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    nephilim's Avatar
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    Going Green

    My mrs and I have agreed that when we buy our next house (current one is too small, looking for a new house for the new arrival on Friday/Saturday), we want to get Solar Panels.

    Now to buy outright they will set us back £10000 for 8x 1kWh solar panels which should in theory generate 3500kWh per year (based on current shading of our house, angle of the roof etc). We also currently use solar for heating our water, and all in, I have worked out it will cover 85% of our total usage, so looking at the other 15%. Could this be made up with a Wind Turbine?

    I am also looking at other "green" aspects of living, such as water recycling for our plants, along with adding to my composting etc.

    Now my question is, has anyone gone down the solar/green energy route and managed to get off the grid completely?

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    Pottsey's Avatar
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    That seems like and odd system as most people don’t go above 4 kWh for home use as the amount of you get paid to produce electricity drops for systems above 4 kWh. What will your payback time be? Surly that system well take well over 10 years to pay its self-back.

    Just a few weeks back I had a 4kWh system installed and have all the data of energy produced recorded to SD card. I get about 1kWh in a cloudy rainy day, 2 to 3 on an average day and 3.8+ on sunny days. My panels are not directly south and power everything in the house.

    If you haven’t already LED bulbs goes well with solar panels. Wind Turbines have a long list of problem, from location has to be right, only works in wind, moving parts means break downs which take away from pay back time. Over turbines it might be better to buy an energy storage device of some sort for excess solar energy.


    EDIT: Your price looks good for a 8kWh system.
    Last edited by Pottsey; 25th June 2014 at 01:51 PM.

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    nephilim (25th June 2014)

  4. #3

    nephilim's Avatar
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    Will answer after lunch (hurray for meetings!)

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    Domestic wind turbines are unlikely to make financial sense over solar PV. Houses themselves cause a lot of turbulence and generally rob the wind of energy. You would be better adding PV capacity. Going off grid entirely is difficult because you then need local storage and you don't then get the feed in tariff. Top tip if you are moving, make the energy efficiency of the property itself the top priority. It's easy to be green if your house doesn't lose energy like a sieve. Ideally you seal the house and look at a heat exchange system on the air feed (you recover heat on stale air going out and heat the incoming air (or in summer you might do the reverse)).

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    nephilim (25th June 2014)

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    nephilim's Avatar
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    Quote Originally Posted by Pottsey View Post
    That seems like and odd system as most people donít go above 4 kWh for home use as the amount of you get paid to produce electricity drops for systems above 4 kWh. What will your payback time be? Surly that system well take well over 10 years to pay its self-back.

    Just a few weeks back I had a 4kWh system installed and have all the data of energy produced recorded to SD card. I get about 1kWh in a cloudy rainy day, 2 to 3 on an average day and 3.8+ on sunny days. My panels are not directly south and power everything in the house.

    If you havenít already LED bulbs goes well with solar panels. Wind Turbines have a long list of problem, from location has to be right, only works in wind, moving parts means break downs which take away from pay back time. Over turbines it might be better to buy an energy storage device of some sort for excess solar energy.


    EDIT: Your price looks good for a 8kWh system.
    OK, on the house we are looking at, 8kWh was suggested because of the angle of the roof, the potential shade from trees in 10-20 years time etc. We use LED bulbs where possible and I think our total light wattage is around 9w for the whole house. We also have A+ or A++ appliances everywhere (with the exception of the washing machine which is B and tumble dryer which is also a B). Our usage over the whole day is something around 4kWh all told, unless I am doing a day on the PC where it will go up to around 7kWh.

    The price includes installation and is done by a local company who get government funding to cover a large part of the cost.

    Quote Originally Posted by pcstru View Post
    Domestic wind turbines are unlikely to make financial sense over solar PV. Houses themselves cause a lot of turbulence and generally rob the wind of energy. You would be better adding PV capacity. Going off grid entirely is difficult because you then need local storage and you don't then get the feed in tariff. Top tip if you are moving, make the energy efficiency of the property itself the top priority. It's easy to be green if your house doesn't lose energy like a sieve. Ideally you seal the house and look at a heat exchange system on the air feed (you recover heat on stale air going out and heat the incoming air (or in summer you might do the reverse)).
    Local storage isn't an issue in terms of the power. I have a current set up of a 500Wh panel, and a battery set up which has a 200ah (2400kWh) battery. I would expand this to 5 batteries to be on the safe side so they can store up the juice without an issue. Each battery (again from the local supplier) is able to be put into an array so they can be charged simultaneously and used simultaniously. As for energy efficiency, the house we are looking at has been surveyed, and it has been insulated everywhere possible (cavities, attic etc), and has triple glazed windows.

