Saturday 6 July 2013


My Asterisk server packed up two weeks ago and I've only just got round to installing its replacement.  (By the way, telephonistas: If you install a version of Dahdi that is too new for your Asterisk version, you'll need to rebuild Asterisk.  The clue is to rerun ./configure and make menuselect.  If chan_dahdi is XXX'ed out, you need a new Asterisk.)  Of course, it did more than Asterisk; it also published the telemetry data from my solar panels, so I've been unsure of how much I've been generating at any given time for a fortnight.  The generation meter next to the fusebox has still been clocking up the units, of course, but I've been too slack to read that.

This is actually low-carbon cooking!  The small burner uses 850 watts.  At the time of cooking, the inverter output was of the order of 1.5 kW.  All the electricity needed to run the hotplate was coming from the sun; therefore, the process of cooking generated no CO2.  Using the gas cooker would have generated some CO2, but less than generating electricity plus waste heat in a power station, then sending it over a lossy transmission network to heat the electric hotplate.

But also while the sun has been shining, my thoughts have been turning to .....  POWER!  While I'm doing nine to life, selling my brain to The Company, I'm doing nothing with several kilowatt-hours of energy.  Now, I get paid for them; but, due to the way the installation is carried out, I would still get paid for them even if I used them myself instead of electricity I was paying for.  Which is equivalent to getting paid double!

What I am on the lookout for now, is a 3 kVA UPS  (the biggest thing it has to be able to run is the washing machine, which asks for 2.2 kW when heating the water.  I can do laundry in the dark if I have to)  and four nice big leisure batteries  (this size UPS takes a 48 volt battery pack), plus a suitable charging arrangement.  Now here it gets interesting.  A small leisure battery is 50 Ah.  At 48 volts, that's 2400 Wh.  Even with a conversion efficiency of just 85%, which is almost certainly a pessmistic estimate, that's still just over 2 kWh.  Enough for 2 loads of laundry on the trot, anyway.

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