Designing heating & hot water system for off grid new build

[A.L.]

It is Scotland but the far western isles hardly ever freeze and surprisingly, this island is one of the sunnier places in the UK - the solar yield forecast is similar to Birmingham in spite of the higher latitude. (You can see this on solar maps).

- Tiree?

[kdmnx]

Blimey!!! Thanks everyone for the replies. This is the first time I'm been on any kind of forum so quite a surprise to be honest. A lot of you have asked further questions so I'll try to answer them all here with some more background ...

... and no I'm not a student! I am late 50's and planning to retire to the island with which I have a long association. It is an exposed location in the Hebrides with avg. wind speed of 7 to 8 m/s so plenty for a turbine. The problem with turbines is they all break in the extreme climate.

There are no trees harvested on the island (very few actually grow) but lots of people import wood/coal via the ferry. You can actually buy it there for a premium too.

The house is designed to be highly efficient. Sealed/MVHC (heat recovery) Thick SIPS/CPS panels and foundation insulation etc. So the 4kw heating estimate is probably worse than reality.

It is Scotland but the far western isles hardly ever freeze and surprisingly, this island is one of the sunnier places in the UK - the solar yield forecast is similar to Birmingham in spite of the higher latitude. (You can see this on solar maps).

I can get a grid connection but it will cost nearly £20k (!) so I'm trying to go off grid instead. This might not actually be cheaper but it is and good thing to do and hugely interesting. I'm really enjoying the learning and the planning.

There is enough land around the house if needed for solar/turbines etc. but hope that my planned 5kw array and one part-time 1-2kw turbine will do. The 5kw array of solar will produce a min (10 day avg.) of 3kw/day in winter and max (10 day avg.) of 20kw/day in summer. This doesn't mean I can rely on that though. One of you mentioned freezing fog for example - not something I considered.

I intend to build my own turbine (eventually) with the great help of Hugh Piggot's toils from Scoraig but that will be later on. A lot of the islanders have turbines and most of them have had bad turbine experiences. When it gets wild it is really wild! That is why I don't want to rely on one but want to use it opportunistically. I also want to be able to fix my own one when it (and it will!) breaks.

I am also installing rainwater harvesting - there is a burn relatively close by but the water is coloured (peat) and the rain water is really good. I have a static caravan on the plot just now and collect water from the roof - it is clean and clear of any debris so the filtration will be easy - but will include a Uv and Ph-raising stages.

So, back to the heating, my basic assumption is that I might have to exist for a few days at a time without electricity. When we have none or little, we will cook with bottled propane (both hob and oven) and the WBS must be able to heat the house and produce hot water. In the summer, I expect to be able to heat the house and produce hot water from the solar PV generation via some kind of heat pump. If and when I have excess energy generation (turbine/solar), I will probably want to use an immersion as a dump load too. If the turbine works well, it will compensate somewhat for the poor solar yield in winter but I'm nor banking on that.

I really appreciate all your comments and suggestions. I've got about about 4 months to plan, select and order the necessary kit!

Cheers, Rusty.

Just to emphasise a couple of points:
- You have to plan for your solar panels generating (effectively) no power at all for multiple days in a row. That is just how it works. You get huuuge amounts of power when the sun is shining and little-to-none when it isn’t.
- Solar panels are cheap. If I where you I’d plan for 8-12kWp of solar. On sunny days you’ll be generating way more power than you can use. However on bright-overcast days you’ll generate enough power, and if the sun does poke through briefly you’ll get maximum benefit.
- If you’re off-grid you will need a generator. Some people run it for a few hours every day for 3-6 months a year, even though they have wind and solar. Over sizing your solar, having a functional WT, and good insulation/ heat-pump, will mean you use it infrequently, but you still need it.
- Do you have the possibility of hydro? This can genuinely provide a few 100W of reliable, 24/7/365, power generation.


As I said before, I’m jealous. I’d love to be building an off-grid home on an island somewhere!

[brackwell]

If you have diggers around for the house consider a ground source HP.  Air source HP do not work very efficiently in very moist air close to freezing temp as they keep producing a lot of water and even ice as the HP drops the air temp.  Also the underground storage idea sounds good but i would need to speak to someone who has it.  I have read of eg in Canada.

[nowty]

Only 5kW PV ?,

If you have got the land I would go for 10 or 20kW of PV, its cheap as chips and ultra reliable.

[camillitech]

Only 5kW PV ?,

If you have got the land I would go for 10 or 20kW of PV, its cheap as chips and ultra reliable.

  

[billi]

I can get a grid connection but it will cost nearly £20k (!) so I'm trying to go off grid instead. This might not actually be cheaper but it is and good thing to do and hugely interesting. I'm really enjoying the learning and the planning.

Well , take all those saved  units for free then into account too .... should be a no brainer to  create something cheaper !!

I as well would consider 10 kW  and more PV  and  a big battery bank  a small ground source heatpump   and  the 40 -60 kwh stored in the battery  then are equivalent  to 200 kWh of heat storage , if you treat that battery bank  nicly it will be  your friend for 15 years plus

Billi

[biff]

Exciting!!!
   
