Free solar panel discussion

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  • Cardew
    Cardew Posts: 29,036
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    The monitor will for the most part be measuring high current. A small margin of error is acceptable for the intended purpose. What level of accuraccy do you require?

    Most people will not have an export meter, however, many people will have an energy monitor. Its a far better solution to find out how much of the generated leccy you have used based on real measured figures rather than guesswork.

    Your energy monitor is effectively being used as an 'export meter' for the purpose of this exercise - which is to calculate how much of the generated electricity is being consumed in the house.
  • Nang
    Nang Posts: 109 Forumite
    I think what Nang is saying is that the amount of solar energy used isn't necessarily the saving. For example, say he puts the dishwasher on at lunchtime when half full, just to use the solar power, then, although say 3kwh may be used, the saving over what would otherwise be the case without PV is only half that (1.5kwh), because the dishwasher would otherwise be run only when full.

    Jon - do you mean a quite sophisticated energy monitor? I ask because my Owl would be pretty useless for monitoring PV usage - mind you, mine can't be connected to a PC. Are you assuming a pc connected energy monitor for real-time (and constant) monitoring of pv output and load?

    Yep you got it Changing of habits means you don't have a baseline even with your export meter. So you can't really understand your saving cos you didn't capture a snapshot when you didn't have the free electric, (or electric for 3p if you have an export meter).

    Now I have a few folk who email me with ideas, because people want to consider how to get the most out of their investment.

    Some people have sussed that they will only get 3p for there elect if they export or that there power companies will assume they will only use 1/2 of what they make(this is what they do with the ones of us that dont have the export meters). But if they use it they can save 9p (or more in the latter) so obviously they are changing their habits.

    Stick your immersion heater on if its sunny and don't use your gas, that's where it gets so much more complicated. Cos then you have to work out how much gas you saved too by having the solar panels.

    Sense of irony here cos it's usually Cardew who is putting me straight for thinking a bit to simplistically.

    My point is :-

    Get me a baseline. How much did you use last year. How much did you pay for this year with your panels, how much did you pay for last year without them. I want to know.

    I know you will challenge me on this one Cardy I will be disappointed if you don't.

    Andy..
    Follow the progress of 7 domestic arrays at :- http://www.uksolarcasestudy.co.uk/
  • I think what Nang is saying is that the amount of solar energy used isn't necessarily the saving. For example, say he puts the dishwasher on at lunchtime when half full, just to use the solar power, then, although say 3kwh may be used, the saving over what would otherwise be the case without PV is only half that (1.5kwh), because the dishwasher would otherwise be run only when full.

    Jon - do you mean a quite sophisticated energy monitor? I ask because my Owl would be pretty useless for monitoring PV usage - mind you, mine can't be connected to a PC. Are you assuming a pc connected energy monitor for real-time (and constant) monitoring of pv output and load?

    Ah, ok, I see the point now - and agree.

    For the record we never put half loads in the washing machine or dishwasher and dont run appliances for the sake of it just because its free leccy - however I can see that some people may be tempted to do this.

    Energy monitors such as the Owl measure the current, the direction of that current doesn't make any difference. So this means that the Owl is in fact measuring both import and export. Your leccy meter reads the import and your generation meter reads the generated leccy.

    So to calculate the solar generated leccy used:

    Generation kWh - (kWh from Owl - kWh from leccy meter)
  • Cardew
    Cardew Posts: 29,036
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    Nang wrote: »
    Stick your immersion heater on if its sunny and don't use your gas, that's where it gets so much more complicated. Cos then you have to work out how much gas you saved too by having the solar panels.

    Sense of irony here cos it's usually Cardew who is putting me straight for thinking a bit to simplistically.

    Talking about simplistic calculations!

    Let us assume that on a wonderfully sunny summers day, when your 4kWp system is blasting out over 3kW, you switch on your immersion heater for 2 hours around noon and use, say, 6kWh.

    You now calculate, if I understand your reasoning, you have used(saved) 6kWh @ 12p = 72p and you have also 'saved gas too' a further 6kWh at, say 3p/kWh = 18p. So according to your logic you have saved a total of 72p + 18p = 90p

    Now my logic would say you have saved just 18p. (i.e. the cost of heating the water with gas)

    'Having one's cake and eating it too' comes to mind;)

    Don't forget also that if you only getting 2kW from a system(95% of the time even for a large system) and you put on the immersion heater, then you are losing money. You will be drawing 1kW from the mains, so for that 6kWh consumption you will be paying 24p(1kW for 2 hours) in electricity costs instead of the 18p gas would have cost.

    As explained above by zeupater it is impossible to establish a baseline of electrical consumption in a house and assume that it would be replicated year on year.
  • grahamc2003
    grahamc2003 Posts: 1,771 Forumite
    edited 20 November 2010 at 9:57AM
    Cardew wrote: »
    Talking about simplistic calculations!

    Let us assume that on a wonderfully sunny summers day, when your 4kWp system is blasting out over 3kW, you switch on your immersion heater for 2 hours around noon and use, say, 6kWh.

    You now calculate, if I understand your reasoning, you have used(saved) 6kWh @ 12p = 72p and you have also 'saved gas too' a further 6kWh at, say 3p/kWh = 18p. So according to your logic you have saved a total of 72p + 18p = 90p

    Now my logic would say you have saved just 18p. (i.e. the cost of heating the water with gas)

    'Having one's cake and eating it too' comes to mind;)

    Don't forget also that if you only getting 2kW from a system(95% of the time even for a large system) and you put on the immersion heater, then you are losing money. You will be drawing 1kW from the mains, so for that 6kWh consumption you will be paying 24p(1kW for 2 hours) in electricity costs instead of the 18p gas would have cost.

