Optimise renewable energy use with solar panels you your roof


This is a bit of a departure from my usual discussions about warehouse design. This blog is based on my wider interest in how technology can help protect the environment. I wanted to share some of my personal findings after owning an electric vehicle (EV) for 15 months. I also explore the impact of installing a solar photovoltaic (PV) system at my home 10 months ago. My experiences have convinced me of the viability of EVs and their potential role as part of the national energy network. 
I’m genuinely very excited when someone wants to chat with me about solar panels and my EV. I’m asked a variety of questions: “What’s the payback on the solar system?”, “How far does the car go on a charge?”, “Do you get range anxiety?”, and “Should I have batteries?”. I aim to answer these and other questions, based on my experience. 
Some of my friends describe me as an ‘expert’ in this area, but I think that’s an exaggeration. However, I do have more than a passing interest in this subject. 
Recently there has been a lot of negative press coverage about EV ownership. Some journalists have reported they are ‘as expensive, or more expensive’ to run than internal combustion engine (ICE) cars. 
I will discuss this but, if you only read this introduction, please don’t think EVs are more expensive to run than ICE cars. It’s not the case in most instances. Most EV drivers can charge from home and enjoy significantly cheaper motoring than ICE car drivers. 
My overall experience of using solar panels combined with an EV is very positive. However, what works for me might not work for you. I have advised many friends about the potential costs and benefits of installing solar panels, using batteries, and running an EV using a standard charger. You might find my conclusions at the end the most interesting part. 
I have considered payback calculation methods carefully, which has delayed publication of my findings, as the figures change each week. 
The wholesale cost of gas, which ultimately affects the cost of domestic electricity, changes from one month to the next, so it’s difficult to be exact. The cost of equipment discussed also continually changes and could go up or down. 
Hopefully, if you have an interest in the subject, you will already be thinking about whether you should have one, some, or all of the following: 
solar panels 
an EV 
battery storage. 
I have shared a series of blogs about environmental issues, and this subject is closely related to my discussions of solar panels on warehouse roofs and lithium ion powered forklift trucks
I intend this Blog to be thought provoking, so hopefully this overview will lead to some further discussion. I would appreciate your feedback and comments. 

