Christmas is over

Well Christmas is over!  How do we know?  The supermarket has stocked the shelves with hot crossed buns and the Easter Eggs are starting to appear.  Consumerism at its worst!

Four days of struggling to resolve the issues with the trailer 12V power distribution board has been finally completed.  Of course I’ve only been working on the problem in the morning and evening.  It’s been too hot to be stupid enough to do anything outside during the day.  There were four issues.  By tracing my wiring I found a bullet cable connector which had the positive and negative cables reversed.  Then I discovered sometimes there was no power from the battery.  The reading from the Maplin multimeter was intermittent which initially had me searching for an intermittent fault in the wiring connections.  The following day there was no power from the battery.   @#$%^&!  Had I somehow fried and flattened the battery.  How would I explain destroying the expensive AGM battery to Jan.  After a restless night mulling over the problem I decided I wasn’t going to remove and disassemble the sealed battery box prematurely.  Instead I tested the Maplin multimeter by measuring the voltage of a spare torch battery.  Zero volts!  Could the problem be the Maplin multimeter.  I have an old multimeter purchased back in 1981.  That also produce a zero reading on the torch battery.  Could both multimeters be defective?  Highly unlikely!   But they were…

There was a quick trip to the nearby Jaycars (Maplin equivalent) outlet where I purchased a very cheap ($9.95) third multimeter.  There is voltage from the battery!  <relief>

The next problem was identified as a defective Watt meter which I’d fitted between the battery and the rest of the trailer electrics.  Bypassing that resulted in the 12V distribution board finally working.  But I decided not to do the final installation until I’ve tested all the trailer electrics.

Jan doesn’t appear very impressed with her Christmas presents.  I’ve ordered everything on eBay using a 10% discount voucher.  Sometime during the next week she should receive a pair of fishing sunglasses, a head for the gas torch and a pair of 1200mm drawer slides for the camper trailer.  Meanwhile I have to decide what to do with all the sheets of piano music she has ordered for me!

Purchasing a storage battery for our house solar system isn’t currently viable.  The payback period on the cost is about 15 years but the batteries only have a useful life of 10 years.  This is one reason why I’ve been considering the idea of making my own battery.  The question is “What is the required battery storage capacity?  I’ve started to identify that by using data collected from the two power monitors I’ve connected to the house.  One measures the total amount of electricity generated by the solar panels and the other measures our consumption.  By subtracting the total electricity consumed from the solar power produced I can calculate the surplus solar power being returned to the grid. 

Sometimes we use more electricity than we produce.  This has to be purchased from the utility company.  My spreadsheet calculates how much electricity we purchase on a daily basis.  During December it peaked on one day at 7.6kWh and it averages approximately 5kWhs.  Of course we are likely to have less sunshine in winter and will corresponding need to purchase more electricity during that period.  So a 10kW battery appears to be about the right size. 

Obviously I also need to ensure we have sufficient surplus solar electricity to recharge the battery on a daily basis.  Assuming we recharge the battery daily and need to add 50% to the battery capacity in order to achieve this then we require 15kW daily (31x1=451kwh). This month we sent a total of 641kwh back to the grid.  The power company pays us $0.07 for every kWh we send to the grid which means we would earn $13.30 for our surplus electricity after recharging the battery.  There is a daily service charge of $0.97 or $30.07 for the month.  Deduct the $13.30 from the service charge and we would have a monthly power bill of $17.27 despite using no electricity from the grid.