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by texasbigdata 1489 days ago
Did you study electrical engineering? Can you recommend a laymans resource for getting smart on how you did those calcs? For example I’d struggle to figure out the battery size for a given wattage / amp of draw.
3 comments

Not the commenter, but it’s fairly straightforward.

I’ve actually made a simple calculator[1] for this, but you don’t really need it.

What you want to do is get a good picture of your actual usage per day in kWh. You can use a Kill-a-Watt plug or similar (a device that kWh that pass through it).

Once you have your daily kWh use, you can multiply by however many days you want to run without charging the battery. A lot of off grid solar people go for 2-4 days.

That gives you the useable battery size in kWh you need.

LiFePo4 batteries (arguably the best for this setup) typically have 80-90% useable capacity. Lead acid (the more traditional kind) have around 50%.

Adjust for that and you know what size of battery to buy.

A lot of batteries are defined as Amp hours and voltage. Multiply them together to get watt hours.

Max_kWh = (Ah * V) / 1000

Useable_kWh = Max_kWh * useable_percent

[1] https://uplevelgreen.com/off-grid-solar-calculator

Awesome thank you.
I got my ham radio license in March and I learned a lot about practical electricity while studying. Might be worth checking out some of the YouTube videos to see if it's up your alley.
I recommend Will Prowse on YouTube, he has tons of good content on DIY solar systems including sizing your array and battery bank.
Thanks!