@chandykris 

In the winter period, i boost the temp during the 8 cosy hours by 0.5C, and the 4-7p period drop it by 0.5C

This gave me 85%+ usage off the night rate, i have a 5kW battery. I worked out i would need 10kW battery to take me to 95%+, that would take 20years to payback so not viable unless battery prices halve this year.

Now were in the summer usage period, heat pump is set to maintain only overnight until 7am when cheap cosy ends, then i switch to solar for the day

@agentgeorge 85% usage during off-peak rates is quite good. We have an Aira heat pump and can't boost temperatures during certain times of the day. Technically there is a smart tariff control option and comfort control that allows more variations in indoor temperature. So, the system should automatically boost and drop temperature based on tariff rates. But whenever I have turned it on, it just runs hot water at peak times, so I have lost faith and turned it off. To be fair, the Aira support team has mentioned that let it run for a couple of days and Aira Intelligence should learn by itself. But, the control freak in me won't allow the system to take full control!

Makes sense about holding off the battery expansion with a 20 year payback, end of the day renewable tech investments should give financial returns too.

@chandykris ive mentioned previously i researched heat pumps for over a year, reading mars’ forum extensively. I learnt R290 was the new gas, which id come across in Automotive forums as being the future regulated cooling gas. R134a was phased out by EU by 2025, wonder if thats for all new installations. 
i chose cosy6 as it used R290, octopus initially tried to tell me i needed a Daikin8, i argued i would insulate more to achieve a heat loss under 5.5kW/h at -6C to get the BUS grant. I didnt agree with Octopus’s heat loss calcs as id done my own and got lower. We argued for weeks but i stood my ground and we came to an agreement that i would improve the insulation by the time they applied for the grant, bit of a fudge but i accepted the challenge. The first winter was not good for the Cosy6, it barely coped with the heat loss. I should add i am renovating and extending my 3 bed house to 4 bed 2.5 bath, Octopus wont quote on renovation projects so again we had to look at the heat loss when building work completed sufficient for them to quote again 6 months after the first survey, when the manager came in to redo the survey with all the improvements, then they agreed to install. Ive also opted for UFH which works well with low flow temperature heating, you dont need a blend valve and second pump!

i have a full years costs in for running the house on electric, heating, cooking, EV, ive averaged £60/month for the past year, 85% of my usage being at the cheapest cosy period of 8hours

My yearly SPF is 3.89

My average unit cost was 12.56p/kW

My energy bill this year is 47% using cosy6 tariff than using Gas Boiler.

if I was on a standard tariff i would only just break even

i read yesterday government is “looking” at the ridiculous cost of how electricity is priced per kWh per day. Linking it to Gas price is arcane and punishing businesses in UK

According to BBC news, US electricity costs 6.5p/kW, UK 26p/kW

@agentgeorge And the Americans think that their energy prices are high! Hey Ho, Toodles.

@agentgeorge Our running costs are so similar and off by £1 per month! Our running total for the past 12 months is £708 and averages to about 11.7p per kWh. The heat pump running costs are about £330 per annum, only 40% of what it would have cost us had we been on gas. Not to mention the additional savings of £30 per month for boiler cover, as we got the 15 year all inclusive warranty from Aira that covers maintenance as well.

Having said that it's likely to go up to £800 after we decided to fix Octopus Go for the next 12 months. I was thinking our off-peak usage is about 75% to 80%. While that's the case during winter months, for the whole year we are averaging 85% too. 

If I were to design a combined tariff for all renewable tech combined, I would do the following. Two off-peak slots, 12:30 am to 5:30 am and then again from 1 pm.to 4 pm, at around 12p over kWh (average of Fixed Octopus Go and Cosy Octopus off-peak rates for our region). This will enable people who need more charge into their EVs who don't want to be restricted by just 3 hours off-peak of Cosy in the morning. This would also enable heating the hot water during afternoon off-peak slots. Usually DHW takes about 1.5 hours to 2 hours during the winter months, and it means heating has to run at full pace again after DHW run as indoor temperatures do drop a bit if house is not heated for a couple of hours in the winter. We can also run appliances like dishwasher during the afternoon off-peak slots, charge the batteries again and put some heat into the house. So, we can avoid touching the grid from 4 to 7 pm which invariably happens with Octopus Go in our case. Also, as the off-peak import rates at 12p would be same as export rates at 12p, there's no incentive to charge off-peak and export later during peak PV generation months. But, for consumers with larger battery capacity or South West/West facing panels, export during the 4 pm to 7pm will help the grid from April to August. Overall, it wouldn't be much different financially, but just suit consumers with all the renewable tech better. Or may be it will just suit our house better!!

@chandykris Well, there are a few factors that I think helps me to heat the house for 6 hours and be enought for the whole day in winter conditions.

Factor 1:When we built the house, becuse of mistake we had to put 15cm of celotex insulations in the floor under the underfloor heating tubes.

Factor 2: My brother, who did the underfloor heating put in 20mm piping in which is bigger the usal British way.

Factor 3: The heatpump is bigger oversized for the house.

Factor 4: I use the immersion heater to make the hot water so that the heatpump can focus on only heating as we only have 6 hours to run it.

Factor 5: I never used to use the backup heating in my hetpump as it is not needed when u use it normal. 24/7 Also your cop goes down when it kicks in. But when the electricity is almost 5 times cheaper it doesn't really mater and it only kicks in below 0 Celsius outside temp.

Factor 5: I turn up the weather comp so the flow temperature is higher.

I have to admit when it is really cold the upstairs, where I have radiators that does kick in for short time, but I have never seen the downstairs kick in. The temperature downstairs kept nice and warm about 21.5-23c.