OBIS 24

OBIS SHEET TWENTY FOUR

Subject: Solar powered refrigeration

I often get asked about freezers suitable for solar power. My usual advice is that solar technology is best applied to flourescent tube lighting and low power appliances including TV/VCR, tape and CD players, etc. Appliances such as power tools, even kettles (which often draw 2000W - about the same as 110 18W tube lights!!!) are not really suitable, although it is possible to cater for such appliances with careful planning and very careful use. The same applies to freezers and refrigerators, which draw a lot of power. For example, I calculated that our old rusty fridge was using 4kWhours per day - one would need about sixteen 80W solar panels to supply the power for that!

However, there are manufacturers of low power, highly energy efficient refrigerators and freezers that run on 12Vdc and it would be economically practical to run them from solar panels. A few examples are shown below. from a Queensland company. If anyone is interested, I have full details and can help design an appropriate solar power supply.

The cost comparison on the next page shows that a solar powered system using expensive but long life gel type batteries would still work out as only one-sixth of the cost of using a small generator 4 nights a week over 10 years.

12Volt 150Litre Freezer
Price - @$1192 (Aust. dollars) (approx SBD$3,500 plus freight)
Capacity - 150L Freezer
Average Power consumption - 700 Watt Hours daily @30degrees ambient
Weight - 50kg (Volume = 0.468m cubed)

12 Volt 140Litre Refrigerator
Price - @$1192 (Aust. dollars) (approx SBD$3,500 plus freight)
Capacity - 130L Refrigerator
- 10L Freezer
Average Power Consumption - 700 Watt Hours daily @30degree Ambient
Weight - 40 Kg (Volume=0.334mcubed)

12 Volt 250L DC Refrigerator
Price - @$1352 (Aust. dollars) (approx SBD$4,000 plus freight)
Capacity - 220L Refrigerator
- 30L Freezer
Average Power Consumption - 750 Watt Hours daily @30degree Ambient
Weight - 50kg (Volume = 0.468m cubed)

Solar Power Supply Required
To supply enough power for the above appliances, you would need three 80W panels and at least 200Ahours of battery storage, preferably 400Ahours. I have calculated the cost price of such a system imported from Australia including shipping, not including customs duty. As a rough guideline:

240W system with 400Ahours deep-cycle solar batteries SBD$9,000
240W system with 400Ahours gel-type solar batteries SBD$12,000

You can compare that to the cost of a generator plus the fuel costs over up to 10 years or more with the one-payment, maintenance free solar power:

Cost of operating generator 4 days a week for 12 hours a day, over 10 years (in SBD)
Small 0.7kW Generator $5,000
Fuel (at 1L per hour @ $3/L) $74,880
Total cost over 10 years $79,880 (not including maintenance costs)

Cost per year (SBD$)over ten years: Solar versus Generator
Solar, gel-batteries, on all the time $1,200
Generator, used on average 4 days/week for 12 hours/day $7,988

That is IMPRESSIVE!

Please contact me, the webmaster, if you want any more information or assistance.

Solar Icemaker
Usually we feature renewable energy applications and when I came across this item I immediately saw it's potential here. This machine will cost about SBD$40,000 or more, but will produce up to 68kg of ice per day with no need for a generator or any fuel. It would be ideal for a small community fishing operation. It does not use solar panels, but uses a chemical process as described below. Contact me, the webmaster,.for more details.
"Isaac" is the acronym for Intermittent Solar Ammonia Absorption Cycle. Ammonia absorption refrigeration technology was developed in the 19th century and is still used in industrial applications. Energy Concepts has adopted this technology to a machine which uses the sun as the only energy output. The particular advances in the design and configuration have resulted in a low cost and reliable method of making significant quantities of ice in areas without electricity.
How Isaac Works
During the day the solar collector focuses the energy of the sun onto the ammonia generator in the collector trough. Solar heat distills pure ammonia vapor from the water-ammonia solution in the generator. The vapor condenses in the cooling coils and collects as liquid ammonia in the receiving tank in the evaporator.
At the end of the day, the user switches three valves from the Day to Night position to allow the ammonia to evaporate in the ice compartment, providing the refrigeration to freeze the water. The resulting vapor is absorbed back in the generator. Critical to the operation of Isaac is a passive thermosyphon that operates in the Night mode to remove the heat from the generator and allow the ammonia vapor to absorb into the solution at lower pressure and temperature.
At the beginning of the day, the operator harvests the ice from the ice trays, operates a drain sequence to remove traces of absorbent from the evaporator, and places the unit back into Day mode to begin the next cycle.
The solar collector is re-aimed weekly to follow the seasonal movement of the sun. Occasionally the solar collector should be rinsed with water to remove dust.
The primary effort involved in operating the Isaac is filling the ice trays with water in the evening and removing the ice each morning. The valve operation only adds a few seconds to the tasks.

Isaacs come in three standard sizes:
1. The Midi Isaac (37 ft collector) is designed to supply vaccine storage capacity for remote health clinics: daily capacity is 35 lbs/15kg of ice per day. Price US$5,150 FOB Colorado USA.
2. The Standard Isaac (63 ft collector) will supply a small farm or fishing operation, yielding 70 lbs/32 kg of ice per day. Price US$7,950 FOB Colorado USA.
3. The Double Isaac (125 ft collector) is suitable for a small village, with a yield of 150 lbs/68 kg of ice per day.
Price US$11,750 FOB Colorado USA

For contact details,
Contact the Ministry of Commerce on Email: commerce@commerce.gov.sb