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creeky · 09-23-12, 01:37 PM

strider, you are correct. I posit that mppt solar controllers should be the only way to go. Ryland, an analogy would be batteries. Nobody would build a solar system with car batteries for storage. You get the best deep cycle batteries you can afford.

With mppt in the solar controller you get two things 1) mppt captures the most power from the available power in the panels 2) mppt controllers convert Voltage to Amps.

So, in my case I have 48 volt "ongrid" panels and a 12 volt battery bank. With a pwm controller my 4 250 watt panels at 48 volts become 4 62.5 watt panels at 12 volts.
The effect you see at the batteries is:
- a pwm controller shows 15 amps at 12 volts
- while a mppt controller (converting the 48 volts to amperage) shows 60 amps at 12 volts

So a mppt controller offers higher real output to your battery/home system; as well as more flexibility within the system itself.

I make this point because I had to assemble my own system from here there and everywhere as there was no option to buy reasonably priced "complete" systems. My system, which I put together myself for under $5k was selling for 14k from solar suppliers at that time. and they were assembling it from pieces that they had caged together.

As part of this self assembly I took advice from many sources on the internet. Largely to their credit (suitable wiring etc). However a number of sources recommended that pwm controllers were adequate for battery systems that rarely fell below 80% fully charged. What wasn't clear, was the inability of pwm controllers to handle variables like 48 volt panels and 12 or 24 volt battery systems. (note that some of these advisers have since added pwm/mppt provisos to their advice pages). And the thing is, deals happen all the time. I got my high voltage panels, at the time, at about a 20-30% discount over what was available, and I could drive to the guys farm and pick them up.

A lot of people thinking or in the process of building offgrid systems read these posts. That's why I want to propose that mppt controllers become basic spec. No one should be putting in a pwm controller.

09-23-12, 01:37 PM	#5
creeky Journeyman EcoRenovator Join Date: Jun 2011 Location: a field somewhere Posts: 304 Thanks: 64 Thanked 44 Times in 31 Posts	strider, you are correct. I posit that mppt solar controllers should be the only way to go. Ryland, an analogy would be batteries. Nobody would build a solar system with car batteries for storage. You get the best deep cycle batteries you can afford. With mppt in the solar controller you get two things 1) mppt captures the most power from the available power in the panels 2) mppt controllers convert Voltage to Amps. So, in my case I have 48 volt "ongrid" panels and a 12 volt battery bank. With a pwm controller my 4 250 watt panels at 48 volts become 4 62.5 watt panels at 12 volts. The effect you see at the batteries is: - a pwm controller shows 15 amps at 12 volts - while a mppt controller (converting the 48 volts to amperage) shows 60 amps at 12 volts So a mppt controller offers higher real output to your battery/home system; as well as more flexibility within the system itself. I make this point because I had to assemble my own system from here there and everywhere as there was no option to buy reasonably priced "complete" systems. My system, which I put together myself for under $5k was selling for 14k from solar suppliers at that time. and they were assembling it from pieces that they had caged together. As part of this self assembly I took advice from many sources on the internet. Largely to their credit (suitable wiring etc). However a number of sources recommended that pwm controllers were adequate for battery systems that rarely fell below 80% fully charged. What wasn't clear, was the inability of pwm controllers to handle variables like 48 volt panels and 12 or 24 volt battery systems. (note that some of these advisers have since added pwm/mppt provisos to their advice pages). And the thing is, deals happen all the time. I got my high voltage panels, at the time, at about a 20-30% discount over what was available, and I could drive to the guys farm and pick them up. A lot of people thinking or in the process of building offgrid systems read these posts. That's why I want to propose that mppt controllers become basic spec. No one should be putting in a pwm controller.