Solar Battery Sizing 2025: Complete Guide with Dynamic Tariffs

Today, solar battery sizing is a key factor in optimizing your photovoltaic installation. With the introduction of dynamic tariffs in Belgium at the beginning of 2026, the traditional rules are changing radically.

Whereas traditional sizing was based on your average night-time consumption, the new tariffs transform your battery into a genuine financial optimization tool. With batteries like the Delong 15kWh at less than €3,000 from Wattuneed, or €0.04 per kWh restored, the economic equation changes completely.

"Since I resized my Delong 15kWh battery in anticipation of dynamic tariffs, I'm already saving €140 a month on my bill, even in winter!" - Marc D., Wattuneed customer in Liège

☀️ Traditional Sizing vs. New Dynamic Tariff Approach

Traditional approach: night-time consumption

Historically, battery capacity calculations followed this simple logic:

• Average night-time consumption: 4-6 kWh for a typical Belgian family
• Safety margin: +20% for days without sunshine
• Recommended battery capacity: 5-7 kWh

This method works perfectly... when your photovoltaic system produces enough surplus! But what happens in winter?

🎯 Revolution 2026: The tariff arbitrage strategy

Dynamic battery tariffs introduce 5 time bands in Wallonia:

Result: with this new logic, a 12-15 kWh battery becomes more profitable than a small 5 kWh battery!

🔋 Which Battery Capacity for your Profile?

24-hour consumption analysis

To optimize your solar battery sizing, first analyze your complete profile:

• Night-time consumption (10pm-7am): 30-35% of your daily total
• Morning peak (7am-11am): 25-30% - household appliances, preparations
• Mid-day peak (11am-5pm): 15-20% - ideal recharging period
• Evening peak (5-10pm): 30-35% - cooking, lighting, TV

Our recommendations by consumption profile

"Our Victron system with 3 Pylontech automatically manages cycles according to tariffs in real time. ROI achieved in just 24 months!" - Sophie M., architect in Namur

💡 Intelligent Charging Strategy to Maximize Your Savings

The optimal 4-phase cycle

To maximize your energy autonomy with dynamic tariffs:

1. 🌙 Phase 1 - Nocturnal charging (22h-7h)
   → Battery recharged to 100% from the grid at the lowest tariff.
   → Cost: ~0.10€/kWh
2. 🌅 Phase 2 - Morning Discharge (7am-11am)
   → Battery use during the 1st tariff peak
   → Savings: 0.15-0.20€/kWh
3. ☀️ Phase 3 - Solar Recharge (11am-5pm)
   → Combination of solar generation + moderate-rate grid
   → Preparation for evening peak
4. 🌆 Phase 4 - Maximum Discharge (17h-22h)
   → Battery use during maximum tariff peak
   → Savings: 0.25-0.30€/kWh

📊 Economic analysis: ROI and battery profitability

Comparison of conventional sizing vs. dynamic tariffs

🧮 Detailed calculation for a Delong 15kWh

Let's take the concrete example of a Delong 15kWh battery (2950€):

• Night-time arbitrage: 12 kWh × 0.12€ differential × 365d = 525€/year
• Evening arbitrage: 10 kWh × 0.20€ differential × 365j = 730€/year
• Optimized self-consumption: additional gain = €400/year
• 🎯 Total savings: €1655/year
• 📈 ROI: 1.8 years

⚙️ Installation and compatibility: our turnkey solutions

Compatible hybrid inverters

Our lithium batteries integrate perfectly with :

• 🔋 Victron Energy: MultiPlus-II, EasySolar-II GX - intelligent tariff management
• ⚡ Deye : Hybrid inverters 5-12kVA - excellent value for money
• 🌟Solax: X-Hybrid series - advanced monitoring included
• 🏆Fronius: GEN24 - premium Austrian technology

🔧 Simplified installation with Wattuneed

Installing a Delong battery takes less than 5 minutes :

1. 🎲 Stackable system: plug-and-play connection
2. 🛞 Mobility: integrated castors for easy movement
3. 📱 Auto communication: RS485/CAN automatically detected
4. ⚡ Commissioning: Quick configuration via app.

Discover our complete selection of lithium batteries recommended by our experts.

🌡️ Seasonal adaptation of your sizing

Seasonal optimization

Your solar energy storage adapts to conditions :

☀️ Summer (May-August)

• 📈 Abundant production: 25-35 kWh/day depending on installation
• 🎯 Strategy: Maximum direct self-consumption
• 🔋 B attery use: Surplus storage for evening peaks only

❄️ Winter (November-February)

• 📉 Limited production: 3-8 kWh/day
• ⚡ Strategy: Systematic night-time grid charging
• 💰 Focus: Pure tariff arbitrage - maximum ROI!

🍂 Interseasons (March-April, Sept-Oct)

• ⚖️ Variable production: 12-20 kWh/day
• 🎨 Hybrid strategy: Mix of solar generation + grid arbitrage

💰 Solar Battery Price Guide 2025-2026

Price trends and technologies

Solar battery prices have fallen by 60% since 2020 :

🚀 Evolutions 2026 and Future Anticipations

Trends to watch

• 🤖 Predictive AI: Automatic optimization according to weather and tariffs
• 🔄 V2H (Vehicle-to-Home): Your electric car as a backup battery
• 🏘️ Energy communities: energy sharing between neighbors
• 📱 Smart apps: Total control from your smartphone

"By 2027, our community battery will power the whole neighborhood at peak times. The future is smart energy sharing!" - Pierre D., smart-grid pioneer in Ghent

📋 FAQ : Your Questions about Solar Battery Sizing

How long does a properly sized solar battery last?

A correctly sized LiFePO4 lithium battery lasts 15-20 years (6000+ cycles). Oversizing by 20% in relation to your actual needs significantly extends this lifespan by avoiding repeated deep discharges.

Are batteries profitable without solar panels?

Yes, with the dynamic 2026 tariffs, pure arbitrage is enough. By charging at night at €0.10/kWh and returning at peak hours at €0.35/kWh, you save €0.25 per kWh. That's 1100€/year for a 15kWh battery - ROI of 2.7 years without any panels!

Can I add more batteries later?

Absolutely! Our Pylontech (up to 16 units in parallel) and Delong (up to 4 stackable units) systems are 100% modular. Start small and expand according to your needs or changing tariffs.

How can I protect my battery in the event of a power cut?

A hybrid UPS with backup function (Victron MultiPlus-II, Deye) automatically switches to battery power. Depending on your profile, you should be able to maintain your essential equipment for at least 6-12 hours.

What's the difference between kW and kWh for a battery?

kWh = storage capacity (how much energy), kW = power (charge/discharge speed). Optimum ratio: 1:3 (e.g. 5kW for 15kWh). The Delong 15kWh offers 5kW of power - perfect for a family home.

🎯 Your Personalized Sizing with Wattuneed

Every project is unique! Our team of experts will work with you to determine the optimum solution according to :

• 📊 Full energy audit: Detailed analysis of your consumption profile
• 🏠 Technical constraints: available space, existing installation
• 💰 Economic objectives: target ROI, available budget
• 🌱 Long-term vision: future expansion, electric vehicle

Use our smart simulator for a pre-sizing or contact our experts directly for a free personalized study.

"The Wattuneed team helped me perfectly size my Pylontech. With the new rates, I've already recouped 70% of the investment in 18 months!" - Jean-Pierre L., entrepreneur in Brussels

Ready to maximize your savings with dynamic tariffs 2026? Request your free personalized sizing now.