PVGIS Solar Rennes: Solar Simulation in Brittany Region

Brittany's Viable Solar Potential

Sufficient and Profitable Solar Irradiation

Rennes displays an average production yield of 1,050-1,150 kWh/kWp/year, positioning the region at the French average and largely sufficient for attractive profitability. A 3 kWp residential installation generates 3,150-3,450 kWh annually, covering 60-80% of household needs depending on consumption patterns.

Breton myth to debunk: "It rains too much in Brittany for solar power." In reality, Brittany receives as much sunshine as Paris and more than northern France. Breton rain, often light and brief, doesn't prevent solar production. Panels even produce during cloudy weather thanks to diffuse radiation.

Regional comparison: Rennes produces as much as Paris (±2%), 10-15% more than Lille , and only 20-25% less than the Mediterranean south. This difference is largely compensated by Brittany's cool temperatures optimizing panel efficiency.

Characteristics of Brittany's Oceanic Climate

Moderate temperatures: Brittany's oceanic climate maintains mild temperatures year-round. Photovoltaic panels gain efficiency in cool weather. In Rennes, moderate summer temperatures (rarely >28°C) avoid the significant thermal losses experienced in southern France .

Diffuse radiation: Brittany's climate generates significant diffuse radiation. Even during overcast conditions (frequent), panels produce 20-35% of their maximum capacity. Modern technologies efficiently capture this indirect light characteristic of the oceanic climate.

Cleansing rain: Regular Breton rain ensures optimal natural cleaning of panels. Unlike dry regions where dust and pollen accumulate, Breton installations maintain maximum production without intervention.

Luminous summers: May-June-July benefit from very long days (up to 16 hours of daylight in June). This sunshine duration compensates for lower light intensity. Summer production of 400-480 kWh/month for 3 kWp.

Mild winters: Unlike eastern France, Breton winters remain mild (rarely <0°C). Winter production of 140-180 kWh/month, superior to northern and eastern France thanks to oceanic mildness.

Calculate your solar production in Rennes

Configuring PVGIS for Your Rennes Rooftop

Brittany Climate Data

PVGIS integrates over 20 years of meteorological history for the Rennes region, faithfully capturing the specifics of Brittany's oceanic climate:

Annual irradiation: 1,150-1,200 kWh/m²/year average in Brittany, placing the region at the French average with exploitable and profitable potential.

Geographic variations: Brittany's climate presents relative homogeneity. The Atlantic coast (Brest, Quimper) receives slightly less (-3 to -5%) than inland areas (Rennes, Vitré). Southern Brittany (Vannes, Lorient ) displays the best performance (+3 to +5%).

Typical monthly production (3 kWp installation, Rennes):

• Summer (June-Aug): 400-480 kWh/month
• Spring/Fall (Mar-May, Sept-Oct): 240-320 kWh/month
• Winter (Nov-Feb): 100-140 kWh/month

This regular year-round production, characteristic of the oceanic climate, facilitates self-consumption and guarantees stable profitability despite average production.

Optimal Parameters for Rennes

Orientation: In Rennes, south-facing orientation maximizes annual production. Southeast or southwest orientations retain 88-93% of maximum production, offering reasonable flexibility.

Breton specificity: Slightly southwest orientation (azimuth 200-210°) can be interesting to capture often clear afternoons in Brittany, particularly in summer. PVGIS allows modeling these options according to your consumption.

Tilt angle: The optimal angle in Rennes is 35-38° to maximize annual production, slightly higher than the south to best capture the lower sun on the horizon.

Traditional Breton rooftops (40-50° slope for rain drainage) are naturally close to optimal. This steep tilt improves mid-season production and facilitates runoff (permanent self-cleaning).

Adapted technologies: High-performance monocrystalline panels in low-light conditions are recommended in Brittany. Technologies capturing diffuse radiation better (PERC, heterojunction) can provide a 3-5% gain, a justifiable investment in the oceanic climate.

