15kW solar system is a substantial solar photovoltaic (PV) installation. It can suit a large home with high electricity demand, a farm, office, workshop, school, retail premises or other property that uses a significant amount of electricity during daylight hours.
The right design depends on much more than the number printed on the quotation. Panel wattage, roof layout, shading, inverter design, electricity use and grid connection requirements all affect the final installation. In Ireland, a 15kW system can produce useful renewable electricity throughout the year, although output varies considerably by season and weather.
This guide explains how many 15kW solar panels may be needed, the likely 15kW solar system roof space, expected generation, battery options, grants and the main points to check before requesting a quotation from an installer.
What is a 15kW solar system?
A solar PV system’s capacity is normally expressed in kilowatts peak, written as kWp. The “peak” figure is the combined rated output of the panels under standard test conditions. Therefore, a 15kWp array is designed with panel ratings that add up to approximately 15,000 watts.
It is important to distinguish capacity from energy generation:
•kW or kWp describes the system’s power rating at a point in time.
•kWh describes the amount of electricity generated or used over a period.
A 15kW solar panel system will not produce 15kW continuously. Solar output changes with daylight, cloud, temperature, orientation and shading. It produces electricity during daylight hours, with a much larger share of annual generation occurring between May and September in Ireland.
A system of this size may be considered for:
•A large or highly electrified home.
•A property with a heat pump, multiple electric vehicles or a home office.
•Farms and agricultural buildings.
•Offices, workshops, warehouses and retail premises.
•Schools, community buildings and other non-profit organisations.
•Businesses with consistent daytime electricity demand.
For many ordinary homes, 15kW may be larger than necessary. The system should be sized around actual and expected electricity use, available roof area and the value of using or exporting the electricity.
How many solar panels are needed for a 15kW system?
The basic calculation is:
15,000 watts ÷ individual panel wattage = number of panels
Because panels are installed as whole units, the result is rounded up where necessary. The table below shows common configurations. The resulting capacity is calculated from the rounded panel count, so it may be slightly above the 15kWp target.
Panel rating: 350W
Calculation: 15,000 ÷ 350 = 42.86
Approximate panel count: 43 panels
Resulting system capacity: 15.05kWp
Panel rating: 400W
Calculation: 15,000 ÷ 400 = 37.5
Approximate panel count: 38 panels
Resulting system capacity: 15.20kWp
Panel rating: 450W
Calculation: 15,000 ÷ 450 = 33.33
Approximate panel count: 34 panels
Resulting system capacity: 15.30kWp
Panel rating: 500W
Calculation: 15,000 ÷ 500 = 30
Approximate panel count: 30 panels
Resulting system capacity: 15.00kWp
Panel rating: 550W
Calculation: 15,000 ÷ 550 = 27.27
Approximate panel count: 28 panels
Resulting system capacity: 15.40kWp
In practice, the most suitable panel may not be the one with the highest wattage. A lower-wattage panel can sometimes fit a roof more effectively, while a larger panel may reduce the total number required. The installer also needs to consider string lengths, voltage ranges, roof sections and the inverter’s operating limits.
Why the final system may not be exactly 15kW
A quotation might describe a system as “15kW” even if the panel array is 15.2kWp or 15.3kWp. That is normal. Available panel ratings do not always divide exactly into 15,000 watts, and the best configuration may be determined by the roof rather than the target number alone.
The panel capacity and inverter capacity can also be different. For example, an installer may design an array with a slightly higher DC panel capacity connected to an appropriately sized AC inverter. Any proposed design should state clearly:
•Total panel capacity in kWp.
•Inverter model and AC rating.
•Number of panels and their wattage.
•Expected annual generation.
•Any export limitation or grid connection condition.
15kW solar system size and configuration
Panel wattage is only one part of the design. Panel efficiency affects how much power can be produced from a given roof area, while the roof’s shape determines whether the panels can be arranged in neat rows or need to be split across several faces.
An installer may use separate electrical strings for different roof orientations. An east-facing roof and a west-facing roof, for example, may need separate maximum power point tracking inputs. Shading from a chimney, dormer or nearby tree can also influence the choice of inverter, optimisers or microinverters.
The inverter converts the panels’ DC electricity into AC electricity that can be used by the building. It must be compatible with the panel array, the building’s electrical supply and the applicable connection route. A 15kW design may require a three-phase supply or a specific connection assessment, particularly where the property has a large commercial load. This must be checked by a qualified installer rather than assumed from the panel rating alone.
15kW solar system roof space requirements
The roof area needed depends on the number and dimensions of the panels. Many current panels are roughly 1.7–2.0 metres long and about 1.1 metres wide, giving a surface area of approximately 1.9–2.2 square metres per panel.
Using a broad estimate of around 1.9 square metres per panel, the panel surface area could be approximately:
350W panels: approximately 43 panels, covering around 82m² of panel surface area.
400W panels: approximately 38 panels, covering around 72m² of panel surface area.
