Free solar panel discussion

HanSpan

This seems to be the most important question if you are considering one of the free systems (far less important if you are going for purchasing yourself). I've read all 50 pages and it took a while but I think I now understand how it works and just can't see how its ever likely to get anywhere close to 50% use. I'd got all excited about the idea of applying but am now thinking not so much!

Someone please tell me if I have this wrong but as I understand it, because you can't store the power, whether its going out or coming in is on an instant by instant basis. So to me it seems there might be lots of time where you are using a part to all of what you are generating, but far more time when you are having to draw all or some back from the grid.
(I'm using made up numbers and 'thingies' rather than kw... so as not to fall foul of using the wrong type of units or the potential output of various systems)

Its 12:00 on a sunny day:
generating 4 thingies & using 1 thingy doing nothing much = 3 thingies back to the grid (using 25% generated, feeding back 75%)

12:02 turn on the kettle
generating 4 thingies & using 6 thingies = 2 thingies FROM to the grid (using 100% generated plus taking 50% more from the grid)

17:00
generating 2 thingies & using 1 thingy doing nothing much = 1 thingy back to the grid (using 50% generated, feeding back 50%)


17:02 turn on the kettle
generating 2 thingies & using 6 thingies = 4 thingies FROM the grid (using 100% generated plus taking 400% more from the grid)

22:00 (kettle on or off!)
generating 0 thingies & using 1-6 thingies = 1-6 thingies FROM to the grid (taking 100% from the grid)


To do the maths for every second of all 365 days of the year and all the things you can switch on and off is not something I fancy trying but my gut feeling is you'd be lucky to use 25% of what you generate, probably much less. So you are still going to have to pay at least 75% of your normal electricity bill even if you generated exactly as much over a year as you use (not likely?).

I'd be really interested to know, from anyone who has a system installed and does NOT have a backward running meter (which changes all this but can't be relied on so I'm not factoring in) how much power they took per month before, and how much they take now.

footnote - allthough the thingies are made up I think I have the factors about right - I have en eco-eye attached to my meter and its goes from showing about £1.50hr at 'resting' to about £10 with the kettle on (1:6ish), and from earlier posts it sounds like a kettle on uses about 1.5 times as much as you'd generate at noon on a sunny day (4:6).

Gizmosmum_2

Hi HanSan

Congratulations on reading all 50 pages - you may need a lie down now!

As far as using 50% of electricity generated is concerned, obviously those who are at home through the day will be able to manage it better but to achieve the 50% saving even they will need to work hard at it. It requires huge behavioural changes and they will need to be sustained. Some will be able to manage that - and over the years it may become as normal as using electric through the night is/was with economy 7 but I suspect it will take a while.

Washing machine, dishwasher, showering, cooking main meal if cooking with electric - all through the day.

grahamc2003

Gizmosmum wrote: »

Hi HanSan

It requires huge behavioural changes and they will need to be sustained. Some will be able to manage that - and over the years it may become as normal as using electric through the night is/was with economy 7 but I suspect it will take a while.

Washing machine, dishwasher, showering, cooking main meal if cooking with electric - all through the day.

But that, on a UK scale, is counterproductive. Economy 7 shifts demand from high cost periods (and that means higher emission periods too) to lower cost periods when demand is very low and when you have the cheapest generation with pretty much zero emissions (i.e. mainly Nuclear).

If the bavioural change is to shift demand to midday, then it depends where that demand is shifted from. Great if from periods of high demand, such as 6pm in winter, when the most inefficient stations are scheduled, not so great if shifted from nightitme use. The point has already been made that turning on a kettle (or dishwasher or washing machine) will require taking much of the power from the grid, even on a very sunny day at midday. Perhaps only on the sunniest midsummer's day, and only around midday, would a large system fully supply the power for a kettle. Something like a dishwasher, washing machine or cooking (where the power varies greatly thoughout the cycle, alternateing between something lik 0kW to 4Kw) would have, on a minute by minute basis, all the solar output, plus grid power one minute, then a small percentage of solar power used, the rest exported, the next minute (i.e. it isn't easy using all the power the solar cells generate).

In terms of the what's best for the grid (i.e. the UK consumer), any shifting of large power use from nightime to midday would be very detrimental, even with solar panels, imv

Gizmosmum_2

grahamc2003 wrote: »

But that, on a UK scale, is counterproductive. Economy 7 shifts demand from high cost periods (and that means higher emission periods too) to lower cost periods when demand is very low and when you have the cheapest generation with pretty much zero emissions (i.e. mainly Nuclear).

If the bavioural change is to shift demand to midday, then it depends where that demand is shifted from. Great if from periods of high demand, such as 6pm in winter, when the most inefficient stations are scheduled, not so great if shifted from nightitme use. The point has already been made that turning on a kettle (or dishwasher or washing machine) will require taking much of the power from the grid, even on a very sunny day at midday. Perhaps only on the sunniest midsummer's day, and only around midday, would a large system fully supply the power for a kettle. Something like a dishwasher, washing machine or cooking (where the power varies greatly thoughout the cycle, alternateing between something lik 0kW to 4Kw) would have, on a minute by minute basis, all the solar output, plus grid power one minute, then a small percentage of solar power used, the rest exported, the next minute (i.e. it isn't easy using all the power the solar cells generate).

