S2D2

If you have a DCC connected smart meter, see here for sizing the battery: I was looking at panel orientation rather than E/W split but found when using a battery vertical mounted panels saved the most on energy bills for my specific location/consumption - you sacrifice summer export to generate more in winter. Same principle here with south facing panels generating more in winter, that will have a much bigger impact on energy bill savings than extending the generation window slightly when the system has a battery.

Yeah that's why ours is left on the worktop with no lid, not the best aesthetically but way less faff, just chuck things in. We have one with a removable inner shell so fitting a new liner is very quick and looks neat. Milk etc wouldn't work with that though so if the newer waste disposals are better (as others have said they are) it may suit your usage more.

I inherited an old waste disposal unit when we moved in to this house. It took an infuriating amount of effort to keep odour free, new ones may be better. I ripped it out in the end and we use a counter top caddy with compostable liner. I leave the lid off because trapping moisture or heat in the thing speeds up decomposition (spent coffee pucks). Nothing smelly, cooked or animal based goes in and it stays odour free until emptied into an outside compost bin twice weekly to weekly. Keep the container small to avoid the temptation to stretch this longer. Caddy is just quickly rinsed before adding a new liner but can go in the dishwasher if it gets grubby, the liners prevent this well. Makes great compost for the garden as a bonus.

Rockwool is breathable, so (relatively) warm humid air will rise through it (slowly). If your tin roof is below the dew point of that air you will get condensation on the underside of the tin. You are already seeing this overnight on your pictures. The ventilation air current mixes with the warmer moist air to carry the moisture to outside, keeping the tin and insulation dry. This is what you gain. Spray foam solves the problem because it is not breathable, so the warm air does not meet a surface below it's dew point. A dehumidifier solves the problem by decreasing the dew point, again preventing the air from meeting a surface below it's dew point.

https://cpc.farnell.com/search?st=Euro to uk adaptor Free delivery needs a spend of £17.50 though so no good for one off very cheap items.

No, the ventilation is underneath the tin roof, above the insulation and so the heated envelope below is practically unaffected by it, other than a small increase in heat loss from the upper surface of the insulation. The diagram I linked should hopefully demonstrate this. You then condition the air inside the heated envelope as appropriate as it no longer flows freely to outside, the relative humidity of which will be reduced as you have heated it.

If you can provide a 100% airtight seal to stop any internal air meeting the underside of the tin then yes, you will not require ventilation. This is likely to be very time consuming and expensive to achieve, airflow is usually a much easier win to counter condensation, but it's entirely your decision. I am biased because I've had severe condensation issues in the past (resolved by ventilation) as outside humidity is usually >80% around here.

Good to get clarification that insulating the building is the way forward, sorry if I missed that in an earlier post. I don't think I'm being clear about leaving the eaves ventilation open, I'm talking about something like the left hand side of this picture: So the room is closed to the eaves but the roof is not. How you would achieve that with the kind of spans involved in that roof I have no idea but removing all ventilation from roof level will inevitably lead to condensation on the roof as it has nowhere else to go. Breathable roofing felt would be a suggestion to stop fibres dropping, but again how you make that practical is an open question. Might be worth getting a quote for spray foam and a quote to install a flat ceiling with new steels that you could pile rockwool on top of but again the scale is your enemy for keeping prices down. You're probably looking at north of £2k in rockwool just for 200mm then fixtures, felt etc. on top. Hey, at least the walls are easy!

Don't be in a rush to close it up if it is there, it's an easy opportunity to get air temps equalish either side of the tin if the ventilation is sufficient, thereby eliminating condensation risk. You'd then build up your insulation layer underneath this gap. Insulating over would do the same by keeping the original tin warm but I'd want someone to sign off wind loading on a roof that size before proceeding. Have you put your postcode in the availability checker? Not available anywhere near me. If you can get it it'll be the old stuff fully bagged - nothing stopping you from ripping the bag off though for normal, breathable rockwool. Easy win on the walls with EPS beads, you'll want to do that before the roof as you'll lose access to the top of the cavity. Really consider your usage first as this won't come cheap due to the scale. Do you need to keep materials warm or just yourself? The heated jacket option mentioned earlier would be orders of magnitude cheaper if it's a workable solution. Cars were mentioned, if running for even a short period the ventilation required for fumes would render the insulation useless for a good chunk of time.

