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Solar panel question.

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Solar panel question.

Post by colly0410 » Sun Aug 31, 2014 11:02 pm

Been thinking: (took some effort) If mains connected solar panels are generating more power on a single phase circuit than is being used by others on the same circuit, will the excess being fed into the sub-station transformer be fed back into the HV grid? Would this cause problems of phase balance?.... If the HV grid failed would the low voltage circuit fed by the solar panels carry on working?

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Re: Solar panel question.

Post by Red to black » Sun Aug 31, 2014 11:24 pm

I don't do solar, but I will try and answer your questions as best I can :bba

First off phase imbalance, the three-phase supply from the sub-station to your street (or local area covered by that supply) is normally split into groups of houses fed from each phase to balance the load out from the suppliers, this is done in various ways, it could be that 3 houses are fed with L1 and N, then the next 3 with L2 and N the next 3 with L3 and N... and so on, or in some other arbitrary way, but they will be evenly spread out so each group of houses gets a single phase + Neutral supply but on different phases to load balance.

The Inverters which convert the DC from the panels on the roof to AC will amongst other things such as regulate the voltage and synchronise their supply with your incoming mains (it needs an incoming mains supply to synchronise to) will trip out if there is a loss of mains supply, this is so you cannot backfeed on to an otherwise dead supply network (this is very strictly enforced).

This is mainly so that an unfortunate linesman who maybe knee deep in water down a hole in the road doesn't get a belt whilst trying to repair the cable, or other users/operatives of the network, also your inverter (typical domestic feed in tariff types) would not have the power to maintain a supply to all those other houses on the same phase as you (see above) which will have their own loads still connected.

As far as I am aware the inverters (typical domestic feed in types) do not auto-start on re-application of mains, they used to have to be manually re-set, Rob (glowing anode) has had more to do with PV than I, so he may clarify this latter point, although some large commercial or industrial ones may well do, as these types typically have much more sophisticated controls and monitoring equipment by their very nature.

There is another form of Solar power that works in a similar way, only it does not feed into the public supply, this stand alone system is called islanding, this is typically used to power sheds or boats etc. and may use the DC to charge batteries or even to power say Dc lighting directly, it may also use a different type of inverter to power stuff locally, but it will not connect back into the grid.

I have greatly simplified this, as some systems are highly specialised and some can be a sort of hybrid, also some I am not that familiar with :qq1

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Re: Solar panel question.

Post by FIXITNOW2003 » Mon Sep 01, 2014 7:23 am

I have a 16 panel set-up and it does auto-start on re-application of mains

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Re: Solar panel question.

Post by Boater Sam » Mon Sep 01, 2014 9:51 am

Further to the original question, all sub circuits on the mains distribution are fed from 3 phase transformers, and as such they tend to equalise the loads across the phases due to the magnetic/induction effect of a transformer on load.

Load equalisation is a problem with a single end user on a sub circuit who has not spread his loading properly across the phases. This is one reason that the electricity boards used to be reluctant to install all 3 phases in the premises of small users unless they had 3 phase equipment. They knew that one phase would be loaded much more when they brewed up!

As an aside, physics and power being what it is, how can the EU think that reducing the power rating of electric kettles in the near future, as they have with vacs, will reduce energy usage?

Boater Sam.

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Re: Solar panel question.

Post by sideband » Mon Sep 01, 2014 10:40 am

ppppenguin wrote:Even more usefully mandate clear markings to show how many cups worth of water you have in your kettle.

Our cheapo Sainburys kettle has these markings. As to whether they are clear... they are etched into the plastic fill indicator but I wouldn't say they were clear. I believe that these markings are being made mandatory on properly tested kettles sold in UK which means that they will have to be of a certain size and also be durable.

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Re: Solar panel question.

Post by turretslug » Mon Sep 01, 2014 10:55 am

Unless the EU's powers are now so far-reaching and over-whelming that it can order water to have a lower specific heat capacity, it's difficult to imagine how making a cuppa can be made significantly more environmentally friendly. I'm sure trimming at the edges (fast-acting cut-outs, maximising insulating qualities, minimising surface-area-to-volume ratio and making kettle inners with metal flat bottoms with element bonded underneath for low minimum fill) can help but these must be minor and incremental, rather than ground-breaking. Surely the most efficient way to boil water is with the maximum power for minimum time? That would average out over the grid as a whole but minimise individual heat-loss time. "Standby" kettles sound like outrageous lifestyle profligacy to me...

As a thought-exercise, how inefficient is boiling a kettle with solar-derived electricity compared to directly focussing the sun onto it to achieve the same goal? :bba

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Re: Solar panel question.

Post by Red to black » Mon Sep 01, 2014 11:36 am

Thanks guys for the clarification on domestic inverters auto-re-starting :aad

I don't do solar, I briefly looked at getting involved a few years back when it was still in its infancy, but the hoops that needed to be jumped through was unbelievable, you need very deep pockets to set up this type of operation.

It has been quite a fast moving industry both from a technological point view as well as a legislative point of view.
There were many Solar company start ups at the time, and a lot of these firms subsequently went to the wall in this highly competitive market, I just kept out of it because I could not afford the start up/running costs and put up with the hassle of the many hoops needed to be humped through, as well as the financial high risk factor . :qq1

In the last year or two the "rent-a-roof" brigade have also put a lot of PV companies under even more pressure, but I digress here, relative to this though I was lead to believe that installers now have to provide post code details before permission is granted to apply the feed in tariff (FiT), and if so many installs are already on the same post code then it may be denied.

Granted this may only apply in certain DNO areas, or it may be if there are too many solar installations in one area, like I say I am behind the curve on this aspect, but if true it could well be that Solar is causing the network some problems.

Apparently Germany's network is/was suffering horrendous problems due to the sheer amount of Solar installs there.
As I say this is outside of my interest zone and I only just barely keep half an eye on current developments so some of my information may well be out of date. :bba

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Re: Solar panel question.

Post by Ed Dinning » Mon Sep 01, 2014 7:27 pm

Hi Folks, as a basic law of physics it takes a fixed amount of heat or energy to raise a litre of water to boiling point. Reducing that heat input will only mean it takes longer to boil. Therefore there is greater time for heat to dissipate (increased losses), so more energy, not less is used!
I can only think it may reduce maximum demand at a time when we may all turn our kettles on at once.


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Re: Solar panel question.

Post by Refugee » Mon Sep 01, 2014 7:36 pm

I have a feeling that the peaks of demand for kettles has almost gone now we have more TV channels with commercial breaks that are staggered to some extent.
It was soap operas with a commercial break in the middle that were the worst but time shifting with DVRs has largely got it sorted and the viewer benefits from fast forwarding the adverts to boot.

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