Impact of solar PV on national grid

SallyKing

larkim wrote: »

Actually, when you are talking about coal, oil or gas powered power stations the answer is no it doesn't - on the day that you first start saving energy, the power station burns the amount of fuel it thinks it will need for that day. However, if your reduced usage is noticeable to the grid then they will plan to burn less on the next day.

So if we all (unexpectedly) switched off everything at 11.01am tomorrow for a couple of minutes then the amount of fuel being burned at that time would remain the same.

Matt

So does the same work in reverse, i.e if turning things off burns no less fuel, then what happens if we turn things on? Do we essentially get free energy?

Also, if we turn things off and the power station is still burning fuel and generating electricity, where does the surplus go? Can I have it for free

Ben84

It's about quantity and averages really. The national grid is always being supplied with more electricity than is being consumed (excess is dumped to ground to dispose of it). The grid has no power storage ability, it's a constantly flowing source of electrons that you divert through your appliances when you turn them on, meaning there always has to be more available than is being used so that the lights aren't dimming and appliances stopping all the time. It's fairly well controlled through a combination of continuous base load from large plants like coal and nuclear that run at full output all the time and smaller gas/oil plants which are turned on during peak times, such as early evenings when many people are cooking or watching TV or very cold weather when electric fires are being used. There are even fast response plants are turned on 10-15 minutes before advert intervals in popular TV programmes to power up the thousands of kettles that will be turned on.

However, despite these attempts to match production to demand, electricity is always being generated in excess to the amount being used. Turning off your appliances and saving energy or using solar power doesn't immediately save any fuel from burning at the power plant, but averages come in to this as when many people do these things the national average electricity use reduces and that leads on to less electricity being generated at that time of day in the medium term and long term if enough people do it less power plants needing to be built in the future. So, turning off your electric fire doesn't make the power plant burn less coal or oil, but if lots of people do it and keep doing it then the national grid will eventually be provided with less electricity.

Solar power is something of a random variable. How much will the national grid rely on the output of solar panels? They should be fairly consistently behaved in large enough numbers based on the time of day and year so I expect their output is useful. I doubt a kWh from a solar panel directly converts over time in to one less kWh generated at a power plant, but it should turn in to something reasonable. Wind power however is the bad one, it does not behave so consistently in large numbers as the wind adjusts rapidly, far faster than any power plant can. The national grid cannot rely greatly on their output so very low guaranteed outputs will have to be assumed from large numbers of them. The key point here is that measuring the electricity generated at the solar panel or wind turbine isn't the full picture, it's about how probable their output is at any moment in time and how much the grid can depend on them so that power plants can be used less without the adverse effects of the grid being underpowered.

grahamc2003

SallyKing wrote: »

Graham, thanks again for another useful reply.

So the answer is that solar PV does save fuel from being burnt at the power stations, its just a question of ecomonics.

So what is the solution?

Our oil and gas are running out fast so we increasingly have to import expensive supplies from abroad.

Nuclear would be great if wasn't so expensive and being built by French companies who will stitch us up on price once they are built. There is also the risk and the waste issue.

Coal releases mercury and while we have a fair bit of coal left we have already mined the best stuff.

Wind is going nowhere due to the nimbys

PV works but is expensive


So is not just a case of we all need to use less energy? Would this not solve all of the issues we face?

The problem we face is that, in general, the Uk electricity need is rising (some years it doesn't, but overall it does). So in general, the maximum demand we have to meet rises, so we continually need more generation at that period (around 17:30 on a winter's evening). Cutting comsumption in the day won't really help, because there is plenty of spare capacity (that is, plenty of generation is available if required) - cutting consumption on a winter's evening will help massively, which is where the government should be heading.

Likelwise adding unreliable capacity which can't be relied upon to generate at 17:30 will not address the problem at all, but at the moment, virtually all new additional capacity is the unreliable type.

If that situation weren't bad enough, about 20% (a massive amoount) of our current capacity is planned to be decommissioned within the next several years. So we are closing generation which can be relied upon (Nuclear and coal), and adding generation (solar and wind) which can't be relied upon. (The coal station supplying 5% of our needs is being closed due to new emission regulations, while it is not near the end of its desgin life - a few billion quid down the pan there then).

The thing about saying cutting consumption is the way to go is that it will in practice only slow the rate of increase of demand, and not lower the demand itself.

grahamc2003

larkim wrote: »

So if we all (unexpectedly) switched off everything at 11.01am tomorrow for a couple of minutes then the amount of fuel being burned at that time would remain the same.

