Home Battery 2025: The Ultimate Guide to Choosing Your Storage Solution

Domestic Batteries 2025: The Self-Consumption Revolution

The year 2025 marks a turning point for domestic batteries in France and Belgium. With the dramatic collapse of the French photovoltaic feed-in tariff in March 2025 (from €0.1269/kWh to €0.04/kWh), energy storage is no longer a luxury option: it has become the essential solution for maximising the profitability of your solar installation.

With battery prices at an all-time low (€159-208/kWh at Wattuneed), the return on investment for a storage installation is now 3-5 years in Belgium and 5-7 years in France for a typical prosumer profile.

Why invest in a domestic battery in 2025?

1. Maximise self-consumption = maximise savings

Without a battery, your self-consumption rate is capped at 30-40%: the surplus produced during the day is sold back to the grid at £0.04/kWh (France) or £0.04-0.06/kWh (Belgium). With a battery, this rate rises to 70-85%, and each kWh stored avoids a grid purchase at £0.27/kWh (France) or £0.30/kWh (Belgium).

Sources: CRE, EDF OA Solaire (Q1 2025 tariff decree), SPF Economy Belgium, CREG

2. Avoiding the Capacity Tariff in Belgium

In Wallonia and Brussels, the capacity tariff (€56-87/kW/year depending on the DSO) charges you for your monthly peak consumption. A battery smooths out these peaks by discharging during peak times,saving you €150-300/year depending on your profile.

3. Autonomy and backup in the event of a power cut

Modern batteries offer a UPS function (hybrid inverter required): in the event of a power cut, your installation switches to island mode in <15 ms, maintaining power to critical circuits (refrigerator, internet box, heating, etc.).

Battery technologies: LiFePO4 vs Li-ion NMC/NCA

"For domestic storage, LiFePO4 is the benchmark chemistry: maximum safety, exceptional longevity and unbeatable total cost of ownership over 15 years."

Grade A Cells: Why Does It Make All the Difference?

Wattuneed batteries (Delong, Pylontech) incorporate certified Grade A cells:

• Guaranteed actual capacity: 100Ah advertised = 100Ah actual (vs. 90-95Ah for Grade B)
• Minimal capacity drift: <5% in 10 years (vs. 10-20% in 5 years for Grade B)
• BYD cells (Delong 5.12 kWh): world leader in automotive batteries (Tesla, Toyota, Mercedes)
• CALB cells (Delong 15 kWh): prismatic format 314Ah, optimal thermal stability

Battery sizing: Wattuneed method in 3 steps

Step 1: Analyse PV production and consumption

Example of a standard French house with a 6 kWp installation:

• Average PV production: 18 kWh/day in summer, 8 kWh/day in winter
• Total consumption: 15 kWh/day
• Daytime consumption (8 a.m. to 8 p.m.): 6 kWh (40%)
• Night-time consumption (8pm-8am): 9 kWh (60%)
• Average PV surplus: 12 kWh/day in summer, 2 kWh/day in winter

Step 2: Calculate the optimal capacity

Wattuneed formula:

In our example: Average annual surplus = ~7 kWh/day → Optimal capacity = 4-6 kWh

Step 3: Select the appropriate Wattuneed model

Profitability in 2025: ROI by profile (France & Belgium)

Here are 6 real scenarios calculated using actual Wattuneed 2025 prices:

* Battery cost only (hybrid inverter not included: +£1,200-1,800)

"Since March 2025, the ROI of a domestic battery in France has been halved. Self-consumption is no longer an ecological choice, it is a rational economic choice."

Brand comparison: Delong vs Pylontech vs Others

Batteries and Electric Mobility: EV + PV + Battery Synergy

Recharging your EV with PV Surplus

An electric vehicle (EV) consumes an average of 15-20 kWh/100 km. For daily use of 40 km/day (14,600 km/year), this represents:

• EV consumption: ~8 kWh/day (2,920 kWh/year)
• Grid electricity cost: 2,920 kWh × £0.27/kWh = £788/year
• Petrol fuel cost (7L/100km × £1.80/L) = £1,839/year

With a 9 kWp installation + 10 kWh battery + smart charging station:

• EV-dedicated PV surplus: ~1,500 kWh/year (51% of charging)
• Annual EV savings: 1,500 kWh × £0.27/kWh = £405/year
• ROI for battery + terminal: (€1,936 battery + €800 terminal) / (€790 home + €405 EV) = 2.3 years

V2H and V2G: EVs as giant batteries?

Vehicle-to-Home (V2H) and Vehicle-to-Grid (V2G) technologies allow energy from EVs to be fed back into the home or grid. Situation in 2025:

Wattuneed 2025 verdict: V2H is interesting for large-scale backup (rural areas, frequent power cuts) but has a high entry cost. V2G is still marginal. Stationary batteries remain more cost-effective for everyday use.

