pdf27

Not especially - burning hydrogen in CCGTs is a much simpler solution than burning it in domestic boilers, since the ASHPs in the middle reduce the total hydrogen demand by a factor of ~3. Infrastructure costs on the grid are vastly lower too, while ASHPs aren't vastly more expensive than domestic boilers. At a system level, it's probably quite a bit cheaper.

Only if they use the original radiators. Fit correctly sized radiators and it's fine. One thing that will need care - the insulation on the storage heaters needs to be much better than in ones that were made historically, otherwise you're likely to have issues with overheating early in the heating period and under-heating later. Once the insulation is good enough, you can probably get away with direct heating when power is cheap rather than storage heating - and the window between storage heaters not working and not being necessary is probably quite narrow. Probably maintenance rather than refuelling. Peak demand on the grid is actually very peaky - the last GW only needs to be provided for a few tens of hours per year - and diesel generators and/or batteries are a very good solution to this. They're unlikely to be constantly refuelling them though - maintenance is possible, but even that should be pretty limited. The economic attraction compared to power stations is that they're pretty much fit-and-forget, so the man-hours needed to keep them going should be pretty low. In a well insulated house, yes - provided that the time constant of the house is long enough, you can use the whole house as a storage heater. Essentially that's what TerryE is doing.

Headache with that is that as soon as you've got a bit of hydrogen it's really easy to burn it in gas turbines to cope with nil-wind days. Using hydrogen for heating as well means vastly more wind turbines are needed than heat pumps with hydrogen backup for the grid during calm periods - it's a very expensive solution as a result, unless you derive it from fossil gas.

Nope - persuade wealthy people to invest their money in a company which is extremely unlikely ever to make any money. They'll lose their investment, but the (less wealthy) people running the company will get a good living out of it for a few years.

Wasn't it also an unventilated cupboard?

Crudely, you're unlikely to be generating PV at the same time as your thermostat will be calling for heat. Most of the year you're using the grid as a giant battery with a round-trip "efficiency" (ratio import:export costs) of about 30% on one of the better tariffs, more like 0% on one of the Big 6 tariffs. Views differ on what is worthwhile and isn't - personally I'd be reasonably happy with that system and cost, but I'd also be fine with a payback of >10 years and doing a fair bit of work on load-shifting and time of use tariffs. I certainly wouldn't consider it a good investment from a purely financial point of view however.

If you're only using it for cleaning access then just providing a secure fixing point near to the access is enough - you'd then use a "fall restraint" system (basically a rope too short to let you reach the edge) and no further safety provision is required. If you want to use it as a roof terrace you need a properly engineered system of barriers - nobody is going to believe a claim about using fall restraint for that - and then you need full planning, building control, etc.

I thought it was no more than 200mm from the roof surface to qualify as Permitted Development. On a 45° roof that means no more than 140mm above ridge height if it goes right up to the ridge line. In practice you're going to have to work very hard to get it noticeably above ridge height and still waterproof.

Where do you get your sizing rules from? That's a lot more than I find when I look elsewhere and I'm trying to work out why - is it just running the cylinder very cool? Why do you need full access? You need sufficient access for the G3 inspection, but that's about it - the cylinder itself should last for decades.

Electricity isn't the source of power though, it's a transport medium. Unlike oil, coal, etc. it's inherently diverse due to the different sources of generation - and there is also a significant demand diversity which you get in larger grids which also helps.

