Synergy Between Renewable Energy Resource And Water Supply

It is critical to recognize that there can be synergies between the availability of a renewable energy and water resources.

One interesting example that illustrates this is the provision of clean drinking water to remote communities in outback Australia. While arid

Table 1 Comparison of all existing renewable energy powered desalination technologies

Technology

Operating principle

Disadvantages

References

Phase change processes

Solar still

Solar thermal energy evaporates the

a

High SEC of 639 kWh/m3

[11]

water, which

a

Low daily

condenses onto

production

the sloping glass

a

High

surface and it then

maintenance costs

drains into a

a

Glass sheets

collection trough

vulnerable to storms and vandalism

Multistage

Saline water held

a

Both thermal and

[12-14]

flash (MSF)

under pressure at b 120 °C and

electric energy required

''flashed'' into

a

High SEC of 20-

vapor in a series of

64 kWh/m3

b 50 chambers,

(electrical

which then

component

condenses and is

b 4 kWh/m3)

collected.

Multiple effect

Thin film

a

Both thermal and

[12]

distillation

evaporation

electric energy

(MED)

process where

required

vapour formed

a

High SEC of

one chamber

15 kWh/m3

condenses in the

(electrical

next, providing a

component

heat source for

b 2 kWh/m3)

further

evaporation.

Mechanical

Evaporative system

a

Both thermal and

[12]

vapor

where vapor

electric energy

compression

boiled off in the

required

(MVC)

evaporator is mechanically compressed and reused as the heating medium

a

High SEC of 1116 kWh/m3

Operating principle

Disadvantages

References

Freeze separation

Ice crystals formed in feed-water are then separated and subsequently melted to form the product water

High SEC of 97 kWh/m3 Separating ice crystals from the brine; operation in vacuum required due to lower freezing point of saline water

Membrane separation processes

Reverse

Pressure-driven

Low SEC of

[13,16]

osmosis

separation of two

4 kWh/m3 for

(RO)

solutions with

seawater

differing salt

Specialized

concentrations

chemicals not

across a

available in

semipermeable

remote locations

membrane

Chemicals

required to

control fouling:

increases system

complexity and

cost, and reduces

system reliability

Membrane life 3—

5 years

Nanofiltration

As above

As above, but

[13,17]

(NF)

reduced SEC for

brackish water

(2 kWh/m3)

Not suitable for

seawater

Electrodialysis

Electromigration of

Low SEC of

[13,18,

(ED)

ions through

2 kWh/m3 for

19-21]

cation and anion

brackish water

exchange

Chemical

membranes

cleaning required

No pretreatment

for removing

particulates

Not suitable for

seawater

Technology Operating principle

Disadvantages

References

Electrodialysis reversal

As above, however, electrode polarity is periodically

• As above, however reduced chemical cleaning required

reversed to facilitate cleaning of ED membrane countries experience minimal rainfall and hence limited freshwater availability, there is often an abundance of solar radiation received at such locations. In addition, there are often significant groundwater reserves available, although these are often of marginal (total dissolved solids [TDS] 0.5-1.5 g/L) or brackish (TDS 1.5-5 g/L) quality. This is the situation in Australia, where the majority of the rainfall occurs along the coastline, compared to 200-300 mm annual rainfall in central and Western Australia, as shown in Fig. 7a [23]. The arid region in central Australia receives a daily average of at least 6.7 h of full sunshine (kW/m2) [24] as shown in Fig. 7b, which is 20-50% more than is received along the wetter coastline. While this climate and freshwater availability reflects very strongly in the country's population distribution, as shown Fig. 7c, a large fraction of Central Australia is farmland or home to indigenous communities that often rely on poor water resources, with many communities being too small to have controlled and monitored water supplies. Drinking water for these communities is generally supplied from groundwater bores, which are of varying quality ranging from drinkable water to inconsumable brackish water. Fig. 7d indicates that brackish groundwater can be found in significant volumes throughout the majority of Australia, mostly with good extraction rates [26]. Given that the consumption of brackish water has been linked to poor health and that many of the central regions of Australia are not serviced by the national electricity grid, communities are often drinking water of substandard quality, as they do not possess the electrical power or appropriate technology to purify the water. Therefore, application and feasibility of PV-powered desalination systems, both on a small [17] a large scale [27] have been investigated as a sustainable technology for the provision of clean water in remote areas of outback

(a)
Number of hours of full sunshine (kW/m2), daily average

;ydney

ANBERRA

BRISBANE

1985 Review of Australia's Water Resources and Water Use

Major groundwater resources

PERTHfi .

ADELAIDE i Based on statistical local boundaries: 1 dot = 1000 people

Total gigalitres based on information available in1984

Legend Gigalitres

;ydney

ANBERRA

1985 Review of Australia's Water Resources and Water Use

Major groundwater resources

Total gigalitres based on information available in1984

Legend Gigalitres

Data Reliability no reliability data available

Figure 7 Australian (a) annual rainfall [23]; (b) solar radiation resource [24]; (c) population distribution [25]; (d) major brackish groundwater resources [26].

Data Reliability no reliability data available

BRISBANE

Figure 7 Australian (a) annual rainfall [23]; (b) solar radiation resource [24]; (c) population distribution [25]; (d) major brackish groundwater resources [26].

Australia. A further advantage of solar technologies is that peak energy production in the summer months coincides with peak water demand.

A second example, in Townsville, Australia, involves the addition of a water recycling aspect to the existing Cleveland Bay Purification Plant, enabling up to 20 ML of water per day to be recycled from the main treatment plant. Currently, the treatment plant discharges the treated waters into Cleveland Bay, however, future limits on water and nutrient disposal necessitate the utility to develop a water recycling program in conjunction with private sector partners [28]. A further driver is the security of clean drinking water throughout periods of drought by reducing Townsville's raw water demand. A preliminary study indicated that both the cost and energy consumption of water recycling were about 10% lower than the only other alternative of pumping in 28 ML of water over a great distance and allowing 8 ML losses incurred via evaporation. The potential renewable energy sources capable of powering this large-scale project include:

wind power (in the form of two 2MW REpower MM70 wind turbines); and

• methane, sourced from

- the wastewater treatment plant itself,

- a nearby landfill, and

- a meatworks settling pond.

This average wind speed at the site is about 6.9 m/s, which, while low for Australia, is nonetheless a valuable resource potential yielding 4.3 GWh of electricity per annum. If all proceeds to plan, this project will demonstrate that raw water consumption of 28 ML can be reduced via the addition of a carbon neutral water recycling plant.

Sometimes, the motivation is purely financial, demonstrating that renewable energy is no longer solely applicable for niche applications, such as remote area power supplies. This is demonstrated by a water treatment plant in California's San Fernando Valley that is powered by 1.6 MW of PV, including both crystalline silicon and thin-film technologies [29]. The solar farm will provide almost all of the power needs for the South San Joaquin Irrigation District water treatment plant, which provides 40 million gallons/day for 155,000 residents and businesses, as well as irrigation water for 55,000 farm acres. The main goal of the project is to stabilize electrical costs, which can spike in summer months because of time-of-use metering implemented in California, which result in the cost of grid electricity reaching US$0.32 kWh 1, however the peak times for water demand also coincide well when solar output is at a maximum.

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