Thursday 2 February 2023

A Year of Solar and 6 Months Heat Pump

It's been just over a year since we had our Solar installed and 6 months since we had the heat pump installed.  I've had a couple of people ask me how it's all been going, so thought I would do a brief update.

So first of all, our timeline.

  • 7th December 2021 - Solar Installed.  This was 17 panels and an 8.2 kWh Solar Battery.
  • May 2022 - Energy Efficiently Improved Our Home and Applied for the Heat Pump Grant
  • July 2022 - Heat Pump Installed
  • Aug 2022 - Got rid of the Gas Fire and Hob and moved the house to completely electric
  • Oct 2022 - Got a second 9.5 kWh battery installed and an EPS setup.
  • Dec 2022 - Had an Audit by OfGem
So what has all this meant ?  Well first of all, look at our energy consumption.

Our Energy Consumption from the Grid

So you can see our energy consumption for 2022 is significantly less than it was for 2021.  Typically our overall KWh consumption is around 50% of what it was before the changes.  Bear in mind I am running an electric car as well.  Also bear in mind, that for most tariff's,  electricity is nearly 3 times the cost of gas,  so we're probably around breaking even in consumption cost terms.

Solar Results

If you consider the electricity we have generated month on month, you can clearly see great levels of solar production between March and November.  In November, with the cold spell and the heat pump warming the house,  we had much less surplus electricity to sell back to the grid.  But the results are definitely encouraging.

Solar Generated and Sold

So our primary goal for solar is to be able to run as much as possible without huge grid demand.  Hence the batteries,   we would rather charge and consume our own electricity, saving 38p / KWh rather than sell to the grid and earn 5p / KWh.  Government if you're reading this,  the SEG rates are rubbish and really need to be improved.  

Octopus do do a 15p SEG,  but it's not compatible with the Octopus Go / Octopus Go Faster tariffs that give very cheap overnight electricity.  Our savings for Octopus Go Faster far outstrip how much extra we could earn on the SEG.

Solar Batteries

One question people often ask is,  are the batteries worth it ?  Well, charging excess into them in Spring, Summer and Autumn to use overnight, plus charging them at cheap overnight rates in winter means they definitely are.  In fact,  being able to use the batteries for a large part of our demand means that,  our average cost per KWh per day in winter is around 19p per 24 hour period.  Around 50% of our day time tariff rate.   

So a huge saving, when you consider we are still using considerable Grid energy during the winter months.  In fact, if I look at the electricity purchased, this month, it would have cost £490 as opposed to the cost of electric we have purchased overnight and used during the day, our bill for the last 30 days is £226.

In addition,  the national grid has been running trials this winter, to avoid potential power cuts and we've been taking part.  Being on Octopus, having a smart meter and batteries puts us in an ideal position.  The idea is,  24 hours in advance,  we will get notified of a time period to reduce our electricity demand.  Each KWh we save,  we get around £2.25 paid to us.  So we have taken part in 7 sessions,  each session has been 1 or 1.5 hours.  All we have done is avoided using any expensive items (dishwasher, washer, tumble dryer, oven, hob, kettle etc),  turned off the heat pump, watched tv on the laptop / iPad and switched to the EPS batteries for our lighting.  So far, we have been paid just over £50 in savings.

Having an EPS

One other advantage of having batteries, is the support for an Emergency Power System.  Here, the inverter will, during a power cut,  switch over to the batteries.  Now the batteries are only able to run with a maximum load of 2.6KWh.  So, when the inverter switches it only handles the lights plus a plug socket in the garage.  The heat pump, normal sockets etc all lose their power.  However, it's pretty nice in the event of a power cut not having to worry about candles or trying to feel around your house in the dark.

We're able to set a reserve power limit (e.g. 20%), the batteries should retain this percentage for use by the EPS,  but GivEnergy have a bug at the moment that means it doesn't always work and a new firmware release is due shortly and should fix this.

Heat Pump Results

It is really funny when I talk to people about having a heat pump,  it is hilarious how many people have opinions about a subject they know absolutely nothing about.  In fact, some of the statements people have said to me and my wife include :-

"I would never have one because they can't heat your house more than 18 degrees which is too cold"

"I would never have one because they are noisy"

"Energy cannot be 300+ percent efficient,  it's too good to be true"

"Electric Costs more than gas so it's not saving"

"It costs too much to install"

So, first of all,  our heat pump can easily heat our house to 25 degrees (and we have done it to see).