Optimization for Oceanic Climate

Reduced system losses: In Rennes, thermal losses are minimal (cool temperatures). The PVGIS rate of 14% can be adjusted to 12-13% for quality installations, as panels never overheat.

No soiling: Frequent Breton rain ensures exceptional natural panel maintenance. Manual cleaning unnecessary (annual visual inspection suffices). An underestimated economic advantage of Brittany.

No snow: Contrary to misconceptions about "Breton cold," snow is extremely rare in Rennes (<5 days/year, immediate melting). No snow-related constraints for Breton installations.

Marine corrosion: In coastal zones (<3km from sea), favor aluminum or stainless steel structures resistant to salt corrosion. In Rennes (70km from coast), standard structures are suitable.

Breton Architecture and Photovoltaics

Traditional Breton Housing

Stone houses: Characteristic Breton architecture (granite, slate) features steep roofs (40-50°) in slate. Available surface: 30-50 m² allowing 5-8 kWp installations. Integration on slate is aesthetic and respects heritage.

Breton longhouses: These traditional elongated houses offer linear rooftops ideal for panel alignments. Optimal production on these configurations.

Suburban pavilions: The Rennes suburbs (Cesson-Sévigné, Chantepie, Saint-Grégoire, Bruz) concentrate housing developments with 25-40 m² rooftops. Typical production: 3,150-4,600 kWh/year for 3-4 kWp.

Breton Identity and Environment

Strong ecological awareness: Brittany traditionally displays strong environmental sensitivity. Bretons are pioneers in marine, wind, and now solar energies. Photovoltaics fit into this culture of environmental respect.

Energy autonomy: The Breton spirit of independence translates into marked interest in self-consumption and energy autonomy. Battery installations develop faster than elsewhere in France.

Local circuits: Brittany favors short supply chains. This philosophy applies to energy: produce locally what is consumed locally.

Urban Areas and Metropolis

Rennes Metropolis: The Breton capital is developing rapidly (sustained demographic growth). New districts (Baud-Chardonnet, Beauregard) systematically integrate renewable energies.

Eco-districts: La Courrouze, an exemplary sustainable district, integrates photovoltaics, geothermal energy, and green spaces. Model of contemporary Rennes urbanism.

Activity zones: Rennes has numerous technological and commercial zones (Route de Lorient, Nord-Ouest) with warehouses offering significant surfaces.

Regulatory Constraints

Protected sector: Rennes' historic center (heritage rebuilt after the 1720 fire) imposes moderate architectural constraints. The ABF validates projects but the city encourages renewable energies.

Heritage villages: Brittany has numerous classified villages (Locronan, Rochefort-en-Terre). Installations must respect architectural harmony in these sectors.

Condominiums: Check regulations. Breton environmental sensitivity generally favors acceptance of photovoltaic projects in condominiums.

Rennes Case Studies

Case 1: Single-Family Home in Cesson-Sévigné

Context: Recent house, family of 4, heat pump heating, environmental sensitivity, self-consumption objective.

Configuration:

• Surface: 35 m²
• Power: 5 kWp (13 panels 385 Wp)
• Orientation: South (azimuth 180°)
• Tilt: 40° (slate)

PVGIS Simulation:

• Annual production: 5,500 kWh
• Specific yield: 1,100 kWh/kWp
• Summer production: 720 kWh in June
• Winter production: 240 kWh in December

Profitability:

• Investment: €12,000 (quality equipment, after subsidies)
• Self-consumption: 58% (heat pump + remote work)
• Annual savings: €680
• Surplus sale: +€280
• ROI: 12.5 years
• 25-year gain: €12,000
• Energy autonomy satisfaction

Lesson: Rennes suburbs offer good conditions. Heat pump/solar coupling is relevant in Brittany. ROI is correct and strong environmental motivation among Bretons compensates for average production.

Case 2: IT Company Headquarters in Rennes

Context: Offices in digital sector, recent building, high daytime consumption, CSR commitment.

