I went down a rabbit hole on solar power in the UK.  Most UK homes use gas for heating.  The amount of heating varies through the year because of climate.  The climate varies partly due to the amount of sunlight. That should be a clue that solar isn't really a great choice for heating.

This chart shows how my gas (heat and hot water) varies through the year.  My peak requirement for heat is approximately 14kWh per day.  That's approximately the capacity of a Tesla Powerwall 3 and that doesn't include the electricity used.  This also implies the need to completely charge the Powerwall every 24 hours.  However to provide electric heat the most likely solution would be a heat pump.  A heat pump installed correctly would use about 1/3rd the power, so about 5kWh.  If we add in the electric my total consumption would be about 6kWh per day.

Domestic solar panels don't generally track the suns path through the sky.  In the UK they are pointed south at about 30 degrees.  This is a compromise that gets the most sun while keeping the install simple.
I snagged these images from Viridian Solar's website.   You can link to the relevant pages here:

• Average daily light energy through Year
• Effect of orientation and inclination

What should be obvious is that the amount of energy available from solar is significantly less in winter and the orientation of the panels is important

If we assume a target of 6kWh electricity consumed and a Powerwall or similar as a buffer battery how many panels do we need?
​I assumed the panels could be placed ideally.
Using this calculator I reverse calculated required installed peak power kWp to be about 70.   

Now we need to figure out how many panels are needed to get to that 70kWh figure.  Obviously it depends on a bunch of factors but it seems like the answer is around 160.  I've seen some widely varying figures for the number of panels needed btw. 

Here are a couple of example websites suggesting the number of panels needed:​

• www.homebuilding.co.uk/advice/how-many-solar-panels-do-I-need
• https://heatable.co.uk/solar/advice/how-many-solar-panels-do-you-need

Obviously this isn't practical for most homes and would be very expensive. 

Maybe we need to think more about home design and try to go for something like the passivhaus standard which claims to barely need heating at all.  Hard to believe and a topic for anther day. 

Also it isn't all doom and gloom. A moderate solar system like that installed on many homes will reduce the amount of gas burned over the year to generate electricity and will also save some money for the owner. 

The conclusion I'm drawing (assuming no solar or incentives) is that a heatpump will emit significantly less co2 but it will cost the user more because electricity is a lot more expensive than gas. 

​Maybe a sensible solar installation could make up the cost difference between gas and electric while providing another reduction in co2.   If you could generate 1.5kWh per day from solar in the winter rather than 6 that would cover the cost while reducing co2 by another 25%.  You would still need a sizable solar array to achieve this.  Possibly as many as 30 panels. 

I use this blog mostly to collect things I think I might need later.  It's kind of like a notebook. 
I'm not a professional. 
I know less about houses than most people I know. 
Prices vary a lot over time.  Solar panel technology gets better over time. 

​There's a good chance my numbers are off somewhere or I've misunderstood something, in which case, let me know and I'll update. 

​You should probably do your own research, starting by being clear what your motivations and goals are. 

​I’m basically a vegetarian for climate change reasons but I still eat some chicken, fish, eggs and cheese. Also I never learned to cook meat. I don’t waste a lot of food which the chart assumes.
I’m going to estimate my food footprint at 1800 kg  of co2.
That's significantly more than my car and my heat combined, which is crazy.
​The article gives a nice chart of various food co2 impacts per kg.

​​Are you as surprised by this, as I was?

For context a return flight from London to San Francisco in economy is 2600Kg of co2. 
​That's more than my food and heat combined. 

I was thinking about taking a plane trip, so decided to compare co2 output of various activities.  I thought comparing activities would give some perspective. 

• Powering my flat for a year   Approx 1t (metric tonne) of co2
• Annual car use Approx 10k km 2.8t

So that gives me an output of about 4t.  I've seen different estimates for food but it seems like given my mostly pescatarian diet my diet is probably about 1.5t, so maybe we say my co2 is about 6t.  Average European is about 9, but I drive, heat and eat less probably. 

A return flight  from London to San Francisco is about 0.9T (This seems lower than last time I checked). 

So flying is bad but still much less than driving depending on how often you fly.  Switching to a Tesla Model 3 ( assuming that was practical for me which it isn't yet) would almost half my vehicle co2 emissions.  A VW Polo or similar would split the difference. 

My actual agenda is a speculative trip to Salzberg.  A return flight from Bristol is about .25t and takes under 3 hours.  To go by train I'd have to split the trip over several days which adds in the need for at least one hotel stay, which in itself adds co2 footprint as well as time and stress.  So dunno, but at least I can picture the co2 figures in my head better now. 

