# Technical question on Converting a Home Electrical System to Solar

Posted by Edlikestoboogie on February 17, 2011, 2:35 pm

Hey I have a technical question. Im building a battery solar system.

I would like to figure out how many 12v car lead acid batteries @ 100
amp hours with 500 cranking amps rating it would take to power a
household using an average of 100 KVA per day. I will be using 48v or
96vdc 200watt solar panels and converting thru a 5000 watt dc to dc
inverter to 12vdc to charge batteries. I will then invert power back
thru a 5000watt dc/ac to 110Vac. What are your thoughts. Thanks

Posted by Morris Dovey on February 17, 2011, 2:59 pm

On 2/17/2011 8:35 AM, Edlikestoboogie wrote:

My thoughts are that you would benefit from going to

http://www.catb.org/~esr/faqs/smart-questions.html

sections. The document was written for computer folk, but applies
equally well here.

--
Morris Dovey
http://www.iedu.com/DeSoto/
PGP Key ID EBB1E70E

Posted by Bruce Gordon on February 17, 2011, 9:28 pm
In article

You should NOT be even considering a 12 Vdc Battery bank with anything
over 1 Kw....  It just makes the DC side way to cumbersome... At 5Kw,
you should really be thinking at least 24Vdc, and a much better Battery
Bank Dc Voltage would be 48Vdc. When dealing with Inverter/Chargers and
Charge Controllers, in the 5Kw and above, range you would be much better
off looking at some of the Industrial Traction Batteries systems, rather
than anything in the automotive size and capacity....

Just Say'en....

--

Posted by g on February 17, 2011, 9:32 pm
On 17/02/2011 06:35, Edlikestoboogie wrote:

100 kVA per day?
Maybe you mean Energy usage of 100 kWh in a 24 hour period? (assuming
1kVA = 1 kW)
If so, this is :
Power P = Energy/time =  100 kWh/24h = 4.16 kW

At DC voltage 48 VDC:
Power P = 48 VDC * 87A = 4160W
This is 4 12 V 100 Ah batteries good for 100Ah/87A = 1.15 hours

You need 24 hours:
number of 4 group batteries is 24h/1.15h = 21

You need 21 * 4 = 84 12V batteries.

This is of course rather simplified, there are losses in the system, no
max load have been stipulated. how much discharge of the batteries is
recommended by the manufacturer?

And automotive lead acid batteries may not be your best choice, RV
batteries are better, they are more forgiving with deep discharge.

Then you have to assume days with little or no sun. How many days
autonomy do you need?

The solar array have to be large enough to charge the batteries plus
supply the energy usage after a day of little sun.

Posted by m II on February 17, 2011, 10:23 pm

On 17/02/2011 06:35, Edlikestoboogie wrote:

100 kVA per day?
Maybe you mean Energy usage of 100 kWh in a 24 hour period? (assuming
1kVA = 1 kW)
If so, this is :
Power P = Energy/time =  100 kWh/24h = 4.16 kW

At DC voltage 48 VDC:
Power P = 48 VDC * 87A = 4160W
This is 4 12 V 100 Ah batteries good for 100Ah/87A = 1.15 hours

You need 24 hours:
number of 4 group batteries is 24h/1.15h = 21

You need 21 * 4 = 84 12V batteries.

This is of course rather simplified, there are losses in the system, no
max load have been stipulated. how much discharge of the batteries is
recommended by the manufacturer?

And automotive lead acid batteries may not be your best choice, RV
batteries are better, they are more forgiving with deep discharge.

Then you have to assume days with little or no sun. How many days
autonomy do you need?

The solar array have to be large enough to charge the batteries plus
supply the energy usage after a day of little sun.

-------------------

Don't forget the Peukert factor on those batteries.

If you discharge them that quickly you will may only get about 40-60%.

The Ah rating is only good for the stated rate of discharge, usually 20 hour
rate.

Better to stay with the grid. In most cases it is much cheaper.

mike (the uneducated one)