In terms of the what's best for the grid (i.e. the UK consumer), any shifting of large power use from nightime to midday would be very detrimental, even with solar panels, imv

Sorry should have expanded - obviously not everyone is going to be taking advantage of solar pv, the numbers will remain relatively low and of those who do a lot won't be using energy during the day.

I wasn't suggesting that we all change from nightime electric to daytime, that obviously wouldn't make sense in relation to supply and demand. The question (I think) was whether it was possible to use 50% of what was generated and my view was that it was possible but whether it would happen or not would depend on whether people were prepared to make major behavioural changes. The Economy 7 probably wasn't the best analogy to use - maybe a better one would be the change to healthier eating?????

Cardew

HanSpan.

The big factor that you haven't considered is the size of your system - and hence output.

Taking silly examples, firstly that you had one 125Wp panel(generates a max of about one eight of a thingy!!) on your roof(I know you don't get FIT for that size) you would have no difficulty in using 100% of the generated power. Put a 20kWp system on your roof(20 thingys!) and you will be lucky to use 10%.

This has been discussed in the green forum and there are a couple of people posting (yakky58 and mcfi5) who have had systems for a couple of years and have export meters so know exactly how much they generate in the house i.e. they know what the panels produce and what they export, so consumption in house is known.

Mcfi5, who is a solar enthusiast, has a small system. He has a wife and small children who are home all day and 'works' at using as much electricity from the panels as possible. He uses approx 500kWh per year in the house - so a saving of £40 to £50 a year. He is of the opinion that if he had a 4kWp system(the largest for max FIT) he wouldn't be able to use much more than 500kWh a year.

The regulations allow an assumption of 50% of generated electricity to be claimed as exported if you don't have a export meter - which seems about right for small systems from the evidence I have seen on line.

Elainemary

geoff2 wrote: »

Elaine, help us out a bit and reveal what said publications had to say about the subject. Then we can comment.

Sorry Geoff2 but I've recycled the paper already. Maybe you can look it up in the Daily Mirror's morgue (?). I've never had a response before to anythingI've said, so forgive my surprise and I'll cut things out ni future and keep them for a week or two in case anyone wants a full quote. Once again - sorry I can't help. I remember there was a quote from the Homesun MD but that's about it.

Elainemary

geoff2 wrote: »

Best of luck, I hope you do too - but having read the Which? opinion above, I remain a proud naysayer. :cool:

only just found this reply. guess you've found the Which? comments already

Pincher

grahamc2003 wrote: »

But that, on a UK scale, is counterproductive. Economy 7 shifts demand from high cost periods (and that means higher emission periods too) to lower cost periods when demand is very low and when you have the cheapest generation with pretty much zero emissions (i.e. mainly Nuclear).

If it costs 2p in fossil fuel to generate 1kWh of electricity at noon, it still costs 2p at 3am.

Behaviour change is easy. Make ALL tariffs Economy 7!
Charge 7p off-peak and 10p peak, instead of 5/13p.
I am assuming 7p is break even, so the supplier doesn't lose money at night, so there is no need to bump up the price during the day.

The majority of people will fit timers to their washing machines etc.

Storage heaters will still save money, but day time boost will cause less heartache.

From 2011, when we start charging electric cars, it will be a heart ache whether to go for Economy 7 or not for those without storage heaters. With Universal Economy 7, you get the benefit of cheaper charge without being penalised during the day.

Who knows, people might use the 7p tariff so much, that night time suddenly becomes the peak time. To alter behaviour, you adjust the two rates, until you balance out the demand to a healthy level.

As micro-generation become more popular, you re-adjust the two rates to accomodate, always with reducing peak load in mind.

People may not like to pay more for peak train tickets, but everybody accept the logic.

John_Pierpoint

I think the big discussion in 5 years time will be "who controls the intelligent grid".
Can we trust the grid supplied & controlled software to make this decision "Oh its a sunny morning in mid summer, BUT the weather is suddenly changing and thunder storms area expected for two hours in many areas this afternoon. Now shall we schedule another power station to fire up this afternoon or shall we turn on everyone's freezer this morning and turn them off this afternoon; thus delaying the use of the extra power station until (say) 16:00.

There is a thread on here somewhere all about getting experimental refrigeration for free so, in exchange for allowing the technicians to remotely monitor how it is used by a cross section of the market.

Pincher

John_Pierpoint wrote: »

There is a thread on here somewhere all about getting experimental refrigeration for free so, in exchange for allowing the technicians to remotely monitor how it is used by a cross section of the market.

If you put the weekly shop into the fridge and freezer, you need instant recovery, not wait two hours for the grid. Breaking the cold chain has food poisoning implications. I use an Igloo box when I buy chilled and frozen food, because I hate melted ice cream.

I am not keen on finding mouldy clothes in the tumble dryer because the grid decides I have lower priority.