How to design and size a solar battery system

Learn how to calculate the battery capacity, or battery size, for your solar electric system.

⏱️Timestamps:
0:06 Intro
0:53 --- Why are batteries needed?
1:10 --- What batteries are available?
1:40 --- What is the useable energy?
2:16 --- What is the battery longevity?
3:06 How to assess your energy demand
5:57 How to estimate system losses
6:23 --- round trip efficiency
7:07 --- wiring losses
7:32 --- conversion efficiency
8:20 How to calculate battery size
8:28 --- select a battery voltage
10:44 --- select days of autonomy
11:51 --- consider thermal losses
12:25 --- specify depth of discharge
13:42 --- calculate battery capacity
14:19 --- calculate number of batteries
15:14 Other videos and resources

[aatirehrarsiddiqui]

By far the best video I have seen on the topic. Precise and to the point.

[martinlebl]

By far the best breakdown on how to calculate power needs; how to play with battery voltage and solar panel sizing to accommodate said power needs; I’m working on an OTG cabin and wish I could have seen this video last year. Thank you for producing. Consider another video on examples when you increase the solar panel array voltage or the battery voltage capacity, to a fixed power consumption need. Great work!

[SamWinchester-xmes]

Most clear explanation about solar system set-up I've ever seen ❤ Good job 👍

[davidrumsey]

A very well explained and thorough video, far better than most others out there. Thanks for this and others you have presented.
However, unless I have misunderstood, there seems to be an error in one of the calculations:
At 7.00 minutes you said you would assume using lead-acid batteries at a round trip efficiency of 85%, and the use of these batteries was confirmed by later calculations using a depth of discharge of 50%.
But, at 8 minutes you calculated the combined system losses using a round trip efficiency of 0.95 (matching lithium batteries) not 0.85. This throws off the Load Subsystem Efficiency by quite a bit.. it should be 0.76 not 0.85.
In turn, that throws off the calculation of final battery capacity: it should be around 7645 Ah, not the 6835Wh given.

[NA-kwex]

Excellent presentation- thank you very much for the outstanding info

[cowboymcq]

Fantastic videos dude 👍🏼❕
I’ve been dealing with solar for about 2 years now part time in Maine on my total off grid cabin and at my house in CT running the essentials in the house TV Wi-Fi freezers fridge raider
Keep the awesome videos coming
Thanks 👍🏼👍🏼👍🏼👍🏼

[miguelangellopezdiaz]

Very well explained!! but the number of batteries is double the quantity you get, cuz you are using 12V batteries, it means you will need 64 batteries.

[JamesG]

Start undersized and live with it. You'll figure out how to manage loads by time of day and season. You can always add more later. If you go too big, it's money down the rat hole.

[SalahBinTaleb-redi]

The best video that analyze this topic. Thanks

[PalithaAlahakoonDAP]

Thanks a lot, I appreciate your knowledge-sharing session. got a lot of things to my knowledge base.
Thank you again best wishes

[mikatekochabani]

Thanks for the video. Easy to follow. All complexities broken to simpler, digestible chunks.
South Africa.

[ghz]

@6:20 round trip battery efficency has zero to do with battery capacity and should be removed from this calculation.
It's a one way trip not a round trip.
It measures how much more energy you need to charge the battery than it can deliver.
This is added to the charge energy but not subtracted from the capacity.
You rate capacity on energy delivered not energy to recharge.
Likewise line losses don't belong here there are no long runs of wire here.
The inverter should be only a couple feet from the inverter.
Wire from the panels to the charge controller are only involved in charging not discharging.

[henrygonzalez]

Thanks so much for that information, but I still got a question. If the voltage system selected is 24V, why do you use 12V batteries? that only means that you will have to set more batteries in paralel which, as far as I know, it is not recommended. I'd really appreciate your answer. Thx

[swss]

Also you should include the battery degradation after lots of cycles in the denominator such as 0.8 after 500 cycles for lead.

[nathanwiel]

What about the inverter efficiency ? Inverters have a stanby consumption,
Meaning at night even with zero load they will draw some amount of watts from your battery, shouldnt this be in the calculation?

[robertsimpson]

Great explanation with the general math, but the math application is very very bad😂. Math formula says 24 volts but got 12v batteries, choose lead batts with 50% round trip but used 95% lithium round trip. Number of batteries should be x2 since they are 12V and not 24Vdc, etc. But the general logic is sound with much details without the insignificant details that usually don't matter but cause a lot of confusion.

[zhouyong]

Dear Mr. Schiavone, I have a doubt at last two formula. Temperature conpensation factor 1.19 should be at lower part of the formula, so the result is: The last formula, the battery voltage is 12V, not 24V, so the quantity should be: 4826*2/215=44.9, roundup to 45 pcs. Just for your consideration. Thanks.

[valramsingh]

Very well explained .thanks Prof..I dont see one done for battery bank recharge rate.. the time a system takes to recharge esp one using solar by day and wind by night.

[engr.usmanullah]

7:05 Selected (0.85) Lead acid battery
but in
8:13 you used 0.95 (Lithium ion) why?

[paolopetrozzi]

At 00:10 Your name is "Schiavone", and not "Sciavon".