Just one fairly minor correction.

(1) As noted, DC power conversion circuitry was not available when electricity first showed up in mains systems. AC can be stepped up and down by a transformer. The model for DC was literally "A power station every few blocks."

By the 1880s when the debate took place the were well established AC and DC machines, what was lacking were sensible converters between the two, particularly from DC to AC. True there were rotary converters (one shaft with a DC motor at one end and an AC generator at the other), but they were very inefficient and large for what they accomplished.
The other big component that was lacking were DC breakers of a sensible size and speed. DC will grow arcs to quite substantial lengths, and will not self extinguish. Such breakers that existed were massive and even the somewhat prone to burning themselves to the ground in damp or dusty conditions.

One thing you didn't mention, and this may have been a critical factor, Edison didn't have the financial clout of Tesla and his baker Westinghouse who had a big pile of money....


As to getting systems stable with a large number of "free range" inverters and one big generator. One can tell when the various standards committees involved are sitting by the sales of headache cures in the area. There are so many external factors that are outside their control (direct or indirect) that the meetings tend to be very drawn out and heated. The most obvious are the existing network structure and topography, local climate and weather, and geology..... This is going to be a major consideration with the increasing trend for new properties to be legally required to have solar panels with their associated inverters connected to the grid and a long established town to grid connection.

DC will grow arcs to quite substantial lengths, and will not self extinguish.

Hence the instructions with grid tied domestic PV to ensure mains isolation switch is off before turning DC isolation switch either on or off. It may not be strictly necessary with the size of my set up but it is good practice and will ensure the DC switch lasts longer even if it doesn't prevent anything more spectacular.

Eh, the DC disconnects are load break rated, and I'm not planning to cycle mine often enough that I worry about it. Also, depending on what you're doing, the inverters will start producing immediately if you've not interrupted the AC side (when you connect the DC side again).

My point was more in the context of "home DC power distribution," as was mentioned earlier. It's the sort of thing that sounds really, really good on paper, if you don't know much about the area (which means I should probably get a Kickstarter going for something of the sort - they thrive on that sort of thing). And the more you dig into the details, the worse the idea gets. Much like, say, Solar Roadways (mad respect for getting their retirement crowdfunded, though).

Low voltage DC isn't hard to break without trouble - under 20-30V, unless you've got some staggeringly inductive loads (like, say, ignition coils...), it's not much trouble. Just, you can't move any serious amount of power around.

As you raise the voltage to reduce your wire sizes and give you more headroom for voltage drop (a 5V drop at 12V is unusable, a 5V drop at 600V is nothing worth bothering with optimizing out), your interruption problems get rapidly more expensive, and high voltage DC breakers are usually at least a few DC breakers in series (until you get into the specialty stuff, which is priced accordingly). But you simply can't just use a regular light switch sort of construction to break high voltage DC. It's not uncommon to see switches rated for something like: AC 240V/20A DC 12V/2A - it's simply arc suppression that limits them. And if you do get a DC arc, it'll just keep on going.

I've looked into it extensively. I planned a separate DC power system in my office. And it's not made it out of the planning stages, because it just adds a lot of complexity and cost for not much in the way of gains.

No, they are neither constant current, nor constant voltage, devices, you need to look at both the voltage and current curves against light level for the panel under consideration. The best controllers work by maximising the power delivered at a given light level. But they will NEVER deliver more power than the product of maximum power and maximum voltage.

Since the device is quoted as a "12v" system with a working current rating of "5.76A" that's the limit, just under 70 watts. Even if this was an 18v system it this panel would only be capable of delivering about 104 watts - a long way below the suggested 250w.

I could continue shredding that advert, but there are so many inconsistencies in it (basically lies to make fools spend their money with a gang of fraudsters) that it would be a pointless exercise as you've already been conned and are in total denial.

No, quoting it as a 12V system means it's capable of charging a 12V battery. With a charge controller in broad daylight it will be a higher voltage.

Why do you think its a VERY SMALL lead - big leads (more than a couple of degrees) can cause some very interesting (or exciting) results.
A small over-voltage is in effect a small lead, and can be used if you have very good voltage control in the inverter coupled with a good understanding of what the grid is doing on a cycle by cycle basis.

A small overvoltage would look like alternate leads and lags, changing every quarter cycle.

They could always have something just making a small amount of exactly 50Hz, and they'd all follow it. You just need one. It could be a large commercial wind farm, just pick whoever is the biggest contributor and make that the master.