1. The car 

Kia EV6
Collection Day: December 2021 at Kia, Leicester. 
I ordered a Kia EV6 because: 
I was impressed when I first test drove an EV6. The car is fast, quiet, very comfortable, and packed full of technology. I would have loved a Tesla model Y because I need a big hatchback but it was beyond my budget. My car usually has at least one bike in the boot at weekends. I could have also benefited from the Tesla charging network. All the same, I am pleased with my choice. 
The Kia 7-year/100,000 miles warranty gives ‘peace of mind’. Battery technology is developing quickly and people often ask: “What happens to a car, and in particular the battery, when the dealer warranty expires?”. The 7-year warranty helps alleviate this concern. I’m hopeful reservations about EV batteries will prove to be misplaced. However, only time will tell, and some battery degradation is inevitable. 
In addition, I considered a number of key features: 
Charging speed – the Kia EV6 has 800-volt architecture and, with a compatible charger, can charge at 240kWh. Theoretically the car can charge from 10% to 80% in 18 minutes. In practice this is unlikely because factors such as battery temperature and charger capability will affect the charging rate. 
Range – my EV6 has an official range of 328 miles. In my experience the real range can vary between 200 and 300 miles due to: 
driving speed – motorway speed driving at 70mph is not very efficient and will reduce the range. The car seems to be more efficient at 50 to 60 mph. 
energy use – using headlights, wipers, air conditioning, heated seats and the heated steering wheel all results in reduced range. 
temperature – the batteries operate more efficiently at temperatures over 20°C. 
driving style – if you drive more enthusiastically the range will reduce. 
regenerative braking – this affects the overall range and will depend on the terrain. 
economy mode – provides slower acceleration and improved efficiency will increase the range, although I don’t use this in normal driving conditions. 
Price – the Kia is competitively priced when compared to other 300-mile range EVs. This has changed in recent weeks with Tesla’s announcement that new car prices will reduce by up to £8,000 for certain models. 
Vehicle to load – this allows domestic appliances to be plugged into the car for a limited time in the event of a black out, I have never used this feature. 
Servicing costs – EV6 servicing is predicted to be £80 for the first year’s interim service and £200 for the second year’s full service. The service intervals are every two years or 20,000 miles. The servicing of an EV requires very little time compared to an ICE vehicle. An EV needs coolant level and brake checks. EV cars have regenerative braking which means that brakes don’t wear as fast as ICE cars. 
Road tax – battery EVs (BEVs) are currently exempt from road tax (Vehicle Excise Duty or VED) but this will change in 2025. A charge of £165 per year will apply for BEVs from 2025. If your EV is registered from 1 April 2025 you will pay £10 for the first year and then move to the standard rate. EVs won’t be exempt from the ‘expensive car supplement’. £310 a year VED will apply for cars with a list price over £40,000 for their first five years on the road. 
Congestion charging – EVs are exempt from congestion charges which are, for example, £8/day in Birmingham and £15/day in London. 
Performance – at 226 brake horsepower and with acceleration of 0 to 60 miles per hour in 7.3 seconds the car is a real pleasure to drive and live with on a daily basis. I opted for the 2-wheel drive option but the 4-wheel drive option is even faster. 
Portable power supply – vehicle to load, or V2L, allows you to use an EV6 as a portable power supply with up to 3.6kWh available. You can use it for camping equipment, film projectors, or to charge other electric vehicles. 
The cost of an EV remains at a premium compared to their ICE equivalents and I appreciate I’m fortunate to have the option to run an EV. 
I was very lucky to get a quick delivery just six weeks after ordering, which at the time should have been eight months. I think I must have received a cancelled order. 
Second hand values of electric cars have dipped sharply recently, so the residual value of the car is not as strong as it was before the Tesla price reductions. New car supply also seems to be less of a factor, and increased interest rates have reduced demand for big ticket items such as cars. 

2. The solar panels 

Solar panels on a residential roof
12 solar panels fitted to the roof of my house. 
The solar panels were ordered in March 2022 on the day that Rishi Sunak, the then UK Chancellor, announced a five-year suspension of VAT on solar panel installations for residential properties, along with other energy saving materials. The panels were installed in May 2022. 
TH tip: I would advise everyone to check with their local council to confirm whether installing a solar system is considered a permitted development that doesn’t need planning permission. 
The 3.6kW system is made up of 12 x 360-Watt panels and a 3.6 kW inverter. In simple terms, when operating at maximum capacity, the system will generate up to 3.6kW of electricity per hour. 
The overall installation cost was £5,200 and VAT was not applied. 
TH note: Haggling on the price wasn’t an option. At the time of placing my order the panels were in very high demand. I did negotiate free pigeon guards to stop nesting on the roof. The work was completed tidily by a company based in Market Harborough which I would be happy to endorse. 
A 3.6kW inverter for use with solar panels
Inverter fitted in the loft space. 

