Dillsue

If I charge the battery from PV then I'm charging at 15p/unit(export rate) rather than 8.5p/unit(off peak rate). If I power the house from PV rather than drawing off peak battery charge then it's the same....15p to self use PV and 8.5p to use the battery. I appreciate your description is the normal PV/battery set up but I'm just trying to see if it's possible to force export of all PV generation and use the battery until it's empty then use any available PV followed by the grid if there's no PV.

What's the rationale for switching between the tariffs?

A flip side to the companies approach maybe that the guy that attended for the service is an employee with a set schedule of services to complete in the day with householders taking time off work to wait in for him to arrive. If he gets drawn into doing unscheduled work there's a fair chance he'd mis subsequent appointments and the company would have an unhappy customer or two??

I'm looking to install batteries to charge on discounted off peak to then supply the house during peak time. We have significant PV that we get paid to export at 15p/unit. On our current Octopus Go tariff we could charge the battery at 8.5p/unit so it will help our £ROI if we can let all our PV go to export and run the house on off peak rates via the battery. I can't see a way to stop us using the PV when it's available so is there a way to force house loads to use the battery and not draw on the PV??

If the Go rate disappeared I assume I'd be able to jump onto the Cosy rate if that wasn't withdrawn as well??

That's true, if the available surplus remained static which don't beleive is the case. AFAIK there's still considerable wind power still to be installed to reduce the peak time reliance on gas. If that's the case then that wind power will need somewhere to go during off peak periods which could include any batteries I get:). Assuming I've not dropped a clanger in my calcs then what I have in mind will easily pay for itself in 3-4 years and it's a fair bet cheap TOU tariffs will last that long, if not much longer

Demand is 24/7 from the HP which is the biggest user. EV gets charged in the 8.5p off peak period every few days. The rest is consumption that can't really be shifted in any meaningful way.....asking the missus to cook overnight isn't an option. The majority of heating emitters are radiators so I don't have the thermal capacity to boost heat into a big slab using a Cosy like tariff. Ramping the HP up and down to track a Cosy like tariff would likely give us swings in temperature which I'd like to avoid.....we've just had 3 months of a steady 21 degrees with the HP running WC 24/7

The 20kwh/day is battery capacity charged at 8.5p off peak and discharged to offset 32p peak use.....daily usage can be way more than that. ASHP has gobbled an average of 40kwh/day on its own over the last week in freezing temps. We've already got PV but it doesn't do much in the winter

Maybe I'm missing something but has the system been seen to be over pressured and lifting the relief valve that likely feeds the tundish?? OPs video shows the tundish dripping with the pressure guages showing around 1 bar?? At that pressure the relief valve shouldn't be passing which suggests a leaking relief valve?? Giving the releif valves manual actuator a full turn or 2 to lift the relief valve may well get it to reseat??

So a year on from this chat and I wonder if things have changed significantly from an environmental and £ROI perspective?? Having just had our Octopus Go day rates go up to 32p/unit I've been looking at getting batteries to charge with off peak rates and use during peak rate times. Having put in an ASHP in the autumn our usage has jumped up significantly and Nov and Dec total usage averaged around 30kwh/day. If we could shift 20kwh/day of that and most of our usage for the rest of the year to off peak rates that would be quite a saving. Other than the Octopus rates changing and charge/discharge losses what else needs factoring in??

For reference on expansion vessel longevity, our solar thermal EV is 20 years old this summer and had its pressure topped up with a bike pump around 10 years ago

Anything outside the heated envelope ie everything in the shed and pipes between the shed and the house, use at least 25mm wall thickness. You can buy guides to make accurate cuts but with a bit of practice you can do a pretty good job with a pair of large scissors. Search eBay for pipe insulation cutting guide. For insulating valves and compression fittings use soft insulation a size up from the pipe work, so use 28mm insulation on 22mm fittings. Armflex black nitrile insulation moulds itself very well around fittings. Hold it in place with insulation tape but only tight enough to close up any gaps without overly squashing the insulation

Questionable UFH and known undersize radiators are never going to give you a working system. Running at 50 degrees flow temp is always going to mean bigger bills than running at lower temps. One thing to be conscious of is that ASHPs guzzle electricity when it's cold so best not to get too hung up on what it's using in a cold snap. Look at the average for a few weeks or month at a time. If your landlord cut corners to save ££ at what seems to be at your expense then her being an acquaintance is where your biggest problem lies. If a tactful conversation doesn't get her to sort out the heating then you're a bit stuck. If you want to sort out the heating then starting point is a heat loss assessment so you can resize the radiators and get someone knowledgeable to see if they can make an educated guess at the output of the UFH. If it's not adequate for a low temp heat pump flow then it can either be replaced or add radiators to the rooms with UFH. If the landlord isn't going to sort it out then there's alot of effort and expense for you to do it!!

