THE WATER ENERGY NEXUS

by Herbot Mesnard

ARTICLE II

Optimising electricity supply

The water and energy sectors are closely linked: it’s what is commonly called the water-energy nexus. In this series of articles, we will study the interactions between water and electricity and how changes in one sector are affecting the other. The development of renewable energies (RE) and lower power consumption water treatment technologies are not only deeply transforming the water sector, they are also increasing the possible synergies between the water and energy sectors.

“The water sector is defined as the sector that provides drinking water and wastewater treatment services to different end users (communities, businesses, industries). This sector can be divided into 4 sub-sectors following the water cycle: water collection, treatment, distribution, and overall management.”

The technologies used in water projects are very dependent on the scale, the raw water quality, the location and the end-use. In this series of articles, we will only consider small to medium scale, decentralised water treatment plants in developing countries as this is our core business at Impact Water Solutions (IWS).

In this second article of the “water-energy nexus” series (2/3), we study the electricity supply for decentralised water projects. With the current energy transition from fossil fuels to RE sources, the water sector is already evolving. Like the energy sector, the water sector is seeing an increase in small-scale decentralised projects, especially in developing countries. However, these decentralised water treatment plants are not necessarily connected to an electricity grid and therefore need other sources of power.

ONGRID POWER SUPPLY CHALLENGES

Across the world, most water treatment plants are connected to the local electricity grid. However, in many developing countries, and especially in sub-Saharan Africa, being connected to the grid raises various issues.

Firstly, national grids in developing countries are often not reliable as there may be power outages or significant load shedding. Water access being an essential need, water treatment is therefore an essential industry: it cannot afford having an unreliable power supply.

Furthermore, in many sub-Saharan African countries, the cost of electricity is higher than the global average. According to a recent study from the World Bank ¹, electricity tariffs can reach $30-50 cents/kWh whilst the global average is roughly $10-20 cents/kWh. However, for water treatment plants a large part of the operating costs is due to energy consumption – up to 75% of total operating cost for water desalination and 60% for WWTP. Therefore, high electricity costs lead to high operating costs. This in turn leads either to high water tariffs or else water treatment plants running at a loss, which in both cases is unsustainable.

Finally, many grids in developing regions generate electricity using fossil fuels. Indeed, fossil fuels (coal, gas and oil) accounted for more than 75% of the electricity generation in Africa in 2018 (according to the International Energy Agency ²). This intensive use of fossil fuels leads to high CO2 emissions. Therefore, in these regions, using the grid supply to power a water treatment plant is not environmentally friendly.

Whilst the electricity grid (ideally) provides a constant power supply, in sub-Saharan Africa this raises various issues, amongst which security of supply, cost of electricity and environmental impact.

HYBRID POWER SUPPLY FOR WATER PROJECTS

Sub-Saharan Africa is one of the regions with the lowest electrification rates world-wide, therefore many communities and businesses don’t have access to grid electricity. For such clients, having a drinking water treatment plant used to be impossible as it would have to be powered by costly and polluting diesel generators. However, the recent developments in RE generation and water treatment technologies have now made it possible to have 100% diesel free, hybrid or off-grid water treatment plants.

Photo of the water desalination plant IWS helped install in Bethanie (Namibia)

An increasing amount of RE (especially solar PV) projects are being built in sub-Saharan Africa as the cost of renewables is decreasing. Also, batteries are becoming cheaper and more efficient, therefore making hybrid “solar + battery” systems increasingly affordable. Overall, the emergence of RE has led to an increase in hybrid power supplied water projects (on-grid or off-grid). Such projects use on-site RE production with a complementary grid/battery/diesel generator backup. Having different power sources increases the design complexity, however it can ensure a constant, reliable and competitive power supply for clients who require it. For example, the OSMOSUN® SWRO desalination unit installed by IWS in Witsand (South Africa) is powered by solar panels (in priority) and the electricity grid (which is used as backup). Also, in Bethanie (Namibia), IWS recently developed an off-grid BWRO desalination project (integrating the OSMOSUN® desalination unit) for a small community (450 m³/day) powered by wind turbines, solar panels and a battery storage system.

NEW OPPORTUNITIES WITH OFF-GRID PROJECTS

Finally, RE developments and subsequent evolutions in drinking water treatment technologies have made fully off-grid water projects feasible. Indeed, water treatment projects using solar power only (no battery storage required) are now possible, even though such a power source has a high intermittency. For example, the OSMOSUN® Reverse osmosis (RO) desalination technology can cope with high drops in power supply (due to a cloud passing over solar panels) thanks to a patented pressure accumulator technology. This technology smoothens the system’s pressure variations (that are due to solar power variations) and ensures longevity of the RO membranes. Therefore, 100% solar powered desalination plants are now feasible and affordable, which is particularly interesting for islands or isolated off-grid communities, industries and businesses. Regarding WWTPs, using only RE is more challenging (and less developed) as most technologies require a constant 24/7 power supply.

Scheme of an IWS hybrid or off-grid water desalination plant

As the cost of renewables continues to drop and water treatment technologies keep integrating devices to cope with intermittency, it is very likely that the amount of decentralised off-grid water treatment projects in sub-Saharan Africa will increase over the coming years.

At IWS we believe that RE now enable affordable, high-performing and sustainable water projects in challenging contexts.

Previous article:

I. Water-Energy nexus (1/3): Electricity consumption trends

 Next article:

III. Water-Energy nexus (3/3): Water & Electricity synergies

Sources:

¹ “Electricity Access in Sub-Saharan Africa”, M. Blimpo and M. Cosgrove-Davies, 2019 https://openknowledge.worldbank.org/bitstream/handle/10986/31333/9781464813610.pdf?deliveryName=DM10178

² “Africa Energy Outlook 2019”, International Energy Agency, 2019 https://www.iea.org/reports/africa-energy-outlook-2019