Visualising electricity and water consumption of a solar estate

4 minute read 19 Feb 2020

I live in a lifestyle estate that outsources it’s electricity and water meter management to a third party company. Even though we have solar panels, a recurring complaint from residents is that they are receiving unreasonably high utility charges. Monthly usage reports are available on our estate management portal, so I spent some time over the December break (January and half of February managed to sneak by) making some plots to let the data speak for itself.

The estate consists of total of 432 apartments one (n=288), two (n=72) and three (n=72) bedroom apartments. I was able to find electricity usage reports from May 2019 onwards, but, for some reason water usage reports for the month of May and June are missing. Keeping that in mind, here’s a monthly breakdown of the electricity and water usage for the estate,

There’s nothing too out of the ordinary here, but I’d like to comment on the following:

1. Electricity usage peaks in the months June through August and tapers off towards January. This usage pattern corresponds well to the South African winter season¹ when heaters and tumble dryers are often used, and geysers are less efficient due to lower ambient temperatures.

2. I expected to see less water being used in winter than in summer; however, there doesn’t seem to be a clear relationship between water usage and the time of year.

Taking a closer look at the data, here are monthly usage plots grouped by the size of each apartment,

I noticed the following:

1. The usage patterns identified in the earlier plots are also present when looking at the electricity usage by apartment size. This makes sense, as using more electricity in winter likely isn’t dependent on the number of people living in an apartment. A couple/family and single person are probably just as likely to use a heater when they are cold.

2. There are significantly more outliers² in the set of one bedroom apartments. One possibility is that the number of occupants per one bedroom apartment is more unpredictable than two and three bedroom apartments. It’s quite common to have couples (and in rare cases, a couple with a child) sharing a one bedroom, while the majority of two and three bedrooms are occupied by couples and families rather than a single person.

3. At first glance it may seem interesting that there is a stark increase in water usage between two and three bedroom apartments while there is only a gradual increase in electricity usage as the size of the apartment increases. There is actually a simple explanation: all three bedroom apartments are ground floor units with a garden.

4. The water usage of some residents is seriously concerning. Cape Town has just recovered from the worst water shortage³ in history, and looking at some of these numbers indicate that a handful of people have returned to their water-wasting ways now that the immediate danger is over.

As mentioned in the opening paragraph, the motivation behind this post were the numerous complaints from other residents about their utility accounts. To see if there is any merit behind these complaints, I found the following benchmarks for comparison:

• According to the World Energy Forum, the average monthly electricity consumption per household in South Africa was 268 kWh in 2014.
• The International Benchmarking Network for Water and Sanitation Utilities states that the average residential water consumption was 114.48 L per person per day in 2017.

Using the number of bedrooms as a substitute for number of people living in each apartment, I worked out the average water usage per person in the estate, as well as the average monthly electricity consumption per apartment:

Monthly Electricity Consumption Per Apartment (kWh)	Average Water Usage Per Person Per Day (L)
238.85	112.27

Comparing these to the benchmarks, it seems that the usage within the estate is in line with the national average. This indicates that it’s unlikely a systematic problem with the electricity and water usages being reported. Moreover, we can look at the units (hashed for anonymity and number of bedrooms in brackets) that used the most electricity and water across all the months:

Top Electricity Usage	Top Water Usage
yT6x (3)	toiG (3)
pzGF (3)	yT6x (3)
a6cu (3)	ohqG (1)
QQRq (1)	KWH2 (3)
YUmy (3)	8D8y (3)
RmCd (2)	RmCd (2)
ohqG (1)	fY2j (3)
LWdW (3)	a6cu (3)
8D8y (3)	pzGF (3)
ByAc (1)	BGhv (3)

There are clearly ‘repeat’ offenders⁴ that are topping the list in both categories. Having a faulty water meter and a faulty electrical meter seems unlikely to me, so I would assume this was due to behavioural patterns of the resident.

So are the complaints justified? Hmm, I’m not convinced.
–Alex

Footnotes