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

Bruce Geddes b.geddes at clear.net.nz
Thu Apr 22 15:23:35 PDT 2004


 

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Hi Gary,
                I have done a couple of PV/hydro jobs down here but not
usually with the generation size that you have on the PV.

What I have found is that the diversion load does not (in real life) have to
be the same size as the generation source unless there are long periods of
very light power use co-inciding with periods of peak power production.

The C40 is a 3 stage PWM controller so you can set the bulk and float volts
where you like and it won't divert until those voltages are reached.  It is
still a useful device from this point of view.

Assuming you want to float at around 55 volts the C40 will give you 2200W of
diversion.  Be careful when selecting your dump load as bulking at around
58V would mean dumping 2320W.  Also if auto-equalise is selected there will
be even more power dumped then.  I would suggest selecting the dump load to
operate at the highest voltage (equalise) that you will see to ensure the
higher voltages don't overdrive it.

If the building experiences intermittent power use during the max PV output
period of the day and the dump load does not prove to be enough, you may
need to set the MX60 to regulate or use the aux contacts to drive a
contactor of whatever sort to switch in an additional but smaller air dump.

I have a system running an earlier Harris producing 500W, 480W PV and an
AirX on 24V configuration using a C40 with 800W of dump and the C40 only
dumps for around 20 seconds every few minutes.  The house uses the rest.
The MX60 wasn't around when I did this and it grew over several years hence
the spread.

Oh, for customers with so much surplus power!

Bruce Geddes
PowerOn



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.

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