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Clean Energy Technology, Explained
Practical guides to solar panels, home batteries and EV charging, plus deep coverage of the materials behind them, from critical minerals to rare earth magnet alternatives.
How many solar panels do I need?
Free tool. Change the numbers to size a system for your home.
21 panels
of 400 W, an 8.4 kW system
- System size
- 8.4 kW
- Estimated output
- 907 kWh/month
- Yearly output
- 11,038 kWh
- Roof area (approx.)
- 420 sq ft (39 m²)
Estimate for planning only. Real output depends on your roof angle, direction, shading and local weather. Roof area assumes about 20 sq ft per panel and excludes walkways and setbacks.
Explore topics
Solar, batteries, EVs and the materials behind them
Solar
Sizing, costs and panel types for homeowners.
How many solar panels do I need?All solar guides →Home Battery
Backup power, power stations and battery chemistries.
How long will a power station run a fridge?All battery guides →EV & Charging
Home charging, running costs and EV motor technology.
Which EVs don’t use rare earth magnets?All EV guides →Magnets & Materials
Rare earth magnet alternatives and rare-earth-free motors.
Rare earth magnet alternatives: the complete guideAll materials guides →Critical Minerals
Lithium, nickel, cobalt, rare earths and their supply chains.
What are critical minerals? The complete listAll minerals guides →Run the numbers
Calculators built into our guides.
Solar panel calculatorFridge runtime calculatorLatest guides
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- Generator vs Battery Backup: Which Is Better for Your Home?
- Enphase Battery Cost in 2026: IQ 5P and 10C Prices Installed
- kW vs kWh: What’s the Difference?
Our specialty
Rare earth magnet alternatives
Most EV motors and many wind turbines rely on rare earth magnets, and their supply is concentrated in one country. We track every material and motor design that could change that.
Explore magnets & materials