No offense intended, but I'll listen to the power systems engineers who say "Yeah, this is a hard problem to make safe and stable," over someone who is more than a bit casual in their understanding of power systems who says "Well, why not just do it this way? Sounds like it'd work!"

Presumably where I wrote "you could always have something", that something needs to be a certain percentage of the generation before it works out.

How about a seperately transmitted frequency over radio waves? And make invertors stick to that. Or something similar to synch on green on TVs - send some kind of little pulse at regular intervals down the power lines so the invertor can lock onto that. It sounds better to hand out instructions rather than getting everything to try to follow. It's the difference between an army trying to march in time by watching each other, and having a Seargent shouting left right.

DC will grow arcs to quite substantial lengths, and will not self extinguish.

Hence the instructions with grid tied domestic PV to ensure mains isolation switch is off before turning DC isolation switch either on or off. It may not be strictly necessary with the size of my set up but it is good practice and will ensure the DC switch lasts longer even if it doesn't prevent anything more spectacular.

Surely a decent DC switch simply has gap big enough so an arc extinguishes. And since you're dealing with about 12-48V DC, that shouldn't be any more of a problem than switches in cars.

Much like, say, Solar Roadways (mad respect for getting their retirement crowdfunded, though).

Do you mean that idea to have roads as solar panels? Why didn't that work out? Too much physical wear? Too much dirt?

As you raise the voltage to reduce your wire sizes and give you more headroom for voltage drop (a 5V drop at 12V is unusable, a 5V drop at 600V is nothing worth bothering with optimizing out), your interruption problems get rapidly more expensive, and high voltage DC breakers are usually at least a few DC breakers in series (until you get into the specialty stuff, which is priced accordingly). But you simply can't just use a regular light switch sort of construction to break high voltage DC. It's not uncommon to see switches rated for something like: AC 240V/20A DC 12V/2A - it's simply arc suppression that limits them. And if you do get a DC arc, it'll just keep on going.

So make the switch correspondingly bigger.

I've looked into it extensively. I planned a separate DC power system in my office. And it's not made it out of the planning stages, because it just adds a lot of complexity and cost for not much in the way of gains.

I'm going to have a 12VDC system. I already do, supplied by a handful of 2600W old HP Blade Server PSUs. But with off grid, that will simply be the batteries. Although I may use something to drop the voltage a bit. PCI Express likes 11.4 - 12.6V. I use 12.6V, it works better on old knackered cards. What voltage are LiFePO4 batteries at with various stages of charging, discharging, charge level? I wonder if I can use a solar charge controller to "charge" the PCI express power bus from the batteries? It should just think the battery is a solar panel and the cards are a battery. The cards are covered in capacitors, and I can always add a supercapacitor if the charge controller doesn't like constantly varying currents and can't keep the voltage straight.

Surely a decent DC switch simply has gap big enough so an arc extinguishes. And since you're dealing with about 12-48V DC, that shouldn't be any more of a problem than switches in cars.

I don't know how it is done in other countries but the ten panels on the West facing side of our roof are wired in series giving a lot more than 48V at peak!

Surely a decent DC switch simply has gap big enough so an arc extinguishes. And since you're dealing with about 12-48V DC, that shouldn't be any more of a problem than switches in cars.

I don't know how it is done in other countries but the ten panels on the West facing side of our roof are wired in series giving a lot more than 48V at peak!

I've only heard of 12/24/36/48V arrays, but the peak is higher. They're just designed to charge 48V batteries, but that would be four panels in series.
Maybe on-grid invertors (is that what you have?) use different input voltages, and 12-48 was chosen for sensible battery arrangements (mind you the charge controllers are quite happy changing 48V to 12V etc). I have actually seen on sale battery equalisers for 96V, so maybe there are higher voltage setups.

I was surprised to read you can still get some power with your panels completely the wrong way round, vertically on a north wall you still get 25% of what you would facing south with the best slope.

One of the places I was looking to buy has a lot of land, and the house roof would be in the shade of trees, so I'd probably go for putting them on the ground at the edge of the plot, with manual adjustable tilt for different times of year. Tracking them east/west during the day probably costs as much as it saves on panels.

