I thought it was about to time I wrote something non work related on here. I often get asked by colleagues/friends about how I power my home. They know I have a Tesla Model S, they know I have Solar panels and they know I have "home batteries" because I like to draw as little energy from the national grid as possible. I almost gave a lightning talk at CommCon 2019 about this topic but time was running short as it was so here's what would have gone into the lightning talk. I guess whether you find it interesting or not is whether you're interested in reducing your carbon footprint going forward.
A Quick TLDR;
Ultimately the energy we use from the National Grid is greener, the energy we use in the summer is mostly self generated and I love driving an EV.
The goal isn't really to draw as little from the grid as possible, it's to draw as little from the grid at peak times as possible most of all.
A bit of background
It all started when we moved into our current house; we had some money left over from the sale/purchase and wanted to reduce our electricity bills; I work from home and have computers running 24/7, many smart devices etc etc etc - all drawing power constantly - we have a base load of around 1kw/h. It wasn't really anything to do with "going green" at all - we had some money, spent it on reducing our costs every month and in the process got a cheque for our Solar generation/export every 4 months. Nice right?
Fast forward a few years and I got the Tesla Model S, again 100% driven by the fact I wanted a company car (not a personal one) and the only way to do that without spending a lot on personal tax to HMRC was to get electric; the only car that matched long distance and that extra bit of luxury was a Tesla. But this is where I got into trying to shift usage of the National Grid to times where it's not under high demand and therefore electric is cheaper to consume.
What gadgets do I have?
- Tesla Model S - 100D
- 2x Tesla Powerwalls & Tesla Gateway
- 8kw of Solar Panels (pointed in two different directions)
- MyEnergi Zappi EVSE (charger for the car), MyEnergi Hub
Tesla are by far out in front when it comes to electric cars and their home energy products - no-one comes close to the Powerwall's energy density for the price. Inside each Powerwall you get 13.5kWh of storage - we have two so that's 27kWh of storage which works out well when you have around a 1kw/h base-load in the house with occasional heaters going on and off in my outdoor office.
The MyEnergi Zappi and Hub allow us to charge the car using excess Solar during the day. Now that we have two Powerwalls this happens infrequently but when we only had the one (or back when we didn't have a Powerwall at all), it could mean any excess solar during the day could be pumped into the car instead of going back to the grid - it essentially monitors the power going back to the grid, once it gets to the right level for the car, it starts sending that exact amount to the car. Most chargers can't do this variable amount of current. Imagine having the power to put "free" miles into your car just by the power of the sun - pretty damn cool.
This is better described by a picture. It's definitely a non-simple setup; but I wouldn't call it a complex one either.
Did you know electricity can flow in either direction within all of your circuits inside your home? That's how this all works. Powerwalls consume energy as well as push it out to keep up with what the house is trying to consume from the grid. The Grid can cope with us asking for energy as well as us pushing it back out to them for someone else to use. Solar panel inverters (they take the DC the panels generate and convert it into AC which is what we use in our homes) only generate electricity, just as the Model S can't push energy back into the house because the inverters in the car (yes, the energy is stored as DC in the car too) can't chuck that energy back into AC (well maybe they can in something called Vehicle To Grid charging but thats a completely separate topic.)
TLDR; We signed up to an energy supplier who could give us cheap electric at night to charge the Powerwall (and now the Powerwalls) as well as the car and we run off that stored electric all day. The image below is a pretty standard day where the Powerwalls are almost empty and we need to top the car up.
That's 55kWh of energy at 5p per kw - resulting in £2.75 to run the house and the car that day. This is in the height of winter with almost no Solar generation the day before (3.2kWh) to help top up the Powerwalls. Some may say that's still pretty expensive to run your house all day but if we take a closer look around 28 of that 54 would be energy for the car, 4 would be the normal base load for the house during that time, and around 23 is going into the Powerwalls; 23+4 = my house load that day would have cost £4.05 (if we take around 15p per kWh average for my area) just for one day - not even taking into consideration the car.
In the summer you can pretty much say that my solar generation will top the Powerwalls up close to full every day and we'll never top them up from the grid (there's a mode called Self-powered in the Tesla Gateway) meaning our only cost for energy during the summer is from topping up the car.
To be able to do all of this I rely on my energy provider - Octopus and an energy plan called Octopus Go - 4 hours of energy at 5 pence per kWh - if you're interested in using Octopus you can use my referral link and get yourself a £50 credit on your account. They're what you call a very green provider which is nice to know too.
The long and short of it all is that while reducing my carbon footprint has become more important to me (we'll soon probably replace a Land Rover 4x4 with another EV); that's not really been the primary goal through all of this - saving money by using the right tech has been, it's just that a nice byproduct is becoming more green in our energy usage. Some of you may read this and say, sure you're saving money now but you've spent X on a Model S, and Y on 2x Powerwalls and Solar panels and you're absolutely right; but ultimately that money in savings accounts really wasn't giving us much of a return and this reduces our monthly bills now and in around 9-10 years time, the Powerwalls and the solar panels would have paid for themselves - even quicker if you're in a different part of the world where you have sun all year round and electricity prices are much higher than what we have in the UK.
If you're looking at purchasing a Model S, X, 3 you can use my Tesla referral link for some free supercharging.
Let me know if this is at all interesting on twitter. I could talk about EVs, Battery tech, the in's and outs of charging curves all day but it's probably not that interesting to anyone unless they've also got a Powerwall or an EV.