E-News Issue #23
Dichroic Halogen Bulbs
We are still trying to source some 24V-20W units. We have 35W ones available in 24V. If you know where to get some 20W ones, let me know! (12V-20W is no problem).
The black "butterfly" spotlight for the dichroics is back in stock after a three month absence. This is an LYF-074 in your price list.
Computer and Power DrainIn the last newsletter we gave you some power consumption figures for IBM type computers. Our friends from Sun Real Energy Systems are into Apple computers and have given us some power figures for their computers.
If you're into Apple/Macs and want more information let me know and I'll put you on to these folks.
Renewable Energy Web Site
Nigel Martin has started a new site at http://www.rocknet.net.au/~jessydog (edit 6.5.11 no longer online)
Nigel works for the Queensland Dept of Mines and Energy. Check it out!
RefrigerationWith spring in the air, I've decided to do this month's longer article on fridges.
Refrigeration is often the largest electrical load in a home power system. The first option that people often consider is conventional 240V units. Despite improving efficiency in the last few years, standard domestic refrigerators are still rather power hungry. Manufacturers make them with price, appearance and space in mind and efficiency is a minor consideration. We have tested a number of these fridges and in general terms they take 2 - 3 times more power than a 12/24V Danfoss compressor driven fridge. This extra power requirement will result in an extra 4 - 8 large solar panels (at AUD$670 each) being required. Added to this cost is the cost of a larger inverter to power such a fridge and an ongoing cost for larger batteries. In general terms, we would not recommend using 240V domestic fridges unless you plan on having a back-up diesel generator coupled to a large battery charger or interactive inverter-charger in your home power system.
Another alternative to consider is an LP gas fridge. These are fairly costly to buy and a 220 litre unit will use a 45kg bottle of LP gas every three months. They do need a bit of ongoing maintenance and they generate some heat and fumes that need to be vented out of the building. There is also some anecdotal evidence that they can have difficulty coping with extreme tropical conditions such as in North Queensland and Darwin.
Some of these fridges are often known as 2 way or 3 way in that they can also run off 12V or mains power electricity. These use the electricity to first make heat similar to the gas flame. Depending on size, they typically draw 10 - 25A @ 12V and will run non-stop for 24 hours per day. This type of fridge is okay to run on gas but is too power hungry to run it off solar.
The last and best option to consider is a 12/24V Danfoss compressor driven fridge. This Danish made compressor is renowned for its efficiency and reliability. These compressors are used in the majority of vaccine fridges around the world for these reasons. With 12/24V fridges, the chest type is more efficient than a front opening one which lets all the cold air fall out.
A further innovation is the use of eutectic fluid in some of these fridges. In the old days this used to be a brine solution. The idea with the eutectic fluid is similar to the esky freeze packs you put in your deep freeze for camping trips.
Eutectic refrigeration is often used in fishing vessels.
The basic principle is that when the engine of your boat or vehicle is running (and therefore generating power), you run your fridge so that the eutectic fluid goes below O° C. This then keeps your fridge cold for a further 24 - 48 hours (while your engine is off). The advantage of a eutectic fridge in a solar set-up is that you can time the fridge to come on in daylight hours only (when your solar panels are generating power). This lowers the system voltage a bit and helps to get a bit more amperage from your panels. More importantly, it helps reduce the battery inefficiency which results from storing power in your batteries during the day to run the fridge at night! And the last bonus is that 1-2 days holding capacity of your fridge is a bit like having some more battery storage.
We have monitored a 73 litre eutectic fridge (chest type) for a one year period in our area. If you are not familiar with our location, Nimbin is fairly close to Brisbane. Basically it is a sub-tropical climate with typical summer day temperatures around 32°C and winter day temperatures about 20°C.
Cheers from Dave and all the RPC crew.
Dave Lambert (Director)
- Issue #92 - 06/12/2005
- Issue #91 - 15/11/2005
- Issue #90 - 20/10/2005
- Issue #89 - 29/09/2005
- Issue #88 - 01/09/2005
- 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