Panel recommendations for "48V" grid tie

Sheldon

Trying to figure out what is "best" setup for adding PV to my Whisper 200 turbine.

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 storgage.

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.

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.

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)

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

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.

BB.

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