One of the places I was looking to buy has a lot of land, and the house roof would be in the shade of trees, so I'd probably go for putting them on the ground at the edge of the plot,

Makes sense to put them on the ground if you have the space. If on the edge of the plot, worth remembering there is no legal right to light in UK. If whoever owns the land next to your plot puts trees there that shade the panels you have no redress. (There have been a couple of test cases go through the courts on this.

Makes sense to put them on the ground if you have the space. If on the edge of the plot, worth remembering there is no legal right to light in UK. If whoever owns the land next to your plot puts trees there that shade the panels you have no redress. (There have been a couple of test cases go through the courts on this.

Easy enough to move the panels. And the neighbour is Network Rail. I guess the trains would cast a shadow for 20 seconds several times a day. But they hate trees incase they fall on the line, so no chance of them building those.

On the subject of rights, my neighbour (3 doors down just round the corner in the culdesac) is building an extension on the front of his house. For some reason I was notified. Yeah I could see it from the front garden I guess. But also notified was two houses behind him on another street. How could they see through two houses to the extension? Also, in the list of "reasons for objection", you're not allowed to object due to a loss of view, but you are allowed to object due to loss of enjoyment. Er.... a bit contradictory? I can enjoy a view.

He's not too bright, he already has a rear extension, which he went and applied for permission for, and ended up having to fit a circuit breaker box for the whole house, not just the new room?! (he only had fuses), put in insulation (it's his heating bill!), and provide adequate drainage round it (for some insane reason, since water which used to fall on the ground is now collected by the gutter and disposed of in the drain). If he'd done what I did and not stick it two feet out to the side, and make it entirely at the back, no permission is required.

Why were you notified? Quite simply because there is a legal requirement to directly notify everyone within a certain distance, that distance varies according to the nature of the development, its location.
There's a legal difference between "loss of view" and "loss of light" -crudely the view is what you can see at a distance, light is your property being shaded, in whole or in part, by the new works.
When it comes to electrical installations those are covered by the building regulations, and the wiring regulations, in place at the time of constructing the building or extension.
The rules and regulations around drainage are just plain confusing and are ever changing. In parts of the UK you have to apply for permission to resurface one's drive but can build a new one without permission; in other parts you need permission for both; and to add to confusion there are various definitions of the area considered and where the run-off water goes.

Why were you notified? Quite simply because there is a legal requirement to directly notify everyone within a certain distance, that distance varies according to the nature of the development, its location.

But the law being stupid as usual, required notification of everyone with property within 20m of his property, not 20m of the extension. It also took no account of it being behind the existing building.

There's a legal difference between "loss of view" and "loss of light" -crudely the view is what you can see at a distance, light is your property being shaded, in whole or in part, by the new works.

And it would appear we don't have a right to either. Makes a mockery of buying a property with a nice view.

When it comes to electrical installations those are covered by the building regulations, and the wiring regulations, in place at the time of constructing the building or extension.

I thought building regulations were only for selling a house. For example I only have a fusebox, so that would be noted on a buyer's report. Even then I don't have to upgrade it before sale, it just might increase the sale price.

As for him having to upgrade the wiring in the existing part of the house because a new bit was added is ridiculous.

The rules and regulations around drainage are just plain confusing and are ever changing. In parts of the UK you have to apply for permission to resurface one's drive but can build a new one without permission; in other parts you need permission for both; and to add to confusion there are various definitions of the area considered and where the run-off water goes.

I didn't ask for permission when I had mine changed from gravel to monoblock. No idea if I was supposed to. Not the sort of thing I care about, or even suspect I'd have to tell anyone about.

And as I said, an extension to the rear of a house only 1 storey high does not need any permission. He could have done it 2 feet further over and kept quiet.

And it would appear we don't have a right to either. Makes a mockery of buying a property with a nice view.

You have a right to a view, hence it is listed as being an allowable objection to a planning application.

I thought building regulations were only for selling a house. For example I only have a fusebox, so that would be noted on a buyer's report. Even then I don't have to upgrade it before sale, it just might increase the sale price.

Well, you've learned something - building regulations apply to building works not to sale. The latest electrical installation regulations apply to "new works" and are quite specific in how they apply to additions and amendments to the existing part of an installation - crudely, if you add something that is covered by the new regs then you have to have the existing installation inspected and brought up to a defined standard.

I didn't ask for permission when I had mine changed from gravel to monoblock. No idea if I was supposed to. Not the sort of thing I care about, or even suspect I'd have to tell anyone about.

