[RE-wrenches] PV Assist

[Jason Szumlanski]

Not to hijack the thread, but I'd like to add that the inverter rating
required for enormous loads can also be beyond practical limits. We are
getting a flood of grid-tie with PV and battery backup requests for whole
house coverage. The reason for the consumer demand is obvious here in
hurricane-prone SW Florida, especially this time of year.

The answer is usually to steer the customer into a critical load system,
still with a sizable battery, and a very large PV array. Theoretically this
could result in similar multiple discharge cycles per day if daytime loads
are significant enough relative to the battery and the PV production is
variable (think air conditioning).

I'll watch this discussion with interest...


Jason Szumlanski

Fafco Solar





On Fri, Aug 16, 2013 at 1:53 PM, 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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