I must confess I don't see the relevance of the mains plug design to anything to do with a solar array. The European plug - it's actually an old UK style of plug with an internal fuse and designed for use on ring main systems - is rated at 13 A and the Australian plug is rated at 10 A - both of these are for 240V AC 50Hz mains. Also the Australian plug is for double insulated wiring systems as it omits the earthing pin which is mandatory on singly insulated systems. You can also get Australian plugs at 15 A which are a bit bigger. But where is the connection with solar arrays which are (usually) DC and require a totally different switching and wiring methodology?

I was using the disparity between the structure of the two GPO plugs to create a discussion as to the European wiring standards and the Australia wiring rules. When solar pv systems interface the AC network by way of grid-tie inverters a commonly faced problem is that the connection faces rises in AC voltage. A solution to the problem that we have been using is to increase connection wiring sizes by 50 to 100 per cent. It appears the Europeans are not facing the same problems. Could it be that they simply have heavier wiring looms and connections - hence less resistance and lower rises in voltage?

I have made some inquiries of utility senior electrical engineers who have advised me that it is possible but they do not know of any supporting field research. If it is true then ultities and network operators, and of course solar pv installations would face significant additional costs in connecting to HV distribution systems.

@Tony Maine are you able to add to that discussion?

I don't know the voltage rises quantitatively - but it would seem that the input impedance of the supply lines in Australia is a bit higher than in Europe, and one way round this is indeed to use heavier wiring. However, this is of concern only when you want to force energy back into the grid, you need an extra few volts - when everyone has a battery to store it, perhaps this will cease to be an issue! One thing is certain however in my view and that the actual connectors are not an issue. It's a wiring problem.

Actually the UK fused plug you show is a nuisance because at full rated current of 13A the fuse gets extremely hot and can damage the wiring - and the plug . . . so much for fused plugs.

Thank you @Tony Maine for that. That is the answer I was looking for. However rather than push my opinion it is preferable to have support from those qualified to make such statements. I used the connectors just to raise the matter - it did.

Quantitatively, with grid-tie systems voltage rises of up to 30 volts can be experienced. The problem is that once the upper parameters of the inverters are reached they switch off to prevent damage (268 v). The pv supply is then lost and the voltage drops once more. The inverters reconnect and the whole cycle starts over.

A solution, which I do NOT recommend, is to increase the upper parameters of the voltage tolerance. My preference is to use heavier wiring (which reduces resistance). The economic cost becomes a factor in the connection. The use of batteries to divert energy flows is likewise, in my opinion, uneconomic. The volume of energy stored against the cost of the cells is of even less economic return. A 5 kWh storage system (about $1.50) costs around $8 000.

My suggested alternatives are to increase load at site by charging your electric car, increasing the output of airconditioners and other appliances. In that way the heat energy is stored in the building. I have built and connected and ice-works to my solar farm as a demonstration of what one can do 'with the excess'.

Are you aware of any quantitative research that establishes the increase in wiring required to reduce volt rises for dispersed, embedded solar pv systems?

Kind regards

Lex Fullarton

Lex, I am really amazed at the need for inverters to drive up to their safety cut off voltage in order to put power back into the grid. The input impedance of the grid at the connection point must be very high, but, if that were so, it would be impossible to draw much power out of it either.

If driving 5 kW (at 240 V, about 20 A) into the grid requires 30 V overvoltage then the grid impedance is 1.5 ohms, which is far higher than it should be. How long is the wiring run? That would also mean that drawing 5 kW out of the grid at that point would cause a drop to under 200 V (and require a current of 25A) which most devices might regard as too low to work properly.

You don't seem to have much of an opinion of batteries - but cheekily suggest that you charge your electric car - which is charging a battery anyway. In my view ALL local storage PV systems should be based on electric cars, which then enable you to take your PV free energy with you and might even enable you to sell it to your work at a profit. But that's another story!

Storing electrical energy as heat is not to be recommended unless heat (or cold) are the end products. It's dreadfully inefficient to convert heat (an incoherent energy source) back into a coherent one like electricity or even movement.

Best wishes with your researches, though!

Tony,

You are not the only one amazed at the option of lifting the safety parameters. Personally I am appalled, but it is a tempting, short-term fix. I doubt the manufacturers would be as tolerant if they became aware of the practise.

I am not an electrical engineer, but this is pretty basic physics. I believe the run is back to the HV transformer which can be several hundreds of metres. In my case it is over 600 m. There is also a lot of solar pv on the one line. At times it is 100 per cent of the total load.