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    Pottsey's Avatar
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    Quote Originally Posted by nephilim View Post
    Local storage isn't an issue in terms of the power. I have a current set up of a 500Wh panel, and a battery set up which has a 200ah (2400kWh) battery. I would expand this to 5 batteries to be on the safe side so they can store up the juice without an issue. Each battery (again from the local supplier) is able to be put into an array so they can be charged simultaneously and used simultaniously. As for energy efficiency, the house we are looking at has been surveyed, and it has been insulated everywhere possible (cavities, attic etc), and has triple glazed windows.
    The problem with local storage is you do not get a feed in tariff if you have local storage and it’s the feed in tariff that makes solar panels finically viable. Without the feed in tariff it can take as long as 20 years for the system to pay its install cost back sometimes longer or never.

    Something feels off about the information you have given us. I don’t mean you are wrong just something doesn’t seem right. Have you had 2 or 3 company’s give you quotes? An 8kWh system seem overkill for home use. How long did they say the payback time would be?

    An average home needs 9 to 10 units a day. A 4 kWh system produces 20 to 30 units on average a day more on a sunny day. I assume a good 8 kWh system would produce 40 to 80 units a day.
    Is your goal to be as independent from the grid as possible or to save as much money as possible?

    No idea on the colour of your roof but I found black panels look better and blend in better on my roof. Most installers don’t mention black panels. But it might be worth asking as the price shouldn't be much more.

    How much energy are they saying it will produce? How many years before payback?

    EDIT: Without the feed in tariff I work it out as almost 17 years for the £10k system to pay its self back if your Electricity bill is at £50 a month. If your bill is less then much longer.

    EDIT: Another tip I picked up while looking into panels. Look at Google Earth historic photos to see if any shade will hit the house. Assuming its not too new a house.
    Last edited by Pottsey; 25th June 2014 at 04:11 PM.

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    Quote Originally Posted by nephilim View Post
    Local storage isn't an issue in terms of the power. I have a current set up of a 500Wh panel, and a battery set up which has a 200ah (2400kWh) battery. I would expand this to 5 batteries to be on the safe side so they can store up the juice without an issue.
    I'm not sure why you would bother with batteries. The grid is effectively your battery and is much more cost efficient, plus you get the feed in tariff.

  10. #8

    nephilim's Avatar
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    I had 3 companies (all reasonably local, within 25 miles at least) give me a quote. Most expensive was £15.5k for 8kWh, cheapest was £10k for 8kWh, all companies saying they will get a government payback for each set of 2kWh panels they install. Obviously the more they install, the better for them, but also, in the long term, for us due to the conditions I will explain later.

    We have the plan to have local storage, so that we will be off the grid (or using so little grid juice its negligable). However where we are planning to live there are conifers growing which will eventually be so high that it will shade the roof, hence the need for a bigger system early on to compensate for when it does happen. All 3 companies, I have checked companies house, so I know they don't have the same directors etc, which is certainly helpful.

    The overall goal is to be completely independent from the grid, and with my current set up, I can run my house for about 6 hours (longer if various items were not in use) if there is a black out, however I want to be at the point where blackouts don't matter, I can have juice all the time. But also, the solar panels will be used for water heating as well (which is an added cost on top, I forget how much overall), but that would be good for us for the gas as well as it means we wont need to use gas for the boiler (and thus, negate the gas costs also). The colour of the roof is red, and I'll be honest, we haven't looked at the colour of the panels on the roof.

    Total energy it is expecting to produce in a year is around 6500kWh, and our current usage is around 4200kWh, however factoring in the water heating as well, this is likely to go up to around 5200-5600kWh a year. When it gets shaded from the conifers, it is expecting to drop to around 5500kWh a year.

