A photovoltaic (PV) system is an investment for decades. Good planning determines yield, cost-effectiveness and long-term satisfaction. If you ask the right questions in advance and proceed systematically, you avoid expensive mistakes and make full use of your roof’s potential.

This article takes you step by step through the planning process – from the first roof assessment and system sizing through to choosing a professional installer. With this guide you can make informed decisions and know what really matters.

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Step 1: Is your roof suitable?

Not every roof is equally suitable for solar. Before going into detailed design, check whether the basic conditions are met.

Roof condition and structural capacity

A sound roof is essential. Solar modules typically last 25 to 30 years – repairing the roof after installation is complex and costly. Check:

• Roof covering: Is the roof watertight? Are tiles, slates or felt in good condition?
• Age of the waterproof layer: For felt/bitumen roofs older than about 15 years, refurbishment before installation is usually advisable.
• Structural capacity: A PV module weighs around 18 to 22 kg, plus mounting rails and snow/wind loads. For older buildings, have a structural engineer or competent surveyor check the load-bearing capacity.

In the UK and Ireland, this should be in line with local building regulations and structural design standards (e.g. BS EN 1991 for actions on structures and relevant parts of BS EN 1990/1993). For international projects, refer to the local implementation of Eurocodes or national structural codes.

Roof area and orientation

Available area limits the maximum system size. As a rule of thumb, you need about 5 to 6 m² of roof area per kilowatt peak (kWp) of PV capacity. A 40 m² roof can therefore accommodate roughly 7 to 8 kWp.

Orientation has a major impact on annual yield:

Orientation	Pitch	Yield (relative to south)
South	30–35°	100%
South-east / south-west	30–35°	95–98%
East / west	30–35°	85–90%
North	any	60–70% (usually uneconomic)

South-facing roofs are ideal, but east–west roofs are also worthwhile. They generate power more evenly throughout the day, which increases self-consumption.

Shading

Shading is the enemy of every PV system. Even a small shadow can significantly reduce the output of an entire string. Check for potential sources of shade:

• Neighbouring buildings
• Trees (consider growth over the next 20–25 years)
• Chimneys, dormers, satellite dishes
• Rooflights and skylights

For a more precise shading analysis you can use:

• Google Earth with sun-path simulation (free)
• PVGIS with horizon profile (free, online)
• Professional tools such as PV*SOL or Polysun (usually used by installers)

Where partial shading cannot be avoided, micro-inverters or power optimisers can help to reduce losses.

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Step 2: Determine your electricity demand

System size should be matched to your electricity use. An undersized system wastes potential, while an oversized system pays back more slowly.

Annual consumption as a starting point

Work out your average annual electricity consumption from the last 2–3 years. You will find the figures on your electricity bills.

Typical consumption by household size:

Household size	Use without EV / heat pump	Use with EV	Use with heat pump
1–2 people	2,000–3,000 kWh/a	4,000–6,000 kWh/a	5,000–8,000 kWh/a
3–4 people	3,500–5,000 kWh/a	5,500–8,000 kWh/a	6,500–10,000 kWh/a
5+ people	5,000–7,000 kWh/a	7,000–10,000 kWh/a	8,000–12,000 kWh/a

Electric vehicles typically use 2,000 to 4,000 kWh per year, depending on mileage. Heat pumps in single-family homes need around 3,000 to 6,000 kWh, depending on insulation and heating load.

Analyse your load profile

When you use electricity is more important than how much you use in total. A household that is empty during the day uses solar power differently from a home with people working from home.

Ask yourself:

• When do we use most electricity? Morning, midday, evening?
• Which major loads run during the day? Washing machine, tumble dryer, dishwasher, heat pump
• Can we shift loads into sunny hours? Timers, smart home controls, EV charging schedules

A typical domestic load profile shows peaks in the morning (6–8 a.m.) and evening (6–9 p.m.). Solar output is highest around midday (11 a.m.–3 p.m.). The overlap between generation and demand determines your self-consumption without a battery.

Plan for future demand

Look ahead 5 to 10 years:

• Planning to buy an electric car?
• Planning to install a heat pump?
• Considering a pool or sauna?
• Long-term home office?

These changes can significantly increase demand. If you size the system too tightly today, you may regret it later.

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Step 3: Size the system

The optimum system size follows from roof area and electricity demand. The principle is: as large as possible, but only as large as is economically sensible.

Rule of thumb for sizing

A widely used rule of thumb is: 1 kWp of PV capacity per 1,000 kWh of annual consumption. A household using 5,000 kWh per year would therefore need around 5 kWp.

