How Many Batteries Do I Need for a 20kW Solar System - Guide

Thinking about going solar with a 20kW system? Smart move—but don’t forget the batteries. Knowing how many you need is key to storing power efficiently and keeping the lights on when the sun’s not shining. 

This guide breaks it down so you don’t overspend or come up short.

How many batteries do I need for a 20kW solar system?

To store one day of energy, you’ll need around 6 to 8 lithium batteries (13.5 kWh each) for a 20kW solar system, depending on your actual usage.

Key Takeaways

• A 20kW solar system generates about 80–100 kWh per day.
• Battery needs depend on backup hours and energy usage.
• Use the formula: Battery kWh = 20 × hours × 1.3.
• Storing 24 hours of energy = ~624 kWh = ~62 lithium batteries (10kWh each).
• Off-grid systems require more batteries than hybrid setups.
• Lithium batteries cost $7,000–$12,000 each, installed.
• Always match battery capacity to your daily usage, not just panel size.
• Inverter compatibility is essential for performance and safety.

Understanding a 20kW Solar System

A 20kW solar setup isn’t small-time—it’s a heavy hitter, usually for large homes, farms, or businesses. Think big roof, big usage, big energy flex.

On average, this system pushes out around 80 to 100 kWh of electricity per day, depending on sun exposure. That’s enough to power a whole house, a pool, and still juice up your EV.

But here’s the catch: solar panels only work when the sun’s out. That’s where batteries come in. You need storage to keep your power flowing after dark or on cloudy days.

So before you jump into battery math, know your daily energy needs and usage patterns. That’s your cheat code for picking the right battery setup.

What Determines Battery Needs?

It all comes down to how you use power. If you’re running AC, gaming rigs, or anything that sucks juice fast, you’ll need more battery backup.

Next up: how long do you want to stay powered when the sun dips? One hour? Eight? That decision sets your storage target.

Also, are you trying to go full off-grid, or just want backup for blackouts? Grid-tied systems usually need fewer batteries.

And let’s not ignore the type of battery. Lithium gives you more usable energy than lead-acid, but it’s also a bigger flex on the wallet.

Bottom line: your battery needs aren’t one-size-fits-all. They’re based on your power habits, your vibe, and your backup goals.

Battery Sizing Formula for a 20kW Solar System

Here’s the cheat code: battery size depends on how long you want backup power and how much you use. The basic formula?

Battery Capacity (kWh) = System Size (kW) × Backup Hours × 1.3 (for losses).

So, if you want 24 hours of backup for your 20kW system: 20 × 24 × 1.3 = 624kWh. That’s your ballpark.

Now break that down into actual batteries. Say each lithium battery gives 10kWh—you’d need about 62 of them. Go smaller with 5kWh batteries? You’re looking at 124. Big flex.

Not every setup needs full-day storage, though. You might only want evening power, not zombie apocalypse prep. So adjust the formula to match your real-life use, not a fantasy bunker.

How Many Batteries Do You Actually Need?

Alright, let’s break it down. A 20kW solar system doesn’t mean much unless you know how long you want backup power. That’s where battery storage comes in.

If you're trying to store one full day of energy, you'd need around 80 to 100 kWh of battery capacity. That’s because most homes use 4 to 5 times their solar system size in kilowatt-hours per day.

So, how many batteries is that? Depends on the type. If you’re using Tesla Powerwalls, which hold 13.5 kWh each, you’ll need about 6 to 8 of them. Using smaller batteries? You’ll need more.

Also, think about how much juice you actually need during an outage. You might only care about the fridge, Wi-Fi, and a couple of lights. That could cut your battery needs in half.

Bottom line: Don’t buy blind. Figure out your daily energy use, then match your storage to your lifestyle. It’s not about maxing out—it’s about making it make sense.

Off-Grid vs Hybrid Solar System Needs

Off-grid systems don’t play around. You’ll need way more batteries because there’s no backup from the grid. No sun? No power—unless your battery setup is stacked.

Hybrid systems are more chill. They let you store energy but still tap into the grid when needed. Fewer batteries, more flexibility.

So if you’re planning to flex full independence, budget for a bigger battery bank. If you’re just looking to trim your electric bill with some off-grid flair, hybrids give you a nice middle ground.

Cost Breakdown of Battery Storage

Alright, here’s the money talk. A single lithium battery (10kWh) will run you anywhere from $7,000 to $12,000 installed. For a 20kW solar setup, you’ll likely need two or more, depending on usage.

So you're looking at $14,000–$25,000 just for battery backup. Want premium brands like Tesla or Enphase? That bumps things up. Labor, permits, and extras? Add a few grand more.

Bottom line: it’s a chunky upfront cost, but if blackouts aren’t your vibe—or you want full energy flex—it’s worth the splurge.

Expert Tips Before You Buy Batteries

Don’t just look at the price tag—look at the capacity. A cheap battery that taps out early isn’t saving you anything.

Match your battery bank to your daily energy use, not just your system size. That’s the real cheat code.

Go for lithium if you want that long-haul reliability. Lead-acid might look like a deal, but it’s high-maintenance.

And whatever you pick, make sure it plays nice with your inverter. Compatibility isn’t optional—it’s non-negotiable.

Frequently Asked Questions

1. Can I run my whole house on a 20kW system with batteries?

Yeah, if you size your battery bank right. Just don’t expect to power a Tesla and a rave at the same time.

2. How many batteries do I actually need?

Depends on the battery type and how long you want backup. Rough ballpark? 16 to 24 lithium batteries.

3. Do I need batteries at all?

Only if you want power during outages or to go off-grid. Otherwise, grid-tied solar can still flex.

Conclusion

So, how many batteries do you need for a 20kW solar setup? It depends on how much energy you're storing and for how long. But now you’ve got the blueprint.

Don’t just throw cash at batteries—match them to your actual power habits. Think of it like building your perfect sneaker rotation: performance, style, and fit all matter.

Get the right combo, and your system won’t just run—it’ll flex.