TIANON Case Study: 8.4 kWp Solar, 20 kWh LiFePO4 & 6.5 kW Hybrid Inverter with Surge-Safe Design

Project Overview

A family home with a farmhouse-style load profile needed a reliable off-grid-capable power system. The household runs a wide mix of appliances — from a 250 W freezer to a 1,100 W booster pump — and several of these are inductive motor loads with high inrush currents. The real design challenge was not adding up appliance nameplates, but engineering around three different power figures: continuous running power, maximum simultaneous demand, and start-up surge.

TIANON designed a grid-tied hybrid solar system that combines photovoltaic generation, battery storage and automatic backup, sized to lower the monthly electricity bill while keeping the house running through grid outages.

Energy Consumption Analysis

The first step was converting every load into daily energy (rated watts * hours of use per day). This table is the foundation of all later sizing decisions.

Four distinct power figures must be separated here, and conflating them is the single most common sizing error:

• Rated (nameplate) power — the connected total: 5,678 W. Simply summing these is wrong.
• Operating / running power — real-world simultaneous demand: about 4.0 kW after a diversity factor of ~0.7, because not every appliance runs at once.
• Starting / surge power — the momentary inrush of motor loads. A direct-on-line induction motor can draw 3–7* its rated current for a fraction of a second.
• Maximum simultaneous load — the continuous load the inverter must sustain: ≈4.0 kW.

Motor loads — the booster pump (1,100 W), water pump (750 W), washing machine (800 W), freezer (250 W) and refrigerator (150 W) — were treated separately for surge behaviour. The booster pump alone can demand roughly 4,400 W at start-up (≈4* rated). Designing for simultaneous worst-case surge therefore points to a start-up envelope of approximately 8–10 kW — far above the simple sum of running watts.

System Design & Equipment Selection

PV array. Minimum array = 18.04 kWh/day ÷ (3.5 peak sun hours * 0.8 system derate) ≈ 6.44 kWp. TIANON recommends 8.4 kWp (14 * 600 W N-type TOPCon monocrystalline modules) to cover conversion losses, battery charging and long-term degradation with healthy margin.

Battery. With roughly half of daily energy consumed at night and a one-day autonomy target, about 18 kWh of usable storage is required. At 80% depth of discharge this equals ≈22.5 kWh. TIANON specifies 20.48 kWh of LiFePO4 (4 * 5.12 kWh wall-mounted units) — a safe, high-cycle, thermally stable chemistry with an integrated BMS.

Hybrid inverter. A 6.5 kW grid-tied hybrid inverter covers the ≈4.0 kW continuous load with strong headroom and roughly 13 kW peak surge capability to start the pumps. It coordinates PV, battery, grid and backup in one unit.

Balance of system (DC/AC side). DC: string combiner box, DC isolator, Type 2 DC SPD (1,000 V), 15 A string fuses, MC4 connectors and mounting rails. AC: AC isolator, AC SPD, grid-tie breaker, RCD and main distribution panel. Plus a full earthing/grounding system, cable management and lightning protection.

Solar Generation & Battery Backup

• Daily generation: 8.4 kWp * 3.5 h * 0.8 ≈ 23.5 kWh/day
• Monthly generation: ≈ 706 kWh
• Annual generation: ≈ 8,470 kWh

During daylight, PV powers the loads directly and charges the battery; any surplus is exported to the grid. At night, the LiFePO4 bank supplies the home. On a grid failure, the hybrid inverter switches to backup mode with seamless, sub-20 ms transfer — keeping the freezer, refrigerator and router online automatically.

Estimated Cost & Savings

The following figures are engineering estimates based on current typical market pricing; final quotation depends on local labour, freight and site conditions.

Assuming a tariff of $0.30/kWh and ~540 kWh/month of self-consumed solar, estimated monthly savings are about $162 (plus export credits for surplus generation).

ROI / Payback Period

Estimated payback = system cost ÷ monthly savings = $13,200 ÷ $162 ≈ 82 months ≈ 6.8 years. After payback, the system continues to generate essentially free electricity for 20+ years, with the LiFePO4 bank rated for 6,000+ cycles. Rising utility tariffs and grid instability shorten this period in practice.

Why TIANON

This case shows why a storage system cannot be sized by simply adding every nameplate rating together. TIANON designs around the real load behaviour — separating running power, maximum simultaneous load and motor start-up surge — so that high-inrush equipment such as the booster pump, water pump, freezer, refrigerator and washing machine start reliably without nuisance inverter trips. By integrating solar PV, LiFePO4 storage, a hybrid inverter and grid connection, TIANON delivers lower bills, high solar self-consumption and dependable blackout backup in one engineered package. For clients who prefer a pre-integrated package, TIANON also offers a turnkey all-in-one home energy storage system that combines inverter and battery in a single cabinet.

Project Summary

Note: All values marked “estimated" are engineering assumptions for design purposes and are not the client’s actual installed data.