For a factory, warehouse or other energy-intensive Irish business, a 400kW commercial solar project can turn a large roof or suitable site into a source of lower-cost electricity. The financial result depends less on the headline system size than on how much power the business uses while the panels are generating, what it pays for imported electricity, and what it receives for surplus exports.
This guide explains the likely output, panel and space requirements, project costs, current grant rules and a worked payback example. The figures are planning estimates, not a quotation or a guaranteed return. A site-specific design should use the business’s half-hourly electricity data, roof survey and ESB Networks connection conditions.
What a 400kW commercial solar PV system is
A solar array is usually described by its kilowatt-peak (kWp) rating: the panels’ combined DC nameplate output under standard test conditions. A 400 kWp array is therefore not automatically a 400 kW inverter system. Inverters convert the panels’ DC electricity into AC electricity used by the premises and grid. Their combined AC kW or kVA rating may differ from the array’s kWp rating.
That distinction matters for design, grid connection and export limits. The appropriate inverter size and any export-limiting controls depend on the building’s electrical supply, maximum import capacity, load profile and the network operator’s connection offer.
During daylight, the panels feed electricity into the building’s electrical system. The business uses that solar electricity first where there is demand at that moment. Any surplus may be exported, subject to an approved connection and an applicable export arrangement. If solar output falls short of demand, the premises continues to import electricity from its supplier.
A 400kW solar system Ireland project can suit factories, warehouses, industrial units, farms, hotels and large business premises. It is most attractive where there is substantial daytime demand, such as refrigeration, production lines, pumps, ventilation, lighting, data equipment or hotel services. A large roof alone is not enough: if the business is closed or lightly occupied through sunny hours, more generation may be exported at a lower value than electricity consumed on site.
Businesses comparing commercial solar panels in Ireland should size the array against daytime demand and usable area, not roof dimensions alone.
How many panels are needed for 400 kWp?
The count depends on each module’s wattage. For 400 W panels, divide 400,000 W by 400 W to get 1,000 panels, for exactly 400.00 kWp. For 450 W panels, the calculation is 888.89, so rounding up requires 889 panels, giving 400.05 kWp. With 500 W panels, 800 panels make exactly 400.00 kWp. With 550 W panels, 727.27 rounds up to 728 panels, for a 400.40 kWp array. These calculations round up to a whole module, so the installed DC total can be slightly above 400 kWp.
These are arithmetic comparisons, not a final equipment schedule. Panel dimensions and weights vary by manufacturer and model. For an initial roof study, allow roughly 1.8–2.6 m² of panel surface per module across these wattages. The panel faces alone typically total about 1,800–1,900 m². Add space for access routes, fire and maintenance clearances, roof edges, skylights, vents, plant equipment and row spacing. A preliminary usable roof-area allowance of about 2,200–2,800 m² is more realistic than using panel surface area alone; a detailed layout may need more or less.
For a ground-mounted array, an early feasibility allowance might be around 0.4–0.8 hectares (4,000–8,000 m²), including row spacing and access. This is a concept estimate only. The actual land requirement changes with terrain, orientation, tilt, drainage, setbacks, landscaping and the chosen layout.
Before specifying panels, a structural engineer should check roof capacity and condition, including wind loading and the proposed mounting system. The design should also preserve safe roof access and avoid creating maintenance or fire-safety issues.
Expected annual generation in Ireland
The European Commission’s Joint Research Centre provides PVGIS, a location-based tool for estimating solar resource and PV performance. A representative PVGIS calculation for Dublin uses a 400 kWp fixed array, south-facing at a 30° tilt, with 14% system losses. It estimates approximately 389,000 kWh (389 MWh) per year, or about 972 kWh per installed kWp. This is a modelled reference case, not a promise for any particular roof or site.
Actual yield changes with location, roof direction and pitch, shading, module layout, inverter configuration, temperature, downtime and soiling. South-facing panels can deliver strong annual output, while east–west layouts may spread generation across more of the working day and better match a business’s load. A shallow roof pitch is not a barrier to solar, but the design should model the actual orientation and tilt rather than assume an ideal south-facing array.
Ireland’s cloudy weather does not stop PV generation: panels also produce in diffuse daylight. However, output is strongly seasonal. In the Dublin reference model, monthly production ranges from roughly 14 MWh in January to about 51 MWh in May. Winter generation is much lower than summer generation, so annual totals should not be treated as a steady monthly supply. Nearby buildings, parapets, trees or rooftop equipment can cause disproportionate losses if they shade strings of modules. A site-specific PVGIS estimate and shading survey help refine the forecast.
