higher Voc, so that Vmp (max power) is greater than 12-14 volts. That will allow the panel to charge the battery or power the computer.

Once you go to a higher panel voltage, you must incorporate some kind of charge controller to keep the panel from overcharging the battery. You are a few pieces short of a full system.

[alexevt]

Thanks for the reply.

It looks like at 12+ volts the panel can only produce 2 amps.

This was my fear. I have to check the panel...

Once you go to a higher panel voltage, you must incorporate some kind of charge controller to keep the panel from overcharging the battery. You are a few pieces short of a full system.

I have regular (PWC) solar controller, do I need MPPT type? As I understand MPPT will raise the efficiency, but if I need only 5A for laptop the regular controller makes the job (with a panel that really have 100W). Am I right?

[inetdog]

Thanks for the reply.
This was my fear. I have to check the panel...
I have regular (PWC) solar controller, do I need MPPT type? As I understand MPPT will raise the efficiency, but if I need only 5A for laptop the regular controller makes the job (with a panel that really have 100W). Am I right?

There is no need to go to an MPPT charge controller (CC) with the setup you have, as long as you do not raise the panel Voc above the input limit of the CC.

I would worry about whether your panel is large enough though. A Voc of 15 and an Isc of 6 is not a 100W panel unless your Isc measurement was made in only partial sunlight. Assuming that your Isc measurement was under "full sun" then the maximum panel output is probably closer to 60 watts and you need 60 watts at 12 volts for the computer. If you make it an 18 volt panel instead, it will still have an Isc of only 6 amps. That is not a lot of room to spare to the 5 amps you need.

If you were to increase the voltage to 24 volts or more, an MPPT Controller *might* be able to give you a reliable 5 amps at 12 volts, since it can trade off a voltage reduction for a current increase. But some cheap CCs advertised as MPPT do not seem to deliver on that promise.

[alexevt]

Thank you a lot! It was very helpful. I will work on the suggestions.
Thanks.

[PNjunction]

... I have installed 100W solar panel on the roof.
The OC voltage is 15V, SC current is 6A (the max it 8A).
My batteries is small capacity (6AH), because I want to use it with sun only.

WHOA - your battery is too small to start with! Exactly what battery do you have? If you are thinking that you are only going to use the battery as full-time, fully-charged buffer that is rated as the same power draw as your load, think again. You'll need a larger battery with that 100w panel.

Unless you are running something exotic, typically the fastest current charge rate for a small sealed agm (C/4) means that with your 100w panel, you should be using no LESS than about a 25-35ah agm. If a wet FLA, something like 60-75 ah would be more appropriate.

I'll bet that dinky battery has already vented and is toast.

[inetdog]

WHOA - your battery is too small to start with! Exactly what battery do you have? If you are thinking that you are only going to use the battery as full-time, fully-charged buffer that is rated as the same power draw as your load, think again. You'll need a larger battery with that 100w panel.

Unless you are running something exotic, typically the fastest current charge rate for a small sealed agm (C/4) means that with your 100w panel, you should be using no LESS than about a 25-35ah agm. If a wet FLA, something like 60-75 ah would be more appropriate.

I'll bet that dinky battery has already vented and is toast.

The amount of current going to the battery will be dependent on the Solar Controller (at first I thought there was not one since it was not mentioned initially) but we still do not know what the SC/CC output rating is. On the other hand, if the controller is limiting the charge current to a reasonable value for the 9AH battery, it will have no way of allowing the panel to deliver additional current to the load but not to the battery!
Also, with his panel having a Voc of only 15 volts, it is not going to be delivering more than 1 or 2 amps to the battery even if the CC is willing, and that current will fall off dramatically as the battery voltage approaches 15 volts.
It is not a good design, but by sheer luck it may have been a bad enough design that it has not damaged the battery.

[PNjunction]

Alexevt, can you break down your gear into model and make? panel / CC / battery / inverter ?

Also, how long is the wire run to your roof, and what is the wire guage? This plus heat could also account for your low voltage. More info needed...

