Design Hobby

To measure is to know

There is a old dutch saying that goes like this: “Te meten is te weten”. This is very true for energy management. You can not manage successfully without measuring.

About this time last year we were facing the start of load shedding. Very few of us realized at that time that the power interruptions of a several hours a few times per week would cause so much headaches. The whole issue of load shedding continued for at lease six months thereafter. Most of us were ill prepared for this, and rushed off to the nearest hardware or electrical store to purchase a small generator to help us through, just to realize the machine was very noisy, and sometimes too small to cope with all our energy hungry demands. We had to admit of just how much we have become dependent on the utility power network.

At that time I investigated the possibility for greener energy alternatives. The capital outlay for Photo Voltaic (PV) panels, inverters and batteries would have been quite high. The real problem was that I did not know exactly how much peak power we were using at our residence. Not only the peak power (kW), but also daily consumption (kWh) determines the sizing of the whole system. Of course, you can switch on every load you have and just measure the current to determine maximum kW, and use your utility bills to determine the average kWh, but in doing so you may design for an oversized inverter or undersized batteries. This mistake could be very costly indeed.

A more practical approach is to measure and record the intantaneous energy use for a long period, say 24 hours up to at least a week, including week-ends. It would even be better to measure all season times, so that you have all loads covered like heaters in winter and air-conditioners in summer. When you gathered all the data, you start analyzing each load’s contribution, the normal running times of the day or night and the total consumption that is going to determine the design of your solution.


I have designed and built my first prototype meter that measures instantaneous current, calculates the power used and writes all the data to a SD card. When the test period is completed, I load all the data into a spreadsheet and analyze the trends. In the coming posts I will share some of the promising results.

In the mean time, you are most welcome to brainstorm some ideas on how this nifty gadget can be used as an energy management system. It could either warn the user of exceeding the proposed time-of-use tariff hikes, or even automatically re-schedule less critical loads like irrigation or swimming pool pumps during peak demand periods. Integrated with a green energy solution, our utilities untimely load shedding, unprecedented pricing increases and having to inhale the poisonous fumes from your noisy neighboring generator could be something of the past.

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