Hydro and PV diversion, part II [RE-wrenches]

[Gary Higbee]

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Wrenches,

I wrote last week about diverting both hydro AND PV. My first reply was from
Clive--a call from the Falkland's only an hour or so after the post!  Thank
you Clive!!

I was surprised at the lack of other responses. I suppose this is a niche
sort of thing.

Here's another (and last) attempt, outlining some possible configurations,
and asking for thoughts:

BACKGROUND
We've got a potential hydro diversion of about 500 watts, and the PV STC
rating is 2400 watts. System voltage is 48, and we're running an MX60,
FX2548, and Harris PM. Diversion is to be to a water tank, which is a
preheat tank for the domestic hot water system. Off-grid system.

SOME CONFIGURATIONS

1) Around 3kW of diversion, all of which comes on at once via a big relay.
Right, this doesn't sound so swift. Imagine what the battery voltage (and
relay) would be doing!

2) Clive suggested using a staged diversion, where loads were successively
turned on as voltage rose. This models the Proven wind turbine controller
strategy.This technique sounds like a great idea, though it's on the
expensive side for my client. Maybe one could use several voltage-controlled
relays, but then we've got temperature compensation issues, and the fact
that we wouldn't reach an absorb voltage (like # 4 and #5, below).

3) Christopher suggested using a solid state relay on the MX60, with the
time delay set to zero. This would presumably model a PWM system. This
sounds good, and I anxiously await your testing, Christopher. Really, this
sounds like a great solution, since the MX60 is smart about running
diversion relative to absorb or float settings--a very nice feature!

4) For now maybe use a C-40 and divert to two 20 amp elements, using the
MX60 as a "safety net" to turn off the PV array. Maybe OK, but how would one
set up the controller setpoints? It seems there'd never be an absorb charge,
since we'd be diverting before then.

5) Use a C-40 and divert only the hydro. Set the diversion point above the
MX60 absorb point--oh, but this would seem to run the batteries too high.
How do you set up an MX60 for PV with a C-40 for hydro?

Any thoughts on the above? Have any of you done hydro AND PV diversion? Any
experience with solid state relays? How about mechanical type relays rated
for 60 plus volts and 20 plus amps, with a 12 volt coil?

At this point I'm tempted to go with door number 5 for now, since in
bouncing this off of numerous folks nobody has suggested a proven and
cost-effective solution that sounds workable. It seems sad, though, to just
turn off the PV array when there's meaningful work that could be done.

I'm off to the work site Thursday night or early Friday morning, and hope
something exciting comes up soon.

Thanks!

Gary

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                     ~ Windstream Solar ~
     Gary Higbee  (gary at windstreamsolar.com)
                     (541 ) 607-1818 (Eugene)
                        (541) 954-3881 (Cell)
Solar, wind, and hydro site analysis and system design
    Components dealer and installation assistance
 Energy Trust of Oregon contracted system inspector
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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