You are right the overnight (well at the duck's head really) draw is considerable. That is why the transformer taps are set right at the maximum. (and I suspect a little over but no-one will admit to that). During daylight hours the 'load' reverses - hence the high reverse voltage. That is in particular if there is little or no 'local load'.

I am also sure that grid-tie inverters input energy into the AC system by way of a shift in the frequency oscillation rather than an increase in voltage (though simply 'balancing the load' would give that appearance).

I am serious about charging the car. I have a Mitsubishi Outlander PHEV. We go months without using fossil fuel. I have built an ice-works and connected that to my solar farm to develop a 'downstream' processing system for my product (electricity).

As to the heating and cooling of the house - yes it is the end product. I agree using heat energy as a recoverable energy source is a bit wasteful, and not very practical. We also have an electric water heater. Once the water is hot the electricity gets diverted to something else. Thermic solar hot waters systems are in-expensive but once the water is hot what do you do with the excess energy.

I am looking for a qualified researcher to support my hypothesis that generally our network wiring harness is simply too light to satisfactorily absorb dispersed embedded solar pv installations. I am afraid the findings of a PhD in Taxation Law does not cut the mustard amoung the engineering fraternity.

Thank you so much for your help thus far. It is very encouraging.

Kind regards

Lex

Hi Lex, seems that you're in one of those lovely rural blocks with a really long run to the nearest HV distribution feeder. Not surprised at all then at the effect. This is a major issue with large PV penetration in rural areas - there simply isn't the capacity to absorb all the generation so the voltage goes way up in its attempt to use the grid as a battery, it overvolts, and the system shuts down, then starts up and on and on. The only way round it is more local storage or local load. (When you say there's a lot of PV on your line, that's not really a load, it's more like a source and that makes a lot of difference). The cost of increasing the wiring back to the HV transformer will rival the cost of more battery storage (labour + copper etc) especially if the battery's in a car and paid for by a different budget. I highly commend all your efforts to go green by the way. Best wishes for your system, and don't please don't risk blasting your inverter by setting the cut off voltage to a value which the inverter might simply not be able to stand!

Hi Tony,

I hold a CEC Accreditation as a solar pv designer and supervisor. I am also a CER agent for the creation, sale and purchase of renewable energy credits. The story is covered by Genevieve Simpson in many of her publications, and in Watts in the Desert.

I am not sure 'lovely' is an apt description for the Solex project but you are 'pretty much on the money' as to the rest of the description. I have a 185 mm2 main trunk from the LV connection on the roadway as a 'feeder', and a 35 mm2 cable across the block as a 'mains connection'. The rest of the distance to the HV line transformer is that of the utility.

My solar farm and ice-works do not experience considerable volt rise, and I manage the farmhouse 5 kW system as described above. However the rest of the utility side is connected to a number of 5 kW systems. As you have correctly described they are in a rural setting of 4000 to 8000 m2 blocks.

Where possible we have increased the capacity of the mains connections and the utility has been very co-operative in re-configuring and up-grading the transformer to keep voltages under 260v. I would never countenance opening the voltage parameters of transformers. As a Fronius Service Partner I am aware that the programs are pass-protected so the 'ordinary customer' is unlikely to know the codes to alter them (but that is possible). I guess you could say 'We are alright Jack'.

However I am now aware, and confirmed by your good self, that a major problem facing a high penetration of dispersed, embedded solar pv systems could be that the distribution lines, constructed as a supply only system, is simply not robust enough to absorb high volumes of 'reverse

supply.

As you point out the cost of increasing the wiring back to the HV distribution point will be prohibitive. Couple that to the loss of revenue faced by the utilities for facilitating the higher up-take of independent electricity generation, it is little wonder that government owned or sponsored electrical utilities are not inclined to co-operate.

We now face a very clear example of conflicts within the 'triple-bottom-line', as economic interests outweigh social and environmental interests. This is particularly evident in rural (less populated) areas.

I don't think we have a solution to the problem - but at least we have identified it. I believe you have now verified it. I was taught to believe that identifying a problem takes you half-way to solving it. The question now is 'how?'.

I am not convinced that battery storage is a real solution. 5 kWh (1 hour) of storage might help but is that infintisimal in a 12 hour period. Economically, $8000 of capital to store $1.50 of energy, makes me want to look at up-grading that line again. I might be a solution to up-grade the line as a condition of solar pv connections and to distribute the cost to the LV ccustomers within that sector. In Western Australia water main extensions are connected/up graded on that basis.

