Panels make power when the sun shines. Batteries keep you running when it doesn’t. That gap — between when solar produces and when you need power — is what batteries solve. In a standalone system, your battery bank is your independence.
The utility charges peak rates in the evening, right when solar production drops to zero. A battery bank lets you charge on your own solar during the day and pull from storage during those peak hours. You stop buying their most expensive power. That’s money back in your pocket.
And if the grid goes down — outage, storm, rolling blackout — your battery keeps the lights on. The utility has zero obligation to restore your power on any schedule. Your battery has no such limitation.
The formula: overnight load (watts) × hours of coverage ÷ usable depth of discharge = battery capacity needed.
LiFePO4 batteries run at 80—90% usable depth of discharge. At 85%, a 5 kWh rated battery gives you about 4—4.5 kWh you can actually use.
Overnight coverage: 500W overnight load × 10 hours = 5,000 Wh needed. Divide by 0.85 DoD: you need about 5,900 Wh of rated capacity. Call it a 6 kWh bank.
Full autonomy: Want to get through a full cloudy day without the grid or a generator? Add your daytime essentials. 800W × 10 hours = 8 kWh more. Total: 14+ kWh. That’s a real battery bank — most people start with overnight coverage and expand from there.
Server rack batteries (typically 5 kWh, 48V per unit) are the standard for serious DIY solar. Modular. Expandable. Compatible with prosumer inverters from Victron, EG4, and Growatt. Cost per kWh is better than all-in-one at scale. Adding capacity later is a wiring job, not a system overhaul.
All-in-one units (Bluetti, EcoFlow) are simpler to set up and integrate tightly with their matched inverters. The trade-offs: higher cost per kWh and you’re locked into one manufacturer’s ecosystem for future expansion.
If you want the most flexibility and the best cost over time, server rack batteries are the answer. If you want simplicity and don’t mind paying for it, all-in-one units work — just know you’re buying vendor lock-in along with the battery.
On American manufacturing: EG4 batteries are assembled in the U.S. SOK batteries are manufactured in China. Victron is Dutch. Do your research and make the choice that aligns with your values.
Battery expansion is easy. Slot in another unit, wire it in, tell the inverter. Done.
Leave room for it now: space in the rack, wiring sized for the full bank you might eventually want, and an inverter that supports the capacity you’re planning toward. The cost of leaving room is zero. The cost of not leaving room is a forced redesign.
Modern LiFePO4 batteries communicate with the inverter digitally — CAN bus or RS485. This isn’t optional. The inverter uses this link to monitor state of charge, cell voltages, temperature, and health, and to manage charging precisely.
“Compatible” means more than voltage matching. Battery and inverter must speak the same protocol. Victron uses CAN bus. EG4 and Growatt typically use RS485. Some batteries support both.
Spec sheets aren’t always reliable on this. The best resource is actual installer reports and forums. Check before you buy — finding out after the fact is expensive.
Know your numbers and picked your battery? Head to Wiring and Safety for how it all connects. Still finalizing your inverter? Inverters covers how inverter choice drives battery compatibility.
Ready to see what a battery bank would do for your situation? Run your numbers — no salesman, no pressure.
DATA SOURCED FROM: U.S. Energy Information Administration (EIA) — electricity rate and TOU rate data. IRS.gov — ITC eligibility under Section 48. Battery specifications and DoD ratings from manufacturer datasheets (Victron, EG4, SOK). EG4 U.S. assembly location from manufacturer public information. Standalone Solar Design Guide, Section 3D (sizing methodology).