Solar ... In the news

Coastalwatch

An interesting if natural development for PPA's which, if it comes to fruition, would be quite a prize on the way to  Net Zero!

TfL eyes renewables PPAs to power rail network

Renewables could power Transport for London’s rail services as it explores the possibility of forming Power Purchase Agreements (PPAs).

The Mayor of London, Sadiq Khan, today (17 June) announced that TfL has launched a market test into supplying rail services with renewable power direct from generators following setting a goal of a zero carbon railway in the London Environment Strategy.

TfL requires 1.6TWh of electricity per year to run its services, with this currently sourced from the National Grid via the Crown Commercial Service. However, a switch to PPAs is now being explored, allowing the rail network to be supplied by solar and wind generators over its current mix of power generations.

It will also look into the potential of meeting the Greater London Authority (GLA) group’s wider demand for renewable electricity, which comes in at 143GWh, and the opportunity to meet London’s wider public sector electricity demand with renewables which alongside the GLA group’s demand totals 3TWh per year.

https://www.solarpowerportal.co.uk/news/tfl_eyes_renewables_ppas_to_power_rail_network

Martyn1981

It's just getting silly now, PV generation at ~ 1.14p/kWh!

Japanese banks back world’s cheapest solar project

Qatar General Electricity and Water Corp. has announced financial close on the 800 MW Siraj-1 solar project with the Japan Bank for International Cooperation and Mizuho Corporate Bank. The project, secured in a tender by France’s Total and Japan’s Marubeni, will sell power at a record low price of $0.01449/kWh.

joefizz

Solarchaser said:

The argument has always been, fill your most efficient first, then if there's still excess, fill the next most efficient.

I can see why you dont see how.

It depends who is doing the arguing and what their experience is. You are well within your rights to argue that but from a network perspective the arguments are many fold.

You have one argument. Another argument is to fill your cheapest first. Another argument is to utilise older equipment first to get the most out of it. Another argument is to utilise the kit that cost the most to maximise its utilisation. Similarly if you have equipment that has considerable start up/ramp down costs as opposed to steady state you might favour that. Yet another argument is to use the kit/resources that are available within your own borders (if you have your own currency) so it doesnt cost you anything in terms of hard currency or external resources. Another argument is political (just look at Huawei), if your supplier is local and providing local jobs and money into the economy then regardless of how efficient it is, overall it will be a larger benefit to the economy/country/etc.

Its just not a simple matter of applying simple principles learned off the internet when there are often more complex reasons for doing things.
Efficiency is just one variable in the equation, not the sole variable which many internet posters would have you believe.

Pile_o_stone

JKenH said:

Then as you point out there is the local grid. Like you, I have had a fight with my DNO and we have to accept on a local level further integration of domestic solar may cause problems.

Trust me, I would love for everyone to have solar pv but as well as cheerleading it we have to think about how it can be integrated into a balanced grid. 

I have also had a 'fight' with my local DNO about increasing my array size. They are demanding £1500 to 'strengthen' the grid. I had my doubts about whether that was really necessary or would actually happen even if I paid. However I subsequently found out that my DNO allows the use of G100 export limiting devices, so the problem is solved.

"G100 simply means that only a pre-determined amount of energy can be exported back to the grid. To avoid any disturbances with the grid, the DNOs do not have to take any actions for the large amount of surplus energy entering the national grid, this is the case on holidays and weekends when the producers of green energy are not at home to make use of it."

So when I'm in a position to install my 'phase 3' array of a further 3600Kw of panels, I'll link those and the previous 1800kw extension to the same G100 compliant inverter. I'm allowed to export 1500kw on my existing extension so I'll cap my export at that level. My original 3600kw panels are on their own inverter as they receive FIT payments.

joefizz

Pile_o_stone said:

I have also had a 'fight' with my local DNO about increasing my array size. They are demanding £1500 to 'strengthen' the grid. I had my doubts about whether that was really necessary or would actually happen even if I paid. However I subsequently found out that my DNO allows the use of G100 export limiting devices, so the problem is solved.

I mentioned this previously but I'll repeat again as it highlights exactly this problem. This day last year I came home from 6 weeks touring the US to find that shortly after leaving one of the circuit breakers in my outbuilding had tripped, cutting off two freezers (the smell will live with me forever).
Didnt realise at the time (replaced mcb and it didnt happen again) but subsequent investigation of my solaredge, sofar data and talking to neighbours I narrowed it down to the exact time it tripped. Peak output around end of June. Around midday and on a weekday during school holidays in NI.
I was outputting full 3.8kw into the local network (about 14 or so houses). I dont have the figures to hand (travelling again) but I think it was almost 260v in the local network before everthing tripped. A couple of neighbours on the same node to the substation have monitored burglar alarms and when their alarms tripped they got texts, both had their alarms tripped at exactly the same time.

Didnt happen this year even though peak was hit a number of times because most people working from home under lockdown here in NI.

Another one of my neighbours said her microwave failed the same day... felt bad about that...

Nobody else on the same node to the substation is allowed to install solar (or anything else that inputs to the grid), well they are but it would cost them.

