Any Reasonably priced solar diverters?

[Barryscotland]

Held of buying the gadget to divert unused solar to my immersion when we bought our pv kit about a year ago as money was tight but with the rising kWh costs and the  fact I’m giving any unused energy to the grid for free starting to rub me up the wrong way I looked to buy a solar iboost or similar but the price seems to have rocketed to the point there’s no point financially installing one. Is there any cheaper alternative way of turning my unused power into my hot water?

 

it’s a 2.8ish kw install

[PeterW]

£350 is about the going rate but depending on how much you are exporting that’s probably pay back in 18 months. 

[Andehh]

Thanks Peter, 

 

Is there a general preferred product on Buildhub? 

 

We have ASHP, and a 300L cylinder with 3.99kw of solar panels... I'm still leaning to installing one even though a second coil is apparently needed in the cylinder for the solar diverge? (1st coil being for the immersion I presume?) 

[Barryscotland]

13 minutes ago, Andehh said:though a second coil is apparently needed in the cylinder for the solar diverge? (1st coil being for the immersion I presume?) 

 
I was planning on using the original immersion coil? Didn’t think a secondary element was needed but probably wrong ?

[PeterW]

44 minutes ago, Andehh said:

I'm still leaning to installing one even though a second coil is apparently needed in the cylinder for the solar diverge? (1st coil being for the immersion I presume?) 

You can use the standard one - it is how it is wired that matters 

 

28 minutes ago, Barryscotland said:

 
I was planning on using the original immersion coil? Didn’t think a secondary element was needed but probably wrong ?

 See above - the only issue usually occurs when the immersion is in a pre-plumbed ASHP cylinder as they sometimes have a controller for the immersion for the boost or an unneeded legionella cycle. Not difficult to rewire and I’ve seen one where there were contacts for the booster on the controller. 

[Radian]

12 hours ago, Barryscotland said:

the price seems to have rocketed to the point there’s no point financially installing one

It's a piss-take IMHO. Their price is based on the value of the return in your pocket hence as energy tarifs go up, so do their price. Nothing to do with the components they're made with. Typical PV divertor has little more going on inside than a fancy 'smart light dimmer' plus a £10 CT.

[SteamyTea]

3 minutes ago, Radian said:

It's a piss-take IMHO. Their price is based on the value of the return in your pocket hence as energy tarifs go up, so do their price. Nothing to do with the components they're made with. Typical PV divertor has little more going on inside than a fancy 'smart light dimmer' plus a £10 CT.

Reminds me of the interview with the CEO of Coca Cola.  He was asked about the 'secret recipe'.  His reply was 'there isn't one, I will show you now what goes into it'.

He then went on to explain the purchasing, manufacturing, marketing, sales, distribution, waste disposal etc involved in a global product.

Then asked the journalist if he still thinks Coca Cola is just about the recipe.

[Radian]

12 hours ago, SteamyTea said:

Reminds me of the interview with the CEO of Coca Cola.  He was asked about the 'secret recipe'.  His reply was 'there isn't one, I will show you now what goes into it'.

He then went on to explain the purchasing, manufacturing, marketing, sales, distribution, waste disposal etc involved in a global product.

Then asked the journalist if he still thinks Coca Cola is just about the recipe.

 

That's a good anecdote, but I don't want to pay for advertising and that only has to go so far in a decent product. Sometimes the advertising budget outstrips everything else just to push something substandard to market. If you put enough lipstick on a pig...

 

The other little secret about PV diverters is something I discovered when building one: By necessity, an off-the-shelf product won't be able to operate optimally. There has to be a bias towards export to avoid accidental import for a 'one size fits all' approach to the wide differences between utility meter models. It's no big deal but it's a parameter that never seems to find its way into the specifications.

[Gone West]

11 hours ago, Radian said:

The other little secret about PV diverters is something I discovered when building one: By necessity, an off-the-shelf product won't be able to operate optimally. There has to be a bias towards export to avoid accidental import for a 'one size fits all' approach to the wide differences between utility meter models. It's no big deal but it's a parameter that never seems to find its way into the specifications.

Is that why the instructions for my Solar iBoost says

"Solar iBoost+ has a default cut in threshold of 100W of export before diversion commences."

I wondered why.

 

[Radian]

40 minutes ago, Gone West said:

Is that why the instructions for my Solar iBoost says

"Solar iBoost+ has a default cut in threshold of 100W of export before diversion commences."

I wondered why.

 

Almost certainly, yes. Could be leaking 1kWh/day at certain times of the year. If they made it an adjustable parameter, you could tune it to your utility meter although that would involve seeing some indication that it is indeed exporting. My meter has an icon of a ratchet and pawl on the LCD that shows "meter running backwards" harking back to the days of mechanical metering. It also has an export register so incrementally adjusting the threshold over a longish period would allow you to slowly 'turn the tap off' until it stopped 'leaking' but this would be difficult if the diverter maxes out occasionally.

