Here is a tested working code written in JRuby:
gemfile do
source "https://rubygems.org"
gem "rubyXL"
end
uri = URI("https://www.engie.be/api/engie/be/ms/pricing/public/v1/epex-prices/export?exportType=XLSX")
data = Net::HTTP.get(uri)
workbook = RubyXL::Parser.parse_buffer(data)
sheet = workbook[0]
cost_array = (4..27).map { |row| sheet[row][1].value }
logger.info cost_array
Output:
[116.94, 111.36, 108.04, 99.02, 93.44, 91.55, 93.23, 102.7, 114.26, 125.36, 121.5, 109.13, 110.01, 107.95, 104.07, 103.67, 112.29, 123.88, 129.5, 126.3, 110.29, 114.48, 124.69, 104.99]