[RE-wrenches] PV Assist

Fri Aug 16 15:22:14 PDT 2013

Honestly, William, in these type of cases I usually walk away from the job
if the customer isn't willing to reduce where possible. There is no such
thing as a completely fool proof off grid PV system. Like a good lawyer,
the best way to have a stellar record is to know which cases to
take....just one man's opinion of course, but we get approached for many
systems like this, particularly in the Caribbean and I have learned that
there is such a thing as a good solar customer and also a bad solar
customer.

Daryl

> 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,
> _____________________________________________________________________________________
>
>
> Eric Bentsen  |   Schneider Electric   |  Solar Business  |   UNITED
> STATES  |   Technical Support Representative
> Phone: +(650) 351-8237 ext. 001#  |
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>
> *** Please consider the environment before printing this e-mail
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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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