Configuration:

• Surface: 350 m² flat roof
• Power: 63 kWp
• Orientation: Due south (30° frame)
• Tilt: 30° (optimized annual production)

PVGIS Simulation:

• Annual production: 68,000 kWh
• Specific yield: 1,079 kWh/kWp
• Self-consumption rate: 82% (continuous activity)

Profitability:

• Investment: €94,500
• Self-consumption: 55,800 kWh at €0.19/kWh
• Annual savings: €10,600 + resale €1,600
• ROI: 7.8 years
• CSR communication (important in Breton tech sector)

Lesson: Rennes tertiary sector (IT, consulting, services) presents an excellent profile. Rennes, Brittany's digital capital, has numerous tech companies committed to energy transition.

Case 3: Dairy Farm Operation

Context: Dairy farm, significant consumption (milking, milk cooling, buildings), environmental sensitivity (Breton agriculture in transition).

Configuration:

• Surface: 400 m² barn roof
• Power: 72 kWp
• Orientation: Southeast (existing building)
• Tilt: 20° (low-slope roof)

PVGIS Simulation:

• Annual production: 75,600 kWh
• Specific yield: 1,050 kWh/kWp
• Self-consumption rate: 75% (twice-daily milking, cooling)

Profitability:

• Investment: €108,000
• Self-consumption: 56,700 kWh at €0.16/kWh
• Annual savings: €9,070 + resale €3,100
• ROI: 8.9 years
• Improved farm carbon footprint
• Anticipation of environmental regulations

Lesson: Breton agriculture, confronted with environmental issues (green algae, water quality), massively develops photovoltaics. Dairy farms with significant consumption benefit from excellent ROI.

Self-Consumption in Brittany

Breton Consumption Profiles

Breton lifestyle influences self-consumption opportunities:

No air conditioning: Temperate Breton climate makes air conditioning superfluous. Summer consumption remains appliances, lighting, computing. Advantage: reduced summer bills. Disadvantage: less optimal self-consumption of summer production than in the south.

Moderate electric heating: Mild Breton winter limits heating needs compared to the northeast. Heat pumps are developing. Mid-season solar production (April-May, September-October) partially covers light heating needs.

Autumn/winter lighting: Short Breton days (winter) increase lighting needs. This consumption unfortunately coincides with low winter production.

Electric water heater: Standard in Brittany. Switching heating to daytime hours (instead of off-peak) allows self-consuming 350-550 kWh/year.

Developed remote work: Rennes, digital hub (strong IT presence, startups), experiences significant remote work development. Daytime presence increases self-consumption from 40% to 55-65%.

Optimization for Oceanic Climate

Smart programming: With over 180 sunny days (partially or fully), programming equipment during the day (11am-4pm) remains effective in Brittany, especially April-September.

Heat pump coupling: For air/water heat pumps, mid-season solar production (April-May, September-October: 240-320 kWh/month) partially covers moderate heating needs. Size accordingly (+1 kWp).

Thermodynamic water heater: Relevant solution in Brittany. In summer, the thermodynamic water heater heats water with solar electricity. In mild winter, it recovers air calories. Optimal operation year-round.

Electric vehicle: Rennes develops electric mobility (electrified public transport network, charging stations). Solar charging of an EV absorbs 2,000-3,000 kWh/year, optimizing self-consumption April-September.

Realistic Self-Consumption Rates

• Without optimization: 35-45% for household absent during day
• With programming: 45-55% (equipment, water heater)
• With heat pump and programming: 50-60% (mid-season valorization)
• With remote work: 52-65% (daytime presence)
• With electric vehicle: 55-68% (daytime charging)
• With battery: 70-82% (investment +€6,500-8,500)

In Rennes, a self-consumption rate of 50-60% is realistic with optimization, comparable to the French average despite average production.

Economic Arguments for Brittany

Electricity Prices

Electricity prices in Brittany are in the high French average (heating present despite winter mildness). Each self-produced kWh saves €0.19-0.21.

Regional Subsidies

The Brittany Region, committed to energy transition, offers complementary subsidies strengthening photovoltaic profitability.

