Sand Battery Thermal Simulation

A browser-based simulator for residential sand battery thermal energy storage. Models a full year of charging and discharging using real solar production and weather data, helping you evaluate whether a sand battery could store summer solar surplus to heat your home in winter.

How it works

The simulator uses real 2023 hourly data from PVGIS (EU Joint Research Centre) for a 19 kWp solar installation near Basel, Switzerland. Hourly PV output and ERA5 reanalysis temperature are aggregated into 365 daily records.

Starting from a configurable month (default: April), the simulation runs day by day:

• Charging — On days where solar production exceeds a threshold (default: 15 kWh), excess energy heats the sand via a resistive heater (capped by heater power)
• Draining — On days where ambient temperature drops below a threshold (default: 10°C), heat is extracted from the battery for space heating
• Heat loss — Calculated continuously based on insulation properties, box geometry, and the temperature difference between sand and ambient air

The result is a year-long temperature profile showing how the battery charges through summer, stores heat through autumn, and drains through winter.

Configurable parameters

Section	Parameters
Box & Insulation	Dimensions (L x W x H), insulation thickness and conductivity
Fill Material	Choice of 6 materials (playground sand, silica, olivine, magnetite, soapstone, steel shot) with real thermal properties
Solar & Heating	Solar excess threshold, drain rate, drain temperature threshold, heater power, start month
Heat Exchange & Water	Exchanger efficiency, water flow rate, input/output temperatures

Quick start

make dev        # Start dev server with hot reload

Available commands

make help             Show all targets
make dev              Start Vite dev server
make build            Build frontend for production
make fetch-solar      Fetch PVGIS solar data into src/data/solarData.json
make server           Build Go server with embedded frontend
make container-build  Build container image
make container-run    Run container on port 8080

Tech stack

• Frontend: React 19, TypeScript, Carbon Design System, Carbon Charts
• Server: Go with embedded SPA (single binary, ~15 MB container)
• Data: PVGIS v5.3 hourly time series, aggregated to daily records
• Build: Vite, multi-arch container via Kaniko

Refreshing solar data

The solar data is committed as src/data/solarData.json and imported statically. To regenerate it from PVGIS:

make fetch-solar

This fetches hourly data for 2023, aggregates to daily solar production (kWh), average temperature (°C), and sun hours, and writes the JSON file.