3. The car charger 

Balck Zappi tethered EV charger.
Kia EV6 charging in a domestic garage.
Zappi EV charger in my garage. 
The car charger I chose was the black Zappi 7kW Type 2 Tethered option supplied by myenergi with a hub to act as a gateway to the internet. This choice was based on my requirement to use it with solar panels. Any electricity generated by the solar panels is directed via the hub in the following sequence to: 
the house – feeding the lights and appliances 
the hot water system – if there’s an energy surplus it’s used to trickle charge the immersion heater 
the car 
the grid – finally, if there is any further surplus power, it’s directed to the grid for a possible ‘feed in’ tariff which is currently about 6p per kWh. 
TH Note: This functionality was unique to myenergi at the time of purchase. If this is what you’re looking for I recommend you research your options carefully. 
The Libbi system is myenergi’s latest option to store energy from solar panels and the grid. I was quoted £4,600 plus installation for an inverter and 5kW battery. I haven’t explored adding this to my current system as I’m unlikely to go down this route. I discuss battery storage later. 
The myenergi system communicates via an app that allows you to: 
Set up different charge modes. 
Fast – full 7kW of charge which takes 11 hours to charge the EV6 from empty 
Eco – a slow rate maintaining possible use of solar but at a constant charge rate, topped up from the grid as required 
Eco + – using excess power from the solar panels for a ‘free’ charge to the car rather than sending it to the grid 
Start/stop charging. 
Scheduled charging at specific times of the day. 
This allows users to take advantage of cheap rates. 
Work with 30-minute flexible rates (specifically with the energy provider Octopus). 
The Charger cost £1,150 after the £350 grant from the government EVHS grant, also known as the OLEV (Office for Low Emission Vehicles) plug-in grant. The last date for an installation accepted under this scheme was 31 March 2022. 
The myenergi hub.
The myenergi hub. 
The other option to charge at home is via a domestic 3-pin plug connection which charges at 2.3kW, adding up to 8 miles of range per hour. Charging the EV6’s 77 kW battery would take 77 ÷ 2.3 = 33.5 hours. Car charger installers highlight potential safety concerns about charging in this way, so this should probably only be considered as a short term or emergency option. 
TH note: There are different charger connections; the EV6 has Type 2 and CCS connection types for: 
home or public charging using the Type 2 standard socket 
charging using a combined charging system (CCS) socket, this is specifically for high speed charging. 
There are other types of charging connections such as CHAdeMO used for Nissan cars and older vehicles. 
Myenergi’s recently launched Libbi storage and inverter system works in conjunction with energy suppliers that can provide 30-minute flexible rates for both supply and feed in. This effectively allows solar generators to export and purchase electricity at favourable rates. The batteries will discharge to the grid when the rates are high and take electric from the grid when rates are low. Rates can even be negative if there is excess capacity when the energy provider will pay you to use the excess. 

4. Domestic electricity supply 

I have a contract with Octopus which provides different tariffs geared towards PV and EV owners. 
My current contract is due to finish in July 2023, and I was lucky in July 2021 to tie in a tariff at £0.176 per unit. 
TH note: The capped rate for electricity was 34p/unit at the end of March 2023. This rate has been used in my analysis. 
Octopus Go is an EV targeted tariff (rates in November 2022 based on the author’s postcode): 
day rates from 04:30 to 00:30 at 41.11p/kWh 
four hours ‘off peak’ night rate from 00:30 to 04:30 at 12.00p/kWh 
standing charge at 44.22p/day. 
Octopus Agile electricity prices change every half an hour and are based on the wholesale price of energy. A negative rate might apply when there is excess capacity within the grid. People who choose this tariff are taking a gamble because there is no contractual limit to the rates charged. However, there is an opportunity to save money depending on your energy use. 
The myenergi hub I installed can talk to the Octopus system and, with some prior notification of reduced rates, it will schedule car charging and battery top-ups based on this information. 
Octopus Intelligent offers a longer and cheaper night rate (rates in November 2022 based on the author’s postcode): 
day rates from 05:30 to 23:30 at 41.11p/kWh 
six hours ‘off peak’ night rate from 23:30 to 05:30 at 10.00p/kWh 
standing charge at 44.22p/day. 
This looks like a better option than Go as the night rate is cheaper and for longer. 
On the Octopus Smart Export Guarantee (SEG) tariff, customers are paid for any electricity they export to the grid (via home solar generation and smart batteries). Customers earn a flat rate of 4.1p/kWh for every unit of power they export. 
Domestic electricity use 
My average domestic annual electricity consumption is 3,200 units/year. Adding the EV to this and assuming 12,000 miles/year my use goes up to 4,000 + 3,200 = 7,200 units/year. I have therefore more than doubled my consumption requirements. 
Kia EV6
Table 1: Electricity calculations without solar panels. 
Your electricity bill is typically made up of a fixed day rate and a rate per kWh of electricity you use. For calculation purposes I have assumed the capped rate of £0.34 per kWh and a fixed day rate of £0.2263. With the addition of an EV my electricity bill will go up from £1,170.60 (Table 1) to £2,530.60, which includes the extra electricity to power the car (£1360 per year). 
This is a saving of £968 per year compared to my previous petrol powered car assuming 19.4p per mile for fuel. 
TH note: these calculations do not include any allowances for electricity generated by the solar panels. 
Charging costs 
My car has a 77kW battery and my current cost (until July 2022) to fully charge the car at home using electricity from the grid is 77 x £0.176 = £13.55. 
Assuming a pessimistic range of 280 miles this is 4.8p per mile. The same calculations with a rate of £0.34 = £26.18 or 9.4p per mile. 
The cost to charge using a GridServe, Ionity or Instavolt and the other ultra-rapid charge points are all approximately the same at £0.69 per kWh, and this is £53.13 or 19p per mile. 
Solar charging is £0.00 if you consider the cost of installation is written off. 
TH comment: In reality, over the year, and based on my real usage, my charging is probably 50% solar, 45% from the grid and 5% from public chargers. The average I pay to top up the car is £14.44 or 5.2p per mile. 
This compares to my previous petrol car which cost £96 for 60 litres of petrol, assuming £1.60 per litre. This assumes 32 miles to the gallon and a 500 miles range, this is19.2p per mile. 
There have been a lot of press reports that running an EV is now as expensive as running an ICE. This really isn’t true in most cases as EV drivers mostly charge at home. However, mass EV adoption is increasingly difficult without an improved and cheaper charging network. 

