{"id":10,"date":"2022-11-15T18:11:00","date_gmt":"2022-11-15T18:11:00","guid":{"rendered":""},"modified":"2025-06-10T09:00:34","modified_gmt":"2025-06-10T07:00:34","slug":"cost-of-gas-vs-electricity-in-south-africa","status":"publish","type":"post","link":"https:\/\/sandrock.co.za\/carl\/2022\/11\/cost-of-gas-vs-electricity-in-south-africa\/","title":{"rendered":"Cost of gas vs electricity in South Africa"},"content":{"rendered":"

Introduction<\/h2>\n
I have been investing in a solar system at home, since South African load shedding is really getting me down. One of the key elements of going off the grid is to reduce your electricity consumption. I’ve focused on reducing demand by scaling down our geysers from 3 to 1 big one and 1 small undercounter unit. I also managed to find a second hand heat pump, so that geyser is going to be mainly heated using the heat pump.<\/div>\n
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Whenever I have mentioned my plans to tradespeople, I have uniformly been met with suggestions to move to gas. In South Africa, that means LPG. I wanted to do a comprehensive check on costs, so here is the result of that analysis.<\/div>\n
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You can find the Python scripts and Jupyter notebooks I used in the analysis here<\/a>.<\/div>\n

Gas<\/h2>\n

Prices<\/h3>\n
LPG prices are published by SAPIA. They have separate pages for the current prices<\/a> and historical prices<\/a>. Note, if you’re following along, that they appear to have swapped the coastal prices and the Gauteng prices on 2016-08-03 and 2017-08-02, which I have corrected. I have also assumed that the prices quoted here are pre-VAT and have added 15 % to the quoted prices for the sake of comparison. There is a difference around R2\/kg between the coastal and Gauteng prices, which has been moving up by a few cents every year since 2017. I have also included an 8 % per year increase on the values since 2015 for reference.<\/div>\n
<\/a> <\/div>\n

Gas heating value<\/h3>\n
The main thing you do with gas is to heat things. It is therefore useful to know the gas price not based on the mass (kg) but rather on the ability of the gas to heat things. This requires a quick diversion into “heating values” for fuels. When you burn a fuel, it decomposes into simpler components (gases), which are hot. You can transfer the energy from this hot gas to some cold substance like water or a pot. For LPG one of the gases that forms during combustion is water. Of course, at the temperatures of the flame, the water will be in gaseous form. But if the thing you are trying to heat is cold enough, the water will condense and impart an additional amount of heat on the object. In broad strokes, there are therefore two amounts of energy you can impart on a cold object by burning an amount of gas. One, called the Higher Heating Value (HHV) assumes that you can condense the water. If you can’t condense the water, you get the Lower Heating Value (LHV). <\/div>\n
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Here are the numbers I’ve used to figure out the heat you can extract from a kg of LPG:<\/div>\n
<\/div>\n\n\n\n\n\n\n\n
Component<\/b><\/td>\nFraction<\/b><\/td>\nLHV<\/b><\/td>\nHHV<\/b><\/td>\n<\/tr>\n
<\/td>\n<\/td>\nMJ\/kg<\/td>\nMJ\/kg<\/td>\n<\/td>\n<\/tr>\n
Propane<\/td>\n0.6<\/td>\n46.35<\/td>\n50.35<\/td>\n<\/tr>\n
Butane<\/td>\n0.4<\/td>\n45.75<\/td>\n49.50<\/td>\n<\/tr>\n
Total(LPG)<\/b><\/td>\n<\/td>\n46.11<\/b><\/td>\n50.01<\/b><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
<\/div>\n
Lastly, we factor in that 1 kWh = 3.6 MJ. For the HHV this works out to 13.9 kWh\/kg of LPG. I will be using this factor for the later comparison as it presents the absolute best case of extracting heat to gas via combustion.<\/div>\n
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Electricity prices<\/h2>\n
For electricity prices, I have used the historical rates published by Eskom in Excel format on this page<\/a>. I have used Homepower 1 non-municipal rates including VAT since that’s what I pay at my home. I have again included an 8% increase overlay as a guide.<\/div>\n
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Since 2013 the Homepower tariffs have been split into two blocks. You pay the lower price on your usage up to 600 kWh\/30 days or 20 kWh\/day. If you use more, the overage is charged at the higher price. It is important to realise that if you are currently using more than the Block 1 cutoff, electricity savings will save you that full Block 2 tariff until you drop back below 600 kWh per 30 days. It is not correct to reason using your average cost when contemplating savings. Of course, if you are trying to calculate your total monthly bill, you will have to add the monthly connection fee as well, but I have chosen to focus on the marginal costs in this analysis.<\/p><\/div>\n