Looks like it, it is now only one sided which avoids the plastic-bag-full-of-water issue: https://www.knaufinsulation.com.au/product/space-blanket @Roger440 do you have ventilation at the eaves there? If so you could leave a ventilation gap like a loft conversion and have a layer of wool under that?

It doesn't mention it on this listing but afaik this used to be the stuff wrapped in plastic foil. Touted as the perfect mix for loft insulation but the vast majority of the time ended up a sweaty uninsulating mess as it's nowhere near breathable enough for most homes so just pooled water. Used to be many, many reviews with condensation issues that I notice have vanished from that listing...

I wouldn't worry, you have a much higher electric load than I modelled (no MVHR, gas boiler) so I think your selected system will perform well, especially if you combine it with overnight cheap price charging of the battery with weather prediction to top up when the PV can't deliver enough. If you don't mind me asking what was the quote including installation? I'm trying to validate my cost functions at the minute!

Do you have any existing consumption data (or a DCC connected smart meter) that could be used to model PV/Battery performance in the finished build? I could never make the powerwall add up when I looked, have you considered other brands? I was also surprised how significantly battery clipping (fully charged causing export) decreased ROI when modelling with half-hourly data, it really does drive the choice of battery to avoid an excessively long ROI:

The best I've seen recommended are the Iris fans or a basic sprung shutter such as https://www.tlc-direct.co.uk/Products/BG4BS.html Mounted towards the outlet it should have an advantage over the iris type (no cold air circulating the length of the duct above the ceiling) but I'm yet to see anyone state they've used one to good effect, plus I always assume pressure driven mechanisms will be noisy - outdoor wind can still open it. Interested to see what you come up with given you can monitor the change with the thermal camera.

Baseline usage is already as low as I can get it, 30W constant around 50w including fridge freezer. Some of the peaks can be shifted - dishwasher, washing machine, but I've highlighted issues with that above, plus it's not really something I want to have to think about and would reduce the ROI for that benefit. I don't have any error margin data for either dataset, you could estimate for PV but it would be gigantic given how variable the data is. All data stored UTC and in the images above displayed in BST so accurate between series.

I revisited this as the PV data can be interpolated to 30m values to see what the impact of improved fidelity was. Around 5% reduction in utilised PV by moving from 1h windows to 30m windows. This trend would continue as the fidelity increases, so there's probably at least another 5% reduction in utilised PV missed by this model. Much more significant is the error introduced by averaging PV data. If I instead take only the 2020 timeseries utilised PV drops by around 23%. It's intuitive as to why, I was smoothing out daily irregularity by taking an average, which has a big impact on utilisation if we look at the same day as my original image: Poor midday sun causing a large draw from the grid. This helps support a case for batteries; even when shifting load to mid day you might just get unlucky with PV generation, I don't want to have to predict the cloud patterns before setting off the dishwasher. As a result, utilisation for a 3kWp system with no battery drops even further to 31% making it very hard to justify any kind of ROI on PV only when export rates are either 0 or require thousands extra for MCS. I added a crude pre-combi water tank model and with such low utilisation it does become just about viable based on some estimated costs, still keen to hear from anyone who has installation costs for this. More accurate information could be gained by running each year's PV data in turn and averaging the outputs. So with batteries having a few advantages, including offsetting the much higher electricity cost over gas, I went down the route of optimising such a system. With higher PV generation a pre-combi tank could be added as well, but I am space limited on the number of panels I can install. Some rough equipment/install cost estimates (Not MCS) and 133 data points later gives me the following optimisation space: Ignore Excel's bizarre labelling, y-axis is Battery (kWh). The optimal value being around 3.65kWp PV with a 4.56kWh battery. Adding a tank to this system would only save ~£79 a year so fairly hard to justify the extra expense. Does anyone have reference quotes for a similar system to double check my cost functions?

I've seen the pre-combi tank recommended on here but don't really have a handle on installation costs. Can anyone who has done it give a ballpark figure? Because mains gas is still relatively cheap (ironically) it only saves about £90/year on the 3kW system. Add in annual maintenance of UVC and the ROI seems big, but I'm making unfounded assumptions and should price it up instead.

