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Cost to heat a litre of water using gas versus Eskom


Antony
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Haven't worked out cost per gram , but an Atlas gas geyser with a flow of 16 litre per min with self ignition burnt through a bit more than a 48kg gas bottle in a month. That was with the water temperature turned down to about 47°C , and two adults and a young child having relatively short showers.

I'm sure there are more efficient gas tankless geysers out there now , but back in the days of load shedding that is what was avaliable.

If I had to work that out now it would cost just over R1000 per month on gas. Again put an evacuated solar system up and enjoy the hot water

 

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30 minutes ago, seant said:

put an evacuated solar system up and enjoy the hot water

Hi Seant,

 

I want to go tubes, but I wanted to use gas to supplement during evenings (I have 3 long haired humans with me) and possible cloudy days, so instead of the element kicking in during these "cold" periods, rather use gas.

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I've done the calculations in terms of cost per unit of energy. The calorific content of LPG is 46.1MJ/kg, or 415MJ in a 9kg bottle. That's about 115Kwh. So compare the cost of 115kwh of electricity to the cost of a 9kg refill. 115kwh costs just over R200, and a bottle of LPG is around R220 right now, so it costs about the same per unit of energy.

So it comes down to the efficiency of heating. An electrical element inside a volume of water is darn near 100% efficient. The same cannot be said for gas. So electricity has to win this one, though I cannot say by how much.

Since a heat pump typically has a COP of as much as 3, that means a heat pump remains by far the most efficient, with the possible exception of a solar geyser in the right climate.

In terms of cooking on a stove, a suitable utensil that makes proper contact with the heating plate can be around 70% efficient (>80% for induction), gas is about half that. So cooking on gas... also goes to electricity. I think the only place where gas wins is space heating.

That doesn't mean gas doesn't have a place in your energy plan. Just don't expect to save money.

Edited by plonkster
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4 hours ago, seant said:

 

What brand of gas geyser are you using?

A no name fong kong unit i bought on Bid or Buy for R2 400.

I must add that it is almost due for replacement as I have patched a few leaks on the water heating coil.

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I agree that electricity is cheaper or same as gas. In my case it is entirely for convenience due to weekly power and water cuts....

It is also quite handy when you have visitors and everyone can enjoy a hot shower....without waiting for electric geezer to heat up again..

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2 hours ago, plonkster said:

I think the only place where gas wins is space heating.

That doesn't mean gas doesn't have a place in your energy plan. Just don't expect to save money.

I have a space heater in the lounge and I use 48KG every 6 weeks and its only on at night from about 6:30 till 11.

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13 hours ago, seant said:

Haven't worked out cost per gram , but an Atlas gas geyser with a flow of 16 litre per min with self ignition burnt through a bit more than a 48kg gas bottle in a month. That was with the water temperature turned down to about 47°C , and two adults and a young child having relatively short showers.

I'm sure there are more efficient gas tankless geysers out there now , but back in the days of load shedding that is what was avaliable.

If I had to work that out now it would cost just over R1000 per month on gas. Again put an evacuated solar system up and enjoy the hot water

 

I have a Paloma 26l per min that consumes 0,5kg per day. Looking at your figures the Paloma is far more efficient than Atlas.

My figure is for winter (Highveld cold) from a borehole filled tank.

In summer it is less when the water is warmer.

We use a daily 90l (not residing in Cape Town) bath heated to 50 degrees plus the odd basin for washing faces and hair.

I find the temperature / bath fill control very convenient.

Got quotes recently to see if a solar geyser setup would be better value for money but a solar panel setup won as it is more versatile. I need a geyser for an hour a day. 

I already have a battery inverter backup.

Edited by Johandup
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I bought my Geyser from these people , and must say that I have not looked back ever since. Even with being off grid for about 10 months we did not have a problem. From time to time I had to start the genny just to top up the temps if we had a bad day but there are a lot more good days that what there are bad days. 

https://www.thesunpays.co.za/price_list.htm

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I have to agree that a gas geyser is not a good idea. A friend of mine installed a gas geyser and a gas hob. The normal geyser was left in the house but the water flowing to it bypassed.

They are 2 long haired bipods and she had to replace her 19kg cylinder every month because it would be empty. her electricity bill was around 500pm her gas cost around 480pm so in total close to 1k

She started using the electric geyser without using the gas and her bill went from 500 to about 900pm showing that it is costing almost the same using gas to heat water.

