E-News Issue #83
Solar CoursesWe have two courses this month. The first is a 2-day weekend course for homeowners, conducted by Karlin Bracegirdle, on 16th and 17th April. Karlin has lived with solar for over two decades and has conducted solar courses in several countries.
We also have a 5-day course from 21st to 26th April for those who want to get into the industry (designing and installing Renewable Energy systems). This course is for students with prior electrical training or experience and is conducted by Peter Pedals, the author of our popular Energy From Nature book.
See our website for more details about these courses
Buy a fridge this month and get 5% off our recommended retail price!
It is expected that the AGO rebate of $4 per watt will end on 30 June (or even earlier if funds run out). Apply soon if you are an Australian homeowner. More details are on our website.
Variable Speed Domestic PumpWe now stock a new Water Pressure System Pump. The Sensor-MaxTM Constant Pressure Pump produces a smooth and constant water pressure with less wear and tear on the pump, using less energy and making less pump noise. It features -
* nearly silent operation
* solid state pressure sensor
* constant pressure
* self priming
* speed control
* no pump chatter
* no on/off cycling
* operates on 12V and 24V
* can run dry without damage
* thermal protection on motor
* maximum water temperature 70°C
* maximum pump temperature 130°C
* no accumulator (pressure) tank needed
* controls pressure by changing motor speed
* no switch, no points, no contacts
Getting intimate with your Fridge to reduce Power useTo compliment our 5% discount on fridges, I’ve written an article on how you can save even more power running your fridge. Our website FAQ section also has additional articles about refrigeration.
In case you haven't noticed, our FAQ page is not a two page effort answering six simple questions. It is your gateway to over 2000 pages of information!!!
In tropical and subtropical countries like Australia, the power usage of any fridge is a major power drain on one's home or RV power system. Temperatures inside your home or vehicle can exceed the already high ambient temperatures if it is 'locked up in the sun'.
The following are some general suggestions to keep your fridge power usage as low as possible.
1. DC Compressor Fridge: If at all possible use a 12/24 Volt compressor-driven fridge. These are more efficient than a normal 230V AC type fridges and avoids something like a 15% inverter inefficiency loss. So-called '3 way' fridges, which work on LP gas, are very inefficient when run on electricity. Danfoss compressors are generally regarded as the most efficient and reliable DC unit. This is why they are used for most vaccine fridges in rural clinics around the world.
2. Low Ambient Temperature: Try and keep the outside temperature around the fridge as low as possible by good ventilation, roof insulation, or parking your vehicle in the shade.
3. Use cold food: If at all possible, try and buy your drinks, etc, cold. Otherwise place drinks in the fridge in the morning (after they have cooled down a bit overnight). To cool a carton of drinks (9 litres) from 30°C to 2°C would use around 250 watt hours. This is roughly the output of a 70-80W panel on a sunny day. To freeze 20 kg of fish would require 800 Whr of energy in a day more than your freezer would otherwise use.
4. Pick your time and day: Try and place your food in the fridge in the morning when your solar panels are producing power. This helps to avoid battery losses. Try and place your warm drinks, etc, in the fridge on days when you are expecting a day or two of sun on your panels (or when your vehicle alternator can recharge your RV auxiliary battery). Some gain can be achieved by using a timer to turn your fridge off at night and making it run more in daylight hours. Your fridge or freezer will warm up a bit overnight (which may be acceptable to you) unless you have a eutectic model fridge. Eutectic fridges have a ‘cold sink’ of eutectic fluid (usually inside the walls) to help maintain temperature when the unit is shut off.
5. Keeping the cold air inside: The best option is to have a chest-type fridge or freezer. You can place low profile models on a knee high bench for easy access. You can pack a lot more food into a chest fridge than an upright. However, most prefer the convenience of an upright fridge (front opening) and generally these are the only option for larger size units.
If you have a front opening fridge, you can still take some steps to help keep the cold air inside. Studies by Kao ((1996) and Saidur (2000) have shown that about 11 Whr of power is lost each time you open the door. So, if opened say 20 times a day, you might need an 80W solar panel to provide this extra power! So try and keep the door closed as much as possible!
The best way to help keep the cold air inside the fridge when you open the door is to keep your fridge full. Food and containers of juice, water, etc, act as a ‘cold sink’ rather than air, which tends to ‘fall out’. If you have empty spaces in the fridge, consider filling these up with containers of water. Do this on a sunny day when you have solar power to spare. Make certain the door shuts tightly and that you replace the rubber door seal if it gets worn or compressed too much
Other methods to help keep the cold inside would be to use inside drawers like the container for the veggies, or to have a clear plastic 'drape' such as you see on some commercial walk-in coolers and freezers
5. Inside Running temperature: Your fridge will use approximately 5% more power for every 1°C colder that you run it. The recommended temperature for a fridge is 1-4oC. Depending on the type of foods you store and for the length of time you wish to store them, a warmer temperature may be acceptable to you.
6. Some Cautionary Tales: Over my two decades in this industry, I have seen many ‘fridge problems’ that have cost people thousands of dollars with failed batteries, inappropriate equipment, etc. We would advise -
* Listen to experienced industry people (who are trying to save you money rather than just selling you more panels).
* Think twice about 'home made' conversions. Our fridge suppliers test new conversions for a month with data loggers, etc, before selling new models. I have seen many failures (including some done by inexperienced fridge mechanics).
* Think twice about importing fridges, particularly from countries with temperate climates. They may not cope with our humid tropical climate!
* Seek advice about using freezers as fridges, etc. I know of a case where a freezer run as a fridge suffered premature failure from internal corrosion because certain tubing corroded at temperatures above the freezing point.
* Modifications by unqualified people can cause failures. An example is trying to cut off the 'auto defrost' feature. This can cause excessive ice build-up on internal components. Modifications by unqualified tradesmen will probably void your fridge warranty.
* Lastly, I should point out that refrigeration is a complicated business and power consumption is governed by many factors such as fridge model, inside and ambient temperatures, compression efficiency, etc. So the options I have given power consumption data for should be taken as a general guide only.
Please contact our office for detailed advice about your refrigeration needs.
That's all for this month folks! Your comments and questions are most welcome; however, there is no need to send our newsletter back to us when you reply! If you would like a price, or product information, please tell us which country you are from if it is not evident from your e-mail address. This allows us to assess if local GST (tax) is applicable or whether 230 volt 50HZ products will work in your country, etc.
Cheers from Dave and all the RPC crew.
Dave Lambert (Director)
- Issue #92 - 06/12/2005
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- Issue #87 - 29/07/2005
- Issue #86 - 04/07/2005
- Issue #85 - 03/06/2005
- Issue #84 - 05/05/2005
- Issue #83 - 01/04/2005
- Issue #82 - 03/03/2005
- Issue #81 - 23/02/2005
- Issue #80 - 02/02/2005
- Issue #79 - 05/01/2005