Photovoltaic systems: Ground vs. roof - How to make the best choice?

Ground-mounted or rooftop photovoltaics: the complete guide to making the right choice

Investing in a photovoltaic installation is a strategic choice to reduce your energy bill and contribute to the ecological transition. But with so many installation options available, how can you determine whether a ground-mounted or rooftop solution is best for your situation? This comprehensive guide helps you understand the specific features, advantages and disadvantages of each type of installation so you can make an informed choice.

Figure 1: Visual comparison between a rooftop photovoltaic installation (left) and a ground-mounted installation (right)

Roof-mounted photovoltaic installations

Roof-mounted installations are the most common solution for individuals and businesses wishing to generate their own solar electricity.

Advantages of rooftop installations

• Space optimisation: Use of an existing surface without the need for additional space
• No land consumption: Ideal for urban areas or properties with limited space
• Building protection: The panels protect the roof from the elements and extend its lifespan
• Improved security: Less exposed to the risk of damage or theft as they are less accessible
• Little or no administrative procedures: Generally, a simple prior declaration is sufficient
• Lower installation costs: Simpler and less expensive support structures

Disadvantages of rooftop installations

• Structural constraints: Need to check the load-bearing capacity of the roof
• Fixed orientation and angle: Dependent on the existing roof configuration
• More complex maintenance: Difficult access for maintenance and cleaning
• Risk of overheating: Less efficient ventilation, which may slightly reduce efficiency
• More delicate work: Need to ensure waterproofing and risks associated with working at height

The Bernard family's case: Owners of a house near Liège, the Bernards installed 20 panels on their south-facing roof. With a power output of 6 kWp, they cover 70% of their annual electricity needs. "We didn't have any land available, but our roof offered ideal conditions," says Mr Bernard.

"Installing panels on the roof was an obvious choice for us. Without sacrificing any ground space, we now produce our own electricity while protecting our roof from the elements. The return on investment is estimated at eight years, which is very satisfactory."
- Pierre Bernard, owner in Liège

Ground-mounted photovoltaic installations

Ground-mounted installations are an attractive alternative, particularly for those who have sufficient land or whose roof is not suitable.

Advantages of ground-mounted installations

• Optimal orientation and inclination: Total freedom to position the panels in the ideal configuration
• Natural cooling: Better ventilation of the panels increases efficiency
• Ease of maintenance: Easy access for cleaning and maintenance
• Scalability: Easier to expand the installation
• Compatible with solar tracking systems: Option to install trackers to optimise efficiency
• Installation possible even with unsuitable roofing: Solution for historic buildings or fragile roofs

Disadvantages of ground-mounted installations

• Space consumption: Requires sufficient land
• Higher cost: More robust support structures and foundations required
• Administrative constraints: More complex planning procedures depending on power and height
• Increased risks: Greater exposure to vandalism or accidental damage
• Impact on land use: Area becomes difficult to use for other activities
• Risk of shade: Attention must be paid to surrounding vegetation and its growth

The experience of Mr Dupont, a farmer: In south-western France, Mr Dupont installed a 30 kWp ground-mounted power plant on a non-arable plot of his farm. "I chose a ground-mounted installation because my barns had ageing roofs. This solution allows me to make use of unproductive land while benefiting from a stable additional income."

"The ground-mounted installation allows us to maximise production thanks to its ideal orientation. Admittedly, the initial investment was higher, but the simplified maintenance and higher yield more than offset this additional cost in the long term."
- Jean Dupont, farmer in Lot-et-Garonne

Need personalised advice for your photovoltaic project? Wattuneed's experts are available to analyse your situation and offer you the solution best suited to your needs. Contact us today!

Technical comparison: criteria for choosing between ground-mounted and roof-mounted systems

Orientation and inclination

Orientation and inclination play a crucial role in the efficiency of a photovoltaic installation:

• Roof-mounted: You are limited by the existing configuration of the building, which can sometimes compromise optimal efficiency.
• Ground-mounted: You can choose the ideal orientation (generally south-facing in the UK and Ireland) and the optimal inclination (approximately 30° in our regions).

In some cases, a deviation in orientation or inclination from the optimum can reduce performance by 5 to 15%. Ground-mounted installations therefore generally offer better energy efficiency.