450W panels: approximately 34 panels, covering around 65m² of panel surface area.
500W panels: approximately 30 panels, covering around 57m² of panel surface area.
550W panels: approximately 28 panels, covering around 53m² of panel surface area.
*These estimates are based on an assumed panel surface area of approximately 1.9m² per panel. Actual dimensions may vary depending on the panel model.
The total panel surface is not the same as the usable roof area. Roofers and installers may need space for access routes, edge setbacks, mounting clearances, roof valleys and safe maintenance. Skylights, chimneys, roof windows, vents and shaded sections reduce the area that can actually be used.
As a practical early-stage allowance, a 15kW solar system may need roughly 65–105m² of suitable roof area, but the range can be wider. A clean, large commercial roof may use the space efficiently. A complicated residential roof may require much more area to achieve the same capacity, or may not be suitable for a full 15kW array.
Orientation and pitch also matter. A south-facing roof often gives strong annual production, while east- and west-facing roofs can spread generation into the morning and afternoon. North-facing sections, steep shading and obstructions may make some roof areas less productive. The roof should also be checked for age, structural condition, waterproofing and the likely future need for repair or replacement before panels are installed.
15kW solar system cost in Ireland
There is no single national price for a 15kW solar system. The installed cost depends on the equipment and the property, including:
•Panel brand, wattage and warranty.
•Inverter size, type and monitoring platform.
•Roof mounting equipment and cable routes.
•Electrical upgrades, distribution board work and protection devices.
•Scaffolding, access and roof repairs.
•Labour and commissioning.
•Three-phase or other grid connection requirements.
•Battery storage, backup capability and export controls.
A 15kW solar system cost should therefore be assessed from a detailed quotation rather than a simple price-per-panel estimate. Ask for the system’s total price, VAT treatment, expected annual generation, payment schedule, warranties, monitoring arrangements and any exclusions. Battery storage is usually an additional cost and should be evaluated against the building’s demand profile.
The domestic SEAI solar PV grant is currently capped at €1,800, with a separate €600 battery grant for eligible applicants. The domestic scheme is for eligible homes and is not an automatic grant for every system size or property type. The current SEAI conditions include an MPRN, a home built and occupied before 2025 and no previous solar PV funding at that MPRN. Grant approval must be obtained before work starts.
Businesses, farms, schools, public-sector bodies, community centres and non-profit societies may instead be able to consider SEAI’s Non-Domestic Microgen Grant. As of October 2026, the scheme page states that new applications in the enhanced nine-month window from 6 October 2026 to 6 00000000July 2027 can receive support at an effective 45% rate, subject to the scheme rules and the grant cap. It supports systems up to 1,000kWp, so a 15kWp installation may fall within its scope, but eligibility and the final payment must be checked before work begins.
How much electricity can a 15kW solar system produce?
Output cannot be guaranteed from system size alone. Location, roof direction, pitch, shading, panel temperature, inverter losses, dirt and downtime all have an effect.
SEAI states that a well-located 3kW home system using about 20 square metres can generate around 2,600kWh per year. Scaling that benchmark gives approximately 13,000kWh a year for a 15kW system under similarly favourable assumptions. A sensible early planning range might be around 11,000–14,000kWh per year, but a property-specific design should be used for a quotation.
That could translate broadly to:
•Daily average across the year: roughly 30–38kWh.
•Monthly average across the year: roughly 920–1,170kWh.
•Summer months: substantially above the annual daily average.
•Winter months: substantially below it, with short days and more overcast weather.
These are generation estimates, not guaranteed savings. A building that uses electricity during the day may consume a large share of the solar output directly. A property that is empty during daylight may export more electricity or benefit from battery storage. SEAI explains that east- and west-facing arrays can produce electricity at times that better match household demand, even though they may generate less over the year than an ideal south-facing array.
Is a 15kW solar system suitable for a home or business?
For a home, 15kW is usually a larger installation. It may be justified where there is a heat pump, several electric vehicles, a large family, a home business, electric water heating or unusually high annual consumption. It may also make sense where a property is planning to add these loads.
For businesses and farms, the daytime load is often more important than the building’s size. Offices, refrigeration, pumps, machinery, workshops and commercial equipment can use solar electricity as it is produced. This can improve the value of the system by reducing purchases from the grid during working hours.
The best starting point is at least 12 months of electricity bills or interval data. Compare the expected solar generation with the building’s hourly demand. Installing a system far larger than the property can use may increase exports and change the financial return, while installing too small a system may leave useful roof space unused.
Inverter and electrical requirements
The inverter is a central part of the solar installation. It manages the panel array, converts DC to AC and may provide monitoring, battery control and export-limitation functions.
Before installation, the installer should assess the main supply, phase arrangement, consumer unit or distribution board, earthing, cable routes, protection and the intended export level. ESB Networks defines micro-generation as up to 6kVA on a single-phase low-voltage connection or up to 11kVA on a three-phase low-voltage connection. A 15kW design may therefore need a different connection route or a more detailed network assessment rather than simply being treated as standard micro-generation.
