function updateHeaderHeight() {
        // Get the height of #brx-header
        const headerHeight = document.querySelector('#brx-header').offsetHeight;
          
        // Store the height in the CSS custom property --header-height
        document.documentElement.style.setProperty('--brxw-header-height', headerHeight + 'px');
    }

    // Execute the function as soon as the document is ready
    document.addEventListener('DOMContentLoaded', function() {
        updateHeaderHeight();  // Initial update of header height when the document is ready

        // Update the header height on window resize and orientation change
        window.addEventListener('resize', updateHeaderHeight);
        window.addEventListener('orientationchange', updateHeaderHeight);
});

Campervan Energy Calculator — Solar & Battery Sizing

Use the calculator below to get an idea of your total energy usage for your van conversion. This energy total is used to get the minimum battery capacity (in Ah) and minimum solar panel power (in Watts)

For more help with building the electrical system see my van conversion course where I walk you through the entire van build step by step.