    Total current electric costs are around £600 a year
    Total current gas costs are around £900 a year

    The savings from electric alone should be covered, and the reduced gas costs from using the panels as the water heater (which will do the radiators and hot water for bathing etc) should further reduce our expendature on grid supplies substantially. All 3 companies have explained that we will save money overall (should in theory not have to pay for the gas and electric once installed), and that it will have paid itself off in 10 years max.
    Last edited by nephilim; 25th June 2014 at 04:18 PM.

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    Pottsey's Avatar
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    Quote Originally Posted by nephilim View Post
    “All 3 companies have explained that we will save money overall (should in theory not have to pay for the gas and electric once installed), and that it will have paid itself off in 10 years max.”
    Unless I am missing something that sounds impossible. There is no way it can pay its self-back in 10 years if you are using local storage. Without the local storage it might just do it in around 10 years.

    I would also question the shade. It only takes the smallest amount of shade to make the panels useless. 10% shade is a massive drop in performance. If you are going to have shade problem in 10 years the panels will never become finically viable. If conifers will create shade I would expect you to drop a lot lower then 5200-5600kWh.

    What about the winter? All these numbers are averages. You tend to get much higher numbers then average in summer and much lower numbers in winter

    EDIT: I think your idea is sound if you remove the local storage and cut back the conifers in a few years time.

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    nephilim's Avatar
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    Will go back too them and ask. Right now its all in the preliminary stages as we need to agree on the house first (its in a development area). Also depends on the mortgage company as well agreeing to the extra for the solar panels.

    Can you explain why they wouldn't pay back if we pay NOTHING to the electrical companies and save the money from that? I know going for the feed in tariff will get us money for 20 odd years or so, but that doesn't really bother us too much.

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    I can see some merit in having some battery for the odd power-cut but to be able to go off grid is a lot of expensive battery capacity AND deprives you of the feed in, so I struggle to see the rationale.

    Have you considered DIY? There's some interesting info on Solar thermal around and plenty on building your own PV panels. I think you miss some subsidies but if you're not interested in feed in tariff, it might be worth some investigation. £10K would buy a lot of Wh!

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    nephilim (25th June 2014)

  15. #12
    Pottsey's Avatar
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    Quote Originally Posted by nephilim View Post
    Will go back too them and ask. Right now its all in the preliminary stages as we need to agree on the house first (its in a development area). Also depends on the mortgage company as well agreeing to the extra for the solar panels.

    Can you explain why they wouldn't pay back if we pay NOTHING to the electrical companies and save the money from that? I know going for the feed in tariff will get us money for 20 odd years or so, but that doesn't really bother us too much.
    You will not pay nothing to the electrical companies. You will overproduce in the summer but not gain much from that as you do not have the feed in tariff. In the winter you will under produce and need to pull from the grid. The reason the feed in tariff is good is you sell what you overproduce back. Then use part of that money to pay for what you cannot produce in the winter.

    This needs double checking as I do not have time to do precise math. But your system should with a feed in tariff provide you with £700 a year cash or around £17,000 over 20 years. Enough to pay for the installation and cover your bills not even counting the reduced gas and power bills benefits.

    Local storage only saves you at most £300 a year most likely much less and local storage being a major problem in the winter months. Please take these as very quick estimates not accurate. The way I see it, is use the panels to cut electric and gas bill in half or more. Then use the part of the £700 feed in tariff to pay water, gas and power bills. Then pocket the rest of the £700 and profit.
    Another way to look at it. Local storage at best reduces your £50 monthly bill to zero. No profit beyond zero bills. Feed in tariff reduces your £50 bill to zero or perhaps £10 so £120 bill per year but pays you £700. So £580 profit over local storage.

    As for not paying back. After x amount of years the inverter which isn’t cheap needs replacing. No idea on battery life span but I assume they need replacing. Add all that onto the installation costs and you have a large pool of cash that could pay your bills for 15 to 20 years. Shade is the problem if it drops your power produced down to 2kWh. The feed in tariff is what makes the system worth while. As it pays for the install costs and covers gas, water and power bills. Might even stretch to cover council tax.



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