Saying Goodbye to Eskom is cheaper than you think

Batteries
I honestly believe that the only way anyone can justify buying a Tesla Powerwall is if they are a committed “early adopter” of new technology, and that the Powerwall is going to be a conversation piece in the living room.

Conventional lead acid batteries and hybrid batteries do as good a job, at a fraction of the price.  Long term investments in rapidly-changing technologies is a waste of money.  From 2022 — four years away — we will see a revolution in battery technologies with the introduction of solid state batteries, with higher charge densities and fast charging times.  Both Volkswagen and Toyota are committed to new electric vehicles using these batteries by then.

Nissan opened a battery-recycling factory because they replace EV batteries when they reach 80% efficiency — the vehicle’s driving range is its most important feature.  They replace the dud cells with new ones and resell the battery packs for domestic use.  In Japan, a 24kWh battery pack costs 300,000 Yen (R42,000 at R0.14=JPY1).  A 24KwH Li-ion battery pack in SA will cost about R130,000.

What I have learned with the lead acid batteries I’ve been using is the importance of never running them flat and trying to always keep the charge above 50%.  Yes, you can use much more of the charge with lithium ion batteries, but you pay much more.  Battery weight and bulk is critical for mobile devices and electric vehicles, but not at all for houses.  The heavier the battery, the more difficult it is to steal.

I’ve also seen the importance of a proper enclosure for the batteries.  On cold winter mornings, the batteries lose a lot of capacity.  In the next phase of this project, the batteries will be supplied with some warmth on icy days.

The Laptop
The first thing I realised is that this is not a normal domestic test.  This house is used as an office and a home. An empty house would spend the day recharging the batteries for the night.

Habitually, I turn my laptop on when I wake up and turn it off when I go to sleep.  It can be on for 17 hours a day.  That was the first habit I changed.  Just closing it when I’m not using it — putting it into sleep mode — made a big difference in consumption.

Before I became laptop-conscious, I was using over 1000Wh a day — by far the biggest single appliance-user.  It can be equated to leaving a TV set on all day.

Apart from putting the laptop to sleep more often, changing the hard drive for a solid state disk, upgrading my phone and doing more on the new phone wasn’t only more convenient, it saved even more power.  And it’s great for watching movies!

Now if I had a Lenovo Carbon X1 laptop, with a battery life of up to 15 hours, that wouldn’t be a problem.  Its selling price of R40,400 is a problem!

The fridge
The fridge has its own story.  It’s a 150 litre Hisense with a rated consumption of 155kWh/year — that’s 425Wh/day or 18W/hour — very low by fridge standards  The reality is that the compressor motor turns on about three times an hour for several minutes, using a paltry 35W.  But… and it’s a very big but… I have seen very short spikes of 860W when the motor turns on.  At nighttime, that’s a battery killer… or, at best, the quickest way to shorten your battery’s life.

So, during winter when my power supply was stressed, I took a leaf from the book by Indian shopkeepers.  Being as parsimonious as they are, they habitually turn the mains switch off at night when they leave their shops to save electricity.  Of course, this turns all fridges off too.  So, in addition to the unreliability of Indian power supplies, this is why Asian fridge manufacturers were among the first to introduce emergency ratings — the number of hours a fridge stays cold without electricity.  Today, many freezers or fridges have 24 hour ratings.

Not so my Hisense… so I packed a big part of the freezer with refreezable ice bricks, since I rarely buy frozen products.  And that worked.  Turning the fridge off from 9pm to 9am in winter, it still managed to stay cold enough. Of course, you can’t do that if you have separate freezer and fridge sections.

There are inverter-friendly fridges on the SA market — where the compressor remains on all the time — but they all use more power than a top-end, standard fridge.

The best solution is also much more expensive.  A 260 litre A+++ Miele fridge/freezer (R29,000), for example, only uses 174kWh or 0.474kWh per day — not much more than the much smaller Hisense.  It’s power surge is minimal and the storage time if power is switched off is 24 hours.

The First Purchases… and the First Winter
Item	Cost
Victron MTTP 75/15 controller	R1,200
TES modified sine wave Inverter 800W	R1,140
2 x 102Ah deep cycle lead acid battery	R3,400
1 x 150W Panel	R1,710
TOTAL	R7,450

Verdict for the end of the first winter:  150W of solar panel was just not enough to fully charge the two batteries.  There were several days when I had to take one battery away to be charged.  In a normal domestic situation where there is very little consumption during the day, and the panel just charges the batteries, this would not be a problem.

There were a few days when I used the bakkie’s battery to power the house — which didn’t shorten that battery’s life significantly.  (It did last 5 years and finally died when the buzzer reminding me that I’d left the headlights on stopped working!)  This does make the case for a mobile powerbank that can be remotely charged.

