Warming your geyser up with your batteries or charging your batteries via Eskom? I am post paid for the moment.

Edited July 5, 20233 yr by Raiden2912

Not sure what exactly you're asking here. Can you please elaborate on the question?

2 hours ago, Raiden2912 said:

Warming your geyser up with your batteries or charging your batteries via Eskom? I am post paid for the moment.

Be a bit more specific. Is the battery charged from Eskom or solar. 

Batteries charged from Eskom will use about 25% more if used to heat the geyser. 

Ok let me clarify a little more apologies.

so if you start heating your geyser at 4pm it uses what little sun is left and then my batteries or I could change the order to heat the geyser with Eskom from 4pm. Which is cheaper? Battery life or Eskom charging my batteries. Cause I have my inverter set to 10A for Eskom which almost takes around 7-8 hours to charge my batteries fully. I’m not sure if that makes sense 

during the day I run my house off Solar and at night off batteries. So I’m just wondering….

Edited July 5, 20233 yr by Raiden2912

2 hours ago, Raiden2912 said:

Ok let me clarify a little more apologies.

so if you start heating your geyser at 4pm it uses what little sun is left and then my batteries or I could change the order to heat the geyser with Eskom from 4pm. Which is cheaper? Battery life or Eskom charging my batteries. Cause I have my inverter set to 10A for Eskom which almost takes around 7-8 hours to charge my batteries fully. I’m not sure if that makes sense 

during the day I run my house off Solar and at night off batteries. So I’m just wondering….

I understand the problem with batteries taking long to charge. With such a low rate of charging I assume you have spare PV available so try to heat the geyser earlier as it will retain the heat. 

Depending on battery % left in the morning would affect the answer. As indicated to use Eskom to charge the battery to use the power later cost 25% more than to use Eskom directly. PV is the trump card. 

20 hours ago, Raiden2912 said:

Ok let me clarify a little more apologies.

so if you start heating your geyser at 4pm it uses what little sun is left and then my batteries or I could change the order to heat the geyser with Eskom from 4pm. Which is cheaper? Battery life or Eskom charging my batteries. Cause I have my inverter set to 10A for Eskom which almost takes around 7-8 hours to charge my batteries fully. I’m not sure if that makes sense 

during the day I run my house off Solar and at night off batteries. So I’m just wondering….

So the conversion from DC to AC is not 100% efficient and neither is the conversion from AC to DC, therefore charging your battery from Eskom will lead to some losses as well as using your battery to heat your geyser will lead to some losses - these losses are probably quite small though.

 

So it would be cheaper to heat your geyser via Eskom instead of heating it via your batteries (provided your batteries are being charged via Eskom).

If your batteries are being charged via PV and then used to heat your geyser, this would be cheaper as you are not paying for the electricity usage. The only downside being that your batteries are being cycled more, although I feel that is part of the reason we have batteries and a battery can help lead to further electricity cost savings.

If you cycle your battery once a day for 5 years, that is 1826 cycles only. If you cycle them twice a day that is only 3652 cycles over a 5 year period, I have not worked it out but I suspect the cost savings of not heating your geyser from Eskom could have paid for a new battery over this period or come close.

 

I would suggest you look at a geyser timer and have it heat up via excess PV power in the afternoon with sufficient time for the geyser to reach max temperature before the sun sets.

19 minutes ago, PsyCLown said:

So the conversion from DC to AC is not 100% efficient and neither is the conversion from AC to DC, therefore charging your battery from Eskom will lead to some losses as well as using your battery to heat your geyser will lead to some losses - these losses are probably quite small though.

 

So it would be cheaper to heat your geyser via Eskom instead of heating it via your batteries (provided your batteries are being charged via Eskom).

If your batteries are being charged via PV and then used to heat your geyser, this would be cheaper as you are not paying for the electricity usage. The only downside being that your batteries are being cycled more, although I feel that is part of the reason we have batteries and a battery can help lead to further electricity cost savings.

If you cycle your battery once a day for 5 years, that is 1826 cycles only. If you cycle them twice a day that is only 3652 cycles over a 5 year period, I have not worked it out but I suspect the cost savings of not heating your geyser from Eskom could have paid for a new battery over this period or come close.

 

I would suggest you look at a geyser timer and have it heat up via excess PV power in the afternoon with sufficient time for the geyser to reach max temperature before the sun sets.

Let's add real figures to heating the geyser of 150L in the early morning by 10 degrees. The main heating we do with PV during the day. 

This 10deg will use 1.75kw @ R2.55 per kWh. Doing it every day will cost R1628 per year from grid at current cost. Yes power will go up over time and that is where one might get the saving. Thus not a huge gain by using the battery as the battery replacement cost after 10y could also be a lot higher than the current R30 000. Yes if the next generation of batteries are a lot cheaper than now it might be a better option.

Investing the extra battery cost can yield R2400 per year to pay for the R1628 per year you would pay for the early morning 10deg.

The major gain from battery use is not the cost but the convenience of having hot water if the grid might be off. But then the grid won't be off every day in the 04h to 06h time slot. 

18 hours ago, Scorp007 said:

Let's add real figures to heating the geyser of 150L in the early morning by 10 degrees. The main heating we do with PV during the day. 

This 10deg will use 1.75kw @ R2.55 per kWh. Doing it every day will cost R1628 per year from grid at current cost. Yes power will go up over time and that is where one might get the saving. Thus not a huge gain by using the battery as the battery replacement cost after 10y could also be a lot higher than the current R30 000. Yes if the next generation of batteries are a lot cheaper than now it might be a better option.

Investing the extra battery cost can yield R2400 per year to pay for the R1628 per year you would pay for the early morning 10deg.

The major gain from battery use is not the cost but the convenience of having hot water if the grid might be off. But then the grid won't be off every day in the 04h to 06h time slot. 

Thanks, not terrible price wise.

 

I did quick maths and if one were to heat their geyser it via the battery or Eskom only and not via excess PV, a google search suggests a 150L geyser would use 355KWH (units) per month for a 150L geyser. At R2.55 incl VAT per unit (KWH) that is R905 per month, R10 863 per year. I know the figures would differ in summer vs winter as and the amount of water used would obviously affect the energy consumption although it provides an estimate and an idea.

 

To me, it still makes sense to heat the geyser via excess PV. I find that the water temp is still fine the next morning for my girlfriend and I to shower so I do not have a need to turn the geyser on in the morning to heat it up a bit more. So excess PV alone is sufficient for our hot water needs - we do have a geyser blanket and put lagging on the hot water pipes which are exposed on the roof.

6 hours ago, PsyCLown said:

Thanks, not terrible price wise.

 

I did quick maths and if one were to heat their geyser it via the battery or Eskom only and not via excess PV, a google search suggests a 150L geyser would use 355KWH (units) per month for a 150L geyser. At R2.55 incl VAT per unit (KWH) that is R905 per month, R10 863 per year. I know the figures would differ in summer vs winter as and the amount of water used would obviously affect the energy consumption although it provides an estimate and an idea.

 

To me, it still makes sense to heat the geyser via excess PV. I find that the water temp is still fine the next morning for my girlfriend and I to shower so I do not have a need to turn the geyser on in the morning to heat it up a bit more. So excess PV alone is sufficient for our hot water needs - we do have a geyser blanket and put lagging on the hot water pipes which are exposed on the roof.

Thanks for another view. In my house my total power used (PV and grid) per month is not even 355kwh. If my 150L geyser is at 55 at sunset it will be about 35 by early morning so I have to heat it up 4h-5h. We are only 2 but do dishes etc during the evening. 

Averages can give a very distorted view.