10 Solar Hot Water Tubes - Solar Evacuated Tubes - Boil Water with Sun! Heats one appx. 1 liter water per hour (depends on geographical and weather factors) 90%+ energy conversion efficiency. 100% shipping safety guarantee. 20 1/2" long, 2 1/4" outside diameter, 1 3/4" inside diameter, Double wall structure with vacuum between walls More details see http://www.electric-bike-kit.com/solar-tubes.aspx