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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentTimeJun 16th 2015
    Not going to be too much of a problem down in Cornwall. Probably get 10% more generation compared to most places.
    Your North Coast as well, so generally less misty (though that does depend on altitude too).
    The rain will keep then clean too :wink:

    Thing to remember is that there really is very little difference in modules.
    Many are rebranded (you can search that on google).

    Inverters are what they are, generally you only have a choice of 3.

    Then there are EnPhace (micro-inverters), but as you are building new, you should be designing shadows out.

    Stecca is a good make, but again, you should not need to use one on a new build (they work better at lower voltage).

    Trick is with PV is to not be sucked in my fancy sounding technology. PV is really simple, proven and tested.
    • CommentAuthorEd Davies
    • CommentTimeJun 16th 2015
    Posted By: joe90Rather than the ethical issues raised above, some (me) may also be concerned with the pay back period for a typical PV installation.
    100p/W. Generates for, effectively, 800 hours a year so 0.8 kWh/year. 15p/kWh so 12p/year if you can set up to use it all. Be nice to know of anything else which pays 12% interest. Payback in 8 years and four months. If we assume a 25 year lifespan it then pays back another two times after that.

    Or it breaks even against E7 rates or gas “just” giving security of supply, protection against inflation (and a warm feeling that you're not effing things up for future peoples in far off countries - but we're ignoring ethical issues.)
    • CommentAuthorGarethC
    • CommentTimeJun 17th 2015 edited
    12% is great but, as I think ST's mentioned in the past, you need a whacking great "illiquidity premium" relative to savings and investment products to compensate for the inability to get your capital back quickly if you need it (and the hassle vs. buying an ISA).

    Being dull, I'm fascinated by what that needs to be to drive - mass- uptake. I think 10-12% is probably a minimum, less for those that value the issues you mention, but potentially up to 20% (five year payback) for those that don't.
    • CommentAuthorEd Davies
    • CommentTimeJun 17th 2015
    Yes, for an individual tying up the money makes the argument less compelling. However, for a society as a whole it means it's worthwhile to push people in that direction (e.g., FITs which make it worthwhile for people who won't be able to make direct use of a substantial proportion of the generation themselves). Also, it's about the only index-linked pension most of us can buy. Society gives people financial encouragement to save (tax breaks, such as the ISAs you mention) and PV can be thought of in the same way.
    • CommentTimeJun 17th 2015
    If your system costs you £5,000 and it takes 8 years to get your money back, that is when you have to start counting it as an 'investment', until then it is a cost.

    Do people consider other things, like new cooker, or a shower, as an investment?
    Which brings me neatly onto a second point.
    If you think that PV supplied energy is 'free' or paid for, you may end up using more.
    There has been some research about the short term drop in energy usage, but it soon rises again.

    The biggest driver to get more RE onto/into homes is traditional supply price.
    If energy was priced at the same level as PV, we would need to pay about 20p/kWh (assuming 5% interest and 14p/kWh and no fuel price rises).
    Which is really not that high, most people count afford this (they would soon cut usage).

    At 20p/kWh I would pay about £800/year, or about a 60% rise (not so far from government prediction over the next 20 years).

    So it looks like I should wait about 10 years before I install.
    This does assume that you use all your generation. If you only use half of it, then it is still too expensive.

    The other things is that we have become accustomed to low saving rates, but this cannot last forever.

    One problem with PV installation costs is that it is not linear, it costs about the same to install 3 kWp as it does 4 kWp.
    You save on 3 or 4 modules and a bit of rail, a tiny bit on the inverter, but the rest is the same.
    There is an advantage of fitting it on a new build, you can roof integrate, saving on tiles, design in the location of the inverter, run cabling easier, you probably have scaffolding already there and if you can convince an installer that you only want an install (off your drawings), then you should save on the salesman's commission (they used to get about £800/sale when I was involved).
    • CommentTimeJun 17th 2015
    My situation is that I am doing a new build and planned PV for the garage roof, we will have no gas and also plan an ASHP. I see the grid connection as a bit like a battery (without the high cost) so I can dump excess to the grid but take it back when I need it. Ordinarily there will be only two of us but family visiting on weekends etc. with the fit payment and a sunny boy I just wonder if it is worth the outlay and work as we will probably only stay there for ten years? On the other hand I could buy that Harley I fancy :bigsmile:
    • CommentTimeJun 17th 2015
    Just a matter of doing the sums.

    Compare the overall cost of installing PV against the cheapest E7 you can get away with.