Collective self-consumption and co-ownerships

Legal framework in France: Order 2021-236

Collective self-consumption (ACC) allows several consumers to share the electricity produced by a common installation. Conditions in 2025:

• Scope: 2 km radius around the installation (or even building)
• Self-consumption bonus: £300/kWp (≤100 kWp) maintained in 2025
• Management: legal entity required (property manager, association, etc.)
• Distribution: fixed or dynamic distribution key (based on actual consumption)

Belgium framework: Renewable Energy Communities (REC)

• Wallonia: prosumer tariff abolished in 2024, active capacity tariff (€56-87/kW/year)
• Brussels: green certificates maintained for installations ≥5 kWp
• Flanders: mandatory digital meter, progressive capacity pricing

Example: Brussels co-ownership (12 households)

🔑 Key to success: cost sharing + capacity tariff avoided + high self-consumption rate thanks to 12 staggered consumption profiles.

Common mistakes to avoid

❌ Mistake #1: Oversizing the battery

Symptom: battery never charged to 100%, incomplete cycles, ROI extended by 2-3 years.

Solution: apply the 50-80% average surplus rule. A battery at 90% daily charge is ideal.

❌ Mistake #2: Underestimating night-time consumption

Symptom: battery drained at 2 a.m., grid purchase in the middle of the night.

Solution: measure actual night-time consumption (base + refrigerator + standby + HC water heater) before sizing. Add a 20% margin.

❌ Mistake #3: Choosing an Incompatible Inverter

Symptom: battery not recognised, BMS not communicating, inefficient charging.

Solution: check BMS/inverter compatibility on the product sheet. Delong/Pylontech compatible inverters: Deye, WKS, Victron, SMA, Goodwe, Growatt, Sofar, SolaX.

❌ Error #4: Neglecting the storage temperature

Symptom: reduced capacity in winter, BMS in thermal protection in summer.

Solution: install the battery in a temperate room (ideally 5-30°C). Avoid uninsulated garages (FR/BE) and rooms >35°C in summer.

❌ Mistake #5: Forgetting Bebat Contributions (Belgium)

Symptom: final bill increased by €114-342 excluding VAT per battery.

Solution: always add the Bebat contribution to the basket (mandatory in Belgium):

• Delong 5.12 kWh: £144.50 excluding VAT
• Pylontech US5000: €114.73 excluding VAT
• Delong 15 kWh: €342.47 excluding VAT

❌ Mistake #6: Waiting for "the next generation"

Symptom: loss of 2-3 years of savings (€1,500-2,000) while waiting for a hypothetical price drop.

Solution: 2025 prices are at an all-time low (€159-208/kWh vs €600-800/kWh in 2020). Each year of waiting = 1 year of lost savings.

❌ Mistake #7: Confusing nominal capacity with useful capacity

Symptom: a "10 kWh" battery only provides 8 kWh in reality, resulting in a surprise regarding range.

Solution: check the authorised depth of discharge (DoD). Wattuneed batteries: DoD 95% (nominal capacity ≈ usable capacity).

Smart Grid, VPP and Blockchain: The Future of Storage

Virtual Power Plants (VPP): Your Battery Serving the Grid

Virtual Power Plants aggregate thousands of domestic batteries to provide grid services (balancing, peak shaving). Situation in 2025 FR/BE:

• Active pilots: Next Kraftwerke (DE/BE), Restore (BE), Agregio (FR/BE)
• Remuneration: £50-150/year/battery depending on capacity made available
• Constraints: communicating inverter required, battery availability 10-20% of the time
• Advantage: passive income, contribution to network stability

Wattuneed compatibility: Deye, WKS Evo Circle Pro and Victron inverters compatible with VPP via MQTT/Modbus API.

Dynamic pricing and AI: Optimise charging/discharging

Dynamic pricing is coming to France (Tempo 2.0 planned for 2026) and Belgium (capacity pricing already dynamic). AI algorithms (e.g. Deye Copilot, available from Wattuneed) automatically optimise:

• Battery charging: cheapest off-peak hours
• Battery discharge: most expensive peak hours (peak shaving)
• Resale of surplus: peak network hours (if dynamic resale pricing)

Estimated gain: +15-25% annual savings vs. static management.

Blockchain and Green Energy Traceability

The European RED III Directive requires the traceability of electricity origin from 2025 onwards. Blockchain projects enable:

• Certify the PV origin of each kWh stored
• Exchange energy between neighbours (peer-to-peer) with smart contracts
• Automaticallyvalue Green Certificates

Status in 2025: still experimental in France and Belgium, but legal framework in preparation (collective self-consumption ordinance 2.0 expected in 2026).