JKenH

Pile_o_stone said:

JKenH said:

Then as you point out there is the local grid. Like you, I have had a fight with my DNO and we have to accept on a local level further integration of domestic solar may cause problems.

Trust me, I would love for everyone to have solar pv but as well as cheerleading it we have to think about how it can be integrated into a balanced grid. 

I have also had a 'fight' with my local DNO about increasing my array size. They are demanding £1500 to 'strengthen' the grid. I had my doubts about whether that was really necessary or would actually happen even if I paid. However I subsequently found out that my DNO allows the use of G100 export limiting devices, so the problem is solved.

"G100 simply means that only a pre-determined amount of energy can be exported back to the grid. To avoid any disturbances with the grid, the DNOs do not have to take any actions for the large amount of surplus energy entering the national grid, this is the case on holidays and weekends when the producers of green energy are not at home to make use of it."

So when I'm in a position to install my 'phase 3' array of a further 3600Kw of panels, I'll link those and the previous 1800kw extension to the same G100 compliant inverter. I'm allowed to export 1500kw on my existing extension so I'll cap my export at that level. My original 3600kw panels are on their own inverter as they receive FIT payments.

I have also been investigating expanding my solar and explained to the company I approached the problems with my DNO. He also said no problem if I use an export limiting device. 

Now my next question and something I may have asked on here before (in another context and without a satisfactory answer) relates to the first law of thermodynamics. If an export limiting device is fitted what happens to the power (energy) that has been generated by the panels that isn’t exported -  doesn’t it have to go somewhere? Presumably it would be converted into heat. If you or I bolt on an extra 3.6kw (or if your roof is big enough 3600kw) and that is all export limited something somewhere is going to get quite warm if we can’t consume it or store it in batteries. 

Edit: ...or does an export limitation device shut down the generation?

zeupater

Hi

Basically ... what happens on a sunny day when you turn the inverter off? ... Voltage remains on the DC side, but no current flows from the panels, so no power available for the inverter to convert & match to mains AC ... similarly, what happens if you have more kWp of panels than the output of the inverter? ...there's high DC voltage, but the inverter limits the current .... less or no 'work' being done effectively means that there's less or no 'work' associated heat being produced - think of a standard battery, it has a voltage, but (all external conditions remaining equal) the temperature only changes when current flows (ie, 'work' being done) and  internal resistance creates heat.

These are effectively the two options for limiting the output ... switch off the inverter, or limit the performance of the inverter and that really comes down to how sophisticated the installation/inverter is. Many inverters have the ability to derate output (ramp down to a reduced performance level) according to monitored temperature or grid voltage conditions and some manufacturers leverage this feature to offer control equipment to communicate with the inverter's inbuilt logic to balance generation and/or divert to storage to limit export to the grid .... example  ... https://www.sma-uk.com/solar-systems/export-limitation.html ... 

HTH - Z

joefizz

JKenH said:

Now my next question and something I may have asked on here before (in another context and without a satisfactory answer) relates to the first law of thermodynamics.

All to do with the DC to AC conversion. Ideally you want this to be as efficient as possible, but you can reduce the efficiency by changing the rate at which the DC component is 'switched' to form AC. Effectively the DC is 'on' all the time in this scenario but if you use the electronics to switch less often and average it out (obviously more complicated than that but you get the idea), then you will operate at less than optimum and so limit output.
Maximum possible power input is still the same, you are just choosing not to convert as much of it to AC as you can, so no (or negligible) resistive loss.
Thats not to say that equipment with a painted on CE mark  wont have a dirty great resistor inside, glowing away merrily ;-)

JKenH

Thanks Z and Joe.

Martyn1981

zeupater said:

Hi

Basically ... what happens on a sunny day when you turn the inverter off? ... Voltage remains on the DC side, but no current flows from the panels, so no power available for the inverter to convert & match to mains AC ... similarly, what happens if you have more kWp of panels than the output of the inverter? ...there's high DC voltage, but the inverter limits the current .... less or no 'work' being done effectively means that there's less or no 'work' associated heat being produced - think of a standard battery, it has a voltage, but (all external conditions remaining equal) the temperature only changes when current flows (ie, 'work' being done) and  internal resistance creates heat.

These are effectively the two options for limiting the output ... switch off the inverter, or limit the performance of the inverter and that really comes down to how sophisticated the installation/inverter is. Many inverters have the ability to derate output (ramp down to a reduced performance level) according to monitored temperature or grid voltage conditions and some manufacturers leverage this feature to offer control equipment to communicate with the inverter's inbuilt logic to balance generation and/or divert to storage to limit export to the grid .... example  ... https://www.sma-uk.com/solar-systems/export-limitation.html ... 

HTH - Z

Hi Z. If I recall correctly the inverters de-rate by 'simply' moving away from the maximum power point, effectively choosing a less than ideal voltage(?) on the DC side, is that right? So as you say, the inverter doesn't 'see' the extra load, nor the extra heat, it just converts less DC into less AC as per the settings.