Simple comparison<\/h2>\n
Now we are in a position to compare the energy cost from LPG with electricity. The following chart shows all the prices we have calculated so far. What is clearly visible here is that even in the best case for gas (using Coastal prices at the higher heating value), it never becomes cheaper than the best case for electricity (Homepower 1 block 1). There is some room for a more nuanced comparison when you enter Block 2, especially if you are paying Coastal prices. If you’re wondering about the conversion efficiency of electricity to heat, for applications where you are heating water with a submerged element, it is very near to 100 % efficient.<\/div>\n
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It’s also worth remembering that I’ve been talking about “best case” conversions for gas. In real life applications it is very hard to extract the full HHV or even the full LLV.<\/div>\n<\/div>\n<\/div>\n

Cost ratios<\/h2>\n
One way to simplify the analysis further is to compare ratios of costs instead of just costs, since these will stay constant for exponentially growing curves like the ones we’re seeing here. This also has the benefit that it removes the units from our calculations, so we don’t have to worry about whether we’re using kWh or MJ for energy. I will continue from here using Gauteng prices and the HHV for gas since I live in Gauteng and the HHV gives a good upper bound for gas. <\/div>\n
<\/div>\n
We can see in the following graphic that the cost ratios have stayed relatively constant since about 2015. The observation that Block 1 is definitely cheaper than gas is repeated here, but now from the fact that the ratio is less than 1. If you’re in Block 2, the average ratio for the last 5 years is 1.18.<\/div>\n
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<\/a><\/div>\n

Estimated efficiencies<\/h2>\n<\/div>\n
This all started with geysers, so that’s what I’ll analyse first. Electrical geysers feature submerged elements and almost all the electrical energy will be converted to heat. So the controlling factor will be the gas efficiency. To beat electricity, a gas geyser would have to be more than 85 % efficient, which from my research seems quite unlikely. If you are using a heat pump, with a coefficient of performance of 3 or more, you end up with a clear win in favour of electricity.<\/div>\n
<\/div>\n
For cooking, gas is not particularly efficient, with figures quoted between 40 % and 60 %. Anyone who has found their kitchen warming up due to their use of a gas hob can attest the energy doesn’t all go into the pot. Old school electrical hobs aren’t that great either, since the contact between the element and the pot can be poor and there are also long heating times to contend with. I use an induction hob, which is closer to 90 % efficient. So I guess gas doesn’t come out cheaper there either. I am well aware that many people simply prefer to cook on gas and that having a hob that works during load shedding is very useful. <\/div>\n
<\/div>\n

Alternative explanations of savings<\/h2>\n
So what is the explanation of the savings that people describe? I have thought of a few alternative explanations:<\/div>\n
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  1. There might be a psychological “two bucket effect” where the drastic savings on the electricity bill might obscure the extra cost of gas.<\/li>\n
  2. The immediacy of many gas applications may result in lower use overall due to less time spent waiting for things to heat up (this is especially true for cooking).<\/li>\n
  3. For space heating, the high power of gas heaters may mean that you have a large radiative heating effect resulting in immediate feeling of warmth while electrical heaters may need to heat a lot of air to get the same level of comfort.<\/li>\n
  4. For the geyser application, you are keeping water hot, so there are continuous losses. If your geyser is poorly insulated, this can be a big deal. I looked at this technical report<\/a> which reported about 2 kWh\/ 24 h = 83 W of losses from several tested geysers, which I thought was negligible, about the same as an old incandescent light bulb. For comparison, heating 200 L of water from 25 \u00b0C to 65 \u00b0C uses about 10 kWh<\/a>. So I guess it depends on the frequency and length of your showers. If you don’t need a lot of hot water, it’s also best to install a smaller geyser.<\/li>\n<\/ol>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

    Introduction I have been investing in a solar system at home, since South African load shedding is really getting me down. One of the key elements of going off the grid is to reduce your electricity consumption. I’ve focused on reducing demand by scaling down our geysers from 3 to 1 big one and 1 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_post_was_ever_published":false},"categories":[210,4],"tags":[114,211,212],"class_list":["post-10","post","type-post","status-publish","format-standard","hentry","category-home","category-python","tag-analysis","tag-notebook","tag-python"],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/sandrock.co.za\/carl\/wp-json\/wp\/v2\/posts\/10","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sandrock.co.za\/carl\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/sandrock.co.za\/carl\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/sandrock.co.za\/carl\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/sandrock.co.za\/carl\/wp-json\/wp\/v2\/comments?post=10"}],"version-history":[{"count":1,"href":"https:\/\/sandrock.co.za\/carl\/wp-json\/wp\/v2\/posts\/10\/revisions"}],"predecessor-version":[{"id":105,"href":"https:\/\/sandrock.co.za\/carl\/wp-json\/wp\/v2\/posts\/10\/revisions\/105"}],"wp:attachment":[{"href":"https:\/\/sandrock.co.za\/carl\/wp-json\/wp\/v2\/media?parent=10"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/sandrock.co.za\/carl\/wp-json\/wp\/v2\/categories?post=10"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/sandrock.co.za\/carl\/wp-json\/wp\/v2\/tags?post=10"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}