Thank you so much for your interest and consideration. Are you able to provide academic reference for your opinion (can I use your name) in attempting to negotiate with the utilities? Are you interested in further developments? I have been at this for 17 years so will not at all be offended if you do not.

Kind regards

Lex

I think we might even be getting somewhere! If the limiting factor is the run to the transformer then there might be a possible solution but although it saves the inverters it would stress the transformer and raise its operating voltage. Now when you do this you increase the flux density in the core and you can run into saturation conditions. If this happens currents skyrocket and the fuses blow. Assuming this condition is not reached you could look at installing an auto transformer at the property tapped at 90% and connect the inverters to the tap. So you can then run the main wiring at a higher then normal voltage . . . but that might not be safe. It would however spare the inverters.

Fundamentally the problem is that in general terms you are generating a resource at a higher rate than you can absorb it, and distant points of absorption are too remote to allow the resource to reach them without overstressing the distribution system. I don't think there can be a general solution to this because of the principle of conservation of energy. It has to go somewhere!

Another solution might be to have the run from the transformer to the property at a lot higher than 240V (0r 440V for 3 phase). The resistive losses would then be less so the voltage surging will be less. However the increased cost of insulation would be an issue, and the cost of a local HV transformer would not be insignificant.

Keep thinking!

I am not a big fan of increasing pressure to maintain flow. I much prefer to reduce resistance. The solution you have described in what the Utility is doing at the moment.

Ultimately the Utility has decided to cease any further solar pv connections. It is using uncontrolled frequency fluctuations and the cost of spinning reserve as its point of argument. We need to solve their problems to solve ours.

Of course fiscal restraints as to cost of network maintenance and development, the loss of revenue from sales of electricity and of course the concept of stranded assets, are not openly debated. I suspect however they are the primary considerations.

It appears to me that replacing the LV infrastructure with 150 - 200 per cent heavier than prescribed cable will eliminate most of the voltage issues. However not being a PhD in physics I cannot refute their engineering arguments. I believe the Europeans are not facing the voltage issues as they simply have heavier wiring standards and are not facing the problems.

As a sideline and a matter of interest I have found that a 'sweet spot' for AC/DC inverters is around 350v DC input.

That said our utility is trialing a focus on one transformer to gather field data. I would love to be able to suggest re-wiring the LV distribution lines to that transformer but I do not have any substantial authority to do that.

At the moment it is no more than my hunch, and a number of engineers who agree it might work. Right now however no-one can/will place a definitive statement on it.

An overarching problem is the economic one. 'Why should the government sponsored utilities assist the general public to self-generate at the expense of its revenue and capital cost?'. As an accountant and legal academic I have no answer to that. 'For the good of the natural environment' does not appear to be an acceptable answer.

In your photo the text is legible under magnification on the Sansai plug. Top line Input 100 -240V 50/60HZ 250mA. Second line Output DC 5V 2100 mA max. This is not the output of a solar cell array.

This 2 pronged plug is for light duty like powering a small 5V radio. The usual Australian power plug has three prongs and might be rated for 10 or 15 amps.

The European (British) plug could be fused up to 13 amps depending on the service required.

The photo is just an example of an illustration of the difference between the European standards and the Australian standards. As you rightly point out the little two prong plug is more suited to something with a low draw. However that is for common household 10 amp use in Australia. Televisions, radios, refrigerators, freezers and other household appliances. The prongs and associated wiring behind the switch do not get any heavier for normal use.

The English heavy prongs are for exactly the same use. The wiring behind the switch is proportional.

The relationship to residential solar pv systems is that, due to lighter wiring requirements for 'normal use' the voltages at transformer taps are often set quite high to allow for voltage drop in longer distribution lines.

When a solar pv system supports the grid, the voltage tends to rise back to the setting of the transformer, plus the 'line loss'. For example if a transformer tap has been set to 250v to deliver 230v then when the solar feeds back to that line the voltage can rise over the 268v parameter setting of the inverter.

I apologise for not making that clear in the example. I overlooked the fact that others would not be as familiar with Australia wiring systems as Tony Maine from Queensland is.

On investigation with state utilities the answer as to why are we using light wires and high voltages - cost. Australia has very long runs and a relatively low distribution, particularly in rural areas, as correctly identified (as he is from Queensland and familiar with rural and remote Australia).

I trust that clarifies your query.

Kind regards

Lex Fullarton