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Solar Battery Savings Calculator

Already have solar panels — or planning them? A battery lets you store excess solar instead of selling it back cheaply to the grid. Enter your system size, self-consumption rate and battery details to see exactly how much a battery adds to your savings.

Quick Start

Step 1. Your solar system
panel size (kWp) and annual production from your inverter app
Step 2. Self-consumption & usage
how much solar you currently use directly and your daily household usage
Step 3. Battery details
capacity, depth of discharge, cost and expected cycle life
Step 4. See results
self-use rate with battery, annual saving and payback period

Tip: Find your annual solar production in your inverter monitoring app (SolarEdge, Enphase, SMA etc.). Your self-consumption rate without a battery is typically 20–40% for daytime-away households and 40–60% for work-from-home households.

Settings

Your Solar System

Total panel capacity. Find on your installer certificate or inverter app.
From your inverter monitoring app. Typical: 850–1,100 kWh/kWp in Central Europe.
How much solar you use directly now. Away during day: 20–35%. Work from home: 40–60%.
Check your electricity bill. Average European home: 8–15 kWh/day.

Energy Tariffs

What you pay per kWh from the grid. Check your electricity bill.
What you receive per kWh exported to the grid. Enter 0 if no feed-in tariff.

Battery System

Total nameplate capacity. Common sizes: 5, 10, 13.5, 20 kWh.
Usable % of total capacity. LFP batteries: 90–100%. NMC: 80–90%.
Cost of the battery unit itself, excluding installation.
Electrician / installer labour cost.
Full charge/discharge cycles before capacity degrades to 80%. LFP: 4,000–6,000. NMC: 2,000–3,000.

Multi-year Projection

Solar battery savings explained: self-consumption, feed-in tariffs and how to calculate ROI

How does a solar battery increase savings?

Without a battery, solar panels produce power during daylight hours — much of which is exported to the grid when you are at work or school. A battery stores this surplus solar energy and releases it in the evening when you arrive home and your household demand peaks. Instead of buying expensive grid electricity in the evening, you use solar you already produced.

Self-consumption rate: the key metric

Self-consumption rate measures the percentage of your solar production that you use yourself (directly or from the battery) rather than export. Without a battery, daytime-away households typically self-consume 20–35% of their solar. A correctly sized battery can raise this to 60–90%, dramatically reducing grid dependence.

When is a battery most valuable?

A battery adds the most value when the gap between your import and export tariff is large. If you pay €0.28/kWh to import but only receive €0.08/kWh for exports, storing that solar is worth €0.20/kWh — the value of avoiding the import. In countries with no feed-in tariff (exported solar is worthless), batteries offer maximum value. In countries with high feed-in tariffs close to the import price, batteries add less incremental value.

Sizing a battery for your solar system

A battery should be sized to capture your typical daily solar surplus — not your total production. A 6 kWp system producing 24 kWh on a summer day with 30% self-consumption has a daily surplus of around 17 kWh. A 10–15 kWh battery captures most of this. Going larger means the battery sits partially empty most days, increasing cost without proportional benefit.

LFP vs NMC: chemistry matters for ROI

Lithium Iron Phosphate (LFP) batteries tolerate 4,000–6,000 full cycles and can be regularly charged to 100%. NMC batteries degrade faster with daily full cycling — typically 2,000–3,000 cycles. For home solar storage with daily cycling, LFP delivers more lifetime kWh per unit of investment cost, even if the upfront price per kWh is slightly higher.

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