In fact, unless the outside temperature drops below -20 degrees C,  I think the house will remain toasty warm.  We had new radiators sized for the house and the house is the warmest now since we moved in 28 years ago.

Even when it's running at full power,  it's pretty quiet too.  And the 300+ percent heating efficiency is possible.  Our heat pump at full power, is operating at just over 3x,  i.e. every KWh of electric we put in, we get 3KWh of heat indoors.  This is because,  it's not really an efficiency of heat generation in a close system, it is the fact that all a heat pump does is move heat, from the air outside, into a liquid that's used inside.  Provided the outside has enough heat (i.e. is above -20C), we'll be toasty warm inside.

So people say, if it's freezing, there is no heat.  Well, at absolute zero (-273C).  There is no heat,  every temp above this has a level of heat.  So 0C has quite a lot of heat in it,  so as long as you have the right heat pump and the right refrigerant, it will work just fine.  If it ever gets to -273C in Yorkshire,  I think I might me worried about more than the Heat Pump !!!!

The one question I have been asked regularly that does make sense

"Can you run the Heat Pump from Solar?"

Quick answer, yes, but...... longer answer is that,  during Summer when all you need is hot water and you are generating surplus electricity,  you can run the heat pump easily.  In fact, your hot water will probably be totally free April - October.  However,  if it were very sunny in the UK in winter,  then when you needed to heat your home, you would be able to run it from Solar.  However, in the UK, Solar Production is down during November, December, January so we would rarely generate enough electricity to run the heat pump.  But what you do generate,  can go into the Heat Pump and reduce your bills.

Heat Pump Grant

Many of you readers out there will recall that the government provide a £5k contribution to the cost if your house is a D or better rating, you have loft insulation,  you have cavity wall insulations etc.  You may recall we got an A rated EPC and were granted the money.  The heat pump being installed in July.

Something for you to be aware of,  in December we received a communication from OfGem, where they wanted to visit,  carry out an audit and verify that the works were carried out correctly,  that the house EPC really was correct and that the grant has been correctly utilised.

Well, they visited,  and except for a couple of slight hiccups, everything went OK and they have written now confirming that the audit was successful.  But if you get a grant beware about our two little hiccups below.
  1. On proving we own the house they demand a mortgage statement to prove your own the house.  Having not had a mortgage for over 10 years,  we couldn't do this.  It took two attempts with presenting the title deeds before they accepted them. Make sure you have access to the deeds and can show them if you do not have a mortgage.
  2. They also complained to the installers,  stating that the heat pump did not 100% heat our water via the heat pump and occasionally the immersion heater is used.  But this is because the heat pump usually heats the water to 55 degrees C.  Unfortunately,  the water has to be over 60 degrees to kill legionella.  So once every week or two,  our cylinder boosts the temperature to over 60 degrees for this purpose.  This had to be explained to the auditor, which seemed strange as they should know this.


Well it's been an exciting year of change.  Being a bit of an IT Geek, we have a data warehouse with 30 minute meter readings taken from the last year and a half,  30 minute snapshots of Solar Production and Grid Import / Export,  Battery Load and even statistics showing whether the house is using Carbon Friendly electricity or not.  

Household dashboard

This shows a snapshot taken on my energy dashboard, showing actual solar production against forecast,  grid consumption / battery consumption and real time costs.

I have built all of the API integrations into both the data warehouse and a home assistant dashboard including integrations with Octopus Energy, GivEnergy Inverter to provide a real-time (well 30 minute delayed) view of the house consumption.  These are all presented on an always on tablet,  that provides a view of the house energy at any point in time (as well as being able to access cameras, plugs, door bells etc etc). 

Oh, and, the rebel can't believe just how much we have saved over the last 12 months.  Yes, with the cost of living crisis, most things are now costing us more than when we started years ago on our climate journey.  But our costs to run the house are maybe 20 % higher than 18 months ago (and I am now running my car in that as well, so the fuel saving alone means we are better off than before, and significantly better off than many people who's electricity and gas bills have sky rocketed).

I am so excited that our share of Wind Farm comes on-line at the end of 2023 to save us even more.

Update - 21/02/2023

For any of you that are getting Solar and Batteries,  Octopus Energy have recently announced a new tariff specifically for people with Solar and Solar Batteries.  Called Octopus Flux,  it pays considerably more for peak solar (23p per unit was our quote),  and has a cheap tariff 2am to 5am ideal for topping up those batteries.

If you're interested and not an Octopus customer,  use the referral code below,  you'll get. a £50 credit on your bills (and I will too).