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  1.  
    Posted By: fostertom
    Posted By: renewablejohnWhat renewable technology would you use to provide all your heating
    I answered you that but you poured scorn on it, poss because it wasn't a bolt-on 'technology' but something more integral in the (re)design of the house's fabric.


    Fostertom

    I dont know where I am supposed to have poured scorn on using low grade solar but I certainly did not mean to as it can as you say provide the base load heating of a well designed house. Personally I would try and capture thermal solar at a higher temperature either by using a thermal oil store (insulated asphalt container) or caustic soda store (recharge of soda by solar evaporation) which would then allow flash steam to be produced to provide electric and the waste heat can then be used for hot water and central heating.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 17th 2011 edited
     
    Posted By: renewablejohnI dont know where I am supposed to have poured scorn on using low grade solar
    Posted By: renewablejohnNow Fostertom, you are getting carried away. Solar powered Walls! I think I am borderline as it is but that would be OTT (both price and work)
    It's OK anyway - just wanted to nudge you again, as you seem worth it - quick to learn.

    A general strategy/guiding principle towards massive reductions in energy demand without suffering reductions in standard of living/progress of useful technology etc (Holgrem's Green Tech Scenario - the only one of his four Scenarios that has a long-term future), is taking care to use precious energy, for all purposes, in lowest-feasible-grade form. Going to higher-grade energy, on the whole is wasteful in one way or another, looking at in wide energy- and resource-accounting terms.

    Space-heating is a very large and fruitful opportunity to do just that. It is huge - space-heating of buildings accounts for fully 47% of UK CO2 emissions. And no other use that I can think of can make full, uncompromised use of heat of such extremely low grade.

    For a start, only by collecting at v low temp (collector flow temp about 21C) is it possible to do it thro the coldest months Dec and Jan. If expecting to collect at higher temp, you'll need to rely on heat collected up to October and after March, so you'll either need swimming-pool size super-insulated heat storage tanks, or you'll have to burn fuel thro Dec/Jan.
  2.  
    Fostertom

    Why is the system linking quotes to me when its not me who made the comment in this case it was pmagowan
    • CommentAuthorpmagowan
    • CommentTimeFeb 18th 2011
     
    Yes, that is my quote. Not scorn though, tongue in cheek. You have been very helpful, Tom, but various nudges on this forum have probably quadrupled the cost and work I need to do (with obvious benefits). I know you have a penchant for 'solar walls' and they sound a good idea but a step too far for my situation. The bank manager and I are going to get to know one another well as it is! I suppose jocular comments don't translate so well when not spoken.
    Thanks again
    Paddy
    • CommentAuthorStuartB
    • CommentTimeFeb 18th 2011 edited
     
    Posted By: pmagowan The bank manager and I are going to get to know one another well as it is!


    Bank managers still exist? :shocked:
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 18th 2011 edited
     
    Posted By: StuartBBank managers still exist?


    Aren't they 'personal financial assistants', because your an individual just like everyone else:devil:
  3.  
    Posted By: fostertom

    For a start, only by collecting at v low temp (collector flow temp about 21C) is it possible to do it thro the coldest months Dec and Jan. If expecting to collect at higher temp, you'll need to rely on heat collected up to October and after March, so you'll either need swimming-pool size super-insulated heat storage tanks, or you'll have to burn fuel thro Dec/Jan.


    If you design your thermal solar tubes with tracking reflectors you can multiply the solar energy collected per tube by a factor of 3 which then makes high grade solar available all year round and also solves the overheating problem in summer if you phase change the tracking reflector by 12 hours
    • CommentAuthorStuartB
    • CommentTimeFeb 18th 2011
     
    My personal 'business manager' is in a call centre 60 miles away and she is about 12 years old. I tried to discuss a creative business proposal with her and she said that wasn't her department. :cry:
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 18th 2011 edited
     
    Posted By: renewablejohnIf you design your thermal solar tubes with tracking reflectors you can multiply the solar energy collected per tube by a factor of 3 which then makes high grade solar available all year round
    Yes, not bad, at a price, but we're looking at v high whole-system collection-and-use efficiency using large lo-tech collection and input means that double as part of the building fabric. In fundamental principle, it's wasteful to collect at temp higher than necessary and then dilute it down at point-of-use - tho there's reasons like compact storage density and small input radiators that seem to promote high temp collection.
  4.  
    Posted By: fostertom
    Posted By: renewablejohnIf you design your thermal solar tubes with tracking reflectors you can multiply the solar energy collected per tube by a factor of 3 which then makes high grade solar available all year round
    Yes, not bad, at a price, but we're looking at v high whole-system collection-and-use efficiency using large lo-tech collection and input means that double as part of the building fabric. In fundamental principle, it's wasteful to collect at temp higher than necessary and then dilute it down at point-of-use - tho there's reasons like compact storage density and small input radiators that seem to promote high temp collection.


