PV and Voltage Optimisation

[trev]

So, a final stab at getting my point across.
Take a 10 kw item of current using equipment, now that could be anything because in my world it doesn't matter.
At 240 volts it draws (10,000/240)= 41.67 amps
Now lets look at it at 210 volts (10,000/210)= 47.61 amps
You cannot arbitrarily decide that this 10kw thing is now anything other than a 10kw thing. It is what it is. Either the power over time is going to be exactly the same or the output/performance of it is going to be affected.
I can't for the life of me see any way past that. Maybe I'm thick or I've forgotten a lot of the theory I learnt as a boy but for me the maths and science can't be changed.

 

[Worcester]

Trev

Most of us agree with you for almost all households it's a waste of money.

In industrial environments as Sibert pointed out it's different, there is a lot of non inverter controlled and non variable power supply equipement that was designed to work on 220V (remember V=IR and W=V*I) For these items if you reduce V then you'll reduce I so W goes down by twice as much.

With the grid pushing out higher and higher voltages with all the micro-generation going on we have seen well over 240V at some commercial sites. These sites running older compressors, industrial machinery and refrigeration plant which was designed to run on 220V and so will work happily at that level with no reduction in performance, same with the old inefficient fluorescent lighting. In these cases the client sees a payback usually in under three years.

For a household, I don't see the benefit.

 

[davesparks]

Why do plants in this country have kit designed to run on 220V? DNOs have been supplying 250V at their substations since the grid began, and if they are big industrial sites they will have their own transformers which they can change trappings to whatever voltage they need.

 

[davesparks]

So, a final stab at getting my point across.
Take a 10 kw item of current using equipment, now that could be anything because in my world it doesn't matter.
At 240 volts it draws (10,000/240)= 41.67 amps
Now lets look at it at 210 volts (10,000/210)= 47.61 amps
You cannot arbitrarily decide that this 10kw thing is now anything other than a 10kw thing. It is what it is. Either the power over time is going to be exactly the same or the output/performance of it is going to be affected.
I can't for the life of me see any way past that. Maybe I'm thick or I've forgotten a lot of the theory I learnt as a boy but for me the maths and science can't be changed.

At 210V it won't use 10KW, the power is a product of the voltage and resistance.
The resistance will remain constant so as the voltage is reduced the power will reduce proportionally, right down to the point where applying zero volts uses zero power.

Look at a new electric shower and you will see they have a 240V rating and a 230V rating with the 230V rating being less than the 240V.

 

[matthunt]

Sorry Trev but you are totally wrong in your calculations as pointed out by davesparks as current and voltage are proportional on resistive loads so now your 10kw thing is no longer a 10kw thing, probably best to draw the old triangle out and work it through before commenting!
Anyway have we any response over the inverter being fed from an optimised circuit from the manufacturers?

 

[davesparks]

Don't get me wrong, I am 100% in support of Trev's conclusion about voltage optimisation, it's just that particular bit of theory that he is a little mistaken about.

 

[SibertSolar]

@matt - not as yet, as far as I am aware

 

[matthunt]

here's throwing one out there!, I am actually all for it if used in the correct way, by this I mean for equipment protection in the first instance but with an added energy saving as a plus point. As we all know PV system have a nasty little by-product dependent on localised grid conditions being overvoltage, CE rated products really don't like 250v up em for a prolonged period of time

 

[Gavin A]

Don't get me wrong, I am 100% in support of Trev's conclusion about voltage optimisation, it's just that particular bit of theory that he is a little mistaken about.

for resistive loads the power would reduce, but if used in a kettle etc then this would have no impact on overall consumption levels, merely that the kettle would take slightly longer to boil using the same level of energy.

There are energy savings for lights, showers etc as people basically just put up with slightly lower light levels, slightly reduced shower flows, but obviously these savings could also be achieve by using an 8W energy saving light bulb rather than a 10W, or running the shower on 1 setting rather than 2 (and it could be that it resulted in someone increasing the shower setting to compensate, thereby using more power not less).

The real claimed savings come from older fridges, freezers, pumps etc where it's claimed that they operate more efficiently at 220V. Personally I've come to the view that this is a bit of a false saving, as much greater savings could be made by replacing these old fridges and freezers with modern high efficiency inverter driven models. I've also experienced pumps failing after introduction of VO as presumably they can't get the same pressure up as they used to be able to, and can't overcome the pressure drop in the heating system, or something like that (could be a coincidence, but the timing was very suspicious).

Combined with solar, Vo units will also enable the solar to power a greater proportion of a load such as a kettle boiling, as the energy input is spread over a longer time period, which is a minor impact, but still a benefit at some level.

VO units really work though in industrial settings with unbalanced supply phases, with VO units with variable voltage control on each phase designed to rebalance the phases. In this setting I understand there can be some fairly significant savings to be made, plus lifespan extentions on the machinery.

In most domestic settings though, I've come to the conclusion that it's not justified, particularly when you take into account the losses in the transformer. The exceptions being for houses with older swimming pool kit, with huge energy consumption from old pumps, dehumidifiers etc that are running almost continuously.

 

[matthunt]

Hi Gavin, have you thought about the longevity of the appliances rather than the energy saving aspect, what you have to remember is that historically our voltages have ben higher in the evening when industry shuts down, now the voltages are also higher in the daytime due to the growing amount of micro-generation being utilised, there seems to be a pattern here and one that is well known with he ENA, indeed they were even suggesting in line voltage regulators for domestic housing back in 2010 for the DNOs to look at inline with the smart meter rollout, they released a white paper about it

 

[Gavin A]

Re the original post, the link has now been removed, and ENA have requested the company to contact all solar installers they've supplied kit to to advise them that their recommended installation method breached G83 regulations, and any systems installed in this way will need to be rewired to ensure they are compliant.

 

[a1colly]

Good job Gavin!!

 

[matthunt]

Suspect there is going to be a lot of poor PV companies that have now got to go back to all their jobs and connect the PV off the unoptimised side eek!

 

[Gavin A]

Suspect there is going to be a lot of poor PV companies that have now got to go back to all their jobs and connect the PV off the unoptimised side eek!

I suspect that any who were daft enough to follow that advice are also very unlikely to actually be conscientious enough to follow through with that and go back to rewire those houses, unless directly contacted and forced into it.

 

[matthunt]

Here's fingers crossed the manufacturers get in contact with them, although I would imagine it will be nearly impossible for the ENA to police

 

[matthunt]

They Back on line guys!