Vacuum tube vs PV

[Nerfherder]

So I can't see a thread that covers this but have seen this eluded to by some here and would like to know the argument for each.
This is especially for my setup though so also interested in the different cases where one would be better than the other.
My primary objective would be to save money, I'm not set on going off grid and don't really need it either.

I don't have any solar or inverter setup in place yet so working from a baseline. I do have a fairly new geyser that claims to be solar ready, which I assume means its combatable with a vacuum tube panel.
I have plenty of great roof space and two stories so zero shade on my roof.
I have gas stove and i'm on COCT power so we don't get load shedding as bad. Also my theory is that we will experience less an less load shedding but the cost of electricity is going to ramp up as a result.

I do have money to spend, but it would be off the bond so any money spent needs to result in savings that I can recoup and put back on the bond.

The simple option looks to be just get the vacuum tube panel conversion for 20-30k, and get whatever hardware is required to manage this (inc battery backup for load shedding) and then use municipal power to top this up when we have a month of rain.

The more complicated option would be to get enough PV to power the geyser and then some kind of inverter that would supplement my other power usage while the geyser is not being heated. No backup batteries at all.
Would this even be possible at R20-30k ? Its obviously a big ask to make this future proof, so that at some stage if I wanted to scale it up with more panels and some batteries in the mix I would be able to.

Thoughts ?

 

[Speedster]

My take is as follows - you first need to decide if your medium term plan is full solar (PV), or just water heating. Water heating does take up the bulk of residential power consumption, so it is definitely the best place to start.

• If you only want to save electricity, and have no plan on installing a PV system, then a solar geyser is your best bang for buck.
• If you are planning on a PV system, then rather use the funds to add extra PV panels which willl then heat the water, and allow extra for the rest of the home.

 

[Nerfherder]

My take is as follows - you first need to decide if your medium term plan is full solar (PV), or just water heating. Water heating does take up the bulk of residential power consumption, so it is definitely the best place to start.

• If you only want to save electricity, and have no plan on installing a PV system, then a solar geyser is your best bang for buck.
• If you are planning on a PV system, then rather use the funds to add extra PV panels which willl then heat the water, and allow extra for the rest of the home.

Thanks.

So then the answer then is to just save the R20k now ?

 

[shadow_man]

Thanks.

So then the answer then is to just save the R20k now ?

I'd also go for option b.

It's what I did with an existing geyser in place. I simply added solar and more panels as opposed to upgrading to the solar geyser. More bang for buck, better long term use and many like @Snyper564 have also commented the same.

 

[Speedster]

You could get started on a basic solar PV system for R30k. Based on what you said earlier, that would be a R10k Solis grid-tie inverter, R10k for panels (about 1.5kWp) and R10k sundries and installation. You can then add panels as budget allows.

 

[Nerfherder]

You could get started on a basic solar PV system for R30k. Based on what you said earlier, that would be a R10k Solis grid-tie inverter, R10k for panels (about 1.5kWp) and R10k sundries and installation. You can then add panels as budget allows.

So its possible ? i imagine though that as you get more panels you have to change to a more expensive inverter ?

 

[Speedster]

So its possible ? i imagine though that as you get more panels you have to change to a more expensive inverter ?

Not necessarily. You could get a 3.6kW Solis for R10k, which leaves plenty of room to upgrade later.

 

[superskully]

So any solution will save you money as water heating is a huge expense.
I have solar geyser (Vc) which paid itself off in 2 yrs, but is not effective in winter. Later I added full pv system (95% off grid) and use pv to heat geyser in winter.
But here is what I would have done differently, I should have went for heat pump (its super) as that will reduce consumption by 70%, hence would have not needed more capital for panels, batteries etc.

 

[Mike Hoxbig]

Neither, go with a heat pump...

 

[Speedster]

Neither, go with a heat pump...

Have you got one? I'm told they require a regular service. Do you perhaps know what the service costs are?

P.S. if op is planning to go full solar, I'd still use the funds for panels.

 

[agentrfr]

Depends on your usage pattern at home

When I did my dissertation for MSc modelling CSP and PV for eskom country wide, their data showed that ~40% of electricity is used for geysers/kettles/heaters. For modern homes with energy saving devices/lights etc. that percentage goes up. Heat is cheapest direct, so it makes sense to rather go direct with electric as a backup on dark days.

