AlphaESS SMILE-G3: what to check before estimating payback

Which G3 design fits your existing solar?

The S3.6/S5/B5 datasheet, p. 2 names SMILE-G3-S5-INV as a 5 kW hybrid inverter with PV input and SMILE-G3-B5-INV as a 5 kW AC-coupled variant without that PV input specification. It also lists a 3.68 kW S3.6 hybrid. The S5/B5 product page makes the same hybrid/AC distinction. B5 may suit a design retaining an existing PV inverter, but the label alone does not prove compatibility or cost; ask which inverter stays.

The module table separately names SMILE-G3-BAT-3.8S (3.8 nominal/3.6 usable kWh), BAT-8.2P (8.2/7.8) and BAT-10.1P (10.1/9.6) under its conditions. It gives 95% depth of discharge and different module arrangements. The -INV name identifies the inverter; BAT identifies storage. Usable DC-side battery energy is neither annual energy nor a promise of the same AC kWh at your sockets.

Ask for each model and count, connections, meters, backup parts, inverter changes, installation and commissioning. If panels and battery are bundled, get a comparable battery-addition cost rather than subtracting a guessed panel price. List recurring costs separately.

Which energy and price figures matter?

Depth of discharge describes the permitted share of nominal battery capacity under test conditions. The V08 sheet’s 97.3% maximum inverter efficiency measures something else again. Neither it nor the 95% depth of discharge is the whole AC path from otherwise-exportable solar through storage to later home use. Ask for an efficiency estimate across that path, including relevant losses.

First-year AC energy delivered to your home depends on solar surplus and later demand. A 9.6 kWh usable module × 365 does not forecast annual delivery; module size and inverter kW cannot establish timing or power feasibility.

Storing exportable solar also gives up its net export payment. Battery losses mean more AC solar is diverted than later reaches the home. Compare genuinely avoided import costs with that lost income and extra running costs, not purchase price alone.

The older global V08 datasheet states five years for product and ten for battery performance. The separate December 2024 UK G3 warranty, pp. 1–4 and 8 names S5, B5 and BAT models, with a ten-year product term and a distinct 120-month performance term subject to application, throughput, DC-side capacity, connectivity and installer conditions. Request current terms for the quoted models; neither document sets annual decline or expected life.

How avoided purchase cost changes the example

Only the genuinely avoided purchase price changes here. Fixed bill charges are not avoided. These artificial values are not available tariffs or advice to choose a dearer contract; lost export income remains in every row.

What would make the numbers work?

At 0.3800 GBP/kWh, the example recovers its cash outlay after 11.93 years, yet −56.66 GBP NPV misses the 3% real return target. Check your actual avoidable purchase cost, net export payment, annual AC use and extra installed cost. The model keeps real annual prices constant; it does not optimise hourly tariffs.

Separate export stress: return to the base case—avoided purchase price 0.3000 GBP/kWh, extra cost 6000 GBP and year-one AC home delivery 1800 kWh/year. Change only the export payment given up to 0.3000 GBP/kWh. First-year net saving becomes −110.00 GBP, NPV −7268.84 GBP, and payback Not applicable — no sustained recovery over 15 years. This artificial stress is not an AlphaESS forecast or UK tariff.

The calculator compares adding storage with keeping the same solar system. It does not assess a new solar installation, grid charging, hourly tariffs, VPP/reserve/V2G income, backup value, finance, automatic grants or tax benefits, battery replacement, residual value or end costs. It cannot verify annual use or timing, power and state-of-charge feasibility.

Questions to ask your installer

• Is the inverter S5 hybrid, B5 AC-coupled or another G3 model? Which BAT identifiers and counts are included, and what happens to your existing inverter?
• What nominal and usable capacities, AC path and operating limits apply to these parts?
• What compulsory equipment, metering, installation and commissioning costs form the battery addition? Are there ongoing charges?
• Which current UK product and performance terms apply to each model? What supports annual AC delivery and export assumptions?

Get an itemised quote first. Then test its real extra cost and your supported energy and price assumptions.

Check your quote in the calculator

Select GBP and enter your own cost, AC delivery and prices. This compares solar self-consumption, not grid charging or backup value, and cannot verify timing or power. A G3 model name fills in nothing automatically.

Two quick checks

Is B5 a battery module?

No. B5-INV names the AC-coupled inverter variant; storage modules carry BAT identifiers.

Can I use 97.3% as battery round-trip efficiency?

No. It is a maximum inverter figure, not the whole solar-to-battery-to-home AC path.