In the UK and Ireland, 1 kWp typically generates around 850 to 1,050 kWh per year, depending on:

• Location (south of England: towards 1,000–1,050 kWh; Scotland / north-west Ireland: around 850–950 kWh)
• Roof pitch and orientation
• Shading

Across much of continental Europe, yields are similar to Germany (roughly 900–1,100 kWh/kWp). For international projects, check local solar irradiation using PVGIS or similar tools.

Include battery storage in the design

A battery increases self-consumption from typically around 30% to 60–70%. Battery size should match your load profile:

Battery sizing:

• Small batteries (5–7 kWh): For 3,000–5,000 kWh annual use, without EV or heat pump
• Medium batteries (8–12 kWh): For 5,000–8,000 kWh annual use, with EV or small heat pump
• Large batteries (13–20 kWh): For more than 8,000 kWh annual use, EV and heat pump

Rule of thumb: battery capacity in kWh = daily electricity use in kWh × 0.8 to 1.2

A household using 5,000 kWh per year (≈14 kWh/day) would need about 11 to 17 kWh of storage. In practice, 10 to 12 kWh is often chosen as a compromise between economics and autonomy.

Example calculation

Starting point:

• 4-person household
• Annual consumption: 4,500 kWh
• Planned: electric car in 2 years (+3,000 kWh)
• Available roof area: 50 m² (south-facing, 35° pitch)
• Location: southern UK or comparable solar resource

Sizing:

1. Total future consumption: 4,500 + 3,000 = 7,500 kWh/a
2. System size: 7,500 kWh ÷ 1,000 kWh/kWp ≈ 7.5 kWp (using 1,000 kWh/kWp as a realistic UK/Ireland average for a good south-facing roof)
3. Number of modules: 7.5 kWp ÷ 0.42 kWp/module ≈ 18 modules
4. Area required: 18 modules × 2 m²/module = 36 m² (fits on the roof)
5. Battery size: 7,500 kWh ÷ 365 ≈ 21 kWh/day → battery: 12–15 kWh

Result: approx. 7.5 kWp system with a 12 kWh battery

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Step 4: Check the economics

A PV system needs to pay for itself over its lifetime. Key factors are capital cost, energy yield, electricity price trends and available support schemes.

Investment costs (indicative 2026 values)

Current ballpark figures for turnkey residential systems in the UK and Ireland (including design, installation and VAT, excluding major network upgrades):

System size	Cost without battery	Cost with 10 kWh battery	Cost per kWp
5 kWp	£7,000–£9,000	£12,000–£15,000	£1,400–£1,800
7 kWp	£9,500–£12,500	£15,000–£19,000	£1,350–£1,780
10 kWp	£12,000–£16,000	£18,000–£23,000	£1,200–£1,600

Larger systems are usually cheaper per kWp. Batteries add roughly £500 to £800 per kWh of usable capacity, depending on brand and integration.

Internationally, prices vary considerably; always compare several local quotes.

Calculate energy yield

Use online tools such as PVGIS (free from the European Commission) for a detailed yield estimate. You will need:

• Location (address or coordinates)
• Roof pitch
• Orientation
• System size in kWp
• Module type (crystalline silicon)

PVGIS provides monthly and annual yields, taking into account weather data and typical system losses. For complex shading, a professional design tool is recommended.

Payback period

The payback period indicates how many years it takes for the investment to be recovered through bill savings and export income.

Simplified calculation:

Payback period = investment cost ÷ annual financial benefit

Example (UK/Ireland context):

• Investment: £16,000 (approx. 7.5 kWp + 10 kWh battery)
• Annual yield: 7,500 kWh
• Self-consumption: 65% (with battery) = 4,875 kWh
• Export to grid: 35% = 2,625 kWh
• Retail electricity price: £0.30/kWh (30 p/kWh)
• Export tariff (Smart Export Guarantee or similar): £0.08/kWh (8 p/kWh – varies by supplier)

Annual benefit:

• Self-consumption: 4,875 kWh × £0.30/kWh = £1,462.50
• Export: 2,625 kWh × £0.08/kWh = £210.00
• Total: ~£1,672.50 per year

Payback period: £16,000 ÷ £1,672.50 ≈ 9.6 years

After this, the system effectively generates net savings. With a technical lifetime of 25 years or more, that leaves around 15 years of “profit” in the form of reduced bills.

Make use of support schemes

Support mechanisms differ between countries. The German EEG feed-in tariff and KfW loans do not apply in the UK or Ireland. Instead, the following are relevant:

United Kingdom

VAT relief:

• As of 2024, most domestic solar PV and battery installations qualify for 0% VAT (zero-rated) when installed together with energy-saving materials by an eligible installer.
• This significantly reduces upfront costs compared with standard 20% VAT.