400kW commercial solar savings: self-use and exports
The largest source of commercial solar electricity savings is usually electricity the business does not have to buy. Each kilowatt-hour used directly on site avoids the variable import cost that would otherwise apply to that unit. Fixed charges and some network or capacity charges may remain, so the value of solar should not be calculated by dividing the entire electricity bill by total consumption.
The savings model should separate three quantities:
•Self-consumed solar: generation used on site, valued at the avoidable import rate.
•Exported surplus: generation sent to the grid, valued at the applicable export price.
•Operating costs: maintenance, monitoring, insurance changes and any other recurring costs.
The CRU says eligible microgeneration customers are paid by their supplier for metered exported electricity, and the export rate is shown on the customer’s bill. Supplier tariffs vary. A 400 kWp project should not assume it qualifies for a household tariff or that all exported units will earn the same value as avoided imports. Confirm the project’s connection, metering and export-payment route with ESB Networks and the electricity supplier before relying on export revenue.
Worked annual savings example
The following is an illustration, not a forecast. It assumes 390,000 kWh of annual generation, an avoidable import rate of €0.22/kWh, an export rate of €0.08/kWh, and €5,000 per year for routine maintenance and monitoring. The energy prices and maintenance allowance are modelling inputs only; replace them with the business’s own contract terms and supplier quotations.
If the business uses 50% of the solar output on site, it avoids about €42,900 of electricity purchases and earns an assumed €15,600 for exported power. That is €58,500 in gross annual value or about €53,500 after the assumed maintenance cost.
At 70% self-consumption, avoided imports are worth about €60,060 and the remaining exports about €9,360. Gross annual value is €69,420, or roughly €64,420 after maintenance.
At 90% self-consumption, avoided imports are worth about €77,220 and exports €3,120. The gross annual value is €80,340, leaving approximately €75,340 after maintenance.
These examples show why load matching matters. Using more generation on site increases value when the avoided import rate is higher than the assumed export rate. A battery, load shifting or daytime operations may improve self-consumption, but the benefit depends on the battery’s cost, usable capacity, round-trip losses, controls and replacement cycle.
Commercial solar installation cost in Ireland
The commercial solar installation cost depends on module and inverter choice, roof type, mounting method, electrical upgrades, switchgear, cable runs, access equipment, grid studies and any network reinforcement. A LVP Renewables commercial page publishes a broad indicative range of €850–€2,000 per kWp installed and notes that larger projects generally benefit from lower cost per kWp. A simple multiplication for 400 kWp gives €340,000–€800,000 before grant support. This is a broad planning range from the installer’s public guidance, not a 400 kWp quote; the site survey and electrical design determine the actual price.
A quotation should make clear whether it includes panels, inverters, mounting, electrical protection and switchgear, metering, design and engineering, access equipment, commissioning, grid-connection work, monitoring and VAT. Grid reinforcement or major roof repairs can change the project economics materially.
Commercial solar grants in Ireland: current SEAI support
the SEAI Non-Domestic Microgen Grant (NDMG) is available for eligible solar PV systems up to 1,000 kWp. SEAI lists grant values of €300/kWp for systems from 201 to 1,000 kWp. On a 400 kWp system, the tiered calculation is €145,200: €4,800 for the first 6 kWp, €8,400 for the next 14 kWp, €72,000 for 21–200 kWp, and €60,000 for 201–400 kWp.
SEAI currently states that, for new applications made from 6 October 2026 to 6 July 2027, the payment is the lower of the grant value shown on the application summary or 45% of the invoiced project cost. Thus, €145,200 is a ceiling for the 400 kWp example, not an automatic payment. Eligibility, the offer and all scheme rules must be confirmed with SEAI. The enhanced rate does not apply to existing applications, and work must not begin before the grant offer is received. SEAI requires the applicant to select a registered Non-Domestic Microgen installer and agree a formal contract before applying; the installer must also apply for the grid connection before installation and submit the required completion documents.
Other financial supports may apply to particular businesses or projects, but eligibility and compatibility should be checked rather than assumed. For current commercial solar grants Ireland guidance, use SEAI’s live scheme page and application documents rather than relying on older online summaries.
400kW solar payback period: a worked estimate
A simple 400kW solar payback period calculation is:
Simple payback = (installed cost − confirmed grant) ÷ annual net benefit
Using the middle self-consumption case above, the assumed annual net benefit is €64,420. If the installed cost is €400,000, simple payback is about 6.2 years before grant. If the business receives the full €145,200 NDMG amount, net capital cost would be €254,800 and the simple payback would be about 4.0 years. This grant-adjusted example assumes an eligible new application within the current enhanced window, a grant offer before works begin and an invoice that supports the full grant cap.
