How Many Batteries for 5kW Solar System

In this video, I'm going to show you how many batteries you need for a 5kW solar system.

Now, onto the calculation: Your 5kW solar panel system will generate 15kWh of power on an average day in December. And yes, that needs to fully recharge your battery in a single day. So, we need a 15kWh battery to store all that power. That's roughly 3 48V server rack batteries, considering an off-grid scenario.

But here's the thing: sizing a solar system isn't as simple as matching battery size to panel capacity. It's actually the other way around. You start with a load analysis, then size the battery based on three days of autonomy, and finally size the solar panels based on the battery capacity.

To illustrate, let's walk through an example: Say our off-grid home consumes 10kWh of energy daily. Multiply that by 3 days for autonomy, and you've got a total of 30kWh of battery storage needed. That translates to about 6 server rack batteries, costing around $7,000. Then, we size the solar panel array to recharge those batteries in one day, considering our average of 3 sun hours.

So, how much power can you actually consume from that 15kWh battery while maintaining 3 days of autonomy? The answer: 5kWh of daily energy consumption. That's because the battery needs to store enough energy to last through three days of bad weather.

[macroiu]

by the way, you almost kill the rest of solar videos in terms of domestic application as your layout, explanation & calculation are so organized, clear & easiest to understand!!!

[junkerzn]

Your videos are getting better, ah... but your calculation is scaled impractically high. Very few people install storage and solar for a 10kWh/day load based on winter loading. Let alone with 3 zero-sun days worth of buffer. Its usually just too expensive to do that.

Among other things, 2/3rd of the system's output will wind up being curtailed (thrown away) 8 months out of the year from over-production. Literally thrown away due to over-production. Between roughly mid-March to mid-November or so, only roughly 3kWp (p = installed nameplate) of solar is needed to handle 10kWh/day in consumption, for example. That's less than 1/3rd the amount of solar you specified.

And instead of 30kWh worth of batteries to cover 3 days of poor weather most people will only cover 2 days. You get the 3rd day just from solar accumulated over the prior 2 days. 20kWh of storage rather than 30kWh. Even a bit less. 15 kWh of storage for 10kWh/day of consumption is far more typical (a 2 day buffer inclusive of solar accumulated over those 2 days).

For winter most people who live off-grid make due with less power, and they use a supplemental generator. The reason is simple... no amount of solar and battery is going to cover you across a week-long storm. You need to have the supplemental generation anyway. The goal is thus to minimize fuel consumption during winter rather than eliminate it entirely. Eliminating it entirely is almost impossible in most locations.

-Matt

[gavinator]

great vid as always, but one thing i think was missed: you originally used the lowest sun producing month of December to start your calculations, but then when you broke down your load, you included 3 hours of AC. AC wouldn't be used in winter time, so if it's being used in summer time you'd have way more sun, meaning less panels. so maybe there needs to be a different calculation because AC sure used a LOT of energy :)

[herbertvonsauerkrautunterh]

I currently have have 9 270w panels on the ground. I run two rack batteries down to 85% overnight and they charge up in a few hours in the morning even with part shade on some panels.
I will be putting 12-14 270w panels on my shed roof and eventually I will be using a total of eight 48v rack batteries. Plus grid connect for back up power on extended cloudy days as I have a larger grid connect system as well.

I personally go the other way around and size the inverter I require then the batteries for extended days, I go for at least 5-7 days back up and not 3. Then I size the solar array to suit. There will be excess produced so I can run my electric got water system off solar on a timer a as well during the day.
Fully off grid I would the same. Always buy more than you calculate to create a buffer. I'm the example in the video I would buy 4 batteries and also a bigger inverter/charger and more panels. Nothing wrong with oversizing. The argument for cost is irrelevant. This is someone I wouldn't penny pinch on

[telosfd]

I have the impression that the batteries should not be discharged below 20%. Nice video.

[pathfinder]

No more wet batteries for me, going Lithium and don't regret it, LTOs are the way to go⚡👌💪

[lukewarren]

I subscribed as most of my questions are in his video library
I recently from a single 100 watt Renology panel cheap charger controller on the roof of my 4x4 suv
One year later i peiced together 5000 watt pure sine wave with auto selection up to 48 volt
also three large 400 watt panels that seem to produce 49.5 volt on cloudy days my smaller panel is 215 watt also puts out, 49.5
Volts with a smaller capacity ~ i can't afford to blow up my dreams now
( On roof of my 23' travel trailer only two fit currently thanks in advance for any suggestions or comments

[macroiu]

at 2:29 i dont understand the idle of inverter requires power consumption but leaves the mppt uncounted?

[geoffreykaila]

Sizing based on battery size is over sizing. On a daily basis, you do not need to generate battery capacity energy. Maybe generate daily requirement including loses. This would reduce cost of PV array. Array may be adjusted ups to reduce recovery time after days of autonomy.

[Ricardofromage]

Hi there, im building a system for a friend's truck, in your opinion, for battery degredation ( not harvesting or wire gauge/cost ) on lifepo4 batteries, would it be ok to run a 24v system for a 5kw inverter, or am i best off stepping up to 48v so the current draw is halved? 48v kit is far cheaper, and the way it provides the juice is far friendlier for the batteries, cable size, heat dissipationnetc, thats a given, but 24v means i dont have to introduce battery balancers for a 2s 2p set up, i have 4 x 25.6v 100ah LiFePo4 batteries (10kw hrs).
Hope you read this, thank you in advance if you do 😊🙏 Andy.

[SarahStuff-pu]

In general, whatever you need comfortably to make it through the night with a bit of a buffer, I have 10kwh of batteries for a 2kw set of panels....and it is really close to the number...15kwh for 5kw of panels in my real world experience would be a tad undersized....I would advise 20kwh of storage tbh.

[Fats]

It's interesting that starlink uses 50w and runs 24/7 which really adds up

[sanbell]

Well done and very clear. I just bought your book and i subscribed, but i am not getting the free diagrams to my email when i use your link. I checked my spam folder too.

[lgolsen]

I know the headline limits the possibilities of expanding the solar, but I guess you could expand the size of the panels if you bought one less battery ?
In that case the likelihood of running ‘uninterrupted’ during 3 cloudy days in December would increase … am I right?
Is the likelihood higher or lower ?
What’s your opinion on this ‘total cost’ approach?

[ravindradaundkar]

Whats your thoughts on off grid DC homes?

[kevinm]

I live in a snow belt in a semi-rural area of 20 acre lots. When the power goes off we are low on the list because of low population density. All I want is to live comfortably when the power goes off. I do have natural gas which never goes out but running just one of my two trifuel portable generators 24 - 7 is not a good idea considering wear and tear and fuel cost. I am installing 12, 000 watts of battery backup so that I only have to run generstors a couble hours a day when the power is down. Next year I will put in 2400 watts of solar to run some of my usage year round which Which should cover the solar cost in 4 years and the battery backup in another 6 years. Basically it will be an insurance policy to be able to live comfortably during outages that will pay for itself over time.

[malk]

Hi! I love your videos but I'm confused by this one. The reference table gives us KWh/square meter/day. That's not the same thing as "sun hours", is it? I wish you had gone into more detail on that point.

[lukewarren]

It's beginning to make sense ( please correct me if I error ~my 100 watt modified sine wave is 12 volt only so 2~ 100 Ah batteries wired series parallel gives me 12 volts at 200 Amp gives me, 117% just shy of our safety margin?

[codylange]

I need help with the system I'm trying to build. I have and know the info for how much I use monthly for power. Just need help starting and figuring out how much of what I need pls help

[ShaunMatuwane]

So in total. How much solar panel watts does a 5kw system require