[RE-wrenches] PV Assist

[Larry Crutcher, Starlight Solar Power Systems]

William,

I have a couple customers in a similar situation. The homes are Mexico and they need to operate mini split A/C for a few months. There is no space for increasing the PV array. Once the generator run time is balanced to maintain the batteries between 50% and 80% while also handling any heavy loads, the system can perform well daily. 

The downside is that this deficit charging will lead to early battery failure. The solution I use is to have a "Full Charge Day" bimonthly. The customer must operate the generator through the Bulk and Absorb charge and then start a short, high voltage equalization charge for about 2 hours followed by battery SG testing. This method is the best I could come up with and seems to be working well. During the other months, the PV system can keep up with consumption.

I too am getting more large system requests. If space is not a problem, I install large PV arrays to minimize generator use.

Larry



On Aug 16, 2013, at 12:53 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
 
_______________________________________________
List sponsored by Home Power magazine

List Address: RE-wrenches at lists.re-wrenches.org

Change email address & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org

List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org

List rules & etiquette:
www.re-wrenches.org/etiquette.htm

Check out participant bios:
www.members.re-wrenches.org


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20130817/f6583ea4/attachment-0004.html>