    Our philosophy has been to design the system to the maximum temperature which is achievable and with thermal oil and evacuated tubes that would be approx 230C. We then exploit the temperature gradient between 230C and 100C to produce electrical energy then any waste heat below 100C can be used for domestic hot water and central heating.
    • CommentAuthorevan
    • CommentTimeFeb 18th 2011 edited
     
    That's very interesting John!
    I guess you store up a batch of high temperature oil and then fire up a steam engine generator at a peak time for selling, with the exhaust gas being condensed by the central heating / DHW?

    How's the electrical efficiency, and what about the cost compared to a combination of PV and ST?
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 18th 2011
     
    Posted By: renewablejohnthe maximum temperature which is achievable and with thermal oil and evacuated tubes that would be approx 230C
    For which months of the year? and if 230C is the max, what temps do you get other times?
    • CommentAuthorevan
    • CommentTimeFeb 18th 2011
     
    I suspect 230 is the max for the oil / storage system, rather than the collectors. Just a thought.
  5.  
    Posted By: evanThat's very interesting John!
    I guess you store up a batch of high temperature oil and then fire up a steam engine generator at a peak time for selling, with the exhaust gas being condensed by the central heating / DHW?

    How's the electrical efficiency, and what about the cost compared to a combination of PV and ST?


    It could be as simple as that but we have it linked into a biomass system as well so that we have an option on how the thermal oil is heated. Yes we can fire up the steam engine on demand with approx 15% electrical efficiency (but a bristle turbine I am looking at might improve that figure) and overall efficiency of approx 75%. If running purely on solar. If using biomass then the figures rise to 45% electrical and 80% overall. Electrical made up of gas and steam turbines combined. PV was a non starter due to inefficiency of charging batteries. ST with reflectors approx 1/3 of normal price ST arrangement for the same heat output.
    • CommentAuthorevan
    • CommentTimeFeb 18th 2011
     
    Sounds good. I like the aspect of combining all sorts of high-ish grade heat, you could also use biogas from kitchen waste / sewage etc on a very small scale which is difficult to make use of otherwise.

    But "PV was a non starter due to inefficiency of charging batteries. " - Huh?
  6.  
    Posted By: fostertom
    Posted By: renewablejohnthe maximum temperature which is achievable and with thermal oil and evacuated tubes that would be approx 230C
    For which months of the year? and if 230C is the max, what temps do you get other times?


    You can get 230C on a sunny day all year round as the tubes are in series and flow rate is adjusted to control temperature
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 18th 2011
     
    How do you compare efficiencies between fuel/energy input/ourputs?
  7.  
    Posted By: evanSounds good. I like the aspect of combining all sorts of high-ish grade heat, you could also use biogas from kitchen waste / sewage etc on a very small scale which is difficult to make use of otherwise.

    But "PV was a non starter due to inefficiency of charging batteries. " - Huh?


    We wanted a system that operates 24/7 not just daylight hours so by the time you have a 15% efficient PV panel charging a battery bank with 25% efficiency your overall efficiency could be as low as 4% electrical and no thermal heat captured (maybe the batteries heated up slightly but I would not consider it usable heat)
  8.  
    Posted By: evanI suspect 230 is the max for the oil / storage system, rather than the collectors. Just a thought.


    Yes type of oil is deciding factor we could in theory go up to 280C using different thermal oils but then the cost of pumps / valves etc gets very expensive and 230C is still sufficient to produce a useful 25 bar steam pressure.
  9.  
    Posted By: SteamyTeaHow do you compare efficiencies between fuel/energy input/ourputs?


    I use the methods as set out in the CHPQA guidelines which is the basis of any ROC payments that we receive.
    • CommentAuthorevan
    • CommentTimeFeb 18th 2011 edited
     
    Posted By: renewablejohn
    Posted By: evan

    But "PV was a non starter due to inefficiency of charging batteries. " - Huh?


    We wanted a system that operates 24/7 not just daylight hours so by the time you have a 15% efficient PV panel charging a battery bank with 25% efficiency your overall efficiency could be as low as 4% electrical


    Woah there, this is getting very hand-wavey. Battery banks and inverters can be far more efficient than that for round trip storage, better than 90% even if you use the best available. You also seem to be ignoring grid connection.

