Hastings

Still none the wiser, sorry, but the 2000W challenge is right up my street.

Added it in to what?

I am going into my first fully off-grid winter in southern Scotland (Glasgow latitude) so I can't yet be definitive (and even then it would be just the one year) but looking at the data I am finding that my PV production is quite a bit less than the estimate obtained from online tools like PVGIS. Two days ago my 1.9kW PV array produced 270Wh on a grey drizzly day. That's not enough to power the constant background load of charger/inverter (30W), UV water filter (30W), MVHR (15W) and system losses.

Small wind turbines are only really best suited to houses where there is no affordable grid connection - which from a commercial perspective is probably not enough places in UK. PV in northern latitude winters produce little output in many places so a turbine is a good option compared to getting grid connected (I was quoted £250,000 for a 2 mile installation). My 1.9kW PV array (same latitude as Glasgow) does the job in summer but produced only 270Wh today and we're not even in Dec/Jan yet.

I chose to install a 240V inverter with my off grid 2-storey house refurb due to the considerable extra cost of heavy gauge DC wiring that is needed to run wires further than a few metres. Even 48V, which is my battery bank system voltage, can only be run the length of an artic lorry using fairly standard cable. 12V works cost-effectively around a car etc.

150L tank of water started at 41C and finished at 55C. Incoming air temp: 12C Outgoing air temp: 5C Here's the data from my Victron EasySolar 48V 4kVA for the last 30 days: Bear in mind that these figures are for an off-grid system in which power is only generated when there is demand. Very different numbers to a system connected to and feeding the grid (effectively 'maxed' out), which is probably 99.9% of systems posting to the pvoutput.org website (either way, you need to know which). Day 7: the system shutdown due to low voltage. Caused by me being too hasty with the newly installed air source water heater. Days with zero time in Absorb or Float denote that the batteries are not fully charged.

Lovely calm sunny day today here in the southern Hebrides and my 1.9kW PV array powered my 350W air source water heater for 6 hours, with a little spare leftover to top up the 10kWh battery bank at the same time. There was a little high thin cloud so not optimal but the array was averaging around 500W across those 6 hours. 150L tank of water started at 41C and finished at 55C.

Now that's the way to go off-grid!

Presumably though this not all year round - you go over to mainly gas power in winter?

I recommend you concentrate on your autumn/spring period. It's just about do-able, whereas winter isn't (in the UK). Then with the over production in summer connect up a hydrogen generating machine to store hydrogen for winter heating!

Not a gimmick I think although the efficiency of 75% seems low - might be because of the small size compared to normal ones that are for a whole house. BPCVentilation are popular with self-installers on this forum and offer single room units £300 and upwards. They would advise better than I can.

Sadly, off-grid is unlikely to be as eco as being on grid due to the embodied carbon emissions of all the kit you need if building new and therefore required to meet full building regs and planning that often includes eg. strict private water supply standards). If you can have a reasonably large wind/water turbine (most of us are not allowed) then it could be different. The UK grid has apparently reached the point of enough green-ness now that installing just solar panels on individual houses is borderline in terms of saving any carbon emissions, depending somewhat on which country makes the PV you buy. Info from an article on Circular Ecology (Dr Craig Jones the Life Cycle Assessment UK based specialist) I read a while back.

Be very careful of performing calculations using average or mean weather data, which is what is mostly available. It is the minimums that you need to plan for. It is too many years ago that I used the PVGIS tool but I think it may use averages. A more useful resource is pvoutput.org where PV array owners upload their live and historical power production levels. It will show you that a 4kW array in Glasgow produces almost no significant power in Dec/Jan.

Unless you have acres of PV panels you will likely need a generator or wind/water turbine to get you through the winter months. The biggest issue and the one that 'gets' you in the winter is the total background demand ie. the total of all bits of gear that are on all the time. These can include water filters (40-80W for UV steriliser) which could be multiple (iron and manganese filters are common for borehole sources). The DC-240V AC inverter : even a smallish 4kVA Victron consumes 25-30W continuous. You can install an electric-free septic treatment unit or add on another 50-100?W for the normal (and much cheaper) air blower ones. So that takes you into the range of 70-200W. My 6x380W mono-crystaline (better in overcast conditions) PV array sometimes produces a total of 40W in the middle of a dull rainy day in November. Much harder to calculate is the demand from things turning on and off automatically. Heating systems, water pumps, fridge/freezer. Off-gridders with no turbines usually resort to simple wood burners.

Be aware that a UKAS calibration certificate (less than 12 months old) might be asked for if you are being inspected by building control.

All that needless carbon pollution (concrete) - was it filmed 30 years ago?

I think it is very very unlikely to be a requirement. A wheelchair is not normally designed to be used in a shower and therefore a requirement for level access would not be logical. You transfer from a wheelchair onto a WC and I think the thinking is that you could put a seat in a shower to transfer onto. From memory I don't think a shower in a new build is a requirement at all. You can just provide a bath.

I still have not been signed off - aiming for submission before mid November now - so I can't definitively answer yet. The inspector has visited and didn't mention it as a problem but I am not sure that he was checking everything to the degree he will/might when he comes for the final sign off.

We went airtight but weren't attempting PassivHaus level of insulation just current (2018) regs plus a bit more, where it was doable hence only 100mm underfloor insulation. The drawing shows roughly the average situation along 30m of existing 4 walls - but the sections where it was 'worse' were not long enough to worry about. It helped that the subsoil on which the old walls were built was gravel based (raised beach). The internal stud frame carries the weight of the new upper storey, hence the need for thickening of the slab at the perimeter. The engineer originally proposed that the new roof also rest on the new inner stud frame and that would have required even deeper digging and concrete. I vetoed that proposal in anticipation of the old walls being very shallow and I am very glad I did. The thickened reinforced concrete perimeter was wider than shown in my sketch. Sketch is not very to-scale. (Airtight and damp proof layers not shown, for clarity)

I have twice now put new insulated concrete floors into old buildings that have no founds to the walls and both times we had to dig below the level of where the old walls 'stopped'. With agreement from the structural engineer (who was initially prescribing underpinning) we stayed away from disturbing the solum under the old walls mainly by feathering/rounding the lower outer edges of the new inner slab/foundation. At the same time we also raised the new FFL (relative to the original) a little, which we worried about at the time would spoil the space but in practice we don't notice it now. The finished ground floor ceiling height is slightly less than 2.4m.

I am renovating and will get VAT refund because it's been unoccupied for more than 10 years. I decided to renovate, not demolish and rebuild, because I felt it my duty to reduce the carbon footprint.

Be aware regarding manufacturers' installation guides - they don't always comply with building regulations. Eg. Medite 18mm OSB T&G flooring is more than strong enough for a domestic floor (given the correct support) as recommended and tested by the manufacturer but is not dense enough to comply with the regulation on prevention of sound transmission (in Scotland at least).

You are right that the PIR boards must be joined to each other or to something else in an airtight way, to make the thermal barrier continuous. Otherwise it won't do much good. You will get thermal bypass. PIR sheets should be at the very least taped together and where butting up to walls or timber studs. Something like Gapotape can be attached to the edges and is designed to ensure a perfect fit. Your contractor is very typical in my experience - it's very hard to find one that understands how insulation works. You might also need to check you won't create damp problems. I just spotted this, which looks useful:

Somewhere on this forum you will find folk who have very positive experience of simply heating a well insulated house directly with electricity using an inexpensive "Willis heater" heating water in the groundfloor slab briefly, overnight on economy rate electric. You can always add a heat pump to do it instead later.

All done now, no need to respond.