Hydro and PV diversion [RE-wrenches]

[Doug Pratt]

===========================================================
Your opinion counts! We’re conducting a survey for a 
computer service/repair company. When you complete our 
survey, you will also be entered into a drawing for one of 
ten $100 prizes. Just click
http://click.topica.com/caab8K4bz8Qcsbz9JC9a/ Val Rad
===========================================================
Hi Gary,

Some interesting stuff you've got cooking! 
It would be better if you could stage your diversion elements, rather
than slamming them both on together. Turn on the lower element first,
then if the voltage creeps up another 0.2v or so, turn on the upper
element, and 0.5v or so above that, the MX60 starts regulating the PV.
Only trouble is, you'll need a second voltage sensitive switch gizmo and
relay to run the second element. One of the Simple Switches ought to do
it. Sounds like fun!

Cheers,
Doug Pratt

-----Original Message-----
From: Gary Higbee [mailto:gary at windstreamsolar.com] 
Sent: Wednesday, April 14, 2004 1:02 PM
To: RE-wrenches
Subject: Hydro and PV diversion [RE-wrenches]

Wrenches,

I'd appreciate some sage advice on a project. Here's the info:

I'm working an upgrade on an existing PV system, adding another 1200
watts
to the existing 1200, bringing a Harris PM online, and converting from a
24-volt DR-based system to a 48-volt Outback (FX2548, PS2DC, MX60), 16
T-105's. The system is off-grid.

We'd like to be able to divert everything--hydro and PV into a hot water
tank, but if we're maxing out the PV array and adding 400 watts of hydro
we're looking at about 2800 watts maximum. It's unlikely, of course,
that
we'll see full power out of the array--but we've got to design for these
things, right? I do have two water heater elements rated at 20 amps at
48
volts, but this falls short of what would be needed. I see that AEE has
an
element rated at 30 amps at 58 volts. Two of these, then, should be able
to
handle up to about 3400 watts. My plan would be to use the MX60 with a
relay
to run the elements, dumped into a 50 gallon hot water tank--yes, with a
temp/pressure relief routed to a place we wouldn't mind dumping hot
water
now and then. Hmm, how about a thermostat that would change PV array
controller setpoints...

Questions include:

1) Whether the switching of this much current will pull down the modest
battery bank so fast that we'll cycle really fast (even with
hysteresis).
Would it be better to go with a C-60, so we regulate the output?

2) If the controller failed this could be bad (boiled batteries followed
by
hydro damage from over rpm, I would expect). It seems that it would make
sense to set the MX60 to limit the PV just a bit above the diversion
setpoint, so at least we'd turn off the PV if something failed between
the
MX60 and diversion elements. I don't suppose this is really redundancy,
but
rather a safety net so long as the MX60 didn't fail full-on.

3) Does this configuration make sense? Is there a better way to do this?

We'd really like to be able to divert all the power we harvest to do
meaningful work, so I'm hopeful some of you have thoughts on this. Why
just
turn off the PV when we need hot water? I expect numerous folks would
benefit by a clean, safe design that let us make use of all the power we
can
tap.

Thoughts???

Thanks!

Gary

===========================================================
$6.95 .com Domain Name Sale! 
Limited Time! ICANN Accredited GoDaddy! 
http://click.topica.com/caab7pQbz8Qcsbz9JC9f/ GoDaddy
===========================================================

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://lists.topica.com/lists/RE-wrenches/read

List rules & etiquette: www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com
--^----------------------------------------------------------------
This email was sent to: michael.welch at homepower.com

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9.bWljaGFl
Or send an email to: RE-wrenches-unsubscribe at topica.com

For Topica's complete suite of email marketing solutions visit:
http://www.topica.com/?p=TEXFOOTER
--^----------------------------------------------------------------