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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    •  
      CommentAuthorjoe90
    • CommentTimeFeb 25th 2014
     
    I am planning a new build this year and would like PV (if only to help the SAP) as we have no mains gas. SWMBO and I dont want panels on the roof as we are designing a sweet looking cottage (hopefully). I could mount them on the workshop roof (due South) but the angle will be low. Alternatively I could mount them on the ground in the field we have next to the build. The advantage here is I could construct adjustable frames as the optimum angle for PV panels over the year changes from 16 to 64 degrees (from the vertical) this would allow me to optimise the lecky generated. I have found that the FIT payment is nearly half for "stand alone", would panels mounted in the field be classed as stand alone?

    Ta
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 25th 2014 edited
     
    The rules have changed a bit about stand alone, but as your installation is domestic it may be accepted.

    As for the 'optimal angle'. Beau has some panels at 15% (almost looking up) and some at his roof angle, he gets a better yield from the ones that are flat (cause Devon is always cloudy).
    There is maximum power and maximum yield. Max power is really just a case of tracking the sun, maximum yield is a case of getting as much daylight on them for as long as possible. Really is as simple as that.

    The main thing is to decide what you want to do with the energy you generate. For every kWh you don't import that is 18p saved.
    • CommentAuthorEd Davies
    • CommentTimeFeb 25th 2014
     
    The actual angles of the panels doesn't make that much difference over the year and moving the panels up and down doesn't add a huge amount. Steeper panels help quite a lot in winter which is important if you're off-grid but if you're on-grid then the extra production, though nice to have, will not make much difference in comparison with your summer generation.

    In other words, it's not worth spending a lot of time or money on making the panels adjustable and definitely not worth compromising the robustness of the installation for it.
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 25th 2014
     
    How many square meters can you get on the shed roof and, if you have not yet designed the shed, design it to maximise for PV.
    • CommentAuthorbillt
    • CommentTimeFeb 25th 2014
     
    Posted By: joe90II have found that the FIT payment is nearly half for "stand alone", would panels mounted in the field be classed as stand alone?


    No. Standalone means not connected to a building, and I assume that you are intending to use some of the energy generated

    Ed's right, it's not worth adjusting the panel angle. A two-axis tracker might add 30% to the output, but the extra expense could just as well be spent in extra fixed panels.
    •  
      CommentAuthorjoe90
    • CommentTimeFeb 25th 2014
     
    Thanks guys for this info. ST, the roof size of the workshop (subject to planning) I hope will be 44 sq mtrs, will I be limited on production as its a shared feed overhead in the middle of no-where?
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 25th 2014
     
    Probably not as the G83 generally allows connection. There may be an issue with the local transformer if whoever else shares it has an installation. You can always phone up Western Power, it wont prejudice your connection. They are pretty good down here.

    Just make sure your roof can get the modules on with the necessary 'border' around them. Better still, design them into the roof structure so they look better. I like the technology but think they look dreadful when retrofitted.
    • CommentAuthorwindy lamb
    • CommentTimeFeb 25th 2014
     
    I always thought Standalone meant that it was feeding direct to the grid with no on-site energy usage. So field/ground mounted is not necessarily standalone. Our neighbours have 50kW of panels in a field about 500m from the house but as it supplies the house and then grid, it is not classified as standalone. Needs Planning Permission though.
    • CommentAuthorEd Davies
    • CommentTimeFeb 25th 2014
     
    Posted By: joe90will I be limited on production as its a shared feed overhead in the middle of no-where?
    The standard connection allows you to draw up to 100 amps from the grid or put 16 amps in. If your connection won't support you feeding in 16 amps (i.e., the capacity is such the voltage goes over the upper limit of 230 V + 10% = 253 V) then the electricity company can ask you to disconnect your panels temporarily while they fix the local network but they have to do so at their expense. If you want to feed in more than 16 amps you have to get their prior permission and they'll charge you for any engineering changes needed to support it.

    16 amps at 230 V allows 3.68 kW so, in practice, that's the limit you have to work to.