I would tend to agree with you - you're in a big enough plot to make it possible, but not big enough to make it actually worthwhile. That's really two questions: Solar thermal plus a heat pump doesn't work, particularly an air-source heat pump. If you have PV or are willing to switch to a time of use tariff and run the heat pump accordingly then the cost of hot water is very low indeed when the solar thermal would be generating it since the COP is very high (warm air) and wholesale electricity costs are low as there is a lot of other people's PV on the system. That means unless you have an unlimited budget or the solar thermal is a hobby for you, you're better off spending the money on something else. PV + heat pump does work, but you're correct to note that the peak demand and peak supply really don't match. There are some impacts however: It's relatively easy to run the heat pump in summer to generate hot water when PV is available, and with a handful of exceptions (exporting it via Octopus Agile during the evening peak is actually worth rather a lot - bad time to self-consume) you want to use your own PV where you can. However, if you want to do anything more complex than running it off a time clock things get difficult and you're in the region of making up your own control system - that'll change, but nobody is really offering a suitable system yet. To give you some perspective on potential costs, I've been playing around with historical pricing data from 2020 for Octopus Agile for a very efficient new build which runs the heating when prices are cheap as much as possible. For that the electricity used by the heat pump costs about 6p/kWh on average and the electricity generated by the PV is worth about 9p/kWh on average. For me that's enough to make PV financially viable and a heat pump cheaper than gas, but your numbers will no doubt be different. If your import and export tariffs are with the same supplier, you can essentially save up summer PV and use it in winter. Not hugely efficient (you'll typically get paid something like 1/3 of what you would pay to import it), but better than nothing, particularly if you can use cheap night-rate electricity a lot in winter. Essentially you're buying 30 years of electricity up-front at a known rate whether or not you're able to use it yourself. If for instance you're doing a loft conversion and have scaffolding up anyway this can make financial sense since access can make up a surprising amount of the total cost.

<shrugs> They don't want to give up the space for storage, they don't want to pay ~3x their current gas bill for hydrogen and they don't want climate change. They get to pick any one of those, and storage (small tank with rapid recovery as per Mixergy or phase change per Sunamp) is likely to be the most palatable. The problem is that the sheer amount of energy needed to convert more than a tiny fraction of the gas supply is immense. In 2019 the UK consumed ~310 TWh of gas - in the same year total UK electricity generation was 325 TWh. Assuming a round-trip efficiency of 50% for hydrogen and a COP of 3 for heat pumps, that means either ~100 TWh of new generation for the heat pump option, or ~600 TWh for hydrogen. The difference between the two - even before allowing for other hard-to-treat areas like aviation or fertilizer production - is getting on for double the existing UK generation for 2019. Hydrogen can - and IMHO certainly will - be used to sop up excess renewable generation, but given the current price of hydrogen (equivalent to ~$0.05/kWh for hydrogen made by steam-methane reformation) then it'll just go to industrial uses rather than be put into the grid for home heating. I litre of water contains 111g of hydrogen, which is ~4.5 kWh. I'm using 12,000 kWh per year of gas at the moment, that translates to ~3m3 of water - less than a 5% increase in my annual water bill.

I think you're going to have problems with the layout given where the staircase is - you're going to lose a fair bit of room from one of the bedrooms (probably #1) if you want to add a side extension upstairs and the resulting shape might feel very awkward. It's worth thinking about what you could do on the ground floor only to get what you want - if you put a big kitchen/diner on the side as the extension (which as a single-storey may be able to go closer to the boundary) then you could convert the garage/WC/utility into a big bedroom and most of the existing kitchen space into a ground floor shower room plus a utility room. Maybe also worth looking at the feasibility of a loft conversion - because you'd continue the existing stairs upwards that's likely to be more space-efficient with the existing bedrooms than a side extension. Probably depends on how much headroom you have in the loft - looks like you're ~7m front to back with a 45° roof so with a decent sized dormer on the back that's probably a fairly good option. If you're already heating with electricity, you're a very good candidate for a heat pump. There are quite a few people who have self-installed on here and found it cheaper overall than getting a professional install and claiming the RHI. In your case more work would be required to install radiators, but that's true for any heating system and the only difference for a heat pump system is that the radiators need to be a bit bigger - double where you would otherwise have a single for instance. Insulation helps a lot - the better insulated the house the smaller and cheaper the heat pump you need is - but it isn't mandatory.

