Kw/day SOlar Design regarding battery sizing

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Kw/day SOlar Design regarding battery sizing

Postby Mr. Green » Fri Nov 04, 2016 10:50 am

Hello, I am new to this forum. As I have read through the threads, I've realized that the discussions are very helpful here.

I am currently working on a design of solar system project. The categories I intend to design sets into 12V, 24V and 48V system. The voltage identified above are not the nominal battery voltage but is the value for the sets of batteries with their configuration that results in these voltage. Simply they are system voltage.

Please correct me if I am wrong: Depending on the total Wh/day each category is to be selected to suit their designs.
For example, If the total Wh/day is less than 1kWh/d, then 12V system design is suitable. If the total Wh/day is greater than 1kWh/day and less than 5kWh/dat than 24V system design is suitable. Anything above 5Kwh is suitable for 48V system

This is what I am planning to do.

Now here is my query: What I wrote down in the above example is what I am planning to do. Can someone tell me if this set is appropriate that there is other better ways to determine the sizing of battery system. Your help in my design is greatly appreciated.
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Re: Kw/day SOlar Design regarding battery sizing

Postby Gordon-Loomberah » Fri Nov 04, 2016 11:09 am

Welcome to the Energy Matters Forums Mr Green :)

12V is generally consigned to portable/camping systems these days, although a few persist with 12V systems for a house supply.
For many years I operated from 24/26V and frequently used 20 to 30kWh/day, so that voltage can perform perfectly well at much higher than your listed 5kWh/day. 5kWh/day is only averaging ~200W, or 8A drain on a 24V battery. At such low loads, many 24V inverters are more efficient than 48V.

I'd suggest 48V (or 52V for LiFePO4) is well suited to daily consumption of 10-15kWh/day or above. Others will no doubt have different opinions ;)
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Re: Kw/day SOlar Design regarding battery sizing

Postby davidg » Sat Nov 05, 2016 1:18 am

Gordon-Loomberah wrote:Welcome to the Energy Matters Forums Mr Green :)
I'd suggest 48V (or 52V for LiFePO4) is well suited to daily consumption of 10-15kWh/day or above. Others will no doubt have different opinions ;)

And more, I use more like Gordon generally does, although in different ways.
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Re: Kw/day SOlar Design regarding battery sizing

Postby Mr. Green » Mon Nov 07, 2016 11:38 am

Thank you guys.
Really appreciate your advice.

Hey Gordon, if you are given a 6kwh/day system, would you go ahead and use a 12V system?
Thank you.
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Re: Kw/day SOlar Design regarding battery sizing

Postby davidg » Tue Nov 08, 2016 9:30 pm

Mr. Green wrote: would you go ahead and use a 12V system?
Thank you.


I would say almost certainly not, myself, not for a house or similar. Maybe a mobile install for: truck, RV, caravan, maybe unless it was 24Vdc based vehicle, otherwise almost certainly 48Vdc minimum.
Off-grid/Hybrid System Specialist - Store Sun to use later- I Do!
SELECTRONIC SPMC-482 7.5kW, 8.2kW's of Arrays
AC-Coupled Grid-Connect Inverters,
2100Ah 48V Bank

Auto Backup Genset
PVOutput Stats

Sparkys light up your life :)
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Re: Kw/day SOlar Design regarding battery sizing

Postby Gordon-Loomberah » Tue Nov 08, 2016 10:47 pm

I do use 12V for backup air pumps in my aquaponics (ie rarely used, just on standby), but I'd use 24V for any small system running an inverter, that is what I used for many years with 5-10kWh/day usage.
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Re: Kw/day SOlar Design regarding battery sizing

Postby Mr. Green » Wed Nov 09, 2016 3:13 pm

Thank you very much Gordon and David it sure does help.
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