5. Solar consumption vs generation 

My PV suppliers estimated how much electricity the PV solar system would generate. This was based on a system called ‘Zone irradiation’ using my postcode and a climate database. The average irradiation/m2 over the past 10 years by postcode is used to predict performance. The angle of the roof is also considered and the north/south orientation. See the earlier discussion on Solar Panels for Warehouses for a more detailed description of this process. 
TH comment: PV panels are most efficient in the hours of daylight, in particular in the summer months. Like most domestic installations, my panels generate electricity in the warm weather during hours of daylight at the times when I least need it for the house, times when I don’t have the lights on, I don’t have the heating on. I use the cooker less in the summer. In the winter there are days when the system generates no power, so be warned. 
With the solar system providing most electricity when the demand is lowest we have installed a hot water immersion system diverter. Excess power is used during the day to heat water in the tank. We schedule appliances like the washing machine, tumble dryer and dishwasher to operate when the solar system provides most power. Additional power from the grid is used when the power generated by the solar system is insufficient. 
Myenergi app.
Myenergi app.
myenergi app. 
TH tip: Carefully consider how you will use the electricity generated and your consumption vs potential storage and export. 

6. Payback calculations 

My initial objective when installing the solar system was to achieve a payback period of five or six years. The cost of electricity had increased steadily over the years prior to the Ukraine invasion, which resulted in dramatic price increases. Costs are likely to continue to rise, so accurately predicting an exact payback period is difficult. 
My analysis takes account of the cost of petrol for my previous car, the additional cost of electricity to power the EV, less the power generated by the solar panels. 
Kia EV6
Table 2: Electricity calculations with solar panels. 
To run the EV without solar is £968 cheaper per year compared to my petrol car (see Table 1) assuming 100% charging at home. However, when you take 2,000 ‘free’ units of electricity from the solar system in to account, the annual saving is £1,648. This would equate to a four-year payback period for my total system. 
After four years I will save £1,648 each year. There are many variables in this calculation but I think it’s an honest assessment of my experience. I would suggest that this calculation doesn’t consider any additional value solar panels and a car charger have added to the value of the house. The £5,200 (PV) + £1,200 (EV Charger) investment may have added £3,000 to the value of the house – I would welcome some feedback on this. 
I have conservatively estimated that I use 2,000 units of electric generated by the PV panels, any excess is currently going to the grid for which I do not receive a payment under my current tariff. 