Smart Export Guarantee (SEG):

• Replaced the old Feed-in Tariff.
• Licensed electricity suppliers with more than 150,000 customers must offer an export tariff for surplus electricity exported to the grid.
• Tariff levels are set by suppliers and typically range from about 2–20 p/kWh; 5–10 p/kWh is common.
• No central guarantee period, but you can switch suppliers to get better rates.

Local and regional schemes:

• Some local authorities and devolved administrations offer additional support:
  • Scotland: Home Energy Scotland loans and grants may support solar PV and batteries as part of wider energy efficiency and low-carbon heating packages.
  • Wales and Northern Ireland: Periodic grant or loan schemes; check current programmes via official government websites.
• Availability and conditions change frequently; always check local government and energy agency websites.

Building regulations and standards:

• PV installations must comply with UK Building Regulations, particularly:
  • Part A (structure),
  • Part B (fire safety),
  • Part L (conservation of fuel and power),
  • Part P (electrical safety in dwellings).
• Electrical work must comply with BS 7671 (IET Wiring Regulations).
• Structural and wind/snow load design follows UK implementations of Eurocodes (e.g. BS EN 1991 series).

Ireland

SEAI Solar PV grant:

• The Sustainable Energy Authority of Ireland (SEAI) offers grants for domestic solar PV:
  • Up to €2,100 for systems up to 4 kWp (e.g. €800/kWp up to 2 kWp, then €250/kWp up to 4 kWp – check current rates).
  • Additional support for battery storage has been available in some years; current schemes should be checked on the SEAI website.
• Eligibility typically requires:
  • A dwelling built before a certain cut-off year,
  • Use of SEAI-registered installers,
  • Compliance with relevant Irish standards and building regulations.

Microgeneration Support Scheme (MSS) and export payments:

• Households can receive payment for exported electricity under supplier-led schemes.
• Export tariffs vary by supplier; typical rates are in the range of €0.13–€0.20/kWh, but check current offers.

Building regulations and standards:

• PV systems must comply with the Irish Building Regulations, especially:
  • Part L (Conservation of Fuel and Energy),
  • Part A (Structure),
  • Part B (Fire Safety),
  • Part D (Materials and Workmanship).
• Electrical installations must comply with ET 101 (National Rules for Electrical Installations) and relevant EN standards.

International (EU and beyond)

• Many EU countries have their own feed-in premiums, net-metering or investment grants. These are often linked to the Energy Performance of Buildings Directive (EPBD) and national energy strategies.
• For EU member states, PV design and performance calculations often refer to:
  • EN ISO 52000 series (energy performance of buildings),
  • EN ISO 6946 (U‑value calculation for building elements),
  • National implementations of EN 50583 (building-integrated PV).
• Outside the EU, check national energy agencies and utility programmes for:
  • Investment grants,
  • Tax credits,
  • Net-metering or net-billing schemes.

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Step 5: Choose the right components

Component choice affects yield, lifetime and maintenance needs.

Solar modules

Crystalline silicon modules dominate the market. Pay attention to:

Power rating: Modern modules typically deliver 400 to 450 Wp. High-performance modules with TOPCon or heterojunction (HJT) technology can exceed 450 Wp.

Efficiency: 20–23% is standard. Higher efficiency is useful where roof area is limited.

Warranty:

• Product warranty: at least 12 years (15–20 years is better).
• Performance warranty: typically 25 years with 80–85% remaining output.

Technology:

• Monocrystalline PERC: Standard, good value for money.
• TOPCon: Higher efficiency, better low-light performance.
• Heterojunction (HJT): Premium, highest efficiency and good temperature stability.

Well-known manufacturers include Longi, JA Solar, Trina Solar, Meyer Burger (Europe), SolarWatt and others. In the UK and Ireland, many installers work with Tier 1 brands listed by major banks and insurers.

Inverters

The inverter should be matched to system size. A common rule is 90–100% of the total DC module capacity.

Inverter types:

Type	Advantages	Disadvantages	Typical use
String inverter	Cost-effective, efficient, proven	Sensitive to partial shading	Simple roofs without significant shading
Hybrid inverter	Integrated battery charger/control	More expensive, more complex	Systems with battery storage
Micro-inverter	Each module operates independently	Higher cost, more components	Shaded or complex roofs, multiple orientations

Key features:

• Efficiency: at least 96%, ideally 97–98%.
• MPPT trackers: at least 2 for systems with multiple roof aspects.
• Cooling: Fanless designs are quieter and often more reliable.
• Warranty: at least 10 years, with options to extend.