Shade management

Shading is one of the main enemies of photovoltaic efficiency:

• On roofs: Care must be taken with regard to chimneys, antennas, nearby trees or neighbouring buildings.
• Ground-mounted: Greater freedom to move away from sources of shade, but beware of surrounding vegetation growth.

Even partial shading can significantly reduce production: shade on just 10% of a panel can reduce its production by up to 50% due to the knock-on effect on interconnected cells.

Ventilation and temperature

Temperature directly affects the efficiency of photovoltaic panels:

• On roofs: Proximity to the roof surface can create an overheating effect, with an estimated loss of efficiency of between 0.3% and 0.5% per degree above 25°C.
• Ground-mounted: Better air circulation allows for more efficient natural cooling and therefore better efficiency, especially during hot periods.

The advantage of ventilation for ground-mounted installations can represent a 3 to 8% increase in efficiency over the year, which is particularly noticeable in summer.

IMPORTANT NOTE: The costs and returns indicated are averages and may vary depending on your location, the quality of the equipment chosen and the specific characteristics of your project.

Regulatory framework and administrative procedures

In the UK

For rooftop installations:

• A preliminary declaration of works is generally sufficient, regardless of the power rating.
• In protected areas (historic monuments, listed sites), the opinion of the Architecte des Bâtiments de France (French architectural review board) may be required.
• The 2021 Climate and Resilience Act requires the installation of solar panels on new commercial buildings, warehouses and car parks larger than 500 m² from 1 January 2023.

For ground-mounted installations:

• For power <3 kWp and height <1.80 m: no formalities required.
• For power <3 kWp and height >1.80 m: prior declaration.
• For power between 3 and 250 kWp: prior declaration.
• For power >250 kWp: building permit and possibly an environmental impact study.

In Belgium

For roof installations:

• In Wallonia: Generally no permit is required if the panels are installed on an existing roof and do not exceed the height of the roof by more than 0.30 m.
• In Flanders: No permit is required for rooftop installations, except for listed buildings.
• In Brussels: No permit required for installations on flat roofs that are not visible from public spaces.

For ground-mounted installations:

• In Wallonia: Permits are generally required, except for installations smaller than 20 m² and no higher than 1.50 m.
• In Flanders: Permit required for most ground-mounted installations.
• In Brussels: Planning permission required for all ground-mounted installations.

In all cases, it is recommended that you consult your local planning department before starting any project, as local regulations may have specific requirements.

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Economic analysis: investment, yield and return on investment

Figure 2: Graphical comparison of costs between ground-mounted and roof-mounted installations

Installation costs

Ground-mounted installations are generally more expensive than rooftop installations, with an average additional cost of 15 to 20%. This difference can be explained by:

• The need for more robust support structures
• Earthworks and foundations
• Longer electrical connections

For a 3 kWp installation:

• Roof-mounted: Between £7,000 and £16,000 including VAT (depending on the complexity of the roof and the quality of the equipment)
• Ground-mounted: Between €9,500 and €21,000 including VAT (depending on the type of terrain and the structure chosen)

Profitability and return on investment

Despite a higher initial cost, ground-mounted installations can offer better long-term profitability thanks to:

• Optimal positioning increasing production (up to 15% additional yield)
• Better ventilation reducing heat loss
• Simpler and less costly maintenance
• The possibility of installing solar tracking systems (trackers) to further increase production

Case study: Comparison of return on investment

For a 6 kWp installation in France with surplus sales:

Although ground-mounted installations have a slightly longer payback period, they will generate more revenue over their total lifetime. Over 25 years, ground-mounted installations could generate approximately €3,000 to €5,000 more than roof-mounted installations.

