Dillsue

According to our latest bill, our 15p export rate from Octopus is "guaranteed" until next June. How watertight that guarantee is or what happens next June, I don't know!

Lots of the wiring regs are open to interpretation and judgement of the spark/designer of the wiring system so if your expecting/wanting the spark who wires your house to include the DC cabling in his installation cert then probably best to take their advice on how they'd like to see the DC cables installed??

Try and speak to them if you can before you do all the paperwork and pay the application fee. Our DNO was very approachable and we had a verbal agreement within a couple of days. That was formalised with a G99 application. If you've already got one PV system then you should already have submitted a G98 notifcation, or earlier version, for that system. There's not alot of extra work involved between a G98 and G99 application and the single line drawing that you should already have.

Can you get the installers of the system to come round and explain what they've installed and how you should operate it??

Yep, G99 for the second one if it's AC coupled and capable of exporting regardless of where the exported power is coming from. Worth speaking to your DNO before you commit to anything

Don't look at your eleccy usage for the very few days it's very cold as its normal to go through the roof when very cold. For the last 24hrs with it dropping to -2.5 overnight we used 54kwh but this our first winter with a HP so all a leaning curve. WC settings have just been dropped a degree at each end as the wife is too hot:)

If you've already got PV then in most instances any surplus goes to the grid and powers your neighbours. If you then start using the surplus or put it into batteries to power AC then your neighbours are deprived of your surplus so have to increase their draw on the grid. Obviously it's up to the PV owner what they do with the PV they generate, but I don't think that adding AC has no effect on the grid.

If you have 5.68kw of POTENTIAL export then you'll need DNO permission. As rik says a single 3.68kw inverter with dual mppts is the way to go. Each mppt operates independently of the other so will manage the differing output profile from the 2 sets of panels

If youve got AC isn't one of the prime times to run it in the evening and overnight to help with sleeping?

Why 2 inverters? You'll need DNO permission with potentially more than 3.68kw of export. Put the lot on a single inverter. Most/lots of inverters can have way more DC input power than the headline power rating If you enclose the underside then it's no longer a ground mounted PV array but a building clad in solar panels so any planning limits would be those for a garden building rather than a PV array....not sure of Scottish rules though!!

Not sure about that. See https://assets.publishing.service.gov.uk/media/675c0ca798302e574b915336/eep-report-2023-2050.pdf figure 4.1

With a 3kw G98 certified inverter you don't need to ask permission from your DNO, just tell them afterwards, but...... Maybe I'm thinking of someone else but is this Buildings supply piggy backed off another buildings supply?? That might impact DNO permissions. Nothing wrong with secondhand gear but you cant legitimately use an old inverter in a new installation without the inverter complying with current standards.

From the OFGEM guidance for FIT generators, section 5.4- "Generation and export tariffs are also adjusted by the percentage increase or decrease in the Retail Price Index (RPI) over the 12-month period ending on 31 December of the previous year every April, in accordance with FIT legislation." The document is guidance but it does say that the statement is in accordance with FIT legislation?? With the advent of PV diverters and battery storage I could see them varying the deemed export % rate which I beleive the secretary of state can change within the legislation but that likely amounts to peanuts in the grand scale of the countries finances??

Have you got a link to where you've heard that?

A quick glance at gridwatch for this summer says we're a long way off not needing gas in the summer so best dialling down AC for a good while. NESO say for 2024 we had 37% green generation- 30% wind, 5% solar and 2% hydro.

I think the 0.005% of systems that experience a fire is the statistic to be mindful of.

Is that the connectors or the way they've been installed? In my very limited experience of site crimped MC4s out of the couple of dozen I've handled, 1 has had the cable pull out and on removing the pin it was obvious that whoever had crimped it had used a pair of pliers rather than the correct crimp tool.

Agreed. The one I got off ebay works fine. You can see the crimp before you insert the pin into the plastic housing so easy to check it's all secure

Why educate the masses? It's the installers job to understand and set up WC

That's fine if they are plumbers and only tout themselves as pipe fitters. If they see themselves as heating engineers then they are letting themselves and their industry down

What you describe is a classic boiler set up with the boiler starting and stopping under the control of the thermostat. What the man in the street doesn't understand is it would be more efficient and save money to run their boiler under WC. The reason it's more efficient to run WC is that when starting and stopping the boiler looses efficiency so running it under WC makes it run pretty much continuously and makes it run more efficiently. HPs are the same but they loose even more efficiency when starting and stopping than boilers do. You can run a HP under thermostat control but it's almost certainly going to hit the efficiency and running costs

My wife doesn't have a degree and isn't technically minded but got the gist of how the HP works in about 15 mins followed by a couple of questions over the following few days. A couple of those 15 minutes was explaining WC ie the water in the radiators/UFH gets warmer as it gets colder outside and the reverse as it warms up outside. That's all she needs to know about WC and all any householder needs to know.

Might be worth having a trawl through the install manual for your specific model as some features don't appear in the controllers installer menus until switches/links are set in the HP. I'd guess you may not have the ES feature but worth a check if it would be useful to you

Having got our HP up and running a few months ago and switched to WC a week or so ago, I've just had a play with the Energy State feature to see if it can be used to setback overnight running temps, which it can and more besides! On our series 3 model there's 2 wired digital inputs on the control board that can be switched to give 4 differing signals to the HP. This allows you to select 4 differing operating modes 2 of which are fixed, normal and off, with the other 2 modes allowing you to choose from 6 configurable options. These 6 options allow you set back(lower) CH and DHW temps or set forward(increase) temps. I've tested things using a 2 gang lighting switch and all the above works. I've got a 2 channel timer on order so we can switch the digital inputs on a time basis to increase CH flow temp a couple of degrees during our night time cheap period and reduce the flow temp a couple of degrees morning and evening when there's no PV. I've read on the net where some people have boosted CH and DHW temps based on surplus PV so a few options if you can sort out switching a pair of digital inputs. The install manual isn't particularly clear on how to wire the signals and I'd assumed they'd be the same as the thermostat inputs where the HP supplies 240vac that you switch back to a second terminal on the HP via a volt free contact in the thermostat. The ES terminals, TB SG1+2, aren't configured the same!! You have to switch an external 240vac and neutral to each pair of terminals to switch each input!! The terminals are marked L and N.

So long as installers do a reasonable job of heat loss calcs and emmitter sizing, HP manufacturers should have databases of WC settings that I'd have thought should be pretty near. I'm not sure if all HP controllers have this feature but our Therma V has an easily used feature to add or subtract a degree or 5 from the flow target temp which a householder could tweak if the installers settings were a tad out. All a user would need to know is not to be changing that adjustment in more than 1 degree steps and more frequently than every 12/24+ hours. There's a bit to understand about CH scheduling as in how to setback temps if away, understand that it will automatically shutdown as it warms up outside and the change in function of a thermostat as a temp limiter, if there's one fitted. If theyre using a TOU tariff they'd need to know how to get the HP to make best use of that. From a user's perspective I don't think they would need to know more than can be written on a single A4 sheet that the installer can explain in 15mins before they leave. That assumes the installer understands what they've just installed!!