Becoming an Electricity Island Including Free Fuel for the Car – Part 1

Solar Edge PV Panel & Tesla Powerwall Battery Storage Install

This isn’t the sort of thing I would normally blog about. However, it seems like a geeky enough topic considering the gadgets and technology involved, so why not. Hopefully it will also encourage others to do something similar.

In March of 2021 after many months of research I finally went ahead with the installation of a Solar Photovoltaic (PV) and battery storage system. Then in May I replaced the wife’s car with a full electric vehicle (EV) as well.


Let’s start with the obvious theory, what is an electricity island? Well, simply put, because I’m not an electrician, it’s an electrical system that is or can be isolated from other electrical systems.

In my case, my house is an island that can be disconnected from the national grid supply. Practically of course, the feed from the national grid remains in place, but I have my own supply, my own earthing rod, and the means to power the house without help from the mainland. If its ok the extend the island metaphor.


The motivation for this project came in a few different forms, as follows and in order of priority:

  1. Having 3 children who will no doubt face many environmental challenges and hardship in their lifetime if current generations don’t act against the destruction of the planet.
  2. Becoming a little fed up with paying utility companies the constantly increasing prices for energy and generally having them raise direct debit amounts without justification to hoard my money for themselves. The last call center person I spoke to will certainly remember what it means to contact someone that builds data analytics platforms for a living and knows what a rolling average is! 😀
  3. Financially, thinking about how much money I’ll spend on electricity over the next 10 years anyway if I did nothing. More to come on this point.
  4. Wanting a technical solution to power cuts and disruptions, especially while working from home. In short, having a whole house UPS.
  5. Mindful that the UK government want all cars to be electric by 2030.

Given the above, let’s explore point 3 in a little more depth.

  • In 2020 I used 6,653 kwh of electricity as a family of 5 in a 4 bedroom house.
  • At the time the unit price for this from my supplier was 0.1508p.
  • In addition, I was paying a standing daily charge of 0.1836p.
  • Typically, the unit price of electricity goes up every year by at least 2%. Sometimes, more like 7%.

So, for 2020:

6653 x 0.1508 = £1,003.27

365 x 0.1836 = £67.01

Then if we roll that forward for 10 years, including an optimistic 2% increase in energy per year.


As you can see, if I did nothing, in 10 years I could have spent circa £16k on electricity anyway! With that in mind the investment and upfront cost of the equipment/install became very easy to justify. Even the wife accepted it 🙂

The cost of the panels and battery basically mean I’ve just bought my energy in advance for now, then beyond the point of breaking even, I’ll be easily saving £1,000 a year plus making money from any energy I export back to the national grid. I’ll do some more analysis on this in a later post with my breakeven own predictions. A few months more data is required first. Mmmmm, data!! 😀


Right then. Theory done. Let’s turn our attention to the tech! In part 1, I’ll focus on the solar panels and battery. Then cover the car and charging system in the next post.

The Panels

My house is perfectly south facing so I have a total of 18x panels. These are JA Solar (Segen) JAM60S10-345/MR cells each capable of generating 345 watts.

The array on the roof is split between 16x panels on the main part, then 2x panels each side of the dormer window thing. Because of the split and the possibility for shading I also had SolarEdge optimisers fitted to accompany a SolarEdge SE6000H HD Wave inverter. This gives me an output of 6.21 kWp, the ‘p’ standing for peak. In reality, in this country the most I’ve seen it hit is 5.5 kWh.

The inverter lives in my loft, connected to the LAN via Cat6 cable, with the mains 240 Volt twin/earth cable fed inside the cavity wall down the side of the building to the meter box and Tesla Gateway.

The SolarEdge app is excellent for tracking what is being generated as well as offering a view of how each panel is performing. This basically makes the generation meter seen in the picture on the right redundant. This is unfortunately required as part of solar PV install.

Currently my best day was 8th June, where I generated 43 kwh. I didn’t used to care to much about the weather forecast, now I find it’s the first thing I want to know each day!

The Battery

Time to roll out the Tesla shiny things and all-round slick engineering, so slick!

The reason for having a battery. Firstly, the UK government now pay you very little for exporting electricity compared to 5 years ago. It therefore makes much more sense to keep that energy instead of exporting. So, with the battery, the theory is that during the day the solar panels provide enough energy for the house with the excess sent to charge up the battery. Then once the sun sets and during the night the house uses the battery power instead of energy from the grid. Realistically, with a good solar array and being careful with how you use household appliances, for the months of March to November there is enough sun to stay off grid. To be confirmed.

By comparison, without the battery, the excess energy would get exported to the grid at a fraction of the cost that you would otherwise pay to import it. E.g: 5p per kWh to export. 17p per kWh to import. Which would mean you sell it at 5p during the day, but have to buy it back at night at triple the cost. So don’t do that,

As a general rule, I don’t want to export anything, I want to keep all the energy I’ve generated to use.

As mentioned above in my subheading of Why? relating to point 5, having a whole house UPS battery backup is very handy. To my knowledge, only the Tesla Powerwall solution offers this seamless switch over in the event of a “power cut”. It’s probably worth mentioning that this can be purchased on its own, you don’t have to have solar panels to take advantage of the kit. Although, the VAT amount changes from 20% to 5% on the battery if purchased as part of a solar panel install.

Anyway, with UPS server rack/server room concepts in mind, what you can see in the picture above is the gateway/brain that acts of the control box for all things:

  • Handling the power generation input from the solar panels.
  • Handling the flow of power to and from the Powerwall battery.
  • Sitting between the national grid supply and the house consumer unit.
  • In my case, acting as the new primary consumer unit supporting feeds for other things, such as the car charger and air conditioning.
  • Housing about 10 different CT clamps to make sure power is flowing in the right direction based on my setup.
  • Serving the Tesla app, connected to the LAN via Cat6 cable 🙂
  • Connection of an earthing rod to complete the island affect because new build houses rely on mains electric for the earth.

If you’re interested, for my house the power split and connection of stuff could be drawn like the below, where a normal house might have one or two consumer units, mine has four. The main reason for this is in my house the consumer unit as actually located right in the middle of the building, under the stairs, making it almost impossible to reach from outside walls. Hence a more complex set of sub consumer boards was required. Especially for heavy loads.

** I felt the need to include the sun in the diagram as it’s a critical component of everything below! Ha.

Other things to note about the battery:

  • Usable capacity is 13.5 kWh.
  • Peak power output 7 kW.
  • Via the app you can configure a percentage of the battery’s capacity to reserve in the event of power cuts.
  • It weighs 120kg.
  • The green light on the side can be turned off.

A couple of views from the Tesla app, all of which you can easily Google and find in the Tesla marketing material.

How Much?

So, I’m sure the above leaves you with just one question, how much? Via my local, friendly MCS approved installer I paid £14,719.88

Yes, that’s a lot of hard-earned money and I definitely consider myself extremely lucky to be in a position of being able to afford it. However, consider my earlier point, this is just an investment, you’ll spend £16k on electricity bills in the next 10 years anyway! I just paid for mine upfront.

I hope you found this blog interesting. I will do a few follow ups on the car charger, my cost predictions given data collected so far and importantly; what’s the plan for winter to keep things cheap via some home automation and agile import tariff API’s. Stay tuned.

Many thanks for reading.

3 thoughts on “Becoming an Electricity Island Including Free Fuel for the Car – Part 1

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