I've been looking at the economics of putting the geyser onto solar PV directly. I know an MPPT is required for high efficiency. What I'm not clear on is precisely the difference it makes. 

Geyserwise seems to be the most popular option, but the price is over R 7k including their PTC element before you even buy the panels. 

But with panel prices what they are now, if I just buy 4x ~400 W panels for R 5k, won't I be able to deliver about 800 W to my existing 3 kW / ~18 ohm element without needing an MPPT? Just some sort of AC/DC changeover switch? 

What am I missing? How is this not more economical than the Geyserwise? 

Edited May 3, 20242 yr by TTT

2 hours ago, TTT said:

I've been looking at the economics of putting the geyser onto solar PV directly. I know an MPPT is required for high efficiency. What I'm not clear on is precisely the difference it makes. 

Geyserwise seems to be the most popular option, but the price is over R 7k including their PTC element before you even buy the panels. 

But with panel prices what they are now, if I just buy 4x ~400 W panels for R 5k, won't I be able to deliver about 800 W to my existing 3 kW / ~18 ohm element without needing an MPPT? Just some sort of AC/DC changeover switch? 

What am I missing? How is this not more economical than the Geyserwise? 

You cannot feed the panel DC from panels to the element as the thermostat will weld closed due to arcing. 

The cheaper option is the sun pays 4kw solar controller but that only uses the PV available and gets the rest from the grid. Thus it can also heat from grid at night. This MPPT only feeds AC as before and easy install. No need to change element. Priced at R4000. 

 

17 minutes ago, Scorp007 said:

You cannot feed the panel DC from panels to the element as the thermostat will weld closed due to arcing. 

The cheaper option is the sun pays 4kw solar controller but that only uses the PV available and gets the rest from the grid. Thus it can also heat from grid at night. This MPPT only feeds AC as before and easy install. No need to change element. Priced at R4000. 

 

 

Thanks, this is definitely better. How does it avoid the thermostat welding closed? As an MPPT I'm guessing the output is chopped up (so effectively AC)? 

Also how does one configure this unit? What is the changeover point from solar to grid? 

1 hour ago, TTT said:

 

Thanks, this is definitely better. How does it avoid the thermostat welding closed? As an MPPT I'm guessing the output is chopped up (so effectively AC)? 

Also how does one configure this unit? What is the changeover point from solar to grid? 

Not chopped up but output I guess is a pure sine wave AC as per all grid tied units as well as those inverters claiming it is pure sine wave. Thus the same as grid and no welding. 

You choose how many panels you fit. All PV is used 1st and only the rest from the grid. 

Simple install. 3 wires supply moved away from geyser into this unit. 3 wires output from this unit to where the power was connected. 2 wires coming from panels. Done.... 

Edited May 3, 20242 yr by Scorp007

3 minutes ago, Scorp007 said:

All PV is used 1st and only the rest from the grid.

But at what point does it switch? If PV is down to 100 W is that the total output to the element? I doubt it blends. Ideally I'd want it be able to control the changeover so I could put it on grid even when solar is still available, say because it's late afternoon already and temperature is still well below setpoint.

So this product may be too simple. 

If it were some sort of DC-AC changeover / contactor switch I would control it electronically. I would take the thermostat out of the loop as well to avoid arcing. Of course I would substitute my own temperature sensing and control and would have to satisfy myself that it were safe enough. But it shouldn't be a matter of more than a couple grand in parts. 

43 minutes ago, TTT said:

But at what point does it switch? If PV is down to 100 W is that the total output to the element? I doubt it blends. Ideally I'd want it be able to control the changeover so I could put it on grid even when solar is still available, say because it's late afternoon already and temperature is still well below setpoint.

So this product may be too simple. 

If it were some sort of DC-AC changeover / contactor switch I would control it electronically. I would take the thermostat out of the loop as well to avoid arcing. Of course I would substitute my own temperature sensing and control and would have to satisfy myself that it were safe enough. But it shouldn't be a matter of more than a couple grand in parts. 

I only offered you a substitute for the more expensive unit you mentioned. If your thermostat was closed a few hours before sunset the water would already be hot as it would have used the grid for the shortfall for any size element. 

It does blend as any grid tied inverter would do. 

Edited May 3, 20242 yr by Scorp007

11 minutes ago, Scorp007 said:

It does blend as any grid tied inverter would do. 

What product are you talking about? If this one then there's no indication it has an inverter at all, much less a grid-tied one. 

4 hours ago, TTT said:

much less a grid-tied one

Did you read the specs on the website?
AC input voltage. It will use grid power if solar is insufficient. 
 

• Max PV input : 4000W
• PV input voltage range: 160VDC to 350VDC
• MPPT operating voltage : 120VDC to 340VDC
• PV input current max: 20A
• AC input voltage: 180VAC to 260VAC

On 2024/05/03 at 7:50 PM, zsde said:

Did you read the specs on the website?
AC input voltage. It will use grid power if solar is insufficient. 
 

• Max PV input : 4000W
• PV input voltage range: 160VDC to 350VDC
• MPPT operating voltage : 120VDC to 340VDC
• PV input current max: 20A
• AC input voltage: 180VAC to 260VAC

 

Yes. That does not mean there's an inverter inside. It just means it can pass AC through i.e. it contains "some sort of AC/DC changeover switch" as I referred to in my original post. 

But there is no indication what the DC-to-AC switchover point is. What does "insufficient" actually mean? Does anyone have one to confirm? 

 

Edited May 6, 20242 yr by TTT

30 minutes ago, TTT said:

 

Yes. That does not mean there's an inverter inside. It just means it can pass AC through i.e. it contains "some sort of AC/DC changeover switch" as I referred to in my original post. 

But there is no indication what the DC-to-AC switchover point is. What does "insufficient" actually mean? Does anyone have one to confirm? 

 

Bump

In the absence of a technical or user manual, none of us will be any wiser.
Insufficient means the solar panels are not generating enough energy to supply the load of the element at the time, i.e. early morning, late afternoon, cloud cover.....
 

7 hours ago, zsde said:

In the absence of a technical or user manual, none of us will be any wiser.
Insufficient means the solar panels are not generating enough energy to supply the load of the element at the time, i.e. early morning, late afternoon, cloud cover.....
 

It will also help to find out how blending work in a grid tied inverter even if a grid tied inverter is called a controller. 

For practicality I would rate any box that changes DC to AC a inverter even if the information provided does not call it an inverter. Even more so when blending takes place to provide the output needed by the load as you have alerted to a few days ago.