    Biff

[Fintray]

And above all else remember the pictures as your project progresses, we all like pictures! 

[todthedog]

To add to everyone else more PV, ground mount is easy if you have the land.
Loads of pictures, the island, your plans, we love pictures

[offthegridandy]

Hi Rusty, for practical purposes, as your ask for help is genuine I suggest you discount my previous post although I'd love for some one to do the maths and actually build a heat well under a house.

A recent post here covered some of your questions but in a nut shell, as regards space heating.  

1, Insulate the hell out of the house to reduce heat demand to a minimum.  
2, Eliminate all draughts at construction stage and treble glaze windows.
3, High spec doors should also be budgetted for.
4. WBS (if required), plan to have a vent from outside direct to the fire to avoid shortage of combustion air which means you end up opening a door or window.
5, Dont go for too big a WBS. A small stove filled and burnt hard and fast is better than running a stove on "tick over" which creates tar in the flue and puts out very little useful heat.

Even with maximum inulation I'd still go for wet UFH with a radiator loop and large airing cupboard/ drying room. I would treat the UFH floor slabs as an energy store ie plan and design the system so any or all energy surplus goes into the floor rather than into a buffer tank and then into the floor.  Energy transfer is wastefull and the floor has a near infinite capacity to absorb and store energy.  Then when you light your wood burner the floor is already pre warmed and the fire doesn't have to work so hard.

Re wind turbines, they do NOT all fail and I suggest you get in touch with Hugh Piggot at http://scoraigwind.co.uk/  he has forgotten more than most of us have ever known about turbines. I  have a 2mtr dia WT based on his design and it just sits in the air doing it's job with little excitement. EG we had 25MPH winds last night with gusts to 45MPH the WT created 5 Kwh from midnight to 8 AM

At the risk of appearing to toot my own trumpet I  draw you attention to the following discussion. https://www.navitron.org.uk/forum/index.php/topic,32171.0.html

Good luck.

Andy

[camillitech]

And, most importantly, before you build your house build an agricultural shed to house your generator and battery bank and install those first. My mantra for starting life 'off grid' is build a reliable diesel/battery/inverter system first then do all you can to make it redundant. Your DG is your lifeboat and hopefully in the not too distant future you will never need it but at the build stage when your battery is flat in the middle of winter or your tradesmen require high power lighting, chop saws, cement mixers and paddle mixers you need reliable and constant power long before your roof is up to put PV on. You also need somewhere dry and out of the wind to store and cut 8 x 4 everything. Sure they build plenty of houses on islands without building a shed first but trust me, it's a helluva lot better and quicker if you have somewhere out of the weather for working and storage. Place your shed in the right location and you'll get even more PV up before your house is started and it may even prevent your caravan from blowing away in the next storm off the Atlantic. You can also put your washing machine and tumble drier in there, though if you're running your genny you may not need the tumble drier  well unless you actually mind your clothes smelling of oil and diesel 

Good luck, Paul

[marshman]

And, most importantly, before you build your house build an agricultural shed to house your generator and battery bank and install those first. My mantra for starting life 'off grid' is build a reliable diesel/battery/inverter system first then do all you can to make it redundant. Your DG is your lifeboat and hopefully in the not too distant future you will never need it but at the build stage when your battery is flat in the middle of winter or your tradesmen require high power lighting, chop saws, cement mixers and paddle mixers you need reliable and constant power long before your roof is up to put PV on. You also need somewhere dry and out of the wind to store and cut 8 x 4 everything. Sure they build plenty of houses on islands without building a shed first but trust me, it's a helluva lot better and quicker if you have somewhere out of the weather for working and storage. Place your shed in the right location and you'll get even more PV up before your house is started and it may even prevent your caravan from blowing away in the next storm off the Atlantic. You can also put your washing machine and tumble drier in there, though if you're running your genny you may not need the tumble drier  well unless you actually mind your clothes smelling of oil and diesel 

Good luck, Paul

Very wise words indeed!

[biff]

 And maybe a 40ft insulated artic trailer,
      With rear barn doors, or rollers.
     Clear roof. When the sun shines it heats the inside.
   Can keep your car in there, rack out timbers, soil pipes,
  Can store generator underneath.
   But slight problem getting it into a rowing boat for journey to the Island.
      Biff
They are quick,
 They are not expensive and can be sold on afterwards.

[renewablejohn]

Dont want to hijack the thread but now getting old and looking for alternatives to the wood heating we currently use and have come across this.

https://www.sunamp.com/residential/

Anybody have experience as was thinking of using it with our small hydro unit.  Thought it also might be useful for the op and solar panels.

[marshman]

Dont want to hijack the thread but now getting old and looking for alternatives to the wood heating we currently use and have come across this.

https://www.sunamp.com/residential/

Anybody have experience as was thinking of using it with our small hydro unit.  Thought it also might be useful for the op and solar panels.

It has been discussed on here a few times in the past. This thread is a starting point.

https://www.navitron.org.uk/forum/index.php/topic,28109.0.html

Roger