Solar grid or 2 microinverter systems?

[AdironDoc]

I saw a started system for "$549 after tax credit". It's a 235W Trina kit and is coupled to a Enphase MPPT Microinverter. The ad notes that as each panel is linked to one microinverter, several can be added over time, and that a fault or poor performer will not affect the others since each is on its own. I've not heard of this concept but wondered if anyone had an opinion on this. I've been planning for a 500W or 750W system but wouldn't mind getting in one foot at a time.

http://www.wholesalesolar.com/system/1-trina-panel-solar-micro-inverter-grid-tie-power-system.html

Cheers,
Doc

[MountainDon]

slightly confused here... these are grid tie units are they not? I thought you were off grid?

I don't know anything much about these, except my local vendor has discontinued selling the Enphase inverter packages, but I don't know why. They came out a year or so ago and they were prominent on their website, then faded away. They still sell the more conventional equipment. 

[AdironDoc]

You sir, are correct! They are in fact grid-tie units and I am off-grid. Would have been nice to have a system that can start small and easily grow, one panel at a time. I notice most panels are somewhere around 30V meaning a 24V battery array is best. My wind unit on the other hand is more likely to achieve 12V on most days than 24 on occasional days. What to do...what to do..

Doc

[MountainDon]

...most panels are somewhere around 30V meaning a 24V battery array is best.

Not necessarily. It depends in part on the charge controller you use. A good MPPT type can use high panel voltages and charge a 12 volt bank of batteries. My setup runs around 88 volts output from the three panels in series on a sunny day. The FM60 charges a 24 volt bank, but it could also charge a 12 volt bank or a 48 volt bank.  Not all charge controllers can do that.

[AdironDoc]

Not necessarily. It depends in part on the charge controller you use. A good MPPT type can use high panel voltages and charge a 12 volt bank of batteries. My setup runs around 88 volts output from the three panels in series on a sunny day. The FM60 charges a 24 volt bank, but it could also charge a 12 volt bank or a 48 volt bank.  Not all charge controllers can do that.
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While looking at performance charts on wind turbine/alternator combos, I noticed that the wattage ratings are higher at 24V than 12V. 24V arrays are recommended to make better use of the alternator's capabilities. My unit, for example puts out 40W in a good breeze but coupled with a 24V system shows 75W. The performance is under a full load and represents actual battery charging. I'm sure it's the same for solar setups. That and the ability to run thinner wire are the primary reasons I wanted to go with 24V. I'm sure there are other reasons to select one over the other as well. In the end, I'm not opposed to 24V across the board.

Is a higher voltage even better? Your system puts out 88 Volts, but after the MPPT, 24V. What does the MPPT do with the extra voltage? Is it lost or put to use?

[MountainDon]

Is a higher voltage even better? Your system puts out 88 Volts, but after the MPPT, 24V. What does the MPPT do with the extra voltage? Is it lost or put to use?

The beauty of the MPPT system and PV modules is that almost nothing is wasted. When in the bulk charging mode, the charge controller looks at the incoming power from the modules, looks at the state of the battery charge and calculates what voltage will be best suited for charging. It does this continuously to maximize the use of the power from the modules.

EG: if the incoming from the modules is 80 volts and 8 amps (640 watts) the mppt charge controller may convert that to 28.8 volts and 21 to 22 amps. There is some small loss doing the converting, but not nearly as much of a waste or loss that an ordinary charge controller has. The voltage going into the mppt still has to be above the battery voltage.  


The reason I ran my panels in series was to raise the voltage because of the long run from the modules to the batteries. That also necessitated a good charge controller. I have no regrets about the money spent for the Outback FM60.

All the above relates to PV modules and PV charge controllers.

[AdironDoc]

That's great, Don. Thanks for making that clear for me. I see they're reasonably priced too. I suppose I'll end up with one charge controller at each point in my system. PV, wind, and perhaps the microhydro. All will then wire to the battery bank.

[MountainDon]

Yes each different source, PV, hydro, wind, genny must have their own controller.  Some folks with lots of PV modules may run two (or more)  controllers.