We have a gas hob and I buy 9kg of gas every 2nd to 3rd month. with the gas hob I have learned to cook smarter. Thew heat is immediate although some of it is lost around the pot. the moment my food is cooked i switch the gas off and i do not leave it on low as i usually did with the electric hob. I start to cook 20 minutes before we eat and then as soon as the food is cooked we eat, so no need to keep the food warm.

My wife will not give up her electric oven (when it stops working i will not fix it). 

The big problem is that NERSA is now regulating gas, parrafin and just about every thing that are cheaper options than electricity.  

There is some people in Orania that is generating their own natural gas from their French drains and then compressing it to run their geysers. I have not seen this setup but it apparently works very well. (i hope they dont smoke on the loo)

 

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13 hours ago, PaulF007 said:

I bought my Geyser from these people , and must say that I have not looked back ever since. Even with being off grid for about 10 months we did not have a problem. From time to time I had to start the genny just to top up the temps if we had a bad day but there are a lot more good days that what there are bad days. 

https://www.thesunpays.co.za/price_list.htm

i see these guys sell a 1000w geyser element

 

cheers

 

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On 2018/08/13 at 8:30 PM, plonkster said:

I've done the calculations in terms of cost per unit of energy. The calorific content of LPG is 46.1MJ/kg, or 415MJ in a 9kg bottle. That's about 115Kwh. So compare the cost of 115kwh of electricity to the cost of a 9kg refill. 115kwh costs just over R200, and a bottle of LPG is around R220 right now, so it costs about the same per unit of energy.

So it comes down to the efficiency of heating. An electrical element inside a volume of water is darn near 100% efficient. The same cannot be said for gas. So electricity has to win this one, though I cannot say by how much.

Since a heat pump typically has a COP of as much as 3, that means a heat pump remains by far the most efficient, with the possible exception of a solar geyser in the right climate.

In terms of cooking on a stove, a suitable utensil that makes proper contact with the heating plate can be around 70% efficient (>80% for induction), gas is about half that. So cooking on gas... also goes to electricity. I think the only place where gas wins is space heating.

That doesn't mean gas doesn't have a place in your energy plan. Just don't expect to save money.

I wish people would understand this. Somehow there's a stigma that gas is more economical. The only place I see gas more economical, is when used inside a space heater where all the gas is burnt to heat the room, this having almost 100% efficiency. 

It's convenient, but not cheaper, at this stage at least. 

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I am toying with the idea of connecting my gas geyser into my electric one, reason being that the pressure is much better with the head of the electric one.

I am sure that I have read on this forum that someone here is already doing it, just cant seem to find that post?

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27 minutes ago, SolarNoob said:

The actuaries at NERSA make sure that the price of energy is 'balanced' (manipulated) so as to keep the 'value' of energy at a constant and not to favor one energy source over another.Just my opinion

I've had that same thought, and it sort of makes sense. Imagine the sudden rush when people discover that one source has become cheaper. I don't think our distribution system will be able to keep up. We already run out during winter where I live... I have to buy the next bottle in advance because a refill is not a given in this town.

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I like this topic, but I think I may have jumped the gun a bit.

Recent outages (8 days off in a row) has swayed me and my wife to try and do a bit for ourselves. I then installed the solar geyser and gas geyser, and changed my stove over as well. It seems to be performing ok. Nice thing these days is that things can be validated by monitoring actual use. The next thing I need to do is find a method of measuring gas usage. If anyone has a way of doing this, I would be interested. 

Currently running my pre-heated water through a Paloma 26l/min gas geyser which is set at 50 deg. C. From the graph below, I can see a reduction in electrical energy usage, down from let's say a 25kWh usage to about 13kWh. It isn't a mega amount, but it helps. Next step are the solar panels.

My live link to the solar state of affairs: https://www.vbus.net/scheme/57c327c4a4823200c2f6b525615ec955

Temperature data link: https://www.vbus.net/#visualization/diagram/show/14626

image.thumb.png.f5ec128df72e99fad3e7923e7e26ccf2.png

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Sounds about the same maybe we use a little bit more , but on our gas stove a 48kg bottle lasts about 2 years. And that's where you save then the gas was under R700 and now it's about R1000.  Also try and refill your bottles in summer as the price seems to be more competitive

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