Common brands in Europe include SMA, Fronius, Kostal, Huawei, SolarEdge, Solis and others.

Battery storage

Lithium iron phosphate (LFP) has become the standard for domestic storage. LFP batteries are safer, more durable and more cycle-resistant than many other lithium chemistries.

Selection criteria:

• Capacity: see sizing in Step 3.
• Depth of discharge (DoD): at least 90%, ideally 95–100%.
• Round-trip efficiency: at least 95%.
• Cycle life: at least 6,000 full cycles (roughly 15–20 years in typical use).
• Warranty: 10 years with at least 70–80% remaining capacity.

Well-known manufacturers include BYD, Pylontech, SENEC, Fronius, Huawei, LG Energy Solution and others. In the UK and Ireland, compatibility with local grid codes and installer support is crucial.

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Step 6: Find a professional installer

Installer quality is critical. A PV system is a complex electrical and structural installation – mistakes in design or installation cost yield and cause headaches.

Quality criteria

Look for the following:

Qualifications (UK/Ireland):

• For the UK:
  • Membership of a MCS-certified installer scheme for solar PV and batteries (Microgeneration Certification Scheme).
  • Registration with a Competent Person Scheme (e.g. NICEIC, NAPIT) for electrical work.
• For Ireland:
  • Registration as a SEAI-registered solar PV installer for grant-eligible work.
  • Use of qualified electricians registered with Safe Electric.

Experience:

• At least 50 completed residential systems.
• References and case studies in your region.
• Experience with the type of system you want (with/without battery, EV integration, etc.).

Scope of services:

• Site visit and roof survey.
• Shading analysis.
• Detailed, itemised quotation (not just a lump sum).
• Handling of grid connection applications and export registration.
• Commissioning and handover.
• Optional maintenance or monitoring packages.

For international projects, look for installers accredited by national renewable energy or electrical bodies and familiar with local grid codes.

Compare quotations

Obtain at least three quotes and compare:

Prices:

• Total price (equipment + installation + paperwork).
• Price per kWp.
• Payment terms (stage payments linked to milestones).

Components:

• Manufacturers and exact models (ask for datasheets).
• Warranty terms and who backs them (manufacturer vs. installer).
• Expandability (e.g. ability to add a battery later).

Yield estimates:

• Annual yield in kWh.
• Expected self-consumption.
• Economic analysis (payback, lifetime savings).

Timeline:

• Lead time for equipment.
• Installation duration (usually 1–2 days for a typical house).
• Grid connection and export registration (can take several weeks depending on the DNO/DSO).

Be cautious if:

• Large upfront payments are requested before any work.
• Prices are unrealistically low.
• High-pressure sales tactics are used.
• Warranty or accreditation details are vague or missing.

Contract and documentation

Check that the contract clearly sets out:

• Confirmed components (brands, models, capacities).
• Performance expectations (e.g. estimated annual yield).
• Warranty and workmanship guarantees (in the UK, often backed by insurance via schemes like HIES or RECC).
• Evidence of installer insurance (public liability, professional indemnity where applicable).
• Handover documentation and commissioning reports.

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Step 7: Permissions and registration

Requirements differ between countries. In Germany, most residential PV systems are planning-exempt but must be registered with the grid operator and the national market register. In the UK and Ireland, the framework is different.

Planning permission

United Kingdom:

• Most roof-mounted domestic PV systems fall under permitted development rights and do not require planning permission, provided they:
  • Do not protrude more than 200 mm beyond the roof plane.
  • Are not higher than the highest part of the roof (excluding chimneys).
  • Meet specific conditions in conservation areas and for listed buildings.
• Planning permission may be required for:
  • Listed buildings.
  • Conservation areas or World Heritage Sites (especially for street-facing roofs).
  • Ground-mounted arrays above certain sizes or heights.
• Always check with your local planning authority.

Ireland:

• Since 2022, most domestic rooftop PV systems are exempt from planning permission up to certain size limits (e.g. up to 60 m² in many cases), subject to conditions on visual impact and proximity to boundaries.
• Restrictions may apply in architectural conservation areas or for protected structures.
• Confirm details with your local planning authority or via the Department of Housing guidance.

International:

• Many countries treat small rooftop PV as exempt or “minor works”, but rules vary.
• For ground-mounted systems, façade-integrated PV or installations in protected areas, formal planning permission is often required.

