A study done in 2003 concluded that using a dishwasher was more efficient energy wise than doing the dishes by hand, and luckily so as doing the dishes by hand would be were I draw the line between practicalities and being environmentally conscious.. I wrote a similar article like this about buying a washing machine (in norwegian) where I concluded that my new washing machine reduced the energy used to wash our clothes by approximately 50%. If the same adjustment of efficiency could be done for every household in Norway I also calculated that the energy saved on washing machine improvements alone was more than half of the annual energy use of a medium sized Norwegian city (Kristiansand). As our dishwasher decided to give out on us before christmas it was time to upgrade!
I couldn’t find any information on the energy usage of my old dishwasher, but it was getting old and as it only had about a 80% chance of actually making the dishes clean when the 70 degree programme was used I think it will be fairly generous to use the average energy efficiency of the dishwashers used in the study I mentioned below.
My new Siemens dishwasher uses 1 KWh less per washing cycle than a B-rated dishwasher according to the European Energy labeling classification. Compared to our old dishwasher we are therefore, with an average of one machine run per day saving 365 KWh per year. If you weren’t paying attention in physics clall 1 KW is 1000 W(watts) and if an appliance using 1 KW is left on for an hour then you have spent 1 KWh (1 kilowatt hour). With these numbers the energy saving comparing the old dishwasher (approximately energy rating B) with the new one (energy rating A+++) is actually bigger than with the washing machine that we bought earlier. The difference in KWh is about the same, but since we use the dishwasher a lot more the saving does amount to quite a bit, especially when you start aggregating it up.
When adding up the dishwasher and the washing machine our apartment should be using around 500 KWh less each year which amounts to around 500 NOK in savings (80 USD). If this is combined again with a similar strategy for refrigerators, freezers, lights around the house and so on the total number is substantial. So make sure you have a look at the energy rating the next time you buy anything at all!
Sources:
http://www.forskning.no/artikler/2003/februar/1045050482.5
