[RE-wrenches] PV Assist

[William Miller]

Jay:
 
There are four systems in question.  In three the loads are year round and
one is summer only AC loads.  The year round loaded systems have loads day
and night.
 
One is a highway maintenence station with at least 4 residences.
One is a family compound with two homes with electric ranges, water heaters,
AC units (I know its stupid, lord knows I've tried to convince them to
change appliances.)
One is an animal rescue operation with heater loads.
One is a large home with 5 very small, very new, very sophisticated and
frugal AC units
 
I know it is silly to move these loads off-grid, but people do it and they
will hire someone to work on the systems.  It may as well be me, doing the
best I can to use the resources as wisely as possible.
 
William
 
PS:  It always happens like this:  I get a call from a client with problems.
Well, of course their expensive battery bank died and it died because of
wasteful appliances.  The prescription is a new, expensive battery bank and,
at the same time, new, expensive, efficient appliances.  They complain can't
afford both and they have to have the batteries, so that is what they get.
Repeat every two years.  Sad....
 
Wm
 
 
  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Jay Peltz
Sent: Friday, August 16, 2013 12:22 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] PV Assist


Hi William

I feel it's impossible to discuss without more specifics. 

For example if the extreme loads are only every ( just run the genny) so
often vs seasonal ( maybe AC coupling makes more sense vs cycling a
extremely expensive battery 4 x day),  vs year round vs what is do able etc

I would be curious to know what some of the parameters are, as I'm sure
others as well

Jay

Peltz power. 





Sent from my iPhone

On Aug 16, 2013, at 10:53 AM, "William Miller" <william at millersolar.com>
wrote:



Friends:
 
We have been receiving a flurry of requests for design of off-grid systems
where the loads are enormous, relative to normal off-grid requirements.  It
is obvious that the size of PV and battery arrays to power these loads is
beyond what is practical.  We have dubbed these systems Generator/battery
with PV assist, or PV assist for short.
 
These systems will cycle batteries multiple times per day.  It is my
understanding that the extra battery cycels will shorten battery life.
Since generator run is expected, we are willing to increase generator run
time in order to prolong battery life.
 
The parameters I suggest are an aggressive load start and a very high
battery start parameter.  This will prevent deep discharge of the battery
bank.  I know shallow discharge is not the norm, but I don't believe shallow
cycling is a problem as long is it as at the top of the voltage window, i.e.
the batteries achieve absorption at least once per day.
 
We know a load start ciuld result in an abbreviated run time, curtailing
absorption period, but we are assuming there will be a battery votage start
at least once per day allowing full absorption.
 
Has anyone else considered these issues, and what conclusions did you make
 
I am looking forward to a spirited discussion as usual.  I throuroughlyenjoy
and beneift from them, even thought the advice is usually conflilcting.
Thanks in advance.
 
William Miller
 

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