Agreed, they can be cheaper but there's too many poor/mediocre installs that mean gas is still cheaper. Even if boilers and HPs reach cost parity there's still a bigger capital outlay to get an efficient system with large rads and UFH.

Not sure gas will ever be phased out but likely/hopefully it will start to attract an ever increasing carbon tax in the near future.

That will be a whopping battery to run an ASHP for 24 hours in freezing weather. Not sure it's cost effective to have a battery that size rather than use peak time grid eleccy for the few freezing days a year most people have???

From a quick peak at Google gives the following- 14300 kwh of gas@0.18kg co2/kwh gives 2574kg carbon per year currently 14300 kwh from HP at COP 4 uses 3575 kwh grid eleccy@0.177kg co2/kwh which gives 632kg carbon per year with HP. Google suggests 200-400kg of embodied carbon in boiler manufacturer and install. Assuming HP embodied carbon is the same as a boiler then first year of scrapping boiler and installing HP gives 632+300(boiler)+300(HP)=1232kg co2 for new HP versus 2574kg co2 continuing with gas boiler. Half the emissions in year 1 by switching to HP now. Second and subsequent years is 632kg co2 for HP versus 2574kg co2 continuing with gas boiler. Quarter the emissions in future years after switching to HP. More than happy to have these calcs challenged but seems that moving to a HP beats sticking with a gas boiler from an emissions perspective. OP has significant PV and storage which would likely lower the HP emissions further??

If youve got a near new working system then your primary motivation for change is likely only for environmental reasons?? If your boiler is still running perfectly in 20 years time that would be an awful lot of carbon emitted that you could have avoided if you'd made the change now. I'd bin the boiler now but my measure of ROI isn't just £££. Only you know your measure of ROI.

I'd be wary of tampering(repairing) a revenue grade meter given that a replacement is so cheap. FIT payers have an obligation to monitor compliance with the FIT rules and I'd be surprised if the rules allowed for a certified meter to be repaired and not recertified. A FIT meter is supposed to be inspected every 2 years and if an inspection revealed tampering, you could find your payments stopped or worse still reclaimed back to the previous meter inspection.

50vac or 75vdc for ELV. I assume part P applies above those voltages??

Is that for all DC applications? I get that there's been changes in the last few years over the use of SWA for DC PV and the Ultra PV SWA has been developed to meet the specific requirement but not necessarily for all DC applications??

AFAIK std SWA is rated for DC as the SWA I've seen includes ratings for DC as well as AC. I think the issue with DC PV is that the short circuit current(Isc)is limited by the panels to a value only slightly higher than normal generating current(Imp). This makes it virtually impossible to cost effectively fit fuses or circuit breakers that will detect the difference between Isc and Imp and trip on Isc but not trip on Imp. As you can't then reasonably protect against short circuit between the 2 conductors, double insulation is specified to reduce the chance of a short circuit between the conductors. That's my understanding but happy to hear other takes on it??

With a flow sensor rather than a flow switch I guess yours is a gen 4 HP.... model number ending Ux4? In our earlier gen 3 there's a strainer inside the HP on the return pipe. If thats fitted is it clear? Have you got a magnetic filter in the return line? Ours picks up a bit of black gunk which is clearly magnetic. If youre getting a black coating inside the flow sensor and that coating has a metallic content then that could affect the sensor?? A mag filter is stated as mandatory in some LG documentation so well worth fitting and definitely worth fitting if you've got ferrous components like radiators in the system.

Would the 10% inefficiency represent an oversized heat pump not being able to modulate its output low enough to match a more usual winter heat demand and then start short cycling 24/7?? I appreciate that an oversized heat pump might perform better in cold weather if that's what manufacturers say, but cold weather only makes up a small proportion of the heating season. The rest of the time it's mild and an oversize heat pump could be short cycling for months. Do the manufacturers performance figures cover the situation where demand is less than the minimum modulated output?

We've got a calculated 8kw loss at -2 but installed a 7kw HP on the basis that it very rarely gets to low single figure temps and being undersized means the HP should run more efficiently most of the time. It's dropped to -1 a couple of times in the last month and the HP maintained the temp OK, but it worked hard when it was cold!!! We have back up heating by way of an LPG boiler and a wood burner, but would be happy running a fan heater for a few days if we didn't have the backup and the HP couldn't cope. Remember if you oversize you're stuck with potential inefficiency for the life of the HP