Matt

Matt - where do you get this stuff from?

If demand drops, then the grid frequency would rise, automatic systems would close the valves supplying steam to gensets, and as the steam pressure rises in the boilers, the coal hoppers would cut the rate of supply of coal to the boilers.

SallyKing

Some very interesting replies, its given me a few things to think about.

How about smart meters that vary the price of electricity? A bit like a more advanced version of E7 - e.g at 5:30pm in winter electricity costs more to reduce the demand.

We certainly face some big problems with our energy supply and it seems there are no easy answers - every solution currently on the table has problems, only some of which I listed above.

Cardew

SallyKing wrote: »

So, that means the simple answer is that solar PV does in fact reduce the amount of fuel being burnt at the power stations?

I also had never seen your original 'quote' that solar etc wouldn't save fuel.

It obviously will save some fuel and the National Grid engineers are adept at forecasting sunny days and windy days to maximise savings. However it isn't easy because of the transient nature of solar.

As covered above, what has been stated on these forums is that solar and wind will not reduce the UK's generating capacity.

The biggest criticism of solar is simply that it is so inefficient and this is compounded by the Government setting up a system where huge subsidies are paid to very few people by 99.4% of the population.

Burning £5 notes on your open fire will save you money on coal.

larkim

grahamc2003 wrote: »

Matt - where do you get this stuff from?

If demand drops, then the grid frequency would rise, automatic systems would close the valves supplying steam to gensets, and as the steam pressure rises in the boilers, the coal hoppers would cut the rate of supply of coal to the boilers.

But not instantly. I agree the control mechanisms in the electricity supply would probably react quite quickly to reduce the electricity power output, but the fuel delivery would be slower to react. I don't work in a coal fired power station, I'll admit that though!

I was just trying to make the point that the power generation system is reactive - there isn't an instant reaction between what you demand and what is being generated, so there is lag in the system.

Matt

grahamc2003

SallyKing wrote: »

Some very interesting replies, its given me a few things to think about.

How about smart meters that vary the price of electricity? A bit like a more advanced version of E7 - e.g at 5:30pm in winter electricity costs more to reduce the demand.

We certainly face some big problems with our energy supply and it seems there are no easy answers - every solution currently on the table has problems, only some of which I listed above.

The situation is worse than most imagine - I think it's now almost certain that in 7 or 8 years time, the grid will be rationing electricity, by selective power cuts shared out around the country, on winter's evenings. That will happen if current plans are followed, and in a way, somke likley alternatives are even worse - and by that I mean it's likely, with the pressure to keep the lights on, the decomissioning of the Nukes at the end of their life will be postponed, which is a risk too far imo. Hopefully, the closure of Drax will be postponed - (in fact, since writing that google tells me the eu have postponed their requirements to close drax, so a bit of common sense there).

I'm not sure totally variable tariffs could come about within 7 years, but they could help. What is more helpful are contracts with large electricity users to cut their supply after e.g. a 30 minute notice period. (If I were advising such large users, I'd advise being very careful signing such contracts as they would probably be exercised at the max possible rate specified in the agreement e.g. every day).

As an interim measure to help reduce peak time consumption, I would like to see the cheap rate for e7 users to be zero which, given time, would alter the demand curve by diminishing peaks and increasing the utlilisation of the extremely cheap nightime generation. It would probably be self financing.

grahamc2003

larkim wrote: »

I was just trying to make the point that the power generation system is reactive - there isn't an instant reaction between what you demand and what is being generated, so there is lag in the system.

Matt

Wrong. There IS an instant reaction which matches exactly supply and demand. It goes on every second of every day. It's called primary reserve which supplies primary, frequency sensitive response instantly.

energysavingexp

grahamc2003 wrote: »

I can assure you with 100% certainty that that is incorrect. Why do you think that?

because 1 house using about 1kwh will not make the power company
cut down on production as this will be covered in the over production

it would need more than one house to make a difference

if you read the original post, the question was if I ( not every one else) use less during the day will the power station that is using coal etc burn less fuel

they dont say mrs B has put the kettle on so better put another log/coal on to the fire

the fossil fuel generators take a long time to get going to produce enough steam to turn the turbines
short demand for supply is made up from turning on quick start generators like hydro where they can open a valve letting water turn the turbine in matter of seconds