How to sort by woocommerce attribute?

Question

WordPress

function custom_woocommerce_get_catalog_ordering_args( $args ) {
  $orderby_value = isset( $_GET['orderby'] ) ? woocommerce_clean( $_GET['orderby'] ) : apply_filters( 'woocommerce_default_catalog_orderby', get_option( 'woocommerce_default_catalog_orderby' ) );
    if ( 'random_list' == $orderby_value ) {
        $args['orderby'] = 'meta_value';
        $args['order'] = 'ASC';
        $args['meta_key'] = 'pa_nominalnaya-moshhnost-kvt';
    }
    return $args;
}

add_filter( 'woocommerce_default_catalog_orderby_options', 'custom_woocommerce_catalog_orderby' );
add_filter( 'woocommerce_catalog_orderby', 'custom_woocommerce_catalog_orderby' );
function custom_woocommerce_catalog_orderby( $sortby ) {
    $sortby['random_list'] = 'Мощность: по возростанию';
    return $sortby;
}

That doesn't work...