solar pv

Hi,
I recently took the City & Guilds PV course. I haven't done an install yet but i've been to take a look at some possible jobs. At one of the jobs i noticed there was no spare way in the main consumer unit. There was however a smaller 2 way consumer unit spurred off the supply tails via a henley block. This smaller unit supplied an electric shower and had one spare way. If i used this spare way for the PV system am I correct in assuming that the only item of equipment that will benefit from the electriciity generated will be the shower and not the circuits fed from the main consumer unit?
Thanks.

No. If the mini CU is connected to the meter via a Henley block which also feeds the big CU then both will take power in any direction. I don't know anything about PV, and am curious - are you using the spare way as a connection to the bus bar? How is isolation achieved? Could you point to a link to help me understand? Thanks.

Here is a pic of a typical pv system.
http://www.windandsun.co.uk/images/solar/solar_roofs/solar_roofdiagram2.jpg
As you can see the pv system feeds back into the consumer unit via its own MCB. As it is on the load side, all of the other electrical equipment supplied by the same consumer unit can take advantage of the electricity generated by the pv array.

the_pasty said:

Hi,
I recently took the City & Guilds PV course. I haven't done an install yet but i've been to take a look at some possible jobs. At one of the jobs i noticed there was no spare way in the main consumer unit. There was however a smaller 2 way consumer unit spurred off the supply tails via a henley block. This smaller unit supplied an electric shower and had one spare way. If i used this spare way for the PV system am I correct in assuming that the only item of equipment that will benefit from the electriciity generated will be the shower and not the circuits fed from the main consumer unit?
Thanks.

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Surely you need to know more about electrical installation and electrics in general before being able to these systems in properties??

I was wondering when the first self-righteous smug reply would come. Congratulations 1john, the award goes to you. If you've nothing constructive to add, dont bother.

ok, perhaps you could inform me where I can and cant comment. Maybe for the rest of my life.

This is a constructive comment, or question, can you explain to me why you thaught your PV system would only benefit the shower?

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well it is obvious he knows SFA if he thinks that PV will be cost effective in the UK anyways.

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Thanks for the input guys, very useful and informative. A simple' yes that's right because...' or 'no you're wrong because...' would have helped but I suspect you dont know the answer yourselves. You both probably think you're really clever but your rudimentary grasp of grammar and spelling tell me that neither of you are very bright.
PV not cost effective in the UK? With the new Government FIT (look it up) in place a PV installation in the UK should give you a return of 8-10% on your investment. Try getting that in the bank.
Now grow up you pair of tools and try to be more helpful in future.

I do see a problem with the grid tie inverter in that it is able to reduce load but not back feed into the suppliers system and of course with a supply failure it would be dangerous for the workers if the sun coming up produced a back feed onto the system.

Also there is an issue in how much power is produced. If a house was to use between 5A and 60A and the grid tie inverter supplies 5A then in theory all is OK but if the inverter supplies 10A then at some point it will back feed.

The meter type will be critical of course but if the wrong type once could be charged for the power you feed into the grid.

So for the system to work there needs to be a current transformer to work out exactly how much power you can put into the system. So unless that current transformer is around the main incoming then as said it will only allow enough power to compensate what the system thinks the house is using.

For a solar panel to save money it needs to feed into an inverter which allows the input voltage to vary to give max watts. And this is the point it needs to give power when it is available not when it is wanted and the only way this can work is with a battery bank.

So to work efficiently one needs a solar panel, and battery bank, charge inverter and supply inverter. Canal boats use this system and the solar panels do save money especial when one considers the cost of fuel. Also they often work with wind chargers as well.

However in a house the amount of extras required which must include a battery bank to be able to store the power means the only way a grid tie inverter can work is with the special meter allowing one to export power. The extra cost of this type of meter means to pay there is a min size and in general a house is not a big enough user or a constant enough user for the systems to work.

So for a house they are a complete waste of money.

Unless there have been some changes a normal person pays around 10p per Kwh for power used but on a feed in tariff one pays more around the 12p per Kwh and you then get 3p per kwh for anything you export so if you are nearly producing all you need you can reduce the bill but any high power items like a shower or cooker are out one needs to have very few peaks and troughs so for a shop with lights on all day the panels may work. But homes I don't think so.

Thanks for the sensible replies ericmark. From April of this year the Government introduced the Feed-In-Tariff (FIT) for renewable energy generators. For a retrofit solar PV installation, the owner of the FIT is paid 41.3p for every kilowatt hour of electricity generated regardless of whether it is used or exported. As you correctly state, you are also paid a tariff for any surplus exported and you will of course experience lower electricity bills. Over the 25 year period of the FIT being paid, a well designed installation should give a return of 8-10%.
There is a lot of information here.. http://www.fitariffs.co.uk

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the_pasty said:

Over the 25 year period of the FIT being paid, a well designed installation should give a return of 8-10%.

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Should (according to manufacturers/suppliers of these systems), but in reality won't provide any return at all.

Since most people will not have a spare £15k+ to spend on a PV system, they will borrow the money. This of course will incur interest costs, eliminating the alleged financial return from the system.


Apart from the issues rasied by ericmark, another significant item is maintenance.
PV panels require regular cleaning, otherwise the output from them will fall significantly. Since most of these domestic installations will involve panels on the roof, most of them will never be cleaned.

Even in ideal conditions, PV panels don't last for ever, and over a 25 year period it is very likely that some of them will require replacement.

Batteries will most definitely not last for 25 years or anything close to that. They will need to be replaced far more often, at a significant cost.