    Something the DNO will bear in mind is that your neighbours might get PV, or whatever, in the future and they'll have to allow them to put in 16 amps each. So if there are three houses on a transformer which can take 50 amps (a shade over 16 A per house) and you're the first house, wanting to put in 6 kW (about the capacity of your 44 m² extension and 26 amps at 230 V), then you'll likely either get charged to upgrade the transformer despite it not being needed yet or refused permission to put in more than 16 amps.
    •  
      CommentAuthorjoe90
    • CommentTimeFeb 25th 2014
     
    Thanks Ed, thats made it crystal clear, yes there are three houses on one transformer and none with PV (yet) I think I will stick to 4Kw and cover 2/3 of the workshop roof with Panels.
    • CommentAuthormike7
    • CommentTimeFeb 25th 2014
     
    Is it possible to have quite a bit more than 4kWp of panels if you could limit the output of the inverter to 16A? I suspect that the panels will spend relatively little of their time producing even close to their rated output, so little would be lost by lopping off the peaks of generation. Also, your output to grid will not decline so much as the panels age.
    • CommentAuthorjamesingram
    • CommentTimeFeb 25th 2014 edited
     
    Someone was discussing using a Pv-immersion dump to do just that. You could also relay it to electric towel rad etc to guarantee export maximum. Not sure what the out come of the discussion was.
    Might raise a few eyebrow with DNO and MCS etc.?
    • CommentAuthorjamesingram
    • CommentTimeFeb 25th 2014 edited
     
    Sorry slightly miss read your post. you could limit export via dumping.
    You can limit inverter via setting or selection.
    Recently FITS/MCS have clarified banding to mean 4kWP rate total power of panels installed. (TIC)
    was a bit vague prior to this. FITS/MCS only asking for DNC ( declared net capacity ) which was defined output of inverter.
    FITs Banding unfortunately confuses optimum system design.
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 25th 2014
     
    Fit 16 250Wp panels, then add 4 more once everyone has gone home. Just say that the extra rail is the the ST.
    Alternatively go the micro-inverter route and just add as you go along. Then claim that it has been extra sunny since the earthquake.
    • CommentAuthorjamesingram
    • CommentTimeFeb 25th 2014 edited
     
    Posted By: SteamyTea. Then claim that it has been extra sunny since the earthquake.
    "It's that global warming stuff mate " :wink:
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 25th 2014
     
    Yes, all that rain causing more silt in the Bristol Channel caused extra weight on the seabed and as it has rained a years worth, it has to be sunny till next Jan :wink:
    Makes perfect sense to me.
    •  
      CommentAuthorjoe90
    • CommentTimeFeb 25th 2014
     
    Posted By: mike7Is it possible to have quite a bit more than 4kWp of panels if you could limit the output of the inverter to 16A? I suspect that the panels will spend relatively little of their time producing even close to their rated output, so little would be lost by lopping off the peaks of generation. Also, your output to grid will not decline so much as the panels age.


    What is the excepted rate of decline for a PV panel with age?

    Also I see the advantage of more panels but would MCS not accept this?.
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 25th 2014
     
    Each manufacturer will have their own tolerance.
    Here is just one:
    http://www.axitecsolar.com/performance-guarantee.html

    The usual way they do it is to select panels that are over the stated rating, so say a panel is 240W then they will supply a 250W panel, this gives the impression that they loose less over time. There is often a QA sticker on them that shows the test rating, sometimes they forget to take it off.
    • CommentAuthorEd Davies
    • CommentTimeFeb 25th 2014 edited
     
    Posted By: mike7Is it possible to have quite a bit more than 4kWp of panels if you could limit the output of the inverter to 16A?
    Yes, though (somewhat controversially) you'll finish up on the lower FiT band.

    You can either limit the power output in the inverter as you suggest or you can use a diversion to an immersion or other heater if you use the approved equipment (believe there's only one device approved so far - forgotten which one).