Cost of electricity: This assumes that the panels, controller and inverter have a life span of 20 years.  The batteries proved to have a lifespan of 18 months.  It’s a simple sum that doesn’t take into consideration interest charges.

The Cost of Electricity — First 18 months
Item	Cost	Lifespan	Cost per month
Hardware	R4,050	20 years	R16,80
Batteries	R3, 400	18 months	R188,29
Total			R205.69

The Second Winter
Item	Cost
2 x 150W Panels	R3,420
Victron MTTP conttroller	R1,200
TES modified sine wave Inverter 800W,	R1,140
3 x 102Ah deep cycle lead acid batteries @R1 700	R5,100
Total,	R10,860

Verdict for the end of the second winter:  I had bought an extra panel. There were only two days when I actually ran out of power, and the two panels were able to charge the battery quickly enough that I never had to resort to remote charging.

Cost of electricity: The single battery is still going strong 20 months after I bought it, although it is being used alongside two new batteries.  I assume its longevity is due to the fact that the extra panels meant it was discharged totally less often.  In the figures below, I’ve assumed that would have died after 24 months had it been on its own.

[table “” not found /]

[table “” not found /]

Verdict for the end of the third winter:  I bought two extra 102Ah lead acid batteries to supplement the existing one.  My battery usage rarely dropped below 50% (12.20V) and the discharge table from the battery manufacturer shows that these batteries should last about 3 years.  In spite of a very wet winter, I’ve never been able to get even close to exhausting the batteries.

Cost of electricity: Power security comes at a small cost, compared to the previous winter.  I wish I had rather bought Omnipower Hybrid batteries which would have seen costs much lower.

The Cost of Electricity — Through the Third Winter
Item	Cost	Lifespan	Cost per month
Hardware	R5,740	20 years	R23.92
3x102Ah Lead Acid Batteries	R5,100	36 months	R141.67
Total			R165.59

The Cost of Electricity — The Better Option>strong>
Item	Cost	Lifespan	Cost per month
Hardware	R5,740	20 years	R23.92
2x180Ah Hybrid Batteries,7 444,12 years,51.69 id Batteries	R7,444	12 years	R51.69
Total			R165.59

I will be testing the Omnipower Hybrid batteries next and they promise to offer far longer life, making them the most economical bet.

Battery capacity
Batteries	Total stored kWh	Target max. to prolong battery life kWh
1 x 102Ah lead acid battery	1.224	0.612
2 x 102Ah lead acid battery	2.448	1.224
3 x 102Ah lead acid battery	3.672	1.836

Power Generation — 2 x 150W panels
Weather	kWh/day
Best sunny day	1.34
Average rainy/overcast day	0.89
Very worst dark/overcast day	0.23

There has been about 2 hours on 2 days in different years when it was too dark for the panels to generate any electricity.  Many rainy days are still bright, and generate almost as much electricity as the sunniest days.  Dark weather very rarely lasts more than 36 hours.

Since this project started, I’ve generated 765kWh of my own electricity at the time of writing.  That feels very good!  🙂

The next phase will generate up to 5.6kWh/day and be able to handle anything I can throw at it… far more the normal house scenario at a cost of R183/month (using the same methodology as above).  There will also be a ‘mobile Powerbank’ to provide added security during the worst of the winter months.  You’ll have to come back to read about that!

A note for Employers

I’ve been approached by scores and scores of farmworkers asking how they can go the solar route — like the community in Ekanini.  You can help them.

Municipalities get tied into loans/grants from Eskom to provide expensive township infrastructure, which ties them into even more expensive electricity.  The cost of the infrastructure doesn’t warrant the small amounts of electricity provided.

Maybe someone will tell me if the capital costs of PV panels, controllers and batteries can be written off against tax by employers?  Because a simple 12 Volt solar system would cost something like this:

A Simple Solar System
Item	Cost	Lifespan	Cost per month
1 x 330W Solar Panel	R1,819	20 years	R7.58
1 x controller with 12V output	R500	20 years	R2.08
1 x 180Ah Hybrid Battery,R3 722,12 years,R25.85	R3.722	12 years	R25.85
Total	R6.041		R35.51

In 2016, Stellenbosch Municipality was paying the Sustainability Institute R60 a month per household — the value of the free basic electricity subsidy for those connected to the Eskom grid.  All municipalities should be paying that amount for all solar-powered dwellings.

Do the sums, add interest charges, explore the tax benefits and harass your municipality for the free electricity subsidy…   This could be the biggest perk employers can give employees who live without electricity, or want to get off the Eskom system.  #LoyaltyRewards