Grid connection and notification

United Kingdom:

• Grid connection must comply with Engineering Recommendation G98 or G99, depending on system size and export capacity.
  • Small domestic systems (up to 16 A per phase) usually fall under G98 (simpler process).
  • Larger systems require G99 applications and prior approval.
• Your installer normally:
  • Submits the necessary G98/G99 forms to the Distribution Network Operator (DNO).
  • Arranges for any meter changes needed for export metering.

Ireland:

• Connection to the ESB Networks distribution system requires:
  • A NC6 (microgeneration) or NC7 (larger) application, depending on system size.
  • Approval before commissioning for larger systems.
• Your SEAI-registered installer typically handles these applications.

International:

• Grid connection procedures are defined by local distribution or transmission system operators and often reference national grid codes for small-scale generation.

Registration and energy certificates

United Kingdom:

• To access the Smart Export Guarantee and some finance products, systems must be:
  • Installed by an MCS-certified installer.
  • Registered with MCS, which issues an MCS certificate.
• There is no central PV plant register equivalent to Germany’s MaStR, but:
  • The system will appear on your Energy Performance Certificate (EPC) if the property is reassessed.
  • An EPC is required when selling or renting a property, and PV can improve the rating.

Ireland:

• SEAI grant-supported systems must be:
  • Registered with SEAI by the installer.
  • Documented with a post-works BER (Building Energy Rating) assessment if required by the grant conditions.
• The BER is Ireland’s energy performance certificate, similar to the EPC in the UK.

International:

• Many EU countries require PV systems to be registered with national or regional energy agencies or grid operators.
• Energy performance certificates (EPC/BER/APE, etc.) are mandated under the EU Energy Performance of Buildings Directive (EPBD) and typically reflect PV contributions.

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Step 8: Installation and commissioning

Installation of a typical residential PV system usually takes 1–2 days.

Day 1 – Mechanical installation:

• Erect scaffolding (if required).
• Fit roof hooks or mounting anchors.
• Install mounting rails.
• Mount and connect PV modules.
• Install inverter and battery (if included).
• Route DC cabling.

Day 2 – Electrical work and commissioning:

• Connect the inverter to the consumer unit / distribution board.
• Upgrade or adapt the meter cabinet if necessary.
• Coordinate meter changes with the grid operator / supplier.
• Commission the system and perform functional tests.

After successful commissioning you should receive:

• A commissioning report.
• System documentation (schematics, datasheets, warranties).
• User instructions and safety information.
• Access to the monitoring app or web portal.

In the UK and Ireland, you should also receive:

• MCS certificate (UK) or SEAI documentation (Ireland) where applicable.
• Electrical installation certificates (e.g. EIC in the UK, Safe Electric certification in Ireland).

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Step 9: Monitoring and maintenance

A well-designed PV system is largely maintenance-free, but you should still monitor performance and carry out occasional checks.

Performance monitoring

Modern inverters provide monitoring via apps or web portals, showing:

• Current power output (W).
• Daily, monthly and annual yields (kWh).
• Self-consumption and export (if metering is available).
• Historical data and year-on-year comparisons.

Check monthly that yields are in line with expectations. PVGIS or your installer’s yield estimate provides a useful benchmark.

Maintenance

PV systems are low-maintenance, but not maintenance-free:

Annually:

• Visual inspection: any damaged modules? Loose fixings?
• Check for new shading: tree growth, new buildings, antennas, etc.

Every 2–3 years:

• Cleaning of modules if necessary (e.g. in areas with heavy soiling, bird droppings or dust). In many parts of the UK and Ireland, rain is sufficient and cleaning is only needed occasionally.
• Visual inspection of cables, junction boxes and mounting hardware.

Every 5 years or so:

• Professional inspection by an installer or electrician.
• Electrical tests (insulation resistance, earth continuity).
• Thermographic inspection if there is suspicion of hot spots or defective modules.

Many installers offer maintenance contracts (often in the range of £100–£200 per year for domestic systems), though for most small systems, periodic inspections may be sufficient.

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Conclusion

Planning a solar PV system can seem complex at first glance. With this step-by-step guide, however, you have all the tools you need to make well-founded decisions. Take your time with each step – the effort will pay off over decades.

For technical fundamentals, see the article Photovoltaics: the complete guide 2026. For details on system architecture, see Structure of a PV system: from module to grid export.

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Calculate your PV yield now

With our solar calculator, you can use PVGIS data to estimate your expected electricity yield, self-consumption and the economics of your planned system.

→ Go to the solar calculator

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Sources

• PVGIS – European Commission
• UK Government: Smart Export Guarantee
• SEAI – Solar PV for homeowners
• Fraunhofer ISE: Photovoltaics Report 2025
• MCS – Microgeneration Certification Scheme
• Home Energy Scotland / Energy Saving Trust