Real Customer Cases Wattuneed

Case #1: The Dupont family – Lyon (France)

Case #2: The Leroy family – Namur (Belgium)

Case No. 3: Ixelles Co-ownership – Brussels (Belgium)

Installation and Standards: France vs Belgium

Electrical Compliance

Simplified Administrative Procedures

France:

1. BEFORE work: Cerfa 13703 (Enedis connection request) + CACSI if surplus injection
2. Installation: by an RGE-certified professional (QualiPV Bat or Élec) for MaPrimeRénov' subsidies
3. AFTER installation: Consuel (certificate of compliance) + Enedis self-consumption agreement
4. 2025 subsidies: Self-consumption subsidy (if ≤100 kWp): €170-300/kWp depending on power

Belgium:

1. BEFORE work: prior declaration to the DSO (Ores, Resa, Sibelga, etc.)
2. Installation: by an approved professional + mandatory electrical compliance certificate
3. AFTER installation: two-way meter (if feeding into the grid) + final DSO agreement
4. 2025 subsidies:
   • Wallonia: Housing subsidies (€500-1,500 depending on income)
   • Brussels: Energy subsidies (20-40% of the amount excluding VAT, capped at €5,000)
   • Flanders: Local subsidies (varies by municipality)

Maintenance and optimisation

Minimal Maintenance = Maximum Performance

LiFePO4 batteries require very little maintenance:

• Monthly: visual inspection (no swelling, normal temperature to the touch)
• Quarterly: SOC (State of Charge) check via inverter app, connection check
• Annually: cell balancing test (automatic via BMS), cleaning of contacts
• Every 2 years: SOC calibration (10% full discharge then 100% recharge)

Depreciation and Battery Health (SOH)

Wattuneed warranty: Delong and Pylontech guarantee ≥80% capacity after 10 years (i.e. SOH ≥80%).

Software Optimisation: Intelligent Programming

Modern inverters allow you to program scenarios:

• "Self-consumption" mode: priority given to battery storage, then surplus injection
• "Backup Priority" mode: maintains 30-50% battery charge for grid outages
• "Peak shaving" mode (BE): battery discharge during consumption peaks (capacity tariff)
• Off-peak+ mode ( FR): battery charge during off-peakhours (0.20 euros/kWh), discharge during peak hours (0.27 euros/kWh)

Deye Copilot example (integrated AI): measured gain of +18% annual savings vs static programming.

Technical Glossary: 15 Terms to Master

FAQ: 6 Essential Questions

1. What is the actual lifespan of a domestic battery?

A Grade A LiFePO4 battery (Delong, Pylontech) lasts 10-15 years in daily use (6,000-6,500 cycles at 80% DoD). After 10 years, it retains ≥80% of its initial capacity (manufacturer's warranty). Beyond 15 years, it can be used for secondary purposes (light backup) before recycling.

2. Can I add a battery to my existing PV installation?

Yes, in 95% of cases! There are two solutions:

• DC retrofit: replace the string inverter with a hybrid inverter (Deye, Victron, etc.) + battery. Cost: £1,200-1,800 for the inverter + £968-2,450 for the battery.
• AC Coupling: keep the existing inverter, add a hybrid inverter + battery in parallel. Cost: same as above, but installation is more complex.

Compatibility: check that the battery voltage (48V/51.2V) is compatible with the new hybrid inverter.

3. Does the battery work in the event of a power cut?

YES, if hybrid inverter with UPS/backup function. In the event of a power cut:

• Switchover: <15 ms (imperceptible)
• Power supply: pre-selected critical circuits (fridge, box, heating, etc.)
• Autonomy: 6-12 hours depending on battery capacity and consumption
• Compatible inverters: Deye, Victron MultiPlus, WKS Evo Circle Pro, Goodwe GW5000-EH

⚠️ Important: backup function disabled by default on some inverters (e.g. Deye) for network compliance. Activation via installer menu.

4. What is the average ROI in France and Belgium in 2025?

Key factor: since March 2025, the ROI in France has been halved thanks to the purchase/resale difference increasing from 0.14 euros/kWh to 0.23 euros/kWh.

5. Is administrative authorisation required to install a battery?

France:

• Battery only (retrofit): Consuel declaration modification (free of charge)
• New PV + battery: Cerfa 13703 (Enedis connection) + Consuel
• No planning permission (indoor battery)

Belgium:

• Mandatoryelectrical compliance certificate (approved body)
• GRD declaration (Ores, Resa, Sibelga, etc.) if power modification
• No planning permission

6. Can I charge my electric car with my domestic battery?

Technically yes, but not recommended:

• Rapid discharge: a 10 kWh battery emptied in 1-2 hours to recharge an EV (vs. 12 hours to power a house)
• Accelerated cycles: reduced battery life if EV is used intensively
• Inappropriate sizing: EVs require 40-80 kWh (8× domestic battery capacity)

Optimal solution: smart charging station that prioritises surplus PV to charge the EV during the day and reserves the domestic battery for the home at night.

Wattuneed SPRL
Rue Henripré 12, 4821 Andrimont, Belgium
Tel: +32 87 45 00 34 – info@wattuneed.com
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