Property Valorization

On a dynamic Breton real estate market (Rennes in strong growth), a photovoltaic installation improves the energy performance certificate and valorizes the property. Important sales/rental argument.

Valued Energy Autonomy

In Brittany, energy autonomy is culturally valued. Beyond mere economic calculation, producing one's energy responds to a strong Breton identity aspiration.

Choosing an Installer in Rennes

Structured Breton Market

Rennes and Brittany concentrate installers experienced with oceanic climate and local specifics.

Selection Criteria

RGE certification: Mandatory for subsidies. Verify validity on France Rénov'.

Oceanic climate experience: An installer accustomed to Breton climate knows the specifics: optimization for diffuse radiation, sizing for rain/wind, realism about expected production.

Honest PVGIS estimate: In Rennes, a production of 1,050-1,150 kWh/kWp is realistic. Beware of announcements >1,200 kWh/kWp (overestimation) or <1,000 kWh/kWp (too pessimistic).

Equipment adapted to oceanic climate:

• High-performance panels in low light (PERC, HJT)
• Inverters with good efficiency at moderate production
• Stainless steel or aluminum structure (corrosion resistance in coastal zone)
• Reinforced waterproofing (frequent rain)

Enhanced warranties:

• Valid 10-year guarantee
• Realistic production warranty (some guarantee PVGIS production ±10%)
• Responsive local after-sales service
• Included monitoring (important production tracking)

Rennes Market Prices

• Residential (3-9 kWp): €2,000-2,700/kWp installed
• SME/Tertiary (10-50 kWp): €1,500-2,100/kWp
• Agricultural (>50 kWp): €1,200-1,700/kWp

Prices comparable to national average. The mature Breton market offers good value for money.

Points of Vigilance

Realistic estimates: Require PVGIS-based estimates. Announced production must be realistic for Brittany (1,050-1,150 kWh/kWp maximum).

No excessive promises: Beware of commercial discourse minimizing oceanic climate impact. Photovoltaics is profitable in Brittany, but with average production. Honesty is essential.

Production monitoring: In Brittany, monitoring is important to verify the installation produces according to PVGIS expectations and to reassure about actual performance.

Financial Subsidies in Brittany

2025 National Subsidies

Self-consumption premium:

• ≤ 3 kWp: €300/kWp or €900
• ≤ 9 kWp: €230/kWp or €2,070 max
• ≤ 36 kWp: €200/kWp

EDF OA buyback rate: €0.13/kWh for surplus (≤9kWp), 20-year contract.

Reduced VAT: 10% for ≤3kWp on buildings >2 years.

Brittany Region Subsidies

The Brittany Region supports energy transition:

Renewable energy program: Complementary subsidies for individuals and professionals (variable amounts, consult regional website).

Global renovation bonus: Increase if photovoltaics are part of a complete energy renovation project.

Sustainable agriculture: Specific subsidies for farms via the Brittany Chamber of Agriculture.

Consult the Brittany Region website or France Rénov' Rennes.

Rennes Metropolis Subsidies

Rennes Metropolis (43 municipalities) offers:

• Occasional energy transition subsidies
• Technical support via the Local Energy and Climate Agency (ALEC)
• Innovative project bonuses (collective self-consumption)

Contact ALEC Rennes for information.

Complete Financing Example

4 kWp installation in Rennes:

• Gross cost: €10,000
• Self-consumption premium: -€1,200
• Brittany Region subsidy: -€400 (if available)
• CEE: -€300
• Net cost: €8,100
• Annual production: 4,400 kWh
• 55% self-consumption: 2,420 kWh saved at €0.20
• Savings: €484/year + surplus sale €260/year
• ROI: 10.9 years

Over 25 years, net gain exceeds €10,600, correct profitability for western France.

Frequently Asked Questions - Solar in Brittany

Is photovoltaic really viable in Brittany?

Yes! Despite misconceptions, Brittany displays sunshine equivalent to Paris (1,050-1,150 kWh/kWp/year). Breton rain doesn't prevent solar production (diffuse radiation), and even cleans panels for free. ROI is 10-13 years, correct profitability for a 25-30 year investment.

