A brook above the house, a 220-foot drop, and 14 kWh of lithium iron phosphate.

The site

A 1968 hill farm in Walden, 800 feet off the nearest paved road and never connected to the utility grid. Original power: a 6 kW Generac propane genset feeding a single-phase 100A panel in the basement. Lighting was 12V DC for the first thirty years; converted to 120V AC fed from the genset around 1998. The customer's father built the place; the customer (now in their late 50s) inherited it in 2019 and called us in November 2025 to ask whether the brook would do anything for him.

We measured the brook in late November (low-flow season, by design). The intake site was 1,140 feet above the powerhouse vertically; the powerhouse was sited at the existing electrical-room floor of the basement-attached lower wing. We measured 28 gpm at the intake on a cold-morning baseline; design flow we set at 22 gpm to leave headroom. Net head, after expected friction losses on a 4" HDPE penstock running 600 ft, came out to 213 ft. Power calculation:

P = ρgQH × η = 1000 × 9.81 × 0.00139 m³/s × 65 m × 0.78 ≈ 691 W average, with a peak at higher flows of about 1.85 kW.

The customer's annual load (2024 propane usage converted to kWh): 6,200 kWh. Continuous output of 691 W × 8760 h = 6,053 kWh. Marginally under-sized for a year-round-no-genset solution, comfortably over-sized when paired with battery and a 4-week-a-year genset assist. We sized the battery at 14 kWh (3 days of autonomy at average load).

Equipment list

Runner

12-inch Pelton wheel from Scott Hydroelectric. Permanent-magnet alternator, 48V DC nominal output.

Penstock

600 ft of 4-inch HDPE buried 30 in. Trenched by a local excavator using a CAT 305.5; we coordinated.

Intake

Coanda-effect screen, sized for 30 gpm with 30% over-capacity.

Charge controller

Outback FlexMax FM80, 80A.

Battery bank

14 kWh LFP at 48V nominal — 4× SimpliPhi PHI 3.5 in parallel.

Inverter

Outback Radian GS4048A, 4.4 kW continuous, split-phase 120/240V output.

Diversion load

2.4 kW resistive water-heater element in a 50-gallon tank, takes the surplus when battery is full.

Genset interface

Existing 6 kW Generac retained; wired to the Radian's AC2 input. Manual start; we may auto-start on next year's revisit if the customer wants.

Run from powerhouse to house

120 ft of 2/0 aluminum URD, direct-buried 24 in. 1.6% loss at full inverter output.

Engineering stamp

From a VT-licensed PE — required for any system > 5 kW; ours is under, but we did the stamp anyway because the customer's insurance carrier asked.

Timeline

1. Nov 2025: measurement and design. Quote returned 5 December 2025.
2. Dec 2025 – Feb 2026: equipment order. Pelton runner is a 14-week lead time; we ordered first, designed around it.
3. Mar 2026: excavator scheduled for after mud season cleared. Trenching start 30 March.
4. Apr 1–9: trenching and penstock pull. Customer assisted with the surface clearing.
5. Apr 10: intake set, screen installed.
6. Apr 11: powerhouse install — runner, alternator, rectifier, charge controller. Initial water-on at 14:40.
7. Apr 12: battery and inverter commissioning. Cutover from genset-only to hydro+battery at 11:20. Customer's first hydro-powered evening with no genset run was that night.
8. Apr 13: stamping engineer site visit; signoff. VT DFS inspection scheduled.
9. Apr 18: inspection passed.

Surprises

• The penstock route crossed a corner of a regulated wetland we hadn't initially identified. We re-routed 80 ft of the run uphill, adding two days; VT ANR signed off without an extended permit because the disturbance area stayed under 3,000 sq ft.
• The 1968 100A panel was a Federal Pacific Stab-Lok (theme). Customer signed off on a panel changeout as a separate $1,800 line item; we did it on day 11 between hydro work.
• The customer's daughter, who is 12, asked us extensively about the runner geometry and made a clear and accurate sketch of the impulse-jet trajectory in chalk on the powerhouse floor. We gave her a Pelton-bucket bronze keychain Marya had been carrying around since 2018 looking for the right home.

What it produces

14 days of operation at the time of writing. Continuous output averaging 740 W during normal flow. Peak output observed: 1,840 W during a heavy snowmelt event on April 14. Battery state of charge has not dropped below 60% since commissioning. Genset has not run.

We will revisit in November to inspect the intake screen for ice, re-torque the alternator mount, and review the customer's first 6 months of operating data from the Outback's FN-DC monitor.

Final billing

Labor (master + journey + apprentice 3-yr)

38.2 hrs · $4,326 (we under-ran the quoted hours by ~3.5; passed the difference back as a credit)

Materials (Pelton runner, alternator, FlexMax, batteries, Radian, penstock, fittings, URD)

$28,650 + 12% = $32,088. Specialty 4% sourcing on inverter+batteries: + $548

Excavator subcontract

$3,420

Engineering stamp (PE)

$650

VT DFS permit

$285

Working-farm discount (8% labor, ≥ 8 hr job)

− $346

Existing FPE panel changeout (added)

+ $1,800

Total

$42,771

Customer paid 30% at signing, 40% at equipment-staged milestone, 30% net-15 from completion.

Related

J-05 Microhydro & off-grid solar for the technical reference. Federal Pacific notes are in the Greensboro Bend dairy entry.