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Cooling Off Grid Energy options

Cooling, Refrigeration and Freezing

Refrigerators are in increasing demand in rural area for domestic and institutional requirements. However, powering refrigerators is surprisingly complicated and expensive. Refrigeration requires relatively constant energy input and the most common 240 VAC models are not suited for off-grid situations. Specially made efficient off-grid refrigerators are available, but will usually cost more than US$1000 per unit. When powering off-grid refrigerators with electricity, plan to pay as much (or more) for the power source as you do for the refrigerator itself.

 1.0 Refrigeration Considerations:

Refrigeration requirements range from critical ones in health applications (vaccines and medications), to food preservation to comfort (cold drinks). Refrigerators are vital tools in clinics and hospitals, guesthouses, residences (public and private), hotels, restaurants, schools and other institutions. If you are in a remote location, without access to grid electricity and you need refrigeration, there are a number of technologies you can choose to meet your needs.

When selecting a refrigerator and power system, you need to consider your specific refrigeration need. Various types of refrigerators use different fuel sources and different amounts of energy. Before choosing a fridge, you should consider your requirements. Important considerations include the following:

Table 1: Typical Refrigeration Applications

Application

Freezer (space required litres)

Volume required (litres)

Critical/non-critical

Vaccine refrigeration

0-5 l

30 litres

Yes

Institutional & commercial food preservation

50-550 litres

200-1000 litres

Yes

Institutional & commercial drinks, etc. cooling

N/A

200-300 litres

No

Dedicated freezing (institutional or commercial)

500-1000 litres

N/A

Yes

Householdrefrigeration/freezing

15-250 litres

200-550 litres

No

2.0 Available Technologies:

Essentially, there are 2 approaches to off-grid cooling and refrigeration. Table 2 summarises refrigeration choices and the most appropriate off-grid energy sources for each.

Table 2: Refrigerator type, power consumption and appropriate power sources.

Fridge Type Monthly Fuel/Energy Consumption Appropriate Off-Grid Power Source

Absorption Fridges

Operate on heat cycle which requires fuel or electric heat source

Option 1: Gas fridges

(Electrolux, Servel Propane)

24-30 l/propane/ standard 300l unit LPG gas

Option 1: Kerosene fridges

(Electrolux)

15-30 [??] litres per 40-150 l/mo for a 300 l unit. There is a wide range in quality Kerosene fuel

Compression Fridges

Operate using compression cycle which requires electricity

Option 2: Super-Efficient 12 V DC HH fridges

(i.e. Sunfrost, Vestfrost, Nova Kool)

10-60 kWh/ 300l unit

PV

RET

Genset/Battery

Option 3: Vaccine fridges

(EPI/WHO approved)

2-2.5 kWh/mo PV

Option 4: Standard Commercial fridges

(Bosch, Siemens, Electrolux, Frigidaire, etc.)

110 kWh/mo or 300l unit more Generator/Hybrid System

Option 5: Evaporative fridges

Operate on evaporative cooling effect

   

Option 1: Kerosene or LPG Absorption Fridges

Absorption refrigerators operate on a heat cycle normally powered by a kerosene or gas burner. A flame or heat element powers the heating cycle, which creates the cooling affect. Because of their high energy consumption, PV should never be used to power absorption fridges. Kerosene and LPG fridges may present a fire hazard, and kerosene fridges emit particulates (and/or gases) which may make them inappropriate in some situations Several studies recommend PV or LPG fridges over kerosene fridges for vaccine use.

Technology Availability: Kerosene and LPG absorption refrigerators are available throughout the tropics and in both the developing and the developed world. Both types are available in standard sizes (e.g., 300 - 600 litres for cooling, 50 - 100 litres for freezing). They can be used in isolated clinics, hospitals, schools, restaurants, cafes, butcheries, hotels, homes and camps.

Fuel/Energy Availability: Kerosene fridges are ordinarily refilled with fuel on a weekly basis, while LPG fridges are refilled on a more intermittent basis. Kerosene/paraffin is widely and relatively easily available. LPG poses far more difficulties, particularly in rural and remote situations. LPG bottles must be purchased, and supplies are often irregular outside urban areas.

Spare Parts and Service: Kerosene/paraffin and LPG refrigerators are relatively reliable. Kerosene fridges require their wicks and mantles to be changed or adjusted regularly (weekly), and hence need frequent attention (though not by highly skilled technicians). Kerosene refrigerators also need to be cleaned regularly because of the soot build-up in the exhaust flue. LPG refrigerators have far fewer maintenance requirements. Note that finding spare parts for either type of fridge can be problematic in some locations.

Optimum Situation: Absorption fridges are best where self-contained units are necessary. Kerosene-powered units are better in many remote situations because of kerosene’s wide availability. However, kerosene refrigerators should be avoided unless: (1) LPG is not available, and/or (2) spare parts and maintenance for PV fridges are not available. LPG is better where gas supplies are readily available.

Option 2: Efficient Household Fridges and Freezers .

Low voltage super-efficient 12 V DC (direct current) fridges for off-grid applications are available in a number of sizes (though they typically have less capacity than standard AC fridges). These fridges are also available for 240 VAC, but 12VDC is generally preferable for PV and RET systems. Such fridges have very thick insulation, and often place the heat-generating compressor unit above the unit to save energy.

