Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



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.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.
Buy individually or both books together. Delivery is free!


powered by Surfing Waves




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
 Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




Renewable Energy: Free heat from PV inverter

Bottom of Page

1 to 20 of 20

  1.  
    • CommentAuthorjms452
    • CommentTimeFeb 15th 2013
     
    When our PV was fitted we decided to put the inverter inside the house (rather than the in the loft).

    At the time this was because lofts can get hot and many of the failure modes of inverters seemed to be due to over temperature. It also made fixing/replacing the inverter easier (and hopefully cheaper) if and when it breaks.

    However I have since realised that between October and March we get about 100kWh of heat from the inefficiencies within the inverter.

    I know this is small fry but given our (i.e. GBF's) tendency to worry about things like air leakage through key holes 100kWh is actually quite a lot of free heat. To put this into perspective 100kWh over 6 month is ~20W - The same power consumption as a decent MVHR...

    SAP2009 asks if the central heating pump is within the heated space (presumably for this reason) but doesn't care about the PV inverter.

    Is this detail ever considered - I think it should be.

    Discuss!
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 15th 2013
     
    Good point, 100 kWh is a weeks worth of heating for me. In the winter when the loftspace is cold though are you loosing the same amount though inefficiency?
    • CommentAuthorEd Davies
    • CommentTimeFeb 15th 2013 edited
     
    Agree it's a good point in general but how big is your PV? 4 kWp for 6 months at 1.5 hours per day average (guess) would be jut over 1000 kWh so 100 kWh would be 10%. OK, in the winter the inverter's going to be running at low power so low efficiency a lot of the time but 10% losses still seem a bit high.
    • CommentAuthorjms452
    • CommentTimeFeb 15th 2013
     
    Hi Ed,

    Yes 4kWp over dual aspect so 3.6kw inverter.

    The inverter is great at about 96% efficient (for us) at the higher powers but once you are only only generating 100W the efficiency is more like 85%.

    Hence I estimated an average efficiency of 90% in winter but this is a fairly rough n ready estimate and might well be a bit high.

    Maybe I should have writen 60-100kwH...
    • CommentAuthorEd Davies
    • CommentTimeFeb 15th 2013
     
    85% is lower than I was expecting. Ta. Yes, 90% sounds reasonable, then.
    •  
      CommentAuthordjh
    • CommentTimeFeb 18th 2013
     
    Very interesting thought. What about the other half of the equation ... how much unwanted extra internal gains does it represent in the summer?
    • CommentAuthorSeret
    • CommentTimeFeb 18th 2013
     
    The majority of the waste heat will be produced during summer, as that's when the inverter is working. I would expect its heat output to fairly closely match the bell curve for insolation at your location.
    • CommentAuthorEd Davies
    • CommentTimeFeb 18th 2013
     
    Dunno, I'd expect there to be a fixed small loss all the time, a larger fixed loss when the inverter is inverting and then an incremental loss as the insolation increases above the minimum. Hence the lower efficiency at lower powers. So winter heat losses will be reduced by the reduced hours of operation but not quite proportionally to the reduced insolation.
    • CommentAuthorSeret
    • CommentTimeFeb 18th 2013
     
    Posted By: Ed DaviesDunno, I'd expect there to be a fixed small loss all the time


    Don't know about others, but according to the manufacturer my Fronius inverter does shut down to a 0W state when the sun goes down. Even if they only mean <0.5W that's still a pretty tiny amount of heat.
    • CommentAuthorEd Davies
    • CommentTimeFeb 18th 2013
     
    Absolutely, the idle losses should be tiny and not worth thinking about. (I was disappointed to find that my Morningstar MPPT consumes just over 2 W when idle.) It's the operating losses which will not reduce in proportion to the reduced insolation.
    • CommentAuthorSeret
    • CommentTimeFeb 18th 2013
     
    Well I wouldn't expect it to be exactly proportional, but I'd imagine it's similar. My point is the only useful heat you're going to get out of an inverter is a small amount in spring and autumn. It's certainly not going to be worth deliberately shifting it to within the heated envelope if there were other issues such as noise, wiring length or access suggesting it should be elsewhere.