7. Battery storage 

I had some initial discussions about the option of fitting batteries with my supplier before installing my PV panels. I had completed some analysis and concluded that it wouldn’t be a benefit at the time. 
Having spoken to a few installers the consensus is that it makes sense to install the panels first, and to consider retrofitting the batteries at least a year later. You will then have actual generation and usage history to help make the right decision. 
In the back of my mind is the knowledge that car batteries will power the house in the future. They will also be used to provide a power supply to the grid using vehicle to grid (V2G) systems. 
My current view is that batteries can provide significant savings, even without an EV. For example, you could buy a battery system with 10kW storage capacity costing £5,000 fully installed. You could top this up at night at approximately 10p/unit using the lower ‘off peak’ rate and use the battery to power the house at other times. You could also use timers to run appliances during cheap times too. 
My usage demand of 3,200 units/year (without the car) would mean spending 3,200 x £0.10 = £320/year on electric compared to 3200 x £0.34 = £1,088. The payback on the batteries would be 4.6 years and there would then be an annual saving of £768 per year. 
You could also argue that the batteries have added value to the house. For the time being, I have decided that I will have a big battery on wheels in my garage (my EV) which in the future will provide power to the house and to the grid. 

8. Vehicle to grid (V2G) 

Kia EV6
Some EVs are now designed to allow for the car battery to be used to: 
power the home 
store power to sell back to the grid at periods of high demand. 
The EV can then recharge from the grid or when prices are lower, with top-ups from solar panels. They need to be equipped with hardware ready for bi-directional charging. This allows for the grid to supply surplus renewable energy to store for use at a time when there is peak demand. 
Limited trials have been conducted in a scheme involving Nissan and Octopus. In the US the Ford F150 Lightning has also been used to power the grid. The new 2023 VW ID3 and the new Volvo EX90 have been designed for 2-way flow of electric. This is likely to be a standard feature for all new EVs soon. This will however put additional strain on the batteries, so time will tell. 

9. Living with an EV 

From my experience, living with an EV is mostly very easy. You can wake up to a full ‘tank’ of power every morning. I would suggest that having to plug the car in a couple of times per week is more convenient than making a weekly visit to a petrol station. 
I have a large range in my car. 300 miles is realistic in the summer with a pessimistic range of 220 miles in the winter. This means longer journeys do require some planning. 
I like to plan my journey with a 50-mile buffer built in. If I’m doing a 200 mile round trip in the winter, or 250 miles in the summer, I will plan a top up charge within my journey. Recently new chargers located close to my home at Rugby, Cambridge and Peterborough Services allow me to use these as a back-up plan if required. 
If you run an EV you quickly learn where you can get a reliable fast charge. Charging away from home should only be done when absolutely necessary. 