Technology Availability: Efficient household refrigerators and freezers are increasingly common on the world market. However, they are still speciality items that are produced only in few countries in Europe and North America. They can be sourced from catalogues and specialist retailers. (for example visit one of these sites, click here).

Fuel/Energy Availability: DC fridges need to be powered by a battery set which is charged by PV, wind, a genset or another RET. Correct sizing of the battery set, and the PV or wind power system is absolutely critical.

Technology Spare Parts and Service: Battery spares should be available. Critical spares for the fridges (compressor, etc) and energy systems should be available as long as electric fridge maintenance expertise.

Optimum Situation: Efficient fridges/freezers are optimal for institutional, commercial or domestic uses in areas with good wind or solar energy supplies, and where consumer has enough funds for large up front capital costs. Low power, 12VDC refrigerators can easily be powered by simple PV system with regulators and batteries. Wind, hydro or small gensets with battery sets can also be used for power supply. They can easily be incorporated into existing 12 VDC RET systems.

Option 3: PV Vaccine Fridges

For vaccine storage and medical uses, the World Health Organisation's Global Programme for Vaccines and Immunization and its Expanded Programme on Immunization/EPI has approved a number of low voltage DC PV vaccine refrigerators. Solar vaccine refrigerators are designed specifically to meet health needs, and are not appropriate for private use (e.g., refrigerating food and drink). EPI Vaccine refrigerators are made to be powered by PV and are available as complete kits from a number of distributors.

Technology Availability: The WHO has certified a number of models from companies in the world for their GPV/EPI programmes. PV fridges and freezers are generally only available on order from source manufacturers.

Fuel/Energy Availability: Most areas in the tropics have sufficient solar energy availability for PV vaccine refrigeration systems. Individual systems may have to be designed based on particular needs of the clinic or health programme.

Technology Spare Parts and Service: Battery spares should be available. Critical spares for the fridges (compressor, etc) and energy systems should be available. Systems should be checked by qualified technician two times per year.

Optimum Situation: Off-grid rural health clinics and hospitals with more than 4 kWh/m2/day solar radiation. Note that there must be sufficient technical infrastructure and manpower in place to service, monitor and maintain the fridges. In cases where infrastructure is insufficient, consider LPG or kerosene fridges.

Option 4: Conventional Household and Commercial Fridges

Conventional fridges are readily available around the world in a number of sizes and fridge/freezer configurations. They run on standard 240/120V AC power. They are notgood choices for off-grid locations, as they generally consume too much power for RET systems to supply. In addition, wind and PV systems require inverter/battery systems. Therefore, conventional fridge/freezers require generators to run continuously.

Where large power systems are already in place (especially when the energy system is oversized), it may make economic and practical sense to buy a commercial refrigerator. When choosing standard units, pay careful attention to energy consumption specifications, and do not choose units with power consumption above 1 kW.

Technology Availability: Almost universal.

Fuel/Energy Availability: With diesel or petrol gensets, require constant power availability (i.e. genset must be run continuously!) and therefore fuel must be regularly available. For RET applications, you must have inverter and battery source.

Technology Spare Parts and Service: Critical spares for fridges (compressor, etc) and energy systems should be available. Constantly run gensets will require regular servicing.

Optimum Situation: Commercial fridges are best used where there is over-capacity in power supply, where power is constantly available. A genset of about 1.5 kVA would be a minimum for a small refrigerator, if no other applications are in use. PV arrays or wind generators might provide additional power, but in general would not be economic as a sole power source unless the site is unreachable by diesel/petrol suppliers.

Option 5.

Evaporative fridges are a relatively well-tested, proven, low-tech approach to cooling, which cool produce, other food and beverages at about 15-20°C below ambient temperatures. They are most appropriate in hot,dry (not humid) climates where there are no other alternatives (and cannot be used for critical purposes such as vaccine storage). For further reading visit and click on here).

Table 3: Indicative Cooling and Refrigeration Technologies and Costs (US$)

Item

Avg capital cost

PV power System Cost

Running, O&M costs pa

Lifetime years

Life cycle cost

Absorption Fridges

Option 1: Kerosene fridge/freezer (300 l fridge, 50 l freezer)

$1,500

N/A

Option 1: LPG fridge/freezer (300 l fridge, 50 l freezer)

$1,300

N/A

LPG/Kerosene Freezer (240 l)

$1,800-2,200

N/A

Compressor Fridges

Option 2: Efficient 12 V HH fridge/freezer (300 l fridge, 50 l freezer)

$2,500

Option 3: Vaccine refrigerator (30 l)

$900-1,400

Option 4: Commercial fridge 300l fridge, 50 l freezer, 240 V AC

$500-1,200

PV freezer (250 l)

$1,500

Click on any of the icons below, or click here for further reading on refrigeration, cooling and freezing, or here for supplier information on refrigeration, cooling and freezing. If you wish to move on to the next module, click here for "Off-Grid Solutions to Audio-Visual (Module 4)", or click on one of the other modules below. Click here for links to visit some good links to other Internet sites.

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