Archive | October 2015

electricity versus diesel or other Internal Combustion

Dear Troy,

Evaporation for the week 18th to 24th October 2015: 9,9,9,8,8,9,9

This is higher than my average for this time of the year, but with the lack of humidity in the air, hardly surprising. You ought to be aware that 2015 is set to be the hottest year ever recorded (since we invented accurate thermometers). You should also be aware that 2014 was the previous record holder. These increases in temperature are still small, so they probably don’t have much direct effect on our evaporation figures….but will eventually have a bigger impact on our overall climate.

I have been spending a lot of time researching solar electricity, inverters and even batteries. Especially with the solar cells and batteries, there is always the promise that next year will be better. Prices are falling all the time, and the ‘breakthrough’ in batteries is just around the corner. It makes me wonder whether I shouldn’t wait for that breakthrough, or for prices to fall further. Then I realised that, as long as the investment in Solar can be justified now, I should go for it. The big advantage of electricity over diesel engines (or other Internal Combustion Engines – ICE) is that electricity is SO much more flexible….just match the voltage and away you go. Even the voltage match doesn’t have to be perfect, most electrical machines will work within a +/- 10% range….though obviously we have to be careful at lower voltages not to expect the same power output. So, I can spend money on PV panels, Inverters and batteries knowing that the investment will never become obsolete. If that new miracle battery comes onto the market in 5 year’s time, I can eventually replace my old batteries with the new technology, and it will connect very easily to my PV panels, inverters and electric motors. The same cannot be said for my ICE technology. When the water pump goes on my stand-by generator I have to get the exact part….if I cannot get that exact part (or a Chinese/Indian copy) the whole investment in that engine has to be written off. And there are several hundred parts in the engine which are critical, plus as many again in the gear-boxes.

Which is why I am starting to look very closely at an electric vehicle for trips around the farm and into Choma. They don’t use gearboxes and swapping older motors/inverters/batteries with newer versions, is simply a case of connecting the wires correctly.




Close Call

Dear Troy,

You asked for evaporation figures. Without the discipline of a weekly blog I had stopped doing it, but here they are:11th to 17th October, 10,10,8,7,9,7,10 and I hope to keep both the blog an the evaporation figures more regular, now that I have a reliable Internet connection.

I have analyzed the monthly rain effect of El Nino. El Nino does not affect the average January rainfall by much; October and November still get about 90% of normal but it is in February, March and April where El Nino years can reduce the average rainfall (on my farm) to 50%,70% and 50% of the non El Nino years. Doing this analysis one is reminded of just how fickle the weather can be, because some of those records go way out of the “”””normal”””” range.

We had a close call while combining the barley. The cable taking power to the pivot is above ground and I HAD considered switching it off, but didn’t. Either the combine cutter bar nicked the cable or just the weight of the machine driving over caused a short, which started a fire. FORTUNATELY we had been combining upwind, so we only lost about 4ha of stubble – AND I got a free cardiac test! We did not plan to combine against the wind, but it is now obvious that that should ALWAYS be the strategy. I think most of you will have heard the story of the person in Chisamba whose insurance ran out on the 30th September. I was aware of this problem and had bought an extension, but I had only checked the fine print (to see that I HAD actually been given the extension in my policy) on the morning of the fire. I believe the ZNFU should lobby the Insurance companies to make it imperative that the winter cereal insurance is automatically to the end of October and automatically includes frost damage.



Power Factor Correction

ZESCO Power Factor correction

I am not sure if this is going to work, but I have tried to attach an Excel file that will calculate the size of your penalty under ZESCO’s new Power Factor proposal – ZESCO Power Factor correction.xls

Start by filling in the 4 yellow cells – the charges for Maximum Demand, units (kWh), Fixed Monthly charge and the Exchange Rate. What I have put in there (when I saved the file) is my guess as to what might be approved by the ERB – the 300% increase is only what ZESCO has asked for.

Then fill in the 3 pale green cells – the cost of your PF correcting equipment, your monthly Maximum Demand and the amount of power you have used.- from your relevant ZESCO bill. Then the data in rows 11 to 41 will calculate the size of your penalty: for a given PF (before correction) in column A, Kwacha in column B, Dollars in column C and number of months to recover your investment in column D. Remember that if you are curing for 5 months of the year, and you have a 24 month payback time then it MIGHT take you 4.8 years to recover your money – although this equipment (especially if it is a general – transformer based – type) will save you some money even in the non-curing months.

A PF as low as 0.6 may appear pessimistic but, if Mr. Daka (area manager, Choma) is right, ZESCO will base this penalty on the WORST PF reading for the month, not the average. It COULD happen that, at the end of March you have done a lot of curing, but you switch off your fans on the 25th of the month. Then your grading lights are left on one night and the PF of florescent tubes could easily be as low as 0.6 – hence the penalty that you will pay.

One final point: in a paper presented to the Engineering Association of Zambia it is claimed that the cost of a kWh of power, generated by a diesel engine, is 41 US cents per kWh. From what I understand of this technology, it will save you diesel if you correct the PF of the load carried by your generator. I hope to demonstrate that with an experiment…..

I hope that helps,


Simple tools and El Nino

Two simple tools you may need one day:

To check whether your irrigation nozzles are worn (sprinkler or pivot), cut a 15cm length of plastic strapping tape into a long taper – 2mm at one end and 8mm wide at the other. Slide the narrow end into a good nozzle and note how far it can go. Now slide into other nozzles and, if it goes further the nozzle is worn. If you want to check your pivot nozzles, there is a chart on the Internet giving the Internal Diameter of every nozzle. You can set a vernier for each size, slide the plastic wedge into the vernier and mark a line for each nozzle size. Again, if the wedge slides further into a nozzle 26 than it should, then the nozzle is worn and should be replaced. Our pivots are 10 years old this year, so the nozzles are probably overdue for replacement.

The second tool I made for my small scale neighbours who are repairing/building new dams. It consists of a long straight lath about 2m long; roughly in the middle, two shorter laths are attached so as to make a triangle; from the apex of this triangle you hang a plumb bob, which is on an adjustable length string. The shortest length of string hangs straight down, when the long lath is level – to a mark that shows when the lath is level. They use this for leveling the wall and the spillways – which they call the runout. Then I put another mark for a 1:10 slope which is the steepest I will let them build down the slope of the spillway. With good grass and over a short distance, that should allow water to spill without erosion. Then two further marks give them the 1:1/2 slope of the back of the dam wall and the 1:2 slope of the front. To reach these marks, the string of the plumb bob has to be lengthened – I use something like a guy rope on a tent. If the three laths are held together with verandah bolts it can be dismantled and carried on a bike.

I have found river flow data for Vic Falls from 1907 to 2006 and there is NO correlation between El Nino years and river flow. So we cannot say that, because of El Nino, there will be low flow this year. What is interesting is how variable the flow is, even from one year to the next. I am still hoping to get more recent data…from 2000 to 2006 the average is definitely climbing, but it would be interesting to know if that trend is continuing.