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Forum Index : Electronics : Is bigger better?

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petanque don
Senior Member

Joined: 02/08/2006
Location: Australia
Posts: 212
Posted: 12:26am 12 Mar 2008
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Clearly for a stand alone electrical system a battery bank is needed.

But how big should it be?

While a big battery bank has large capacity.

It is also true that a big battery bank has higher costs.

It would also have greater losses from self discharge.

Logic suggests some form of compromise is needed.

Are the loses from self discharge large enough to need to be allowed for?

If so is there a rule of thumb for matching batteries and generating capacity?
 
AMUN-RA

Senior Member

Joined: 10/03/2007
Location: Australia
Posts: 144
Posted: 12:38pm 12 Mar 2008
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First a load assesment then if no generator 3-5 days spare power from batteries to 50% max discharge on worst winter day of solar for your area= batteries
then array size can be found to recharge from sun then if no sun how big genny= how much power do you realy need=how much money have you got???? or something to that effect. Mick
ps battery equlize needed=bigger aray or bigger genny or more sun to late to think mmmmmmmm beeeeeeeeer.
Every day the sun shines
& gravity sucks= free energy.
 
petanque don
Senior Member

Joined: 02/08/2006
Location: Australia
Posts: 212
Posted: 10:59pm 12 Mar 2008
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I suppose my thoughts are assuming that money is an issue and eventually everybody has some sort of financial constraint.

Is it better to spend a bit more money on extra solar panels or a bigger windmill or a bigger battery?

Clearly the 5 day scenario would be a generalisation and if you live in a sunny location you may be able to manage with less.

Or is it just better to have a generator that you will run a bit more often?
 
AMUN-RA

Senior Member

Joined: 10/03/2007
Location: Australia
Posts: 144
Posted: 10:07am 17 Mar 2008
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up to u if you live in a sunny area 1 day may be ok then start the genny that is y the load assesment is important to find out what the needs of the client r so you can design the system around their ideas and needs
Every day the sun shines
& gravity sucks= free energy.
 
GWatPE

Senior Member

Joined: 01/09/2006
Location: Australia
Posts: 2127
Posted: 12:01pm 17 Mar 2008
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hi petanque don,

my experience indicates RE punters under estimate usage. This under estimates battery size and RE replacement sources and then the fossil fuel has to make up the defecit.

I initially sized my system for 2 people, but with visitors and family staying, I have increased by 50%.

You cannot get it perfect. A grid connect system does allow for credits if you inadvertantly oversize, but with a battery system, it will usually amount to a healthy battery. This is not a bad thing either.

Too big a battery is easily dammaged if the RE cannot maintain the required boost and equalize programs. The cost of fuel may exceed any savings on RE generating capacity over the longer time.

A few things to consider.

cheers, Gordon.
become more energy aware
 
Bryan1

Guru

Joined: 22/02/2006
Location: Australia
Posts: 1344
Posted: 07:33am 18 Mar 2008
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Hi Petanque Don,
Mate 5 years has just past since we installed our stand alone Re array for the house. We have 880 watts of PV and 12 2 volt 600ah sonnenschein batteries. We always keep the voltage above 24 volts where we can and once a month I run the 6 kva backup genny to power my staff & stanbury 80 amp charger. Our family size is now 5 and we live comfortable on RE so as you can see our RE array is just big enough to cope without stressing the batteries too much. Always allow a 50% buffer and never really deep discharge the batteries as I consider every deep discharge is about 20 less charge cycles. Time will tell how long our batteries last and I'm pinning my hopes on 10 years atleast.

Just remember RE is substancial cost and care is the most important factor for long term use.

Cheers Bryan
 
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