Interesting idea at the moment but difficult to project far into the future I guess. It requires MCS too but at current rates might cover that additional cost. Thanks!

Yep increased fidelity will improve accuracy if anyone else wants to try this. It's always annoyed me that I can't easily ping the smart meter for a reading, the DCC data is often ~8 hours late so you can't do any real time control with it, but it's good enough for basic calculations like this.

This is one of a number of limitations of the abstracted model which I'm ignoring completely and crossing fingers that the summed effect isn't significant. The data is simply not available at a high enough fidelity to model such events. Another is averaging PV output data, which not insignificantly undermines the battery simulation accuracy as the battery has a min/max which causes clipping.

I've been interested in PV for a while but put off by the variance of estimated savings making it difficult to determine how useful it would be to my specific house. PVGIS is a fantastic tool, but how much of that generation could I actually use? "Around 50%" wasn't specific enough for me but fortunately, my smart meter was recently updated to connect to DCC, so it was time to go down that rabbit hole, results shared here to prompt debate and so others can point out errors and maybe explore a similar study on their own property. Firstly, hourly data for the proposed install location was downloaded from PVGIS and averaged over the 2005-2020 period available: https://re.jrc.ec.europa.eu/pvg_tools/en/. This average was then dumped into an InfluxDB database Next, half-hourly consumption data from my smart meter is available via a DCC connected company, with 13 months of data available. There are a number available, I chose Bright as they have API support: https://play.google.com/store/apps/details?id=uk.co.hildebrand.brightionic. This data was pulled down with a python library into the InfluxDB database: https://github.com/cybermaggedon/pyglowmarkt. Note I had to pull 10000 minutes at a time as there seems to be a limit on request size. Now I have all the data, there's a few options on what to do with it. Firstly, Grafana was used to support detailed interrogation of the data as well as an in-built method for summing timeseries data. Below pictures are for a 3kW system mounted vertically on a ~SSE facing house wall: Annual utilised PV is just the min of usage/generation for each hour in the time series. The result is... disappointing, suggesting if I'd had this system installed over the last year I'd only have used 40% of the generated power. As with most houses, the culprit is significant evening usage - computers, TVs, dishwasher etc. I can shift some of the usage to mid day, but not enough to make a significant enough impact. Inspecting a random day (6th September) confirms an increase in PV size would not solve the problem either: Area on this graph is kWh so it's easy to see a lot of wasted generation mid day (between the blue and orange lines) followed by significant grid usage in the evening (between the green and blue lines). Note that electicity consumption is quite low as my heating and hot water is from mains gas. Ideally this excess could be dumped into a hot water tank but we have a combi boiler and I'm struggling to make the sums add up once you factor in even more initial investment for a tank etc. Therefore I'm ignoring offsetting gas consumption and purely looking at the significantly more expensive unit rate electricity consumption. That aim then brings us to battery storage. I couldn't find a way to simulate state in Grafana so used the InfluxDB Python bindings to set up a basic charge/discharge simulation across the year. It does not factor in battery efficiency due to me being lazy which will slightly skew figures. This simulation takes three parameters: PV system power in kW, battery capacity in kWh and the unit electricity rate to calculate savings. Hard to predict for a long term investment so I just used the current 27.09p/kWh rate. It's then possible to experiment with proposed systems: $ ./battery_sim 0 0 0.2709 0.00kWh utilised and 0.00kWh stored out of 0.00kWh generated. Total 0.00kWh (0%). From grid: 2280.95kWh. Annual Saving £0.00 $ ./battery_sim 2 0 0.2709 750.32kWh utilised and 0.00kWh stored out of 1424.67kWh generated. Total 750.32kWh (53%). From grid: 1530.63kWh. Annual Saving £203.26 $ ./battery_sim 3 0 0.2709 863.03kWh utilised and 0.00kWh stored out of 2137.00kWh generated. Total 863.03kWh (40%). From grid: 1417.92kWh. Annual Saving £233.79 $ ./battery_sim 3 5 0.2709 863.03kWh utilised and 998.04kWh stored out of 2137.00kWh generated. Total 1861.07kWh (87%). From grid: 419.89kWh. Annual Saving £504.16 $ ./battery_sim 4 5 0.2709 930.05kWh utilised and 1102.64kWh stored out of 2849.34kWh generated. Total 2032.69kWh (71%). From grid: 248.26kWh. Annual Saving £550.66 $ ./battery_sim 4 9.5 0.2709 930.05kWh utilised and 1151.73kWh stored out of 2849.34kWh generated. Total 2081.78kWh (73%). From grid: 199.17kWh. Annual Saving £563.96 $ ./battery_sim 5 9.5 0.2709 970.84kWh utilised and 1211.10kWh stored out of 3561.67kWh generated. Total 2181.94kWh (61%). From grid: 99.01kWh. Annual Saving £591.09 $ ./battery_sim 5 13.5 0.2709 970.84kWh utilised and 1221.01kWh stored out of 3561.67kWh generated. Total 2191.85kWh (62%). From grid: 89.10kWh. Annual Saving £593.77 $ ./battery_sim 7 13.5 0.2709 1018.43kWh utilised and 1268.62kWh stored out of 4986.34kWh generated. Total 2287.04kWh (46%). From grid: 0.00kWh. Annual Saving £619.56 Quite easy to spot the return on investment of the PV and battery capacity is tightly coupled, no point having loads of generation you can't store or massive storage with no excess generation. This is where I've stopped for now, it'd be trivial to go one step further and optimise the system for most cost-effective setup but that would need a cost function for £/kW solar and £/kWh storage (installed) that I haven't bothered to put together yet. Note that the upgrade to a Tesla Powerwall (13.5kWh) is very cost-ineffective, but could technically provide 100% of my usage with a 7kW solar array. The 5kWh battery with 3kW PV seems a sweet spot for me and uses 87% of the generated power but I'm unsure on the costs of such a system yet. To go ahead I'd prefer a maximum 10 year ROI which sets pretty tight budgets, ~£2k for a 2kW system with no battery or ~£5k for a 3kW PV 5kWh battery system. This obviously rules out MCS, but has anyone got close to this with self installation and connection by an electrician? Comments and questions welcome, does this line up with actual performance people have seen from their installs?

