So I just had the phone call from hell.
New Koi pond, built by Koi pond experts. 8000l of water to begin with fills me with trepidation - from which it goes downhill I'm afraid.
Here we have a "koi pond" with a 50mm bottom drain feeding a 0,75 kW swimming pool pump - no surface skimmer I might add. The pump feeds a sand filter, splitting to an open filter system via a U/V draining into a water feature and the second back to the pond via a venturi.
By now my eyes had glazed over and in all honesty my mind has shut down - there is nothing I can do for this pond. So the advice given to save power by running the system 3 hours on and then 3 hours off I almost missed.
Having corrected the caller about the illusions of the 3 hour on 3 hour off power saving myth - (namely that especially on a system as poorly designed as this one that 24/7 operation is mandatory) we got into the whole "run it off solar" discussion.
The returns of running your Koi pond off solar are infinitely negative. This is all you need to know. Right now, right here, in early 2015 it cannot be done cost effectively. To run a 075 kW swimming pool pump will cost you R250k. How much electricity does that buy? Plus, solar systems have a running cost associated with them - they are not a once off purchase and then free electricity for all time panacea.
If you run an Ultra Low Power system like I do at home with a power draw of around 100W for my water pumps (which is not bad for 80kl of pond I don't think) you can also never break even - the sheet cost of solar even for this low power draw is so much higher than paying the R100 or whatever it costs me a month to run the system that the return is infinitely negative.
Hence, the best route to follow in my opinion is to go for Low Power or Ultra Low Power wherever you can and hook that up to a decent UPS capable of driving the system for 12 hours at a time for when the power goes off.
A small generator of 1 kVA is then plenty to use as a standby for the UPS in the event the power outage lasts longer than 12 hours (as in when the real blackouts start to hit).
And above all, anyone recommending a swimming pool pump of any description on any new Koi pond should be avoided. Going cheap, actually, these installations are in fact NOT any cheaper to buy and install - so perhaps let me reword this: Going uninformed when building a Koi pond these days, is really going to cost you.