Page - 56 - in Clean Water Using Solar and Wind - Outside the Power Grid

56 Clean Water Using Solar and Wind: Outside the Power Grid Again, the required energy is proportional to the head and to the volume of water. So, instead of lifting the water 10 m we now calculate for the head of 100 m and lift 10 m3 instead of 1 m3. This will require 100 times more (hydraulic) energy or 0.027 ⋅ 100 = 2.7 kWh; in other words, it demands the hydraulic power of 2.7 kW for one hour. The required electric energy for a pump system with 80% efficiency and pipe loss of 10% is 3.8 kWh. If the pump is running during daylight solar hours (assuming eight hours) then the required energy is produced for eight hours (only 1/8 m3 of water is pumped every hour), which will require the power 3.8/8 = 0.48 kW from the solar PV system. This is 1/8 of the power calculated in Example 4.1. In a solar PV pumping system, typically two types of system configurations are prevalent. In the first one a submersible pump lifts groundwater into an overhead tank that serves as an energy store and supplies the pressure needed for the pressurised irrigation system. In the second configuration there is no storage system and the water is pumped directly into the irrigation network. Example 4.3: Experiences from Solar-Powered Pumping Solar PV water-pumping systems are used for irrigation and drinking water in India (Roul, 2007). Most of the more than one million pumps in operation have the motor power 2.0–3.7 kW. Typically, a 1.8 kWp (kW peak power, see also Chapter 8.2) solar PV array is used for irrigation purposes. Such a system can deliver around 140 m3 of water per day from a total head of 10 m. Let us compare this energy need with the theoretical hydraulic power (4.2). Assuming that the pump is working eight hours per day and only 60% of the peak solar power can be used: P W Whydr = = 140 0 6 8 3600 10 1000 9 81 286⋅ ⋅ ⋅ ⋅ ⋅ . . Apparently, the PV/motor/pump systems are quite inefficient, or the solar array is designed with a large safety margin. Example 4.4: Rule of Thumb for Solar Water Pumping A common rule of thumb is that a 1000 Wp (1 kWp) solar water pump can draw and pump around 40 m3 of water per day from a source Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user