In most cases, you are better getting both PV and vacuum, but start with vacuum. Then a 6kW hybrid inverter down the line, add PV as you go

 

[Speedster]

While I agree with pretty much everything you say here, I beg to differ on your recommendation. If PV for the home is in the plan then leave the solar geyser totally. R30k gets you at least 4kWp of panels, which produce about 20kWh on a normal day. That heats up all your water plenty warm, and leaves a stack load extra for the rest of the house

 

[superskully]

Have you got one? I'm told they require a regular service. Do you perhaps know what the service costs are?

P.S. if op is planning to go full solar, I'd still use the funds for panels.

They are basically an aircon, and lifespan is probably 10 years which is less than any solar system. But it still works out cheaper as you won’t need as many panels and bigger inverter and battery storage

 

[Snyper564]

I'd also go for option b.

It's what I did with an existing geyser in place. I simply added solar and more panels as opposed to upgrading to the solar geyser. More bang for buck, better long term use and many like @Snyper564 have also commented the same.

Yeah I still stand by this only consider this if you WILL NOT go full solar otherwise just wait a year or two and put that towards your setup

 

[Nerfherder]

Neither, go with a heat pump...

To replace the geyser or feed into the geyser ?

 

[Nerfherder]

Depends on your usage pattern at home

When I did my dissertation for MSc modelling CSP and PV for eskom country wide, their data showed that ~40% of electricity is used for geysers/kettles/heaters. For modern homes with energy saving devices/lights etc. that percentage goes up. Heat is cheapest direct, so it makes sense to rather go direct with electric as a backup on dark days.

In most cases, you are better getting both PV and vacuum, but start with vacuum. Then a 6kW hybrid inverter down the line, add PV as you go

So with this option I would add hot water taps to my washing machine and dishwasher to reduce power consumption for those appliances as well. Its small but when its hot you might as well use that heat.

The other thing though I have heard with VC is that you can struggle on very hot days, can they get too hot ?

EDIT: the usage pattern is that my wife and I shower in the morning and the kids bath at night. Ideally we should all just shower in the morning for this to work.

 

[SauRoNZA]

"Solar Ready" could mean it has an element inside that takes direct DC connection in which case you simply hook up 2 x Solar Panels to it (800ish Watts) and it basically runs by itself no inverter required.

I can't think of anything else that would make one geyser more solar ready than another.

And yes I got quotes and uhmed and aaahed about geyser upgrades and then doing solar later and ultimately came to the conclusion it made no financial sense to spend the money directly on the geyser when I have a plan to go fully solar.

So ultimately it went towards putting in a bigger inverter (8kW) so I could just run the entire house off it.

Like @Mike Hoxbig says the only upgrade otherwise that would make any sense is going with a heat pump to supplement the geyser.

 

[Nerfherder]

"Solar Ready" could mean it has an element inside that takes direct DC connection in which case you simply hook up 2 x Solar Panels to it (800ish Watts) and it basically runs by itself no inverter required.

I can't think of anything else that would make one geyser more solar ready than another.

And yes I got quotes and uhmed and aaahed about geyser upgrades and then doing solar later and ultimately came to the conclusion it made no financial sense to spend the money directly on the geyser when I have a plan to go fully solar.

So ultimately it went towards putting in a bigger inverter (8kW) so I could just run the entire house off it.

Like @Mike Hoxbig says the only upgrade otherwise that would make any sense is going with a heat pump to supplement the geyser.

Well if its solar ready like that then I'd just go for it. That would then be the cheapest option by far. It wouldn't supplement my power but very good as a first start.

I have always been interested in the heat pump - but as mentioned the geyser is new and I's like to have something that will hold heat for when we do have outages.

 

[Speedster]

Well if its solar ready like that then I'd just go for it. That would then be the cheapest option by far. It wouldn't supplement my power but very good as a first start.

I have always been interested in the heat pump - but as mentioned the geyser is new and I's like to have something that will hold heat for when we do have outages.

Solar ready typically means it has an extra outlet to allow for connecting the solar collector.

 

[SauRoNZA]

Well if its solar ready like that then I'd just go for it. That would then be the cheapest option by far. It wouldn't supplement my power but very good as a first start.

I have always been interested in the heat pump - but as mentioned the geyser is new and I's like to have something that will hold heat for when we do have outages.

Yeah best to find out then.

In most cases they fit a Geyserwise and 2xSolar Panels to it.

Then it can be supplemented from grid over AC as required, and runs on DC most of the time.

Solar Powered Geyser Conversion Kit - Solar Advice PTY LTD

Take your first step in reducing your electricity bill with this geyser conversion kit, power your geyser with the sun.

solaradvice.co.za

Basically like that kit.