To solar or not to solar?

Solar plant

The power is off for the second time today, dogs are barking, kids are screaming and the alarm is beeping non-stop. Depending on who you ask it will end next month or next year. This leaves you with a few options:

  • Light candles and pretend that you are making it romantic
  • Buy the biggest generator that Makro has to offer
  • Buy a back-up battery system, or Uninterruptible Power Supply (UPS)
  • Make the jump to renewable sources
  • Move to Canada, Australia or other countries with greener grass

Today I’ll be looking at these alternatives with an emphasis on solar power to help you decide whether it is the right move for you. This will also help you specify the system you will need if you do decide to go solar.

Light candles

This will be the cheapest option, but if you have kids it will become difficult to manage. Additionally, some of the higher load-shedding stages will become long enough for your freezer to start melting. Most of us will end up going this route, even if it is kicking and screaming.

Generator

This is the go-to option for most South Africans, probably because it is the easiest option. Simply buy the generator, plug it in and start it up. However, the running costs for generators are high. Diesel generators set you back about R3/kWh and petrol even more. It will also leave you and the neighbours with the soothing sound of a billion bees.

Back-up batteries

This is an interesting option that falls somewhere between buying a generator and installing solar panels. You buy a battery bank and inverter, which allows you to store electricity supplied by Eskom. When the power is on, the inverter converts the 220 V alternating current (AC) to 12 V direct current (DC). This can be stored by either lead-acid or lithium batteries. When the power is then switched off, the inverter converters the stored 12 V DC back to 220 V AC for consumption.

This storage system will set you back about R3 to R6/kWh. On top of this, you still need to pay for the units that come from Eskom. This makes it an expensive system. The biggest problem however is that your total consumption will not be reduced. You will simply consume more units when the power is on to compensate for when it is off. This nullifies the whole purpose of load-shedding.

Solar power

This system is like the back-up battery system discussed above. However, it uses solar power to charge the batteries, instead of Eskom power. In South Africa we have an abundance of sunshine, which is perfect for solar systems. Our irradiation varies between 4.8 kWh/m² per day in Pretoria, to 4.2 kWh/m² per day in Cape Town, as seen below.

Photovoltaic power potential

So, what does this mean? Well let’s calculate what my requirements will be, as an example. I live in Pretoria, with an irradiation of 4.8 kWh/m² and consume about 11.5 kWh per day (aka units). My consumption is on the lower side, since I already have a solar geyser and a gas stove. However, a lot of the consumption is because of our air-con at night.

Firstly, we need to calculate the required solar panels. Typical efficiencies of solar panels are around 18%. So, if you want to generate 11.5 kWh, you need to be exposed to 64 kWh of irradiation (11.5kWh/18%). In Pretoria, where the irradiation is 4.8 kWh/m², I will need solar panels that cover 13.3 m² (64 kWh/4.8kWh/m²). If I buy 405 W Canadian Solar panels that cover just over 2 m² each, I will need 7 panels.

The next step is to buy an inverter, which is easy to specify. If I buy seven 405 W panels, that is 2 835 W combined. This requires a 3 kW inverter. It is often a good idea to buy a bigger inverter, since it will determine whether your system can be expanded later.

I also need to determine the battery size. Of the 11.5 kWh we consume, about 6.5 kWh is during the night. So, we need to store at least that much power to ensure that we make it through the night. Since not all days will be sunny, it might be necessary to store even more.

What will this cost?

A basic 2.4 kW system (2.4 kW solar panels and 2.4 kW inverter) with about 8 kWh lead-acid batteries and installation will set you back just over R60 000. The installation is not rocket science, but you will need an electrical certificate. This system is slightly smaller than I require, but with a few adjustments, like buying a gas oven and limiting the air-con usage, we should be able to cope.

A bigger 4 kW system, with 8kWh lithium batteries will set you back about R111 000. This system will definitely be able to supply our needs. The question now is whether it will be financially viable to install solar panels. Our electricity bill is about R660 a month. I also suspect that the Eskom electricity increases will be more than inflation at about 8% per year.

Lead-acid batteries tend to last about 4 years, while lithium batteries have typical lifespans of about 10 years. Solar panels on the other hand, have great lifespans of up to 30 years. Lastly, I assumed that batteries will get cheaper at the same rate as inflation, to effectively cost the same going forward.

Solar calculations

Is it worth it?

Even though the lead acid batteries need to be replaced more often, they are significantly cheaper. Either way, it looks like the payback is just over 10 years. Granted, I did not really shop around for the cheapest price, but I don’t think the prices will vary more than 20%. The battery life will also vary depending on the brand you choose. So, call these ballpark figures.

The first thing that you need to decide is whether you will be living in your present home for another 15 years. Then you also need the upfront finances, which not everyone will have. For me, 12 years is just too long at this stage.

If you do decide to go the solar route, make sure that it is a reputable dealer. If your documentation is not in order it might influence your insurance claim if something goes wrong. That being said, load-shedding is a big concern for a lot of us, especially businesses reliant on electricity. It’s going to take a while for Eskom to get their shit together, while we continue to have intermittent load-shedding.

You can either make the solar power investment now, wait till it becomes even cheaper or wait it out. Either way I’m not leaving South Africa anytime soon, so will need to adapt. A special thanks to my friend Marnus who helped me with a lot of the information.

Be safe out there,

Hendrik

Quote of the week

“Fun is like life insurance; the older you get, the more it costs.” – Kin Hubbard

End note

Thank you for reading to the end. Apparently, the average person spends 8 seconds on a page, so you are special. If you have any suggestions, feel free to drop me a mail on the contact page. If I missed anything or you have questions, don’t hesitate to comment below. I might even notice it and respond.

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Comments

  1. Sharan

    Interesting article, though there’s also the route of going partially solar.

    It would be much cheaper but there would still be a dependence on the grid.

    So that’s like using gas for cooking, heating and solar for just lights and a TV, (bare bones).

    I guess it depends a lot on ones lifestyle.

    Though think of the days before electricity, most people grew their food and if they wanted to eat something they would buy it fresh and cook in the same day.

    I think we have taken electricity for granted so Eskom loves to remind us every now and then…

    1. Post
      Author
      Hendrik Brand

      Hey Sharan.

      I agree, that is a good option as well, simply buying solar panels and an inverter to supply your needs during the day. I quite like that option but like you mentioned, load-shedding will still impact you at night. Had load-shedding not been an issue, I would go this route, buy a meter that measures flow in both directions and use the grid as a battery. Not all municipalities allow this, but it is the logical (and cheaper) option. Granted, quality control on these grid-tied systems will become an issue.

      Thanks for the comment.

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