10. Charging away from home 

Public charge points price their rates based on numerous factors including: 
price of wholesale electricity from the grid 
the charging speed charge points can reach 
location of the charge point 
the type of charge point; for example, a destination charger, fast charger or rapid charge point. 
While public charging is more expensive than home charging, you can still save money by planning ahead, and choosing the right charging network and charger type. 
UK Tesla charging stations open to non-Tesla cars.
Tesla charging stations open to non-Tesla cars. 
TH note: There are now Tesla charge stations open to non-Tesla drivers. However, the charge cables are short and may result in a car taking up two bays to gain access to a charger. This is true for my Kia, and I have not attempted to charge at a Tesla station yet. 
TH tip: When planning charging away from home, I usually look for Ionity or GridServe locations as I have found them reliable, and they are more likely to have a vacant charge point. I look for charge locations that have at least four chargers, and I usually plan locations with ultra-rapid chargers. I have saved my favourite charge locations in Google Maps. 
The cost of the ultra-rapid chargers deters many users. However, the fact they charge so quickly means they are only used for an average of 20 minutes, so chargers are soon vacated. Although using ultra-rapid chargers aren’t the most economical options they are the quickest, and as I rarely visit them it’s a cost I’m happy to absorb. 
Gridserve EV charging station, Essex
GridServe, Essex. 
Ionity EV charging station, Norwich.
Ionity, Norwich. 
Charger types 
Rapid DC chargers provide power at 50kW. 
Ultra-rapid DC chargers provide power at 100kW or more. These are typically 100kW, 150kW, or 350kW. Other maximum EV charging speeds between these figures are also available. 
TH comment: I usually have plans A, B and C, just in case, although I have only ever used plan A so far. As my car charges quickly, if I can find at 350kW charger, a top up charge will take between five and 15 minutes. I either wait with the car or grab a coffee and return to the car when the charge is complete. The Kia app on my phone alerts me 10 minutes before the charge is expected to complete, and at the time of completion too. It’s very easy to use. 
Typical long journey plan 
Assuming I plan to make a 350-mile journey, I will fill the car up to 100% and then, after driving about 100 to 150 miles, I will plan in a coffee stop and a charge. 
Charging up to 80% is considered good etiquette amongst the EV driver community. The reason is that car charging slows at 80% and the final 20% can take as long as the top up to 80%. If the charge location is not busy, and you need to top up to 100% then that’s OK too. Everyone I have encountered at charge stations has been very pleasant and generally very enthusiastic about the whole EV experience. 
However, charging is not without problems: 
chargers aren’t always working 
numerous apps are required to cover all the options 
radio frequency identification (RFID) payment cards aren’t always accepted 
there isn’t a clear queuing system 
drivers have reported aggressive and intimidating behaviour when chargers are busy 
as more EVs are being sold, the number of chargers available needs to increase proportionately. I have noticed the occasional queue, especially over bank holidays. 


I wanted to share with you some of the things I have learnt from using PV panels and an EV for almost a year. It is fair to say that the up-front investment in solar panels and an EV is high. However, the payback period is lower than I initially thought. 
When the sun is shining, and the car is connected to the PV system, it’s quite exciting to watch the power meter on your app showing your EV’s range increase. Running an EV has been a great experience and I am definitely converted. There’s no going back to and ICE car for me unless it is a little sports car in the garage for weekends! 
There is, of course, a bigger picture here. I decided I wanted to make a positive contribution towards our combined responsibility to take care of the environment. The current network of power cables and pylons around the country is insufficient to meet future demands. We don’t have enough capacity to meet the demands of peak use, and this, coupled with a continued adoption of EVs will put a greater strain on our struggling network. We are also very reliant on gas of which a small percentage comes indirectly from Russia, this is not ideal in the current climate. 
We do have an answer to this problem. With continued investment we can increase power generation from renewable energy sources including: 
• hydropower to harness the power of water in large-scale dams and tidal energy projects 
• wind using offshore and onshore wind turbines 
• solar using panels located on domestic houses, solar farms, industrial and commercial units including factories and warehouses. 
We can also store power generated in batteries, possibly even those repurposed from older EVs. Systems such as V2G can send power back to the grid, resulting in a more balanced network. This could even reduce or eliminate the need to use coal powered generating plants during peak demand times. Storing electricity in batteries close to the point of demand will do more than simply help to achieve our country’s sustainability targets. It could also reduce potential energy waste from renewable sources when production exceeds demand. One day we might even consider whether we really need to build additional nuclear power stations in the future. 
Tony’s consulting work 
As an independent consultant specialising in warehouse design, I must stay at the forefront of modern technology and equipment. 
My work for my clients is always impartial and their best interests are my top priority. If you are considering how to improve your environmental impact and are striving towards net zero targets please let me know. 
Please ask me for advice. I would be very happy to have an initial, no obligation chat or, if required, provide a quotation for any assistance on any consulting project. 
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