Battery efficiencies (was: cost per kWh) [RE-wrenches]

[Hugh Piggott]

<x-flowed>
>95% for wiring, like you.
>85-92% for inverter, like you.
>92% for PV/battery mismatch with an MPPT controller (more conservative than
>you), and 75% with a non-MPPT controller.
>96% for battery efficiency
...
Everyone has their own idea for battery efficiency.  And everyone 
uses batteries differently.

But everyone has some DC power usage that never enters the battery at 
all (goes straight past the terminals to the inverter and runs the 
loads, due to convenient timing of loads being on during sunny/windy 
times).

And at other times we charge a battery at 14 volts and discharge at 
12 volts (so that is only 85% efficient even if you get all your 
Amphours back - which you don't...)

And what about the energy that goes into gassing the battery?

And what about the sunny days when the battery is full at noon 
because the array is sized to keep the system working in December? 
Nobody (except Bill) seems to mention this last one but it must be 
one of the biggest losses of all.  Energy we did not need.  That's 
not really battery efficiency.  It's more like 'system design 
efficiency', or even 'user efficiency' if we want to be really 
accurate.

It's a hard one to put a figure on.

I'd like to at least know how much energy I can expect to be 
available to charge the battery, which should be a relatively simple 
question to answer, but I am still a wee bit fuzzy on that.  I think 
I might use 60-70% of STC x sun hours.  I hope that is conservative.
-- 
Hugh

visiting the Isle of Eigg
http://www.scoraigwind.co.uk/

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com
==^================================================================
This email was sent to: michael_welch at sbcglobal.net

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9.bWljaGFl
Or send an email to: RE-wrenches-unsubscribe at topica.com

TOPICA - Start your own email discussion group. FREE!
http://www.topica.com/partner/tag02/create/index2.html
==^================================================================

</x-flowed>