These figures exclude financing costs, tax, inflation, electricity-price changes, panel degradation, inverter replacement, major repairs and the time value of money. They also depend on the illustrative electricity rates and self-consumption share. A project with high export and low daytime demand may take longer to pay back; a business that uses most of its solar output during expensive daytime hours may perform better. A bankable commercial solar return on investment should therefore use interval-meter data and sensitivity-test prices, export rates, grant status and annual generation.
Batteries, system equipment and installation
A 400kW solar PV system typically includes PV modules, roof or ground mounting, DC cabling and isolators, one or more inverters, AC switchgear, protection equipment, monitoring and metering. A battery is optional. It can store some midday surplus for later use, support peak-demand management and give an energy-management system more flexibility. It does not increase the amount of sunlight available, and it adds capital cost and conversion losses. Model battery savings separately before deciding whether it improves the project’s return.
A well-planned project generally moves through energy-bill analysis, roof and structural surveys, layout design, planning checks, grant application, grid application, installation, testing and commissioning. Planning permission is not always required for rooftop PV. Irish Government guidance says that outside Solar Safeguarding Zones, rooftop installations on the listed non-domestic building classes can cover the roof, subject to conditions. Within the 43 designated Solar Safeguarding Zones, the general rooftop limit for non-house buildings is 300 m² per roof; larger proposals may need planning permission. Exemptions also have setback, protected-structure and Architectural Conservation Area restrictions. For non-house buildings, the installation must primarily serve energy use within the building or site curtilage, meaning more than 50% under the Government’s explanation. Check the property’s location and the current rules with the local planning authority before design is finalised.
Grid connection is a separate technical approval, not a formality. ESB Networks’ small-scale generation pathway currently covers inverter-connected systems above about 50 kVA and up to 200 kVA, and its page directs larger systems to the appropriate generation-connection route. The panel array’s 400 kWp label alone does not identify the connection category: the inverter rating, maximum import and export capacities and site connection conditions matter. ESB Networks assesses capacity and may require export limits or network works. Do not install or energise until the applicable connection approval and conditions are in place.
After commissioning, use monitoring to compare actual performance with the forecast and investigate faults, unexpected shading or inverter alarms promptly. Maintenance may include visual inspections, electrical checks, cleaning where justified by soiling, vegetation management for ground arrays and review of monitoring data. Module, inverter, workmanship and mounting warranties have different terms, so obtain each warranty and service responsibility in writing. These practices protect energy production over the system’s operating life.
How LVP Renewables can help
LVP Renewables describes commercial PV systems from 2 kW to 400 kW and offers roof- and ground-mounted solutions. Its commercial guidance says that a tailored assessment considers roof capacity, wind loading, maintenance and safety; the company asks prospective customers for a recent electricity bill and Eircode to begin a quote. A proper assessment should also match half-hourly demand with the proposed generation profile, confirm the connection route and test grant and export assumptions.
For a 400kW commercial solar project, the most useful next step is a site-specific review of electricity bills, roof or land area, structural condition and operating hours. Contact LVP Renewables for a tailored commercial solar assessment and quotation. No savings or payback period should be treated as guaranteed until the design, price, grant offer and export arrangements have been confirmed.
FAQs
What does a 400 kWp commercial PV system cost in Ireland?
LVP Renewables publishes an indicative commercial range of €850–€2,000 per kWp. Multiplying by 400 kWp gives €340,000–€800,000 before grants, but this is not a project quotation and larger systems may have a lower unit cost. Roof condition, switchgear and grid works can change the price.
How much can a business save with a 400kW solar PV system?
In the worked example, annual generation is 390,000 kWh. With 70% used on site, an assumed avoided import price of €0.22/kWh, an export rate of €0.08/kWh and €5,000 annual maintenance, the model gives about €64,420 net annual benefit. Use the business’s actual tariffs and load profile for a reliable estimate.
How long might a large commercial solar installation take to pay back?
There is no guaranteed typical period. LVP Renewables publishes a broad 3–8 year range for commercial systems, but a 400 kWp project can fall outside it depending on cost, daytime demand, tariff and grant eligibility. In the central example above, simple payback is about 6.2 years before the assumed grant or 4.0 years after the full €145,200 grant, if approved.
Are grants available for commercial solar installations in Ireland?
Yes. SEAI’s NDMG currently supports eligible non-domestic PV systems up to 1,000 kWp. As of 14 October 2026, new applications during 6 October 2026–6 July 2027 may receive the lower of the calculated grant or 45% of invoiced cost. Apply through the official SEAI process and wait for the offer before starting work; grant amount and eligibility are not guaranteed.