It all depends on where you are, when the work was done and the attitude of the local authority. Worst case is having to apply for retrospective permission, having that refused and then having to revert the drive to its "former gravelled glory". A couple of my neighbours have suffered this indignity, but when that officious individual in the planning department moved on the new occupant of the post has a more pragmatic approach. I had great fun when I decided to change my drive from decaying tarmac to a "pant covered tarmac drive" - the process started under the "old" person, but the "new" person came out and said something along the lines "I can't see any problem with you adding more green stuff, carry on not spraying weed killer everywhere", so guess what, I don't spray the drive.

I thought building regulations were only for selling a house.

As Rob says any building works have to satisfy the building regulations. We put a loft extension in a few years back and to satisfy the building regs, had to have linked smoke detectors on all three floors. We also had to put rock wool in for sound insulation under the floor boards of the extension, the logic being apparently that our walking about up there could cause problems for our neighbours sleeping on the floor below.

And as I said, an extension to the rear of a house only 1 storey high does not need any permission

Depends. I know Scottish law is different in a great many things but in England, extensions need planning permission if they increase the floor area of the property above a certain percentage.

I was not completely accurate with regards to right to light. There is a right to light in your property and a development can be stopped or reduced in size if it affects the light to your property but you have to have enjoyed that light for 20 years before it applies. That 20 years applies to you personally and not the property, so we have only just started to get any protection from the Right to Light act 1959. That act applies only to England and Wales. Not sure what the position North of the border is.

The Scottish government publishes the rules, which are clear as to what does and doesn't need planning permission. As a home owner or builder planning an extension one should work through those rules step by step and if the "thought of" extension falls outside any one of those rules then either rethink the idea of have a chat with the planning people for clarification (which may lead to the idea being accepted), but going ahead with an extension that falls outside the rules for presumed permission then one runs the risk of having to apply for retrospective permission, which can be very expensive (even more so if it is rejected and the extension has to be demolished - who wants to pay twice for the same job?).

have a chat with the planning people for clarification

That is certainly the route I would go down. They were very helpful with us. Also worth chatting with the building regs people and getting them involved at an early stage. That was helpful for us.

And it would appear we don't have a right to either. Makes a mockery of buying a property with a nice view.

You have a right to a view, hence it is listed as being an allowable objection to a planning application.

As I said, it was listed as not being an allowable objection.

Well, you've learned something - building regulations apply to building works not to sale. The latest electrical installation regulations apply to "new works" and are quite specific in how they apply to additions and amendments to the existing part of an installation - crudely, if you add something that is covered by the new regs then you have to have the existing installation inspected and brought up to a defined standard.

That is absolutely nonsensical. The new building has nothing to do with the old one. And regulations are not law like planning permission. They're just guidelines.

What in the ?!? - the official rules are beyond a joke, nobody follows these:

"You might also need building regulations approval for many alteration projects, including if you plan to:
replace fuse boxes and connected electrics
install a bathroom that will involve plumbing
change electrics near a bath or shower
put in a fixed air-conditioning system
replace windows and doors
replace roof coverings on pitched and flat roofs
install or replace a heating system
add extra radiators to a heating system"

It's my house, I certainly won't seek approval to put in a radiator, change a fusebox, replace a door, or other such tiny petty things. Who does the government think they are? Should I have sought approval to move my gas main?

It all depends on where you are, when the work was done and the attitude of the local authority. Worst case is having to apply for retrospective permission, having that refused and then having to revert the drive to its "former gravelled glory".

Gravel should be banned, it's a pest. You end up polluting everyone else's property as it slides off.

A couple of my neighbours have suffered this indignity, but when that officious individual in the planning department moved on the new occupant of the post has a more pragmatic approach. I had great fun when I decided to change my drive from decaying tarmac to a "pant covered tarmac drive" - the process started under the "old" person, but the "new" person came out and said something along the lines "I can't see any problem with you adding more green stuff, carry on not spraying weed killer everywhere", so guess what, I don't spray the drive.

I don't understand, you changed it from tarmac which was falling apart to what?!

No, they are neither constant current, nor constant voltage, devices,

The reason I call them constant current is this:

Why does http://www.see.murdoch.edu.au/resources/info/Tech/pv/image011.jpg not go into img tags and work in here? I'll reupload to imgur:



No matter what the voltage is, the current stays the same. Unlike a battery where if you made the voltage drop to half, you'd be getting a lot more current.