Do panels produce in the rain?

Yes! Panels produce 20-35% of their capacity even in overcast weather thanks to diffuse radiation. Fine Breton rain doesn't stop light. Additionally, it ensures permanent natural cleaning, maintaining optimal production without intervention.

Doesn't marine corrosion damage installations?

In coastal zones (<3km from sea), favor stainless steel or anti-corrosion aluminum structures. In Rennes (70km from coast), standard structures are perfectly suitable. Panels themselves resist sea air. Numerous coastal installations in Brittany without problems.

How to compensate for average production?

Several strategies: (1) optimize self-consumption (remote work, programming), (2) size to cover April-October needs, (3) install a heat pump valorizing mid-season production, (4) consider energy autonomy as value beyond mere economic calculation.

Does Breton identity encourage photovoltaics?

Absolutely! Brittany displays strong ecological awareness and a culture of energy autonomy. Producing locally what is consumed fits into the Breton philosophy of short supply chains. Energy autonomy responds to a strong identity aspiration.

What lifespan in oceanic climate?

25-30 years for panels, 10-15 years for inverter. Temperate oceanic climate preserves equipment (no thermal extremes). Regular rain, far from being a problem, ensures natural maintenance. Breton installations age very well.

Professional Tools for Brittany

For installers and engineering firms operating in Rennes and Brittany, PVGIS24 provides essential functionalities:

Realistic oceanic climate estimates: Accurately model production in Breton climate to avoid overestimations and maintain client trust. Honesty is crucial in this market.

Adapted financial analyses: Integrate Breton specifics (average production, regional subsidies, energy autonomy sensitivity) to demonstrate profitability despite modest sunshine.

Agricultural project management: For Breton installers working with agriculture (numerous dairy farms), PVGIS24 allows precise sizing according to agricultural consumption profiles.

Professional credibility: Facing pragmatic but ecological Breton clientele, present detailed PDF reports with scientifically validated PVGIS data, without overselling.

Discover PVGIS24 for professionals

Take Action in Brittany

Step 1: Evaluate Your Real Potential

Start with a free PVGIS simulation for your Rennes rooftop. See that production (1,050-1,150 kWh/kWp), although average, is largely sufficient for attractive profitability.

Free PVGIS calculator

Step 2: Check Constraints

• Consult the local urban plan (Rennes or metropolis)
• Verify protected sectors (historic center, heritage villages)
• For condominiums, consult regulations

Step 3: Compare Honest Offers

Request 3-4 quotes from experienced Breton RGE installers. Require PVGIS-based estimates. Favor honesty over excessive promises.

Step 4: Enjoy Breton Sunshine

Quick installation (1-2 days), simplified procedures, production from Enedis connection (2-3 months). Even in Brittany, every sunny day becomes a source of savings and autonomy.

Conclusion: Brittany, Land of Energy Transition

With sufficient sunshine (1,050-1,150 kWh/kWp/year), cool temperatures optimizing efficiency, free cleansing rain, and a strong culture of energy autonomy, Brittany proves that photovoltaics is viable in oceanic western France.

Returns on investment of 10-13 years are correct for a 25-30 year investment, and the 25-year gain exceeds €10,000-15,000 for an average residential installation. Beyond economic calculation, producing one's energy in Brittany responds to a cultural aspiration for autonomy and environmental respect.

PVGIS provides you precise data to realize your project. Don't be discouraged by Breton meteorological myths. Facts and data demonstrate photovoltaic profitability in Rennes and Brittany.

Breton identity, historically turned toward the sea and renewable energies (offshore wind, marine energies), finds in photovoltaics a new expression of its environmental commitment and aspiration for energy autonomy.

Start your solar simulation in Rennes

Production data are based on PVGIS statistics for Rennes (48.11°N, -1.68°W) and Brittany. Use the calculator with your exact parameters for a personalized and realistic estimate of your Breton rooftop.