Apart from the headline which appears to be unrelated to the article, it isn't too bad. Lots of nuance missing, but that's hardly surprising. I'm pretty sure hydrogen boilers are a giant bait-and-switch scheme - get the government to commit to the mass rollout of them, then "discover" that the costs of green hydrogen are ~3x that of green electricity so force the widespread adoption of blue hydrogen (i.e. made from fossil methane with the CO2 split out at a refinery and stored). Still much more expensive than natural gas, but it means their legacy assets are worth something - certainly much more than the cost of lobbying. At a system level, for domestic heating heat pumps, even with the cost of expensive retrofits (insulation + heat pumps) thrown in, are still vastly cheaper than shifting heating to hydrogen. The boilers are the easy bit and a drop in the bucket of costs - it's the bits like the fact we would have to completely replace the high pressure gas network that are the gotchas, and the sheer amount of power generation needed to use green hydrogen for heating make it a non-starter.

Past a certain point, it's questionable whether you'll notice the difference. A problem every 20 years in a domestic setting is really good performance and really not worth paying extra to fix. The same level of reliability in a high-end hotel would mean failures every few weeks which would be utterly unacceptable.

At ~10W/m2 then an MVHR post heater will work and is probably the cheapest option. You probably want supplemental heat in the bathrooms for comfort however - either heated towel rails or underfloor mat. Note that the alternative certification criteria for Passivhaus is 10W/m2 and considered quite hard to achieve in a small house like this, so your heat loss calcs may be optimistic. I'd certainly agree with @ProDave that 16°C temperature difference (i.e. a design low temperature of +4°C) looks very small.

Even with just a fan heater and towel rails, you're looking at heating bills of ~£200/year which is seriously cheap. For that set of requirements unless you really want cooling I'd just go for whatever heater you like the look of best - definitely towel rails, if you've got MVHR a post heater is a good option and if not some sort of small convector. HW is likely to be more challenging - that spec looks like point of use heating plus an electric shower, but that might be a bit clunky and give low flow rates and high costs. A small cylinder with an immersion is probably cheaper if you can cram it in anywhere and can use off-peak power. Might be a very small house with that winter heat demand meaning insufficient space for a cylinder, but if you can fit in a hot water tank run off an immersion heater that's definitely going to be nicer to live with.

Yep, no battery. Basically it makes a prediction for how much heat and hot water is needed in a given day and from that the number of 30 minute slots that a 3kW heat pump would need to run for to fulfil that. They're then allocated to the cheapest n slots per day. No attempt to time-shift anything else apart from using a hot-fill dishwasher.

I've done a crude spreadsheet-based model which sort-of simulates this: it uses data downloaded from PV Live to work out what my own theoretical generation would be over the past few years, and combines this with historical degree-days to get a rough estimate for solar gain, heat demand and COP. Assuming no electric car and that the average daily price profile applies every day (not particularly accurate, but I haven't figured out anything better yet). Assuming demand of about 4 MWh per year and total generation of about 10 MWh (probably a bit high, but I haven't re-run the model recently) it ends up with a net payment to me of about £250 per year. In practice it would be a bit lower since more heating would be in winter when prices are higher than average, but it's probably reasonably close. Assuming those numbers are correct, that's about 4p/kWh for net exports of ~6000 kWh. So the Tesla tariff would get me £420 extra per year - nice, but would take a long time to pay off and as soon as an electric car comes into the picture the financial return drops fast. My view is that that money is better spent on more PV or a higher COP heat pump (e.g. GSHP rather than ASHP), but that's very much what suits me rather than a hard and fast set of requirements.

There's also the assumption that the tariff will be available for an extended period of time into the future, which I'm not very comfortable with. Taking that approach I also struggle to make the numbers stack up against a standard 15p import/5p export type tariff: all of the benefit of having a battery apart from backup power in an outage is baked into the unit cost, and for the predicted costs and usage the cost of that backup is pretty high, particularly if I end up with a non-Tesla electric car in future. Charging at 11p/kWh is expensive.

Digging through the published manuals it looks like a closed system - you can connect to Agile through their app, but as far as I can dig through the manuals (pretty sparse TBH) if you aren't doing so you've only got a fairly dumb on/off switching control. I can't find any mention of Modbus apart from one of your forum posts, or of an accessible API. The ideal would be to be able to read the state of charge and temperature off the API - they clearly do this themselves so the hardware supports it, but I can't find anything in the public domain that suggests it's possible for third parties to do so. While monkeying about with it would be really interesting, it's too complex for me to take on.