As a follow up, I went with option 2, redistributing 50% of the flattened insulation into the other half of the loft and topping up the resultant gaps with new. Nothing to the tip or through the house which was a big win. Average insulation depth now 400mm and loads of storage up on the loft legs, which worked really well with P5 T&G chipboard sheets 2.4x0.6m. In case anyone else is doing something similar, I used a dustpan to scoop the old loose fill insulation and an old bread knife to cut the new rolled insulation, worked a treat. Fitted a couple of 1.5m batten LED lights before doing the job which made everything a lot easier, highly recommended.

Manthorpe G630 is what I used every other truss at the lowest overlaps. I have the bitumen type felt so the only ventilation was from the eaves and there were nowhere near enough soffit vents fitted to prevent condensation at the coldest point of the year. These vents just open up the overlap between the felt a little bit and seem to have done the trick, I pulled the felt open by hand before buying and a fair amount of airflow does come through. Thanks for the link @tonyshouse, I came across this when I was doing the subfloor and paid a lot of attention to foaming up appropriately when I had access to the beam and block floor. There's a great design feature in my house where the pipes run under the floating floor (chipboard on 50mm polystyrene) with big gaps either side of the pipework. Coupled with a few leaks in the beam and block floor this means airflow can traverse the entire downstairs central heating circuit. Whilst I had the kitchen floor up I switched out for PIR taped at seams and fitted pipe insulation, but this has only improved approx 25% of the floor area. The gaps the builders left in the polystyrene were absolutely ridiculous.

Thanks @vala, I noticed B&Q do a similar product now too. I can definitely see the advantage but unless I'm mistaken it's still about twice the price of fibreglass? If I was starting from scratch I'd be tempted but I'm at least keeping the 170mm top up so unfortunately the loft will remain an itchy torture chamber regardless.

Thanks all, leaning towards option 1 or 2 to avoid having to remove any. Here's a picture for reference showing the state of the old stuff, the visible side of the joist should of course be hidden by nice fluffy insulation. Not sure on the insulative properties of kitchen roll, have the previous owner to thank for that. New stuff laid in the same direction in the middle section for ease by the energy company's fitters, I'll correct this to make it perpendicular. I'm also curious on the waxed paper!