# Sawmill (Ara Machine) — Diesel → Solar-Hybrid Conversion Plan

**Location:** Reoti, Ballia, UP | **DISCOM:** PuVVNL (Purvanchal Vidyut Vitran Nigam Ltd)
**Date:** 2026-06-13

## 1. The problem, reframed

Current setup: two diesel engines drive the sawmill via belt/pulley.
- **25 HP engine** → runs the **trolley** (log carriage)
- **15 HP engine** → runs the **bensa** (saw blade)
- Diesel spend: **₹2,000/day** (~21 L/day @ ~₹95/L)

Key insight: nameplate is 40 HP (~30 kW), but the ₹2,000/day reveals the *actual* work done:
- ~21 L diesel/day ≈ **~55–60 kWh/day of real mechanical work**
- Over ~8–10 hrs running → **average draw only ~7–8 kW** (peaks ~20–25 kW when both cut hard)

**Therefore the solar plant only needs to be ~13–15 kWp, not 30 kW.** This is the single biggest cost lever.

## 2. Site profile (confirmed)

| Factor | Answer | Design consequence |
|--------|--------|--------------------|
| Grid | 3-phase present, **unreliable** | Must use **hybrid inverter + battery** (plain grid-tie dies on every cut) |
| Hours | ~8–10 hrs, **daytime** | Perfect solar match → panels feed motors directly; **small battery only** |
| Workload | Most days, 250–300+/yr | Diesel bill is real & recurring → fast payback |

## 3. Why this architecture

1. **Solar cannot power a diesel engine.** The only path to solar = replace diesel engines with **3-phase electric motors**.
2. **Plain grid-tie won't survive an unreliable grid** — anti-islanding shuts solar off on every cut. → **Hybrid inverter** required.
3. **Daytime running = minimal battery.** Battery only buffers clouds, motor surges, and short grid-cut gaps — not a full night's storage. ~10–15 kWh, not 60.
4. **VFDs are mandatory, not optional.** A 25 HP motor on direct-on-line start draws ~6× running current — destroys inverters/batteries. A VFD soft-starts it (no surge), tunes blade/trolley speed, and saves energy.

## 4. Recommended system (BOM)

| # | Item | Spec | Est. cost (₹) |
|---|------|------|--------------:|
| 1 | Solar modules | 15 kWp (TOPCon mono) | 2,55,000 |
| 2 | Mounting structure + DC cabling + protection | — | 1,15,000 |
| 3 | Hybrid inverter | 15 kVA, 3-phase (Deye/Growatt/Sungrow class) | 1,85,000 |
| 4 | LFP battery | 15 kWh (can start at 10 kWh, modular) | 4,20,000 |
| 5 | Electric motors | 18.5 kW (25 HP) + 11 kW (15 HP), 1440 rpm | 70,000 |
| 6 | VFDs (both motors) | 18.5 kW + 11 kW | 72,000 |
| 7 | AC panel, changeover, wiring, earthing | — | 1,10,000 |
| 8 | Civil, structure foundation, motor mount/alignment | — | 45,000 |
| 9 | Installation & commissioning | — | 90,000 |
| | **TOTAL (15 kWh battery)** | | **~13,62,000** |

**Recommended lighter variant (~₹12 L):** 10 kWh battery + **keep the 25 HP diesel engine as a last-resort backup** for worst-case monsoon-cloud + grid-down days. Sell the 15 HP engine (recover ~₹30–60k).

## 5. Economics

| Metric | Value |
|--------|------:|
| Diesel saved | ₹2,000 × 275 days = **₹5,50,000/yr** |
| Residual grid + maintenance | ~₹40,000/yr |
| **Net annual benefit** | **~₹5,10,000/yr** |
| Capital (15 kWh) | ₹13.6 L |
| **Simple payback** | **~2.6 yrs** |
| With 40% accelerated depreciation | effective payback ~2.3 yrs |
| 25-yr net savings (incl. 1 battery + 1 inverter replacement) | **> ₹1 crore** |

## 6. Subsidies / incentives — reality check

- **PM Surya Ghar: NOT applicable** (residential rooftop only). Do not budget for it.
- **Accelerated Depreciation (AD): YES** — 40% in year 1 for the business; real tax shield ~₹1.5 L.
- **Net metering (PuVVNL): apply, but minor benefit** — you self-consume most generation in daylight, so little surplus to export. Useful for Sundays/holidays.
- **UP Solar Energy Policy 2022 / MSME incentives:** worth checking with a local installer; don't bank on it.

## 7. Practical notes

- **RPM / pulley match:** engines and electric motors run at different RPM. Belt/pulley ratios must be re-matched so blade and trolley speeds stay correct. VFD makes this tunable. A local motor-rewinding/electrical shop handles this.
- **Roof vs ground mount:** 15 kWp needs ~700–900 sq ft. Use shed roof if sound, else a ground-mount frame.
- **Keep one diesel engine** at least through the first monsoon to learn the system's bad-weather behaviour before deciding to sell.
- **Vendor selection:** get 3 quotes from MNRE-empanelled installers; insist on TopCon modules, a true 3-phase hybrid inverter (not 3× single-phase), and LFP (not lead-acid) battery.

## 8. Implementation sequence

1. **Confirm sanctioned load & connection** with PuVVNL; check if load upgrade needed for motors.
2. **Measure actual load** — clamp meter on the engines / log daily diesel for 1–2 weeks to firm up sizing (cheap insurance against over/under-sizing).
3. **Get 3 installer quotes** against this BOM.
4. **Phase A (quick win):** swap to electric motors + VFDs, run on grid → instant ~70% cost cut even before panels.
5. **Phase B:** install solar + hybrid inverter + battery → drive cost to ~₹0.
6. **Apply for net metering** in parallel.

## Files
- `sawmill-solar-payback.xlsx` — editable sizing + payback model (change any assumption, payback recalculates)