Panel recommendations for "48V" grid tie

Re: Panel recommendations for "48V" grid tie

Sheldon wrote: »

Driving a Xantrex 4548 with a small (140AH) "48V" battery bank, running in Grid Tie where the batteries are intentionally small and used as a buffer/capacitor than for any intended storage.

In general, for a 48 volt battery bank a 140 AH battery bank would be good for ~1,400 watts of solar panels; ~1,400 watts continuous load maximum for the inverter; and ~2,800 watts maximum surge on the inverter (pump starting surge current, etc.).

Depending on lots of things--You may have issues with battery bank over voltage if you feed more than 1,400 watts during Grid Tie with a 140 AH battery bank (48 volts). GT inverters cannot change the output current to the grid quickly--looks like it takes a few seconds to ramp current up and down to comply with the regulations. Just a guess, but from what I have I read around here.

in discussion with Midnight Solar, I am of the impression that I would need only a few volts above the bank, which is set by the Xantrex setup to "sell" at 52 V.

You can probably set the Solar Charge Controller to ~58-59 volts Absorb voltage--the GT inverter is what will control the "charging/floating" voltages during the day.

To achieve 52V out with good efficiency in the Midnight Solar Classic, I'd need to have a temperature corrected Vmppt of the array (series/parallel) of 56-60 V.

Probably closer to ~70 VDC or so Vmp minimum.

Question: what's typical panel temperature above ambient?

I get summer temps of 40-45C peak at latitude 37, but usually accompanied by a 10-20kt North breeze at roof top, and can space array for convective venting between series panels.

I'd guess at a rise of 40-50C without explicit cooling. (contemplating a "free" pool heater by sprinkling pool water over array and catching the run off)

I think Xantrex uses 35C (63F) as their worst case temperature rise.

Given that Pmp at Vmp/max-temp curves are fairly flat, the system should work pretty well within ~10% of Pmp) even if the Vmp falls close to 60 VDC.

You still should leave a couple of volts of headroom for wiring/controller/circuit breaker voltage drop.

Assuming modest shadowing from adjacent turbine tower 3" pole (unavoidable due to zoning requirements) and guy wires, any preferred panel sizing/bypass setup?

Shading is a real killer for solar power. If you already have panels up and running--have you played with holding a plastic pipe over the arrays and see how much power you loose (or not).

I'd rather not provide an extra 15V at cost of another $4k row of panels, but really don't want to drop below MPPT of array on a hot day.

-Bill