Green Building Forum - Offgrid - how much will it cost? Sat, 18 Apr 2026 15:27:29 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102767#Comment_102767 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102767#Comment_102767 Thu, 17 Feb 2011 16:58:49 +0000 renewablejohn 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.]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102786#Comment_102786 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102786#Comment_102786 Thu, 17 Feb 2011 19:27:02 +0000 fostertom 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.]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102810#Comment_102810 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102810#Comment_102810 Thu, 17 Feb 2011 23:34:50 +0000 renewablejohn
Why is the system linking quotes to me when its not me who made the comment in this case it was pmagowan]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102823#Comment_102823 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102823#Comment_102823 Fri, 18 Feb 2011 08:53:00 +0000 pmagowan Thanks again
Paddy]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102831#Comment_102831 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102831#Comment_102831 Fri, 18 Feb 2011 09:47:25 +0000 StuartB 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:]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102832#Comment_102832 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102832#Comment_102832 Fri, 18 Feb 2011 09:51:54 +0000 SteamyTea Posted By: StuartBBank managers still exist?

Aren't they 'personal financial assistants', because your an individual just like everyone else:devil:]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102836#Comment_102836 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102836#Comment_102836 Fri, 18 Feb 2011 10:08:10 +0000 renewablejohn 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]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102837#Comment_102837 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102837#Comment_102837 Fri, 18 Feb 2011 10:11:41 +0000 StuartB ]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102863#Comment_102863 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102863#Comment_102863 Fri, 18 Feb 2011 12:42:25 +0000 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 roundYes, 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.]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102878#Comment_102878 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102878#Comment_102878 Fri, 18 Feb 2011 13:23:11 +0000 renewablejohn 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.]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102885#Comment_102885 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102885#Comment_102885 Fri, 18 Feb 2011 13:56:55 +0000 evan 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?]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102892#Comment_102892 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102892#Comment_102892 Fri, 18 Feb 2011 14:32:22 +0000 fostertom Posted By: renewablejohnthe maximum temperature which is achievable and with thermal oil and evacuated tubes that would be approx 230CFor which months of the year? and if 230C is the max, what temps do you get other times?]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102893#Comment_102893 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102893#Comment_102893 Fri, 18 Feb 2011 14:37:45 +0000 evan Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102903#Comment_102903 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102903#Comment_102903 Fri, 18 Feb 2011 15:57:55 +0000 renewablejohn 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.]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102904#Comment_102904 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102904#Comment_102904 Fri, 18 Feb 2011 16:03:10 +0000 evan
But "PV was a non starter due to inefficiency of charging batteries. " - Huh?]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102905#Comment_102905 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102905#Comment_102905 Fri, 18 Feb 2011 16:07:14 +0000 renewablejohn 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]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102906#Comment_102906 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102906#Comment_102906 Fri, 18 Feb 2011 16:07:31 +0000 SteamyTea Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102907#Comment_102907 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102907#Comment_102907 Fri, 18 Feb 2011 16:14:05 +0000 renewablejohn 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)]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102909#Comment_102909 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102909#Comment_102909 Fri, 18 Feb 2011 16:19:49 +0000 renewablejohn 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.]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102910#Comment_102910 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102910#Comment_102910 Fri, 18 Feb 2011 16:24:34 +0000 renewablejohn 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.]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102911#Comment_102911 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102911#Comment_102911 Fri, 18 Feb 2011 16:32:05 +0000 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.]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102912#Comment_102912 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102912#Comment_102912 Fri, 18 Feb 2011 16:57:58 +0000 renewablejohn 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%.]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102916#Comment_102916 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102916#Comment_102916 Fri, 18 Feb 2011 17:20:57 +0000 DamonHD
Rgds

Damon]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102928#Comment_102928 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102928#Comment_102928 Fri, 18 Feb 2011 19:32:34 +0000 fostertom
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.]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102930#Comment_102930 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102930#Comment_102930 Fri, 18 Feb 2011 20:19:27 +0000 renewablejohn
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]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102937#Comment_102937 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102937#Comment_102937 Fri, 18 Feb 2011 22:15:59 +0000 fostertom
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.]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102952#Comment_102952 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102952#Comment_102952 Sat, 19 Feb 2011 09:21:26 +0000 renewablejohn 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.]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102959#Comment_102959 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102959#Comment_102959 Sat, 19 Feb 2011 09:58:32 +0000 fostertom 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.]]> Offgrid - how much will it cost? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102961#Comment_102961 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1125&Focus=102961#Comment_102961 Sat, 19 Feb 2011 10:12:45 +0000 SteamyTea That lovely term Exegry has popped into my mind, the usable energy in a system.]]>