This is something I'm thinking a lot about at the moment. Currently at the planning stage and likely to have a heat pump and lots of PV, and since right now we're waiting on Architect and QS I need something to occupy my mind: Start out with conventional controls (thermostat for house and hot water cylinder), running through a transfer switch to the heat pump. That way if the homebrew smart controls don't work, it's easy to fall-back on something which does. On the alternative branch, have something like a Raspberry Pi which does the following: Pulls the next 24 hour pricing from the Octopus API (or another API in future as more tariffs come out). This includes the outgoing prices - the PV array will be facing SW so at least in summer we would probably be exporting during the evening peak which is worth something like 12p/kWh on the Agile version of outgoing. Uses some sort of third party site to predict generation over the next 24 hours - e.g. https://solcast.com/rooftop-solar/ Takes some sort of assumption about demand (say 500W normally, 1kW during the evening peak) and decides if we would be importing or exporting during a period, then assigning the appropriate price to that time period. Take a rough estimate for the required run time to provide the heat needed for the floor and hot water - duplicating what you've done previously, essentially. Assign heating and hot water to the two cheapest continuous blocks over a 24 hour period (one each for heating and hot water, maybe two at most for heating in the middle of winter - don't want to cycle in half hour segments to chase a few pence of savings with a heat pump). Having some sort of interrupt to turn the heating off when temperature hits the target would be nice - not mandatory, but may allow for finer temperature control/badly screwed up programming. In terms of what we need to plan for, it should actually be pretty easy to implement - big hot water tank (Mixergy would be nice but they don't seem to give anybody else access to their resistor switch data), heat pump of some sort, and LAN + power connections nearby. Does this look reasonably sensible, or am I missing something major? The heat pump is primarily because active cooling is a hard requirement for us, and any savings are likely to be pretty modest as a result - I figure the heating demand is likely to be ~600 kWh of electricity per year, plus a bit more than this for hot water. I'd be doing this primarily for the satisfaction rather than any sort of financial reason as a result.

It's worth noting that there is a difference between work (as in provide the desired comfort levels) and work efficiently (i.e. provide the lowest cost means of giving the desired comfort levels). ASHP can be designed to give good comfort levels even in an old building with mediocre insulation, but may be quite an expensive way of doing it. Major issues to address with ASHP would be: Heat emitters that work with reasonably low flow temperatures. If you're digging out and insulating the floor and fitting a new heating system, this might not actually be that hard and you probably want to do this with oil if you can as well because it should help with efficiency no matter what you do. Capital cost - a big ASHP will always be more expensive than a big oil boiler. Running cost is likely to be cheaper for oil at the moment, but that's very dependent on how oil and electricity prices vary over the life of the system so you need to take your own view on what fuel prices will be over the life of the equipment. Power supply - a big ASHP is probably going to need a 3-phase supply, which can be hard to get in a rural property. This may actually be a showstopper for an ASHP, so it's well worth working out what your total heat demand will be and whether you can do that on a single phase. If not and you can't get 3-phase at a sensible price then an ASHP is a non-starter.

Nope, they also do ones with add-ons for external ASHP or GSHP coils not just as EAHPs - https://en.nilan.dk/en-gb/frontpage/solutions/domestic-solutions/compact-solutions/domestic-solutions-total-solutions-compact-p-range/compact-p-geo How well EAHPs work will depend on how big your incidental & solar gains are, my suspicion is that in our case they won't be high enough to work well.

Has anybody apart from @PeterStarck used a compact unit (i.e. combined heating, ventilation and hot water in one box) in their build, and if so what has your experience been? We're in the planning stages for a Passivhaus, and the layout we have at the moment actually looks very suitable for a compact unit in the utility room. We've also got a huge back garden, and since Nilan do a compact unit with a 3kW built in GSHP I'm starting to suspect that might be a very good option for us since it doesn't seem to be much more expensive than the base model.