Saturday, 25 January 2014

Remote Power Supply Performance During Serious Heat

Our maximum daily temperature during the past fortnight has been as follows:
12th January: 42 degrees C, 13th January: 40, 14th January 40, 15th January: 42, 16th January: 44, 17th January: 43, 18th January: 45.5, 19th January: 42, 20th January: 40, 21st January: 38, 22nd January: 38, 23rd January: 35, 24th January: 25 (17 mm rainfall received during the course of the day), 25th January: 30

9 days of temperatures of 40 degrees or more is quite an extended hot spell. It has given us quite an opportunity to see how both we and our set-up handle the heat.

A few years ago we installed what our research suggested was the most energy efficient reverse cycle refrigerated air conditioner manufactured by Mitsubishi Industrial, model number SRK71ZEA-S1. A photo of the external inverter unit is below:

Our original intention was to install an evaporative air cooler but we opted for an air conditioner on advice from many that the former are of little use during high humidity periods. The latter does require considerably more power to run and was not in the calculations for our remote power system. It and the stock water pump are by far and away the two major power use items during summer. The latter is getting more use than normal presently due to the 'Just Add Water Experiment' we kicked off on 6th January.

Our house is not large by any means and during the renovations we did our best to insulate both the roof cavity and walls where we replaced the old plasterboard.

So here are some observations and learnings during the recent hot spell:

  • We both seem to be a bit better at handling heat than the 'average Joe-blow', which might be genetic or physiological
  • Our house insulation combined with fan use is such that we are comfortable inside in temperatures up to about 35 degrees
  • Solar panel performance deteriorates in temperatures above about 35 degrees C. On days below that our solar panels will harvest up to 19 kilowatt hours on a clear day, and when it is above 40 degrees about 17 kilowatt hours is the best we can hope for
  • The inverter we use that converts battery stored direct current to 240 volts AC recently 'chucked a serious huff' during temperatures above 40 degrees while the back-up generator was running.
  • The air conditioner doesn't draw much power when external temperatures are up to about 35 degrees, uses more up to 40 degrees, and heaps more when it is above 40 degrees.
  • We've found that the most appropriate internal temperature setting for us with our air conditioner unit is 28 degrees. The internal unit is near the ceiling so that actual temperature at 'living' height is well below 28 degrees
  • We've found that on above 40 degree days it works well to run the back-up generator for an hour in the morning and another hour in the evening. We see the cost of running the generator as the price of comfort during extremes.
  • We'd need to double the capacity of our solar panels to capture enough natural energy to cater for above 40 degree days. This is not cost justifiable as the reality is that there are not that many days during the year when temperatures are above 40 degrees.
  • On days when the maximum temperature exceeds 40 degrees we run the air conditioner from around 12.00 pm through to 9.00 pm.

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