For biogas projects, REpow uses Napier grass (Pennisetum purpureum hybrid varieties) as a primary substrate, complemented by livestock manure and agro-residues. A 1 MWe digester requires 20 000–25 tons of fresh Napier per year, cultivated on about 1 000 rai under long-term contracted farming.

1. Variety Selection & Nursery (Month 0–2)

• Preferred hybrids: Pakchong 1, Super Napier, or Taiwan Napier, selected for high biomass yield and methane productivity.

• Stem cuttings or root splits propagated in nurseries; planting material ready in 45–60 days.

2. Land Preparation & Planting (Month 2–3)

• Fields plowed, leveled, and furrowed at 0.75–1 m spacing.

• Planting density: 8 000–10 000 clumps per rai.

• Initial fertilization with composted manure or digestate from previous biogas operations.

3. Crop Maintenance (Year 1–5)

• Irrigation: Drip or sprinkler systems ensuring 20–25 mm/week.

• Fertilization: Organic amendments every 3 months.

• Weed control: Mechanical or mulching; no herbicides.

• Rejuvenation: Grass coppices after every cut; lifespan 4–5 years.

• Expected productivity: 180–220 tons fresh weight/ha/year (≈ 18–22 tons DM/rai/year).

4. Harvesting Schedule

• First cut at 90–100 days after planting, then every 60–70 days depending on rainfall.

• Harvested with forage harvesters, chopped to 2–4 cm.

• Fresh Napier hauled within 12 hours to maintain silage quality.

5. Feedstock Logistics & Silage Preparation

• At collection hubs, Napier is ensiled in bunker silos or bale wraps with 2–3 % molasses to stabilize for 6–8 months.

• Moisture ≈ 65–70 %, optimal for anaerobic digestion.

• Silage transported daily to the digester within 10–20 km radius using 10-ton trucks.

6. Integration with Livestock Manure & Residues

• Co-digestion with cattle or swine manure enhances methane yield by 10–15 %.

• Digestate returned to Napier fields as organic fertilizer, closing the nutrient loop and reducing synthetic fertilizer use by 80 %.

7. Feedstock Handling at Biogas Plant

• Silage unloaded into mixing tanks, pre-blended with water and trace nutrients.

• Automated feeding systems ensure constant substrate loading rate.

• Quality control (TS, VS, pH, C:N ratio) monitored daily.

8. Feedstock Assurance

• Feedstock reliability: Contracted farmers within 20 km radius guarantee continuous year-round supply.

• Economic inclusion: > 100 farmers participate, earning stable income from Napier sales and organic fertilizer returns.

• Climate impact: Avoids ≈ 25 000 tCO₂e/year via methane capture and fossil-fuel substitution.

• Scalability: Every 1 MWe module can be replicated regionally with dedicated feedstock clusters.