ESB Networks states that the installer must follow the applicable connection process, use a registered electrical contractor and ensure that the inverter complies with IS EN50549-1 with the current Irish settings. The relevant application must be made before installation proceeds.
15kW solar system with battery storage
A battery stores surplus electricity generated during the day and makes it available later, often during the evening. This can increase self-consumption and reduce the amount of electricity bought from the grid. It does not create additional solar generation, and charging and discharging result in some energy losses.
Battery sizing should reflect the building’s evening and overnight demand, solar production profile, export arrangement and budget. A large battery is not automatically better if there is insufficient surplus energy to charge it regularly. Businesses may prefer batteries for specific load-shifting or resilience objectives, while households may value evening use and backup functions.
SEAI’s official guidance also notes that batteries add cost and that some energy is lost in the charge-discharge cycle. The system quotation should state usable battery capacity, warranty terms, expected cycle life, emergency backup capability and whether the battery can be expanded later.
Savings and payback considerations
The financial return depends on the amount of solar electricity used on site, the price of imported electricity, the rate available for exports, installation cost, grant support and future consumption. A battery can increase self-consumption, but its cost must be included in the calculation.
A transparent assessment should compare:
1.Annual generation in kWh.
2.The proportion used directly by the property.
3.The proportion stored and used later.
4.The proportion exported and the applicable export payment.
5.Annual electricity costs avoided.
6.Maintenance, inverter replacement and finance costs.
For exported electricity, SEAI explains that the Clean Export Guarantee is paid by the electricity supplier at its market rate, subject to eligibility, and that a suitable ESB Networks export connection is required. A smart meter allows exports to be measured precisely. Do not rely on a guaranteed payback period without checking the property’s actual usage and current tariffs.
How to plan a 15kW solar installation
A well-planned solar panel installation in Ireland usually follows these stages:
1.Review electricity bills, interval data and future loads such as EV charging or a heat pump.
2.Inspect the roof, structure, orientation, pitch, shading and condition.
3.Design the panel layout, strings, inverter and any battery.
4.Confirm the electrical supply and grid connection route.
5.Compare written quotations and expected generation.
6.Check domestic or non-domestic grant eligibility before work starts.
7.Submit the required connection application.
8.Install, test and commission the system.
9.Receive the safety file, warranties, manuals and monitoring access.
10.Track performance and compare actual generation with the installer’s estimate.
How to choose a solar installer in Ireland
Compare more than the headline price. Ask each installer to identify the panel model, inverter model, battery specification, system capacity in kWp, expected annual generation and any export limitation.
For grant-supported work, use the appropriate SEAI-registered company and check that the proposed installer is named correctly in the grant documentation. SEAI recommends obtaining several quotes, checking references and requesting a written contract that sets out the work, price, payment terms and warranties. For a commercial project, confirm that the installer is registered for the relevant non-domestic scheme.
Also ask who will manage the ESB Networks application, what happens if the grid connection requires changes, how monitoring support works and who will respond if the inverter or battery develops a fault. A good quotation should explain assumptions rather than promise a fixed saving.
Conclusion
A 15kW solar system can be a strong option for a high-demand home, farm or commercial property, but it is not automatically the right size for every building. Depending on the panel wattage, the design may use about 28–43 panels. The panels alone may cover roughly 53–82m², while practical usable roof space may need to be closer to 65–105m² after allowing for access, setbacks and obstructions.
Irish output may be around 11,000–14,000kWh per year as an early planning range, but the final estimate should reflect the exact location, roof orientation, shading and equipment. Costs, grants, grid requirements and battery choices also need to be assessed together.
To discuss the right design for your property, visit LVP Renewables and enquire about a tailored solar quotation.
FAQs
How many solar panels are needed for a 15kW system?
It depends on the panel wattage. A 15kW system could use about 43 panels at 350W, 38 panels at 400W, 34 panels at 450W, 30 panels at 500W or 28 panels at 550W. The final installed capacity may be slightly above 15kWp because panels are whole units.
How much roof space is required for a 15kW solar system?
The panel surface may be approximately 53–82m² using the example panel ratings in this guide. Allow more usable roof area—often roughly 65–105m²—because of access routes, roof edges, skylights, chimneys, shading and other obstructions. An installer should confirm the actual layout.
How much electricity does a 15kW solar system produce in Ireland?
A broad early planning estimate is around 11,000–14,000kWh per year, or approximately 30–38kWh per day averaged across the year. Actual output varies by location, orientation, pitch, shading, equipment and weather. Summer generation is much higher than winter generation.
Is a 15kW solar system suitable for a home or business in Ireland?
It can suit a large, high-use home or a business, farm, school or workshop with significant daytime electricity demand. It may be oversized for an ordinary home. Review at least 12 months of electricity use and ask an installer to model generation, self-consumption, exports, battery storage and grid requirements.
