Water Storage Tank Sizing for Solar Powered Irrigation
Introduction
Water storage tanks are cost-effective solutions for providing round the clock water supply using solar powered irrigation system (SPIS). They are available everywhere, simple to operate, easy to maintain and thus are better design alternative to batteries. They also increase the reliability of the SPIS.
The energy is stored as potential energy in the tanks and is converted into kinetic energy when the water flows. The tank needs to have enough elevation compared to the downstream system for the water to flow.
Advantages of a water storage tanks[1] :
- Instant water supply during any point of the day when the demand exceeds the water supply using the solar powered water pump
- Emergency water storage in case of pump failure or low irradiance (during mornings or evenings as well as on cloudy day)
- Cheap alternative to battery storage
Sizing a water tank
There are different methods for sizing a water tank. The important thing to keep in mind is that the size should be big enough to meet the peak water need during the hottest month but not over-sized to reduce investment cost.
The size of the water tank depends on [2]:
- Solar irradiation
- Water demand and use (based on seasonal variation)
- Pump size and pumping rate
Water tanks are generally designed to meet the demands for the month where the difference between the hourly supply and the demand is the largest. There are different guidelines for adequately sizing the water tank and are mentioned below:
1. Quick guideline for sizing water tanks mentioned in the book, “Solar Pumping for Water Supply”[2] .
|
|
Water storage tank sizing |
|
Generator/grid powered |
0.5-1 x daily water requirement |
|
Hybrid (solar+ generator/grid) |
0.5-3 x daily water requirement |
|
Stand-alone solar |
1-3 x daily water requirement |
2. Hourly supply vs demand method: In this method, the hourly water supply is compared with the hourly demand for the month with the least irradiance. Then, the water storage tank is designed to meet this difference.
There are also other guidelines such as those from the Kenya Ministry Practice Manual for Water Supply Services, 2005 (explained in the video above). You can also use programes such as PVsyst to calculate your water size.
Further Information
- Webinar Series: Capacity Building and Learning on Solar Powered Water Systems
- Toolbox on SPIS
- Water and Energy for Food on energypedia
References
- ↑ Solar Powered Water Systems in Humanitarian Context – Specific Considerations and Limitation of SPWS, 2021, https://www.youtube.com/watch?v=6DsQEtTowSM.
- ↑ 2.0 2.1 A Kiprono and A Llario, ‘Solar Pumping for Water Supply’, 2020, https://practicalactionpublishing.com/pdfjs/web/viewer.html?file=https://practicalactionpublishing.com/pdf/book/2507/9781780447810_01622987182.pdf.
