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In the average New Zealand home hot water heating is usually the single biggest user of electricity. Surprisingly after hot water heating the next biggest usage is often old and inefficient fridges. This applies especially to old fridges which are often parked out in garages as a second or classic Kiwi “beer fridge”. These usually have very poor and often partially missing door seals as well as inefficient insulation and compressors. Also in many cases the compressors still contain CFCs which are now banned as ozone depletion substances rather than modern non ozone depleting refrigerants.
We decided to look at this issue as a demonstration project for home solar electricity production by photovoltaic panels. Our installation consists of two 175 watt Sharp photovoltaic panels coupled via a charge controller to two deep cycle 12 volt lead acid batteries. The charge controller is a Morningstar Sunsaver which uses maximum power point tracking to maximise the power output of the photovoltaic panel array. This is done using an automatic tracking algorithm which tracks the array maximum power point voltage as it varies with weather conditions ensuring that maximum possible power is harvested from the array through the course of a day. This type of controller can significantly increase the amount of power available from a given array and is a much cheaper option than adding extra photovoltaic panels when more energy is needed. Energy is drawn from the batteries using a Latronics 800watt pure sine wave inverter which inverts 24VDC from the batteries to 230V 50 Hz AC. For our demonstration project we are using this energy to run the LOWENZ office (computer system and energy saver lights) and a high efficiency Gram fridge. The fridge is 220L with a rated energy consumption of only 0.34KWhr/day. However our experience so far is that it is using much less energy than this, only about 0.25KWhr/day, because we are testing the system as a “garage beer fridge” literally in our garage where the ambient temperature is much cooler than inside a house. Clearly the power consumption of a fridge will be a direct function of the difference between the exterior and interior temperatures so it would use more energy if it was run inside a house where the temperatures are warmer. And yes our fridge does have beer and wine stored in it so this is a very practical demonstration. So far we have only run the system over a two month period in winter when sun angles are much lower (only 28o above the horizon in Wellington at midday on the winter solstice. However despite this we have found that the system produces just over 1 KWhr/day on sunny days which is more than enough energy to run the fridge and the LOWENZ office and we have used the surplus energy to cook meals over the course of several hours in a 160 Watt slow cooker or to run lights. The Wellington weather over May and June 2009 has been pretty shocking with a lot of very cold dull southerly days. However, even during these conditions, the system has still generated enough power to run the fridge and office computer although we have had to conserve on extra lights. Its important to note that because this system is not connected to the grid it is not subject to local power failures and will be capable of supplying emergency power if mains power is lost through an Earthquake disaster for example. This has been a fun project, and in hindsight very simple to put together. If you are interested in something like this for your home please contact us for details.
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