Financial assistance available

In the UK:

• Self-consumption bonus: For installations ≤ 9 kWp, up to €330/kWp in 2025
• VAT reduced to 10% on equipment and installation for homes over 2 years old
• Reduced VAT rate of 5.5% for installations ≤ 9 kWp for self-consumption with management or storage devices (since November 2024)
• Feed-in tariff for surplus electricity fed into the grid
• Local subsidies: Many regions and municipalities offer additional subsidies

In Belgium:

• Reduced VAT rate of 6% (instead of 21%) for installations on homes over 10 years old
• Green certificates: Although the system has changed, some regions still offer compensation
• Tax reduction for energy-saving investments
• Municipal grants: Vary depending on location
• Zero-interest loans: Such as the Rénoprêt offered by the Société Wallonne du Crédit Social

"We were pleasantly surprised by the amount of aid available for our installation. The reduced VAT and the self-consumption premium represented a saving of around 20% on our total investment."
- Florence Martin, owner of a 4.8 kWp rooftop installation

Environmental impact and landscape integration

Visual impact

• Roof installations: Generally more discreet, especially when integrated into the roof, they can sometimes even improve the aesthetics of an ageing building.
• Ground-mounted installations: More visible, they alter the landscape more significantly. Solutions such as hedges can mitigate this impact.

Biodiversity

• Roof installations: Virtually no impact on local biodiversity.
• Ground-mounted installations: May reduce the space available for local vegetation and wildlife, but agrivoltaic approaches make it possible to combine energy production and agriculture.

Land use

• Roof installations: Do not take up ground space, optimising an already artificial surface.
• Ground-mounted installations: Require approximately 10 m² per kWp, raising the issue of land development, which is particularly sensitive in areas with high land pressure.

Innovative solutions such as agrivoltaics make it possible to reconcile agricultural production and electricity generation. For example, farmers use the space between rows of panels to graze their sheep, which naturally maintain the vegetation.

Integration solutions

• For rooftop installations: Solar tiles, building-integrated panels, simplified integration systems.
• For ground-mounted installations: Plant hedges, two-tone structures that blend in better with the landscape, raised installations that allow for cultivation or grazing underneath.

Concerned about the aesthetics of your photovoltaic installation? Wattuneed offers a complete range of architectural integration solutions, from classic panels to invisible solar tiles. Discover our catalogue of elegant and high-performance photovoltaic solutions.

Solutions for different user profiles

For residential individuals

• Recommended option: Roof installation in most cases
• Specific advantages: Optimisation of existing space, architectural integration, administrative simplicity
• Typical power: 3 to 9 kWp
• Cases where ground installation is preferable: Poorly oriented/shaded roof, historic monument, fragile or asbestos-covered roof

Personalised advice: For a standard detached house with a roof in good condition and correctly oriented, choose a rooftop installation for its discretion and optimised cost.

For farmers

• Recommended options: Installation on agricultural sheds or on the ground depending on the farm
• Specific advantages: Enhancement of low-yield land, stable additional income
• Typical power: 36 to 250 kWp
• Innovation to consider: Agrivoltaics, which combines crop or livestock farming with energy production

Personalised advice: Farmers can consider hybrid systems, with part of the system installed on the roofs of farm buildings and part on the ground on less productive plots.

For businesses and shops

• Recommended option: Building roofs, car parks with shade structures
• Specific advantages: Eco-friendly image, energy self-sufficiency, asset enhancement
• Typical power: 10 to 500 kWp
• Innovation to consider: Car park shade structures with charging stations for electric vehicles

Personalised advice: Businesses with large flat roof areas (warehouses, factories) can optimise yield with slightly sloped structures facing south, even if the building itself does not.

Technological innovations to consider

The photovoltaic sector is evolving rapidly, with innovations that may influence your choice between ground-mounted or rooftop installations:

Figure 3: Ground-mounted installation with tracking system (solar tracker) in an agricultural environment

Solar tracking systems (trackers)

• Compatibility: Mainly suitable for ground-mounted installations
• Production gain: +15 to 30% depending on the technology
• Additional cost: +30 to 60% on the initial investment
• Types available: Single-axis (east-west) or dual-axis (east-west and tilt) tracking

Trackers are particularly suitable for ground-mounted installations as they require sufficient space to prevent the panels from shading each other as they rotate. Wattuneed offers 2-axis photovoltaic trackers that significantly optimise solar energy production.

Figure 4: Bifacial panels installed on the ground with a reflective surface to optimise efficiency

Bifacial modules

• Compatibility: Ground and roof, but more efficient on the ground
• Production gain: +5 to 25% depending on the environment
• Operation: Capture light on both sides (direct and reflected)
• Optimal environment: Reflective surfaces (light-coloured gravel, sand, snow)

Bifacial modules