    As explained above by zeupater it is impossible to establish a baseline of electrical consumption in a house and assume that it would be replicated year on year.

    I think, due to badly wording on Nang's part, you are misunderstanding him. I think his central poiint agrees exactly with you, that the saving would be 18p, and not 90p. I think he's correclty making the point that by using 6kwh of pv electricity, the true saving is 18p (and not 60p) (just as both you and I say).

    In most of these threads, you get people saing 'i used 1000kwh of free electricity last year, saving me £100' I think all three of us agree 1000kwh used doesn't result in a £100 saving in almost all cases.

    I tried, and failed, to explain this effect a couple of weeks ago, using economy 7 as the example. i.e, if you use pv electriocity instead of using what would otherwise be e7 electricity, the saving is the e7 price, not the day price. I also further tried to say that shifting from e7 could result in higher bills, not lower! This is possible/probably because, if you put a washing machine on at lunchtime to use the pv, then if you are generating 1kw, the wash cycle will sometimes use 4kw, and you'll be paying full price for 3kw (i.e. the savings in this case would or could be negative).

    I think where Nang is going badly wrong is trying to compare bills from last year with this year to estimate the savings due to PV. There are just so many other variables that such a comparison, as you state, is nonsense.

    (For simplicity, I'm using a price of 10p/kwh for electricity).
  • Cardew
    Cardew Posts: 29,036
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    I think, due to badly wording on Nang's part, you are misunderstanding him. I think his central poiint agrees exactly with you, that the saving would be 18p, and not 90p.

    Mmmm

    Even allowing for his wording, I can't agree that this quote means what you are assuming!
    Some people have sussed that they will only get 3p for there elect if they export or that there power companies will assume they will only use 1/2 of what they make(this is what they do with the ones of us that dont have the export meters). But if they use it they can save 9p (or more in the latter) so obviously they are changing their habits.

    Stick your immersion heater on if its sunny and don't use your gas, that's where it gets so much more complicated. Cos then you have to work out how much gas you saved too by having the solar panels.

    The whole point of that quote was that people are going to save 9p for each kWh utilised in the house(instead of 3p) and then savings on gas 'too'.

    Indeed people will save 9p for each kWh used for consumption that would be otherwise drawn from the mains. e.g.if a fridge/freezer draws 0.15kW and might use say 0.5kWh during daylight hours. It is reasonable to think that, on many days in the year, that will be a straight saving. However some days even that consumption won't be covered.(someone just reported that his system generated 8kWh one day and 0.1kWh the next day.)
  • <<<Cos then you have to work out how much gas you saved too by having the solar panels.>>>

    I think you are reading that as 'you have to add on the gas savings to the electricity savings'

    whereas I read it as

    'to do the savings calculation, as well as knowing the electricty variables, you also have to know the gas variables too, (.... and furthermore, the total savings are just the gas savings in the case mentioned).

    (But then again, communication on the internet is incredibly difficult!)
  • I see the savings as simply being the cost of the displaced energy.

    So if displacing gas for hot water heating the savings are only around 3p per kWh.

    If displacing expensive daytime E7 leccy then maybe around 15p per kWh

    If displacing nighttime E7 then around 8p per kWh

    As Graham points out, the big thing to watch out for is to not end up using extra imported (expensive) leccy, especially if on E7.
  • GeeBeeEl wrote: »
    Sorry but you are misinformed Poosmate. It is a Government backed guaranteed 25yr incentive driven by our commitments to meet EU Co² emissions reduction of 26% by 2020 ( from the 1990 level ) , and an 80% reduction in all greenhouse gas emissions by 2050



    Its an incentive to meet EU commitments.
    Why would an energy company pay you 41.3p per kWh for energy you generate and use yourself ?
    It's not really about selling back to the national grid.
    You get paid whether you sell it back to the grid or use it yourself.




    Nope, I'm afraid it's paid for by the taxpayers.

    Have a read of this for clarification.
    h t t p : // w w w .
    guardian.co.uk/money/2010/feb/06/solar-power-bright-investment

    From the article.
    "If the government offered to pay you £1,000 a year for the next 25 years, in return for an up-front investment of £12,500, you'd snap it up in a second. Well, that's pretty much the deal on offer this week after the government finally revealed what it will pay those who install electricity generating solar panels – in and around their homes – through the new "Feed-in Tariffs" (FITs)."

    However! The interest on your £12,500 layout at an average of 4% is £500 per year. Over 25 years that's £12,500 you have to factor into your calculations.

    Essgeebee
  • It's late and my brain just isn't working! A few years ago I installed an ashp and changed my tariff to Economy 10. The ashp lasted 2 months and was then replaced with an oil boiler because the ashp was too small and hadn't been sized correctly.

    I kept the Economy 10 which gives me cheap electric between 12.30 and 2.30pm, 8pm - 10pm and 12 Midnight - 4am. I'm now trying to work out the implications of moving from E10 to a normal tariff.

    I've got pretty good at using the E10 times and even though I haven't storage heaters 60% of what I use is on cheap rate. BUT I'd be lying if I didn't confess to being a bit peeved at not saving 12p for using my peak electricity generation from my panels. I pay 4p for cheap rate and 14p for normal rate.

    Any thoughts????
    Target of wind & watertight by Sept 2011 :D
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