    Personally I'm more interested in keeping mine cool in summer than trying to extract heat from it in winter. Mine is in the loft, but I've run some ducting so it's drawing outside air for cooling. I had thought of cooling the whole loft on really sunny days with a thermostatic fan at the apex of the gable, but it seems like more faff than it's worth.
    • CommentAuthorGotanewlife
    • CommentTimeFeb 18th 2013 edited
     
    Posted By: SeretPersonally I'm more interested in keeping mine cool in summer

    Me too (not a surprise!) - definitely going to fit an extractor fan on a differential temp switch when I renovate the little storage space it's in this year - with 35+ deg air outside i'll just have to accept the small extra heating load to my house.
    • CommentAuthorSprocket
    • CommentTimeFeb 18th 2013
     
    > Personally I'm more interested in keeping mine cool in summer

    Me too.
    I put it in the plant room, to keep the heat in.
    But of course, it's a pretty warm room so is not good for the lifespan of the inverter - better to keep them cool.
    I have a lean-to shed adjacent to the plant room that I could put it in. It would be great in winter but in summer it could still cook in there as the air volume is not great.

    :-/
    • CommentAuthorjms452
    • CommentTimeFeb 19th 2013
     
    Posted By: djhVery interesting thought. What about the other half of the equation ... how much unwanted extra internal gains does it represent in the summer?
    .

    That's what windows are for :bigsmile:

    Posted By: SeretIt's certainly not going to be worth deliberately shifting it to within the heated envelope if there were other issues such as noise, wiring length or access suggesting it should be elsewhere.


    Indeed deliberately shifting the inverter or incurring large wiring loses would be mad but its essentially no extra cost to fit it within the heated envelope at the point of installation.

    Posted By: SprocketPersonally I'm more interested in keeping mine cool in summer


    and it seems to me that putting it inside the living part of the house achieves that - If i ever think our house is hot (say 25C) the loft is unbearable - particularly when the inverted is working hard...


    If someone was offering a free heat window that worked best in winter and had no thermal losses you would snap this up unless your house had chronic overheating ...

    If you could get it in a basement that might be good too but ours got filled in at some point
    :cry:
    • CommentAuthorFred56
    • CommentTimeFeb 19th 2013
     
    It's bright and cold today. Output is hovering around 1360W. The air flow off the inverter cooling fins measured at about 25mm above them is 38.4C, the room temperature is about 27C, rest of the house 21.5C or thereabouts. Feels like free heat to me.

    We have no roof space so the Inverter is in the boiler room (a gas combi) along with washer and comms cabinet. The comms cabinet emits heat too as it has the router, network switch, AV distribution amp and NAS drive - all have little power bricks.

    We always intended this as a drying room and it has lines just below the ceiling. It has a constant volume DMEV fan which we switch to high speed when drying. Works a treat. The only downside is that the warmth of the room influences the ground floor thermostat if the door is left open. I intend to resolve that by changing to an RF thermostat that can be moved around.
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 19th 2013
     
    Posted By: jms452incurring large wiring loses
    They are limited to 1% volt drop
    • CommentAuthorjms452
    • CommentTimeFeb 21st 2013
     
    <blockquote><cite>Posted By: SteamyTea</cite>They are limited to 1% volt drop</blockquote>

    but that's 1% on both the DC and the AC side.

    at ~3400kwh/year (from 4kWp) 2x1% isn't to be sniffed at ~ 60kwH lost electricity.
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 21st 2013
     
    Posted By: jms452but that's 1% on both the DC and the AC side.
    It is between the FIT meter and the billing meter I think, and it is a 1% volt drop not a 1% power drop.
    • CommentAuthorSeret
    • CommentTimeFeb 21st 2013 edited
     
    Posted By: Fred56Feels like free heat to me.


    Sure, every electrical device within your heated envelope is going to give you some "free" heat. Individually their output is small, but collectively over a year you're looking at the MWh range.
    • CommentAuthorjms452
    • CommentTimeFeb 21st 2013
     
    <blockquote><cite>Posted By: SteamyTea</cite>1% volt drop not a 1% power drop</blockquote>

    you're right - but that is an even bigger effect then...

1 to 20 of 20

  1.  
Add your comments

    Username Password
  • Format comments as
 
Back to Discussions Top of Page
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press