Solar panel advice needed - Newer panels or not

[Chris R]

Hello,

 IF you would be so kind as to help me with this decision.

Currently I have a bank of 12 - Carrizo 35 watt, 12 volt panels that generate just over 2 amps per panel in full sun (25 amps total) . I am looking to aquire 2 Sanyo HIP 200 watt panels (200 watt solar module, 55.8 Vmp, 3.59 Imp) and change my 12 Volt setup to 24 Volt.

So as I figure it... from the current panels (25amps @12V or 12.5amps @24V) to the new panels (14.4amps @ 24V..how do you get these panels to 24V ?)

Am I doing the right thing in moving to newer panels ?

 It seems as though I could be losing 10.6amps in charging power by moving to the new panels ? Am I calculating properly ?

Thanks,

Chris

[Nando]

Look your problem as Watts losses and gain -- forget amps

Set the carrizos for 48 volts and 6.25 amps and parallel them to the HIPS

Two hips are set for 48 volts, so you need to place a charger controller like the MX60 to obtain the 24 volts conversion without power losses

Remember to parallel the panels with power diodes for isolation.

You will obtain MPPT capabilities which will give you around 20 to 30 % higher current

you will have Carrizo 6.25 amps , hips 7.18 amps = 13,4 amps converted to 24 volts (top voltage= 29 volts ). from 55.9 VMP

Conversion is (55.9/29 )* 13.4 amps *0.97 efficiency(MX60) = 25 amps charging current into the battery when the bat voltage is 29 volts.

If battery bank is depleted the current would be 25 *29/21 = 34.52 amps

Nando

[DanB]

I think there is a point (in the size of a PV array) where the cost of an MX60 becomes worth it.. (theyre expensive).  To gain 100 watts its a borderline sort of thing - probably not worth the cost vs buying another panel.  But if you plan on growing the system larger then it may be a good investment.

I have about 600 Watts of PV and I believe I'll buy an MPPT controller (MX60) before I buy any more PV, but I feel like I could go either way and pretty much break even with it all.

[craig110]

Using the conservative low-end gain of 25% by using MPPT, the point where the extra cost of an MPPT controller makes financial sense can be calculated like this:

• If you already have a solar setup and want to expand it: If the cost of adding 25% more wattage worth of panels, even if you aren't thinking of adding that many, is greater than the cost of upgrading to an MPPT controller, upgrade to the MPPT controller before adding any extra panels.  (When calculating the upgrade cost, don't forget to factor in the amount you can get by selling your old controller.)
  
• If you don't already have a solar setup: Total up the amount that you are planning on spending for the panels and calculate how much extra you would have to pay to get an MPPT controller versus a non-MPPT.  If the total panel cost is more than 4 times the extra cost to get MPPT, get the MPPT controller.
  
  

Craig

[Nando]

The idea of a MX60 or equivalent to charge batteries and the same time have MPPT capabilities should be based on reasoning for the overall system.

let's say you have a 24 volts bank and have available 48 volts solar panels a great price, here you run and buy the panels and install a MX60 for the conversion to 24 volts and at the same time you obtain MPPT for the additional 20 to 30 % higher watts.

Later you may change to 48 volts, the overall system can be used easily without extra expense.

Also, the system starts to charge with lower solar energy.

Nando

[kenl]

 Seems like easy math to me. Outback MPPT60=499.00 on ebay. 100w panel 500.00+ just about anywhere. I'll vote for the Outback. kenny