Advice sought

[motorbiking]

I'm entirely supportive of FIT subsidies tailing off. My 2.4KW system could be had today for probably around £3-4K. At that price the payback at zero FIT would still be 12 years. My point is that when good things (for society) first come to the market, they need to be encouraged, otherwise they fail.

Plenty of very rich farmers get subsidies for keeping their land un-farmed - that serves little benefit to society. A person who lives in a village with no station doesn't benefit from our train network. Thin people do not benefit from fat people getting free gym membership. Plenty of zero VED cars, do crappy mileage. Plenty of things get breaks, because its deemed for the good of society.

Rich people with PV systems are not getting subsidised by poor people, because they already pay (by definition) way more in than they get out.

 

[StephenOak]

It is nothing, or precious little, to do with FITs. Commercial producers of electricity from wind get paid more than other producers for the same electricity, for onshore roughly twice as much and for offshore roughly three times as much. As that electricity is unreliable a truly free market would value it at less than reliable generation, quite possibly at zero. Those subsidies are not going away.

Plenty of very rich farmers get subsidies for keeping their land un-farmed - that serves little benefit to society.

As far as I am aware, the only farm subsidies for un-farmed land is exactly where there are active measures that are are deemed to be a benefit to society, e.g. increasing biodiversity and improving traditional landscapes. Do you have evidence of farmers being subsidised just to do nothing?

A person who lives in a village with no station doesn't benefit from our train network.

Patently not true. The rail network enables the transport of products and people around the country. Your statement is the same as saying that everyone who does not live on the M1 does not benefit from it.

Plenty of things get breaks, because its deemed for the good of society.

If something is genuinely good for society a small subsidy for a limited period makes sense. Giving someone a years gym membership (costing a couple of hundred pounds) may well save the NHS thousands in avoiding treating diabetes, heart conditions, cancer, etc.

Wind farms are getting a huge subsidy with, it seems, no end in sight and they produce a small amount of unreliable electricity, so the benefit to society is distinctly limited.

Rich people with PV systems are not getting subsidised by poor people, because they already pay (by definition) way more in than they get out.

What you presumably were getting at is that the rich person is not a net recipient of state (i.e. other people's) money because of these schemes. That is true but I have never heard anyone say that, so it is a moot point.

What is true is that poor people are worse off and rich people are better off because of these arrangements.

My 2.4KW system could be had today for probably around £3-4K. At that price the payback at zero FIT would still be 12 years.

Obviously I don't know the details of your system but that does seem surprising. A quick google turns up a price of £5,525 installed but excluding scaffolding, or £1,695 (plus delivery) / £1,895 (collection only) for a system that does not include the mounting kit and obviously does not include scaffolding or the cost of installation.

To pay back £3,000-£4,000 over 12 years you must be saving a minimum of £250-£333 pa in electricity bills. I have seen estimates that a larger (4kW) system will save £220 pa or less. Does that payback period include any necessary maintenance?

 

[JohnD]

Sometimes people show payback figures based on the assumption that Solar PV replaces expensive electrical water heating or space heating. However electricity is so expensive that most people use gas or other fuels, so the payback claim is false.

 

[motorbiking]

Yes - it could be a lot more (without FIT) when you look at NPV, even if you live in the South and have a highly suitable roof. However, there are other factors such as energy security as well as cost per kw.

Without the FIT payment (when I went in) it would have been a no brainer - i.e. no way.

 

[JohnD]

With the ordinary systems connected to the grid, they add no energy security, because as soon as the grid fails (or goes outside tolerance) they must immediately turn off. You can get off-grid systems but they are rare. I don't know how they stabilise the voltage efficiently.

In some parts of the US there is a risk of "islands" appearing when there are so many domestic renewables that they support each other in a mini-grid for a while..

 

[Ian H]

Without the FIT payment (when I went in) it would have been a no brainer - i.e. no way.

How many people did you hope to kill during the time your system takes to pay for itself?

That’s the reason this thread turned to a solar discussion.

 

[motorbiking]

0.063 according to my maths.. if you believe the argument.

 

[SUNRAY]

Sometimes people show payback figures based on the assumption that Solar PV replaces expensive electrical water heating or space heating. However electricity is so expensive that most people use gas or other fuels, so the payback claim is false.

Out of curiosity I decided to place KWh meters on 6 of my circuits, over the course of nearly 2 years of (roughly) monthly readings I averaged 140KWh per year. According to the figures generated by the guy who came to sell PV, by changing all my lights to the 'free CFL's he was going to give me' I was going to save 'at least' 191KWh per year just on the lighting. I was going to cover the £12k cost of the 4KW PV installation in under 3 years using his figures.
I asked him to explain how when my annual electricity bill is around £500 - 600 and lighting accounted for less than 10%. His response was official government methods of calculating it.

 

[bernardgreen]

they support each other in a mini-grid for a while.

until, without an assigned "master" to control frequency and voltage, the mini grid becomes unstable.

The use of tin can transformers that each supply just a couple of houses complicates the process of feeding excess power back into the grid ( be it mini or city wide )

 

[SimonH2]

until, without an assigned "master" to control frequency and voltage, the mini grid becomes unstable.

Not so much that, but with the national grid all interconnected, there is a massive amount of inertia in all the rotating generators - and the driver machines, eg turbines, mechanically coupled to them. An island of inverters has negligible inertia and so will not be frequency stable.
But, between them they may have fairly good voltage control IFF the supply and load powers match - especially if there's a lot of resistive load so load increases as voltage does, while supply remains constant *current reduces) as voltage increases. As a result of a comment in another thread a while ago, I went off and tried to find out what algorithm these inverters use to determine loss of grid - anti-islanding protection. It seems there's no clear answer - there's still research going on into reliable algorithms

Absolute voltage or frequency are not reliable and can cause nuisance trips. One paper I found suggested that a combination of rate of change of frequency coupled with rate of change of voltage was fairly reliable (minimal nuisance trips and reliable real trips).
The bigger the island, the worse the problem as the more embedded generational and load there is, the more averaging will go on. I'd speculate that a large industrial site with loads of DOL motors driving high-inertia loads would also act to stabilise the island.

G59 and G83 seems to be useful starting points for searches

 

[JohnD]

IIRC there have been islands in California where it happens, and they crash when the sun starts going down. Apparently the big domestic load is air con and gets higher the sunnier it is; as does Solar PV.