[RE-wrenches] PV Assist

Fri Aug 16 14:24:56 PDT 2013

Hi William,
In off grid applications, you want to have sufficient RE to keep up with 
load demand 
and only run the generator when RE cannot keep up. However, having too 
much RE is a waste because it will
 result in energy not harvested (if regulating), however, diversion 
controllers can allow the excess energy to be utilized
 (i.e. water heating).
Running the gen up to the bulk level replaces approx 80% of capacity, and 
maximizes fuel consumption, allowing RE to get the
 batteries charged the last 20%. Automatic gen start capability with 
staggered start voltages allow you to target 50% discharge 
more accurately, and minimizes user interaction. Try to calculate the 
total daily kWhrs and match the demand with RE as 
closely as possible. 
Hope that helps,
Rgds,
_____________________________________________________________________________________ 

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From:
Jay Peltz <jay at asis.com>
To:
RE-wrenches <re-wrenches at lists.re-wrenches.org>
Date:
08/16/2013 02:01 PM
Subject:
Re: [RE-wrenches] PV Assist
Sent by:
re-wrenches-bounces at lists.re-wrenches.org

Hi William 

Thx helps a lot. 
I can only say how I do it. 
I'll give the client some options, including the change of appliances and 
usually the price difference makes the sale one way or the other. 

Funny reminds me of the old days, only with much smaller loads/$. 

Good luck

Jay

Sent from my iPhone

On Aug 16, 2013, at 12:49 PM, "William Miller" <william at millersolar.com> 
wrote:

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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