    I think you'll be hard pressed to get anywhere near that with heat storage and steam engines.

    By all means publish and prove me wrong, but please don't (erroneously) put down other technologies just to make your approach sound better.
  10.  
    Posted By: evan
    Posted By: renewablejohn
    Posted By: evan

    But "PV was a non starter due to inefficiency of charging batteries. " - Huh?


    We wanted a system that operates 24/7 not just daylight hours so by the time you have a 15% efficient PV panel charging a battery bank with 25% efficiency your overall efficiency could be as low as 4% electrical


    Woah there, this is getting very hand-wavey. Battery banks and inverters can be far more efficient than that for round trip storage, better than 90% even if you use the best available. You also seem to be ignoring grid connection.

    I think you'll be hard pressed to get anywhere near that with heat storage and steam engines.

    By all means publish and prove me wrong, but please don't (erroneously) put down other technologies just to make your approach sound better.


    Accepted if you have a large battery bank and can afford to top slice the discharge to less than 50% you will get better efficiencies. But in the real world batteries are the expensive item of a PV system and the temptation will be to reduce cost by having a small battery bank and to discharge to 20% reducing the number of cycles and reducing efficiency. Even at 90% efficiency your still down to 13% efficient compared to a solar thermal of 15% and overall of 75%.
    •  
      CommentAuthorDamonHD
    • CommentTimeFeb 18th 2011 edited
     
    The nominal efficiency of solar thermal vs solar PV is [edit: moot] once you include an electrically-driven heat-pump in the system.

    Rgds

    Damon
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 18th 2011
     
    In essence you're using stored hot liquid and making electricity from it on demand, instead of trying to store electricity as such, in batteries? And as a bonus, getting lots of useful heat. Sounds good.

    I understand that by modulating flow thro the solar collectors you can get all your output @230C (which the system depends upon, otherwise no steam). But what kind of flow rate, therefore quantity of heat can you get in deep winter? I'd have thought that collecting at that temp, re-radiant losses to the cold winter outside scenery wd far outweigh any gain, even during (very intermittent) clear sky/sun spells? Unless you can collect @ 230C even during winter overcast periods, you'll have to store quantities of heat to bridge between the rare clear-sky/sun spells, to generate steam on demand through overcast spells - and your heat store will be useless for steam if it drops below 210C.
  11.  
    fostertom

    Your analysis is about right however we dont have a problem as in winter periods we use biomass and any solar heating is viewed as an added bonus. If it was solar only it would be a bigger problem however we think we have the solution using caustic soda. Once we have built and tested a "honigmann" engine we should be able to confirm the figures quoted in the document below. Using low grade solar to recharge a honigmann engine seems to me to be the ideal solution for winter periods.

    http://www.scribd.com/doc/4185040/Honigmann_fireless_engine
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 18th 2011
     
    If in winter periods you're relying on biomass, then which time of year is your 'waste' heat useful?

    If you can find a way to convert low grade heat into electricity, that's really the holy grail! It wd function like a heat pump, because the lo grade heat, once converted into electricity, cd be reconverted into heat at any temp you like! Wd depend on the efficiency of conversion - if v lossy then that's not so good, tho as in your present plan the 'waste' heat cd be used.
  12.  
    Posted By: fostertomIf in winter periods you're relying on biomass, then which time of year is your 'waste' heat useful?



    fostertom

    The waste heat is useful all year round as the biomass plant can be regulated down to 10% of its peak fuel consumption so any solar heating will reduce the amount of biomass used.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 19th 2011
     
    Posted By: renewablejohnOur philosophy has been to design the system to the maximum temperature which is achievable and with thermal oil and evacuated tubes that would be approx 230C. We then exploit the temperature gradient between 230C and 100C to produce electrical energy then any waste heat below 100C can be used for domestic hot water and central heating.
    So I was asking about the waste heat that you get during periods when your hi-temp solar is the heat source.

    You're saying that hi-temp solar generates electricity plus as a bonus (dramatically pushing up overall efficiency) the waste heat is used for space heating. I'm checking whether there's any such need for space heating during periods when your hi-temp solar is the heat source. Because if not, your solar collection isn't being used at all for space heating.

    I was talking about lo temp solar collection for space heating but you preferred an alternative; hi temp collection cd do space heating plus electricity generation as well.
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 19th 2011 edited
     
    So are you saying that if you throw the heat away, because it is not needed, that is dropping the overall efficiency, or it is irrelavant as it is total energy out divided by total energy in?
    That lovely term Exegry has popped into my mind, the usable energy in a system.
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