    The occasional visitor is not really a worry, just turn the immersion on. Get them to pay for at least one decent meal per visit.

    a kWh of electric is about 14p/kWh, a MacDonald's is about £2.40/kWh.
    Even lentils are a £1/kWh, but you don't want to eat 2 kg of them a day.
    • CommentTimeJun 17th 2015
    Posted By: SteamyTeaThen there are EnPhace (micro-inverters), but as you are building new, you should be designing shadows out.

    So you're advocating cutting down trees? How do you suggest rerouting clouds so they don't pass overhead? Admittedly I doubt the behaviour under clouds makes much difference, but I'm certainly happy to pay the fairly small premium for the response to tree shadows and for the 25 year warranty.
    • CommentTimeJun 17th 2015
    No harm is cutting down trees and sequestering the CO2.

    I was being specific to Joe90's new build. Not sure there are any trees on North Cornish Coast.
    The only ones of note I know of are Tehidy woods, totally man made.
    • CommentTimeJun 17th 2015
    Posted By: SteamyTeaNo harm is cutting down trees and sequestering the CO2.
    Assuming N Cornish coast was once wall to wall Sesile Oak, like the rest of Britain, but totally stripped by man, it's a bit time-lapse to call Tehidy woods man-made as if that confers the right to create/destroy at will.
    • CommentTimeJun 17th 2015
    I have no trees involved but a tall beech hedge to the west and that is to be trimmed down anyway.
    • CommentAuthorringi
    • CommentTimeJun 17th 2015
    There is also the issue that mortgage lenders will not lend you more due to having PV. PV can also make it harder to do a loft conversion so may reduce resale value on some properties.
    • CommentTimeAug 28th 2015
    With the recent announcement of fit being reduced big time I thought I would resurrect this thread, not sure it will be worth it for my build now. ( still fancy buying that Harley instead).
    • CommentTimeAug 28th 2015 edited
    On a new build it probably is (can reduce the roofing costs sometimes).
    Existing buildings is a bit harder to call.
    Couple of 'off gas' pensioners may benefit, as may people that heat water with E7.
    The people that will probably not benefit are the 'young aspirational' that work hard and play hard and intend to make a fortune by moving every couple or three years.

    The really hard things to predict are the future price of energy. We do know that nuclear is going to be about £100/MWh (and rise with inflation), Wind is between £120 and £150 (not linked to inflation I think), coal, which is dirt cheap is being phased out or will be taxed more.
    Gas will always be volatile, as will oil (not that much electricity is made that way).
    If we say that the last two years are just a market correction, after the previous 2 or 4 years being higher than normal, then expect electrical generation from gas to be about £60/MWh.
    Fracking will only limit the volatility, it will not reduce the price in the UK in my opinion.

    The big difference is going to be political, they could tax fossil fuels highly, but doubt this government will.
    They could also put a general tax on energy, regardless of how it is generated (I think this is likely).

    I think as a general rule, domestic energy expenditure will account for about 5% of median household income. It has been around this point for a couple of decades now, I can't see anything on the horizon to change this (no new 'wonder' technologies or 'economic' systems).

    But take my last quarter bill, I used 6 kWh/day at a gnats under 13p/kWh. Not bad value really.
    • CommentAuthorringi
    • CommentTimeAug 28th 2015
    What we don't know is how much the cost of PV will come down once the FIT reductions kick in......

    It is a shame that we still don't have any mass market roof integrated PV to save roofing costs.
    • CommentTimeAug 29th 2015
    I don't think the price will drop. Getting rid of FITs does not mean that a free for all installation will be allowed.
    We can't have any old DIYer connecting whatever they like to the grid or nailing modules to a roof.
    MCS was more than just approving the hardware.
    Even though CFSH has gone Councils largely still seem to be setting energy targets for new builds, and to reach this target some form of renewables might still be needed. Won't keep the PV industry going, but you might well find it still gets installed without FIT
    Posted By: SteamyTeaI think as a general rule, domestic energy expenditure will account for about 5% of median household income. It has been around this point for a couple of decades now, I can't see anything on the horizon to change this (no new 'wonder' technologies or 'economic' systems).

    At 5% of income there will be no incentive or driver to change any thing.
    • CommentTimeAug 29th 2015
    Posted By: richardelliotEven though CFSH has gone Councils largely still seem to be setting energy targets for new builds, and to reach this target some form of renewables might still be needed.

    I haven't really followed CfSH stuff, but I thought recent changes meant councils could not impose additional standards/burdens (i.e. Merton rule is dead)? Where have renewables been required as a condition of building (in the domestic arena, not commercial)?
    @DJH I'm honestly no expert, just someone living through it, but my understanding is that Councils can't impose any conditions contrary to the national plans (in line with you comment). However, I get the impression that they can still require a 19% energy usage improvement over 2013 Part L and a water usage target. This doesn't mean you need a renewable depending on you other detailing / volume of glazing but it might well do.
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