Grain store solar in 2026: battery sizing for the drying season

Grain stores are among the largest commercial roofs in UK rural infrastructure — modern arable barns commonly run 1,500–3,000 square metres clear-span. The complication: arable electrical load is heavily seasonal, peaking sharply during the October–November grain-drying period and tailing off through the winter and spring. PV generates the opposite profile — peak in summer, trough in winter. The mismatch matters, and battery storage is increasingly the answer.

The load profile

A typical 1,000-tonne grain store with on-site drying capacity has a peak drying-period electrical demand of 80–200 kW depending on dryer type (continuous or batch), drying duration (a wet harvest can run dryers continuously for 3–4 weeks), and ambient conditions. Outside the drying season, the same store’s electrical load is typically 5–15 kW — lighting, ventilation, monitoring, occasional fans.

The annual energy demand is heavily skewed: 60–75% of total annual kWh consumption sits in the October–November window, with the rest spread across the remaining 10 months. A grain store on its own (without other on-farm load) achieves 25–40% self-consumption on rooftop PV alone, because most of the generation occurs in months when the building’s load is low.

Three strategies

UK arable farms have three rational PV strategies on grain stores: (1) Size for self-consumption only — small system (50–100 kW), maximise economics, accept the rooftop is under-utilised; (2) Size for total roof potential — large system (200–500 kW), lean on SEG export income through the year, accept 6–7 year payback; (3) PV + battery for peak-shaving — large system with battery time-shifting summer generation to support drying-season peaks.

Most of our arable clients now favour strategy (3) once we walk them through the maths.

Battery sizing for drying season

The right battery size for grain-store PV depends on three factors: (1) the size of the PV system; (2) the duration of the drying season the battery needs to support; (3) the on-farm baseload outside the drying window.

A worked example: 400 kW PV install on a 2,500 sqm grain store with a 3-week drying season. Annual generation 380,000 kWh. Drying-season demand 120 kW peak running for 14 days continuous = 40,300 kWh. Without battery, almost all of this drying-season demand is met from the grid (PV generates maybe 20% of October daily demand). With a 220 kWh battery cycled daily during drying season at 90% depth of discharge, the battery covers around 200 kWh per day of drying load = 2,800 kWh across the season. The battery effectively shifts a fraction of the August–September PV generation into October.

The battery’s real value isn’t covering all drying-season demand (it can’t) — it’s shaving the peak grid demand charge during drying season, and time-shifting summer excess generation into shoulder-season morning starts. Demand-charge savings on a 120 kW peak can be £4,000–£9,000/year depending on the supplier’s distribution-use-of-system (DUoS) and triad treatment.

Typical battery economics

Battery capex in 2026 sits at £400–£700/kWh installed for commercial-scale lithium iron phosphate (LFP) systems with 5,000–7,000 cycle lifetimes. A 220 kWh battery costs around £130,000 installed. Over a 12-year operating life (cycle-limited), with 350 cycles per year at 90% DoD, the battery delivers around 730,000 kWh of time-shifted energy. At a marginal grid-versus-PV value of around 14p/kWh (the difference between grid retail and SEG export), that’s £102,000 of value. Add demand-charge savings of £4,000–£9,000/year × 12 years = another £48,000–£108,000.

The combined system economics: PV alone at 6.8-year payback, PV + battery at 6.4-year payback. The battery improves payback by 4–6 months and delivers significant operational resilience during peak load periods. AIA treatment is favourable: both the PV and the battery are plant and machinery, fully expensable in year one for limited companies.

Where battery doesn’t make sense

Battery storage at the larger scales we’re talking about isn’t always right. Don’t add battery if: (1) the farm doesn’t have a clear seasonal peak — equestrian, workshop, dairy parlours with consistent year-round load; (2) the drying season is short (under 10 days) — the battery cycles too few times to recover capex; (3) the farm is already constrained by grid connection — battery is harder to commission on capacity-constrained networks; (4) the farm has very low electricity costs from a fixed price contract — the savings don’t justify the capex.

Multi-building considerations

For arable farms with multiple buildings (most farms above 600 acres) the optimal configuration is often: PV on every suitable building (grain store, workshop, fleet shed), with one central battery sized for the largest seasonal load. Single G99 application covers the whole site. Single monitoring portal. We design the wiring topology to allow battery charge from any of the PV systems, and discharge to support any of the on-site loads. This typically saves £20,000–£40,000 versus separate per-building battery installations.

What to do next

If you’re operating an arable farm with significant grain-drying load and considering rooftop PV, model both PV-only and PV-plus-battery scenarios before committing. We provide both scenarios in every arable-farm proposal as standard. The right answer depends on your specific load profile, lease tenure, and capital position — but for most UK arable farms with serious grain-drying demand, PV plus battery is now the economically rational choice in 2026.