Hi all,

Home project on the go, thoughts appreciated from the fine minds here...

I purchased a low-cost 300W wind turbine to play with. I have a 5kW grid-co=
nnected=20
solar PV system in place, with 20 x 250W PV panels & micro-inverters. What =
I'd like=20
to try is effectively connecting the wind turbine in parallel with 1 of the=
 PV panels.=20
Reasoning is it makes use of inverters already there which are not being fu=
lly=20
utilised each day or even utilised at all each night ;-) And it puts the po=
wer=20
somewhere I can use it, and will use energy monitoring system already in pl=
ace. If it=20
works out ok I could potentially add more wind turbine(s) in the future, on=
e to each=20
inverter.

It's important to state that this PV system uses AC micro-inverters, and th=
ere is no=20
high voltage DC accessible. This not the case with other PV systems, which =
require=20
considerable additional electrical safety requirements. What is discussed h=
ere is not=20
safe for, nor applicable to, string connected PV systems.

If I rectify the 3-phase low voltage AC from the wind generator to DC, and =
if I=20
connect this and a solar panel to an inverter, and if I use a (Schottly) di=
ode to avoid=20
reverse power flow into the PV panel, and if the voltage is compatible enou=
gh, then=20
it might just work. A few questions come up, but on the surface most seem t=
o solve=20
themselves or be not too difficult to overcome...

- Solar inverter MPP regulation is not expected to be optimal when power so=
urce is=20
wind turbine. As long as it plays nicely and doesn't do anything bad I'm ok=
 with that,=20
as I'm not aiming for maximum efficiency or anything. Am I hoping for too m=
uch=20
here?

- Inverter has the smarts to not exceed it's own power rating, i.e. it is n=
ot=20
un-common for a 300W or more PV panel to be connected to an inverter of les=
ser=20
power.

- Inverter has ground fault current detection which I need to be wary of, m=
ay be=20
longish cabling to wind turbine so perhaps some potential for nuiscance tri=
ggering.

- Inverter input mustn't exceed a certain maximum DC input voltage. No prob=
lem=20
from the PV panel as it's obviously designed for that, but wind turbine has=
 no built in=20
voltage regulation. This is where I have to construct something.

I'm thinking a shunt regulator is the way to go with a wind turbine. Set at=
 a voltage=20
above what the solar PV produces (30.8V @ Vmp), but safely below Vmax allow=
ed=20
for inverter (45V operating, 55V Abs max), capable of dissipating 300W or s=
o worst=20
case. Could dump power into a power resistor or incandescent lamp or heater=
=20
element, with say a PIC PWM'ing a MOSFET. Or even use multiple power=20
MOSFET's in linear mode... the heat has to go somewhere and could possibly =
work=20
out cheaper by not requiring expensive power resistor(s). Perhaps a fan on =
the=20
heatsink kicking in as required. Want to keep it simple enough that it rema=
ins worth=20
doing, but done well enough that I don't damage existing PV system or make =
it=20
unsafe.

The wind turbine is rated at 300W, 24VAC 3ph. With a 3-ph bridge rectifier =
plus=20
filter capacitor I'm expecting in the order of (24 x 1.41) - (2 x 1V) =3D 3=
2VDC, current=20
around 300W/32V =3D 9.4A.

Sound reasonable, or not? Experience? Thanks~!

--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.