    In theory you should limit to 16 A as you say. In practice I think most inverters will only limit to a set amount of power. Apparently the DNOs accept 3.68 kW (16 A at the nominal 230 V) even though this power level will result in a higher current if the voltage is below nominal. At the minimum (which I think is 230 V - 5% = 218.5 V) that power would give 16.84 A which is obviously over the limit but would presumably actually be welcome as it's helping to hold the voltage up.
  1.  
    most 80%-90% rated power after 20 years. 10 year manufacturer warranty
    Sunpower offer the best warranty I'm aware of off. 87% power output after 25 years, and a 25 year product warranty. Also one of the best output m2.

    Take a look a REC excellent EROEI approx. 1 year , was market leader and competitively priced
    • CommentAuthorskyewright
    • CommentTimeFeb 25th 2014
     
    Posted By: Ed DaviesYou can either limit the power output in the inverter as you suggest or you can use a diversion to an immersion or other heater if you use the approved equipment (believe there's only one device approved so far - forgotten which one).

    It's called 'EMMA' & produced by Coolpower Products (I've no connection with them & I don't have one).
    • CommentAuthorstones
    • CommentTimeFeb 26th 2014
     
    Some info on arrays >4kwp at the end of the thread

    http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11719&page=1#Item_0

    All I would bear in mind is that regardless of what diversion devices are fitted to reduce export, the DNO will insist on a G53 relay if you go above 4kwp. This is to protect the network and most importantly the engineers working on lines when there is a power cut on their side - they obviously don't want your solar flowing back down the line and electrocuting them. I suspect that MCS would not accredit any system unless the correct permissions were in place.

    I currently have a diversion device (plenty of them to choose from) that dumps excess pv into an old storage heater - works surprisingly well even if only a few kwh available. Plenty of other options, DHW cylinder, electric towel radiator, electric UFH. Generation wise the summer peak of our system (which is just under 8kwp) is over 6kw per hour, 60kwh per day. Yesterday, sun was out and peak generation was 4.9kw per hour, 15kwh total.
    • CommentAuthorskyewright
    • CommentTimeFeb 26th 2014
     
    Posted By: stonesSome info on arrays >All I would bear in mind is that regardless of what diversion devices are fitted to reduce export, the DNO will insist on a G53 relay if you go above 4kwp.

    My understanding, which could be wrong, is that the EMMA provides such a thing or is at least a DNO acceptable alternative?

    http://www.coolpowerproducts.com/uk/emma-with-ec-works.php

    Here's a system which is described in the first post as '30kW, on 7 Samil 4400 inverters.... only allowed to feed 3.68kW into the grid. They use the EMMA (several of them?), and lots of storage heaters to soak up the excess.

    http://www.navitron.org.uk/forum/index.php/topic,20537.0.html
    • CommentAuthorstones
    • CommentTimeFeb 27th 2014
     
    It comes back to what the DNO is happy with.

    I imagine the question they would ask is what happens when all the storage is charged to capacity - be it DHW cylinder, storage heaters etc. Clearly it is possible to have PV off grid, so logically there doesn't seem any reason to me why you couldn't have <4kwp array tied to the grid with any extra capacity >4kwp off grid.

    Whatever you want to do >4kwp, I would strongly suggest speaking to the DNO, as with all things in life, what they accept in my neck of the woods, might not be acceptable where you live. Hopefully the PV installers would do this (given they want to get the work) and all you will have to do is pay the additional fee.
    •  
      CommentAuthorjoe90
    • CommentTimeFeb 27th 2014
     
    Thanks again all for your input, I have to speak to them regarding other things so will add these questions.

    John
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 27th 2014
     
    I found the Wadebridge office almost as helpful as the Camborne one. I think you need the Wadebridge one
  2.  
    There's just been a very interesting "experience so far" addition to the Navitron topic where someone has 30kWp of PV on a single phase supply with ASHP & storage heaters in a 300 year old property...

    http://www.navitron.org.uk/forum/index.php?topic=20537.msg258291;topicseen#msg258291
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