Series Circuit

Cariboocoot wrote: »

Good question.

First of all 3:00 PM is probably not 'prime sun time' so the panels won't be putting out their maximum. Insolation makes a big difference on power production.

Second, how are you measuring "PV Volts"? If that is the input Voltage to an MPPT controller from your two panels is series something is wrong. That's around Vmp for the one 150 Watt panel I should think. It may be that there is not enough sun on the panels or it may be a wiring problem. If your controller is a PWM type you're wasting a whole panel as the battery will simply pull the Voltage down to its level and the power is lost.

Battery Voltage indicates the battery is definitely not charged. By that hour of the day you should have been through Bulk and Absorb and be at Float somewhere above 13 Volts.

Current depends on the panel output (again subject to the sun) and the amount of power the system requires. Since the Battery Voltage indicates a lock of charge I would expect much higher current if the sun is good.

150 Watt panel is 6 Amps and thus should be 25 Vmp (odd numbers).
205 Watt panel is 5.8 Amps and thus should be 35 Vmp (closer to normal).
From that the PV Voltage at noon (i.e. full sun straight on) with these two in series should be around 60 Volts. The array is 355 Watts total, and the peak current to a 12 Volt system would be approximately 23 Amps.

It sounds as though you are not using an MPPT type charge controller, thus wasting a lot of potential power.

Cariboocoot wrote: »

All panels are subject to shading issues.
The only way to get full power readings is with strong, direct sunlight on them.
When the light on the panels drops off for whatever reason (including shading or indirect angle) power drops off.
Your second set of numbers is better, but it still shows less than full power potential at the panels:
4.49 Amps * 53.9 Volts = 242 Watts whereas the most you would see would be (Vmp + Vmp) * 5.8.
Some of that lower power can be due to how much the batteries need. A way to check that you can get maximum output is to turn on some loads equal to the total array Watts and see what it will do under demand at maximum sun time.

Nominal peak power(Pmax): 150W
Maximum power voltage(Vmp): 18V

Maximum power current(Imp): 8.33A

Open-circuit voltage(Voc): 22V

Short-circuit current(Isc): 9.1A

Cariboocoot wrote: »

You can measure Voc easily enough. You can also measure an approximate Isc. But if you have a Voc and a Wattage rating the other numbers can be approximated.
Voc of 22 means the Vmp is likely 18. 150 Watts / 18 = 8.3 Imp. Isc is usually 1/2 Amp higher or 8.8. You will not see Isc into a circuit, only to a short.

In series with a panel that has an Imp of 5.8 the panel will be limited to 18 * 5.8 or 104 Watts. At that point your maximum array is now 104 + 205 or 309 Watts, which you'll typically see 77% of or 237 Watts. At 242 Watts you've got good insolation; the biggest problem is the current bottleneck.

So the question is: good enough?

45 Amps @ 24 Volts would be about 1400 Watts of array. That would be five 255 Watt panels, which is not going to be good because you don't want them all in parallel. Six would be wasting half a panel. Four would be good (two parallel strings of two in series), but again: good enough? Depends on how much battery you're trying to charge.

As a rule trying to get a certain array size by mixing dissimilar panels is frustrating because of the incompatibility of Voltage and/or current specs. It is better to build it either slightly larger or slightly smaller (providing power needs are met) using identical panels.

• Buy as large Charge controller as you can afford, check prices for all available even if you are not going to buy it. (I did spent more than 2 hours with local installer, by looking at Morningstar Ts-45 PWM, it was available . for $250. )
• don't try to mix and match panels.
• search and gets you facts right (I didn't searched for 150W polycrystalline's specsheets, only relied on my own measurements e.g measuring the ISC by shorting the panel through a digital multimeter)
• Mounting should be adjustable, so that you can change according to the time of the year.
• Clear your mind on every silly question you have in your mind
• We have got quite good insolation in Pakistan :cool:

• Chinese Panels cost in 2006 was $4.25 (at current currency rates)
• In 2013 Chinese Panels without warranty were ava. for $0.7. While Canadian Solar, Suntech were available for $1.00 to $1.15 while Japanese and Korean brands used to cost $1.60
• In 2014 Chinese Panels without warranty drop to $0.3 (in winter) and $0.7(in Summer). While Canadian Solar,trina, renesola are available for $0.80 to $0.95. While Japanese brands such as Sharp costs between $1.00 to $1.10. American brands such as Solar world costs $1.33 to $1.40(Polycrystalline)

Cariboocoot wrote: »

I live in Canada. Don't talk to me about prices! Everything is expensive here except grid power which is extremely cheap. At our price structure solar will never achieve parity with grid power; it's unlikely solar will come down much further which means utility rates will have to go up 5X to match and that isn't going to happen when the utility is a Crown Corporation and politicians want to get re-elected.

The only reason I have anything to do with solar is because there are many places here that have no grid available (I own one of them) so suddenly solar is the cheap option (compared to gasoline in a generator at nearly $6 a gallon US).