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Old 02-11-2011, 13:53   #1
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Understanding Solar

I am looking at solar power for my boat however I know, I know nothing, so can the group address these questions. They say there are no stupid questions, so here it goes!

What is the difference between "A" and "B" panels?

If the panel has voltage above 17.7 to 18.0 volts will the amerage be reduced by a controller to get the voltage in line with charging 12 volt battery's?

Wattage is amperage times voltage, so if the panels have too high a voltage is this an issue for charging 12 volt battery banks?

I note that there is a difference in weight between panels, I would want the lightest panels however is this wise.

Is a MPPT controler a must?

To get a 200+ watt panel most have 23+ volts, is this an issue, seems to me if the voltage is stepped down is amerage lost?

Many thanks

Fletch
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Old 02-11-2011, 14:15   #2
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Re: Understanding Solar

There are answers for a lot of what you're asking, but simply put you need 13-17v panels of the same model hooked into a charge controller. It will take care of regulating the voltage and amperage it needs from the panels based on the charging state and temperature of the batteries.

Kyocera makes great panels. The best prices on controllers and chargers I've seen are from these folks: AltE: Solar Panels & Solar Energy Gear | Call 877-878-4060 They have a person who can help you on the phone who's dedicated to boats / marine stuff.
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Old 03-11-2011, 05:16   #3
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Re: Understanding Solar

Let me try to describe the basics:

Most boaters use 17 V panels which are suitable for charging 12 V batteries with a simple controller or even no controller. When a panel that CAN put out 17 V is hooked up to a battery that can absorb only 12 V, the battery puts enough load on the panel so it drops its voltage to 12 V. You lose wattage when this happens as the current is approximately the same. That is what MPPT controllers do, they let the panel operate at its maximum power point, about 17 V, but it converts the voltage to the battery's required voltage, about 12 V.

Most panels bigger than 135 watts are higher voltage, usually 35-40 V. Unless you want to waste more than half of your power, you must use an MPPT controller with these panels. And the input voltage spec on the controller needs to be at least 40 V.

A good panel for boater's use is the Kyocera 135 W panel with a junction box with screw terminals. This lets you easily wire directly to the panel. Unless you have more than about 200 watts of panels, a simple non MPPT controller will work fine.
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Old 03-11-2011, 06:27   #4
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Re: Understanding Solar

This summer i did both wind and solar. I bought an air-breeze and all the associated parts on an a la carte basis in order to get everything at the lowest price. This was a lot of chasing around to save very little money. For the solar I bought a kit from Welcome to eMarine Systems that included solar panels, controller, and hardware for mounting over the bimini. At the same time i looked around the web to see if i wanted to do it a la carte. In the end I bought from emarine because it gave me a single point vendor for everything. Using a single vendor the installation directions across all the components were integrated and therefore were easy to follow. In responses to the OP I often see the comment made that you can get away with not using the MPPT and just wire things to the battery (with a fuse of course). That advice is, in my humble opinion, foolishness. To begin with, with my twin Kyocera 135s in parallel and an mppt controller I get some power even on a cloudy day. Secondly, emarine puts an mppt in a properly sized waterproof box with an appropriate wiring bus. The controller/bus has connections and software to send current to the house bank, a trickle to the start bank, and a shunt for the house when the other banks are charged.

The final reason I did the kit was so that I didn't have to search all over the net only to have to deal with multiple billings, multiple shipping dates, and then have to figure out how to get all the components to play together. My preference is to sail instead of spend time dockside trying to figure out an installation that could be easy. The few extra dollars were well worth it. And no, I don't have stock in either air breeze or emarine.
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Old 03-11-2011, 06:28   #5
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Re: Understanding Solar

Solar panels are constant current devices so the basics of ohms law does not apply. Good solar panels have a specs label on the back similar to this one from Evil Bay
  • Max Power: 120W
  • Max Power Voltage: 18V
  • Max Power Current: 6.67A
  • Open-Circuit Voltage: 21.6V
  • Short-Circuit Current: 7.34A
  • Cell Efficiency: 16.25%
  • FF: >74%
  • Maximum System Voltage: 1000V
  • Temperature Range: -40C - 85C
  • Power Tolerance: 3%
  • Standard Test Conditions: 1000W/m2, AM1.5, 25C
  • Solar Cell: Mono
  • Front Glass: 3.2mm Tempered Glass
  • Maximum Hail Load: steel ball fall down from 1m high
  • Frame: Anodized Aluminium Alloy
  • Dimension: 120 x 81 x 3.1cm
  • Weight: 15kg
the important parts are, the max power current, in this case 6.67A, the max power voltage, in this case 18v and the open circuit voltage, in this case 21.6v.
If a Pulse Width Modulation only (PWM) type controller is used then the best you will get is 6.67amps, the rest is lost through inefficiency due to voltage mismatch.
A Multiple Power Point Tracking (MPPT) type controller is designed to that the max power voltage (Vmp) at the Max Power Current (Amp) and convert it to match the voltage of the battery it's connected to.
Sounds great in theory and if you believe the B/S in the manufacturers ads an MPPT controller will perform miracles, fact is, they don't. If 12v nom. panels (Vmp upt to 18v) are used to charge a 12v battery about the best you will get is an extra 10% more than the PWM controller will give you, that was confirmed on another forum by a technician's email from Morningstar.
If you use panels that have a Vmp higher than 18v then an MPPT controller is a must or a lot of charge current will be lost. MPPt cotrollers aren't cheap, well good ones aren't cheap, cheap ones aren't worth even bothering with. The best of the best by far is the Outback FM80, if you are going to get serious with solar then spend the $$ and get one of these.
If you just want a small system using 12v nom. panels then I'd recommend a Plasmatronic PL20 from Aust, very well built, includes system monitoring and can have a shunt kit plugged in to measure big loads in and out like generator and mains charging and inverter loads.
Hope that helped

T1 Terry
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Old 03-11-2011, 11:53   #6
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Re: Understanding Solar

Quote:
Originally Posted by KestrelBuck View Post
This summer i did both wind and solar. I bought an air-breeze and all the associated parts on an a la carte basis in order to get everything at the lowest price. This was a lot of chasing around to save very little money. For the solar I bought a kit from Welcome to eMarine Systems that included solar panels, controller, and hardware for mounting over the bimini. At the same time i looked around the web to see if i wanted to do it a la carte. In the end I bought from emarine because it gave me a single point vendor for everything. Using a single vendor the installation directions across all the components were integrated and therefore were easy to follow. In responses to the OP I often see the comment made that you can get away with not using the MPPT and just wire things to the battery (with a fuse of course). That advice is, in my humble opinion, foolishness. To begin with, with my twin Kyocera 135s in parallel and an mppt controller I get some power even on a cloudy day. Secondly, emarine puts an mppt in a properly sized waterproof box with an appropriate wiring bus. The controller/bus has connections and software to send current to the house bank, a trickle to the start bank, and a shunt for the house when the other banks are charged.

Does your system use the one controller for both solar and wind, if it does, hat type did you go for??
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