 

[jack]

11 minutes ago, Radian said:

Almost certainly, yes. Could be leaking 1kWh/day at certain times of the year. If they made it an adjustable parameter, you could tune it to your utility meter although that would involve seeing some indication that it is indeed exporting. My meter has an icon of a ratchet and pawl on the LCD that shows "meter running backwards" harking back to the days of mechanical metering. It also has an export register so incrementally adjusting the threshold over a longish period would allow you to slowly 'turn the tap off' until it stopped 'leaking' but this would be difficult if the diverter maxes out occasionally.

 

I have an Eddi and it allows adjustment of both the export threshold and the export margin, although I doubt there's much granularity (it isn't going to allow fine-tuning to suit different meter types, for example).

 

 

 

 

[Radian]

They all make it sound like you're getting/setting precise numbers i.e. 100W threshold but it can't be. The size of the virtual Joule buffer in meters isn't standardised and without knowing it, an uncertainty is inevitable.

[jack]

1 hour ago, Radian said:

They all make it sound like you're getting/setting precise numbers i.e. 100W threshold but it can't be. The size of the virtual Joule buffer in meters isn't standardised and without knowing it, an uncertainty is inevitable.

 

I don't know all that much about them, but there's presumably an upper reasonable limit on buffer size, and I can't imagine it corresponds to a huge amount of energy relative to an offset of, say, tens of watts? Do you have any feeling for the values that are likely to be involved?

[Radian]

2 hours ago, jack said:

 

I don't know all that much about them, but there's presumably an upper reasonable limit on buffer size, and I can't imagine it corresponds to a huge amount of energy relative to an offset of, say, tens of watts? Do you have any feeling for the values that are likely to be involved?

 

3600J is the largest I've seen reported and also seems to be the most common used in the UK.

 

The sky's the limit though. A meter could be programmed to only bill you once a day on average while giving you that whole day to put energy back into the grid and wind your bill back down. But that would break the money-grabbing asymmetry of the prevailing tariffs. That's why I call it a virtual buffer (or sometimes a Joule bucket). 3600J gets consumed in a second with a 3kW immersion plus 600W house load and put back in around the same time with a typical modest PV system. So quite manageable for the diverter.

 

On the other hand, the virtual buffer can be zero if the meter is designed that way. Every cycle can be determined as a nett energy import or export and billed accordingly. It would take some fancy footwork to deploy a dump load in the space of a cycle but it can be done. I think some meters in European countries operate like this.

 

When I assumed 3600J for my meter, it became apparent that it was much smaller as my meter was recording exports where I should have had none. By trial and error I determined it to be a maximum of 900J but I deliberately limit the range I make use of to half of that. The offsets and thresholds are there to mask the inaccuracies of measurements (mostly CT nonlinearity) but an off-the-shelf diverter has to assume that it's dealing with a minimal buffer anyway. This makes it tricky for those that use burst firing as they're committed to 60J (one mains cycle of a 3kW load).

 

Sometimes PWM techniques are used in diverters such as your eddi to get around the one-cycle limit:

 

 

varisine^TM is the proprietary power control technology used in the eddi. The technology enables the output voltage to be very smoothly adjusted in order to alter the power to the heater. The power to the heater is always a sine wave and only the voltage is altered.
This control technology is more sophisticated than many other products on the market and the technology ensures trouble free operation with all inverters and compatibility with all import/export energy monitors and electric meters.

 

Yet it still needs an offset because it can't be sure how close it is to the meter's sensing and could be operating either side of the true balance point without knowing. Utility meters make use of revenue grade power sensing circuitry which entails a series connection to the supply to measure the volt-drop across a calibrated resistance. Consumer grade diverters tend to use CTs for customer safety and convenience - hence the inherent inaccuracies.

[jack]

Interesting, thanks @Radian

 

I hadn't considered that the Varisine stuff might have had anything to do with the one-cycle limit.

[Solarexploits]

I've had a Solic installed for around 10 months or so now. Simple installation, particularly if you have a spare MCB in the consumer unit. Cost was around £130, I believe it's already paid for itself  or is very close to doing so, as we've had free hot water from April thro' to now & used zero gas during that period other than briefly to service the boiler. Up until April it was only assisting with the water heating, & I suspect we'll be back to that situation soon, but even in the winter months there was some limited diversion on sunny days

 

[Wil]

Another one for a Solic, has been excellent and paid for itself in a year. Although I’ve now disconnected it as it was fighting and draining my batteries. And the batteries allow me to use the immersion at full whack for an hour and let the solar ‘make it up’ over the course of the day.

 

When I add some more PV on another phase I’ll definitely put it back in so I don’t need to bother discharging the batts.