[alexevt]

Alexevt, can you break down your gear into model and make? panel / CC / battery / inverter ?

Also, how long is the wire run to your roof, and what is the wire guage? This plus heat could also account for your low voltage. More info needed...

My design is not so good, but it is only for test and understand the solar system before make a big one.

I have the following system:
panel: built from 28 modules of 15.6x15.6mm 4W each (self built panel).
CC: simple pwc (cmp12/24) - a cheap one.
battery: I use 18650 lithium, but I know it is bad idea. I soldered 20 bateries to 12V block, about 6 mAH. Other batteries costs a lot.
inverter: modified sine wave, 300W. I simple one. But I about to receive a pure sine wave 300W inverter. 12V to 220V.
cable: 15 meters length good quality cable good up to 16A (it is long for DC, but I will put all the system on the roof near the inverter, so it will flow 220 AC). The data in my room and on the roof is the same, so the cable not make troubles yet.

I have checked the panel again and saw that the max power is 12V x 3A = 36W. It was not at full sun, so hope I will get about 5 at full sun.
I also saw that if I use 4 modules less (13V OS) the current decreases to 1.5A. So I definitely need 4 more modules, to have 18V. I will try it.

[wotechsolar]

Dear Sir
For the off-grid solar kit.
solar panel, controller, battery, inverter.
firstly, we must confirm the voltage of whole solar system.
if the voltage of battery is 12v, so the voltage of solar panel must be 18v.
the voltage of solar panel must be 1.5 times the voltage of battery, after all, the solar panel charges the battery.
solar panel with 18v --------controller with 12v-----battery with 12v-----inverter with input 12v

but
although the working voltage of solar panel is 12v. if the output toleance of solar panel is so large, can not provide the large working current,

we are the manufacture of solar panel, you also can logo in our website to get more information,

[inetdog]

battery: I use 18650 lithium, but I know it is bad idea. I soldered 20 bateries to 12V block, about 6 mAH. Other batteries costs a lot.
inverter: modified sine wave, 300W. I simple one. But I about to receive a pure sine wave 300W inverter. 12V to 220V.
cable: 15 meters length good quality cable good up to 16A (it is long for DC, but I will put all the system on the roof near the inverter, so it will flow 220 AC). The data in my room and on the roof is the same, so the cable not make troubles yet.
I have checked the panel again and saw that the max power is 12V x 3A = 36W.

I assume that you meant 6000 mah or 6AH. And that you used batteries with manufacturer supplied solder tabs, were careful not to exceed recommended temperatures while soldering.

Are you sure you realize just how bad an idea it might be? If you are putting these Lithium rechargeables into a series-parallel arrangement and have the capability to deliver 3 amps of charge or pull 25 amps or more to your inverter you have created a potential bomb. Any arrangement (particularly series) of 18650s which does not monitor individual cells and/or use exclusively "protected" cells can explode during either charging or discharge. Even protected cells can fail if abused.
The charge controller (CC) has to be designed to work with Li-ion chemistry. And there has to be a solid low-voltage cutoff to prevent permanent loss of rechargability if they are discharged too low.

At the very least, put the battery bank into a solid metal box with an open or breakaway top and make sure there is nothing flammable on your roof anywhere near it!

You can read some cautionary and scary stories at http://www.candlepowerforums.com/vb/...e-of-batteries.

Please excuse me if you are already aware of all of this and have taken it into account. But your casual description might lead someone less informed to try doing it the wrong way.

[billvon]

battery: I use 18650 lithium, but I know it is bad idea. I soldered 20 bateries to 12V block, about 6 mAH

To amplify on what the other poster said -

Put this battery OUTSIDE in a vented fireproof enclosure. It WILL eventually go up in flames.

[alexevt]

ok, it looks scary...
But I don't overcharge them or overheat them. I think in normal conditions it will not explode.
As I know, these batteries have a protect circuit. Hope it will help in normal use.