The amount of co2 emitted during the construction of a car (petrol or electric) is always small compared to the energy emitted by driving it around.  That has always seemed counterintuitive to me.  In my mind it takes way more energy to design and make the thing than to drive it around, but I'm obviously totally wrong. Moving heavy things around really fast uses lots of energy. 
You can read the whole report here. 

 I got an e-bike!  I used to be a keen cyclist, but I'm lazy and unfit.  CV19 seemed like a great excuse to get back out on a bike, especially if a battery could take some of the slog out of it.  I knew I wanted a basic exploring/hybrid type bike rather than an mountain bike and I didn't want to spend a huge amount of money.  Then there were stock issues, many bike stores have pictures of machines on their websites that they don't have in stock.  I didn't want to order something and then wait 3 months...   
Halfords have a family of bikes that all use the same tech, you just need to pick the flavor you like, I went for their urban commuting model called the Subway, which is sort of a cross between a fixie and a hybrid touring bike in appearance.  You could also describe it as an old school mountain bike with bmx tires. 

It's powered by a Suntour HESC system.  That's a geared rear motor system which is street legal.  250W and pedal assist cuts about at 25kph (16mph).  It doesn't have a hand throttle, which means it also doesn't need to have e-bike specific brake levers.  The crank contains cadence and torque sensors which combined with some software result in natural feeling riding experience for the most part. 

So what's it like to ride?
Well it's a lot like riding a bike honestly, but with a couple of foibles you quickly adapt to.  The first foible is that there is a bit of lag between the crank moving and the motor starting.  I'd guess this is around half a second. Same thing with the motor stopping.  This is actually fine for hill starts, you just have to trust the motor is going to kick in as you reach the bottom of your pedal stroke.   Where this can bite you is turning the bike around.  If you aren't expecting it at low speeds, having the motor kick in while manoevering can be bit disconcerting.  It's something that you quickly adapt to.  The motor makes a hum/whine while its operating so you get a useful audio cue as well as feeling the power. The other issue is the speed limiter. It really does limit your speed.  16mph takes about half the effort that 17mph does, so if you wanted a fast bike, this probably isn't it, unless you have the lungs and legs for it.

Batteries
The bike uses a 36v 8.7Ah 313Wh battery and they claim a 60 mile range.  But that range probably involves a small rider who lives somewhere flat and likes to use Eco mode.  What I found was that my range is probably a bit less than half that.  I'm about 240lbs and Wales has hills. Still 30 miles is a good couple of hours pedalling so can't really complain.  Overall I feel that the balance between range and power is pretty good.  I mean if the motor had more power, then the batteries would drain faster.

I'm scared of punctures
The motor is in the rear wheel.  There isn't a quick release for the backwheel.  Removing the back wheel involves disconnecting some electrics and cutting some cable ties as well as the usual stuff. It's not something I want to try for the first time at the side of the road.  At some point when I'm feeling brave I'm going to change out the tires for some puncture proof ones and maybe I'll put slime in the inner tubes. 

I wasn't sure if it had enough gears
It has gone up every hill I've found so far.  Don't get me wrong, I still have to pedal and I'm still a mess at the top but it goes up 1:10 gradients that I would normally have to walk up.


Rest of the bike
I'd budgeted for a better bike, I was kind of expecting this thing to feel cheap which is part of the reason I didn't get a model with cheap suspension, but its actually very solid, the frame is crazy stiff, the welds and paint look top notch. The hydraulic disk brakes work well.  The rear mech is a bit chintzy but easy to upgrade.  I was half expecting it to feel like the cheapest bike possible with a motor thrown on it considering the price. 
The only changes I made so far was to change the ergonomic bar grips out for some round ones and to add an adjustable stem to raise the bars about an inch.  Apart from that its fine, even the saddle is alright.

​Summary
I love it. It feels like riding a bike, BUT WITH BIONIC LEGS. I would definitely like to try one with a more powerful mid drive motor when lockdown ends and the mountain bike parks and trials are open.  I'll probably rent a modern full suspension MTB and see how I like it.  Hey you never know, if I ride the one I have enough, I might even be fit by then. 

Update: Feb23
I just noticed this post still gets lots of views so here's an update.  Bike has now successfully completed 115 rides and is still going strong.  I did get fitter and get a normal bike, but I still like to ride the Subway in winter when there isn't a lot of time to go for a long bike ride.   I think the e-bike marketers are missing a trick by not telling customers that a bike like this is a great way to get back into cycling. 
I did briefly have an issue where I was getting rear wheel punctures caused by cheap rim tape and a bit of swarf on the inner wheel rim.  I filed the sharp bit of metal down and replaced the rim tape with a heavier version.  At the same time I fitted slime puncture proof inner tubes for peace of mind.  
I also fitted swept back touring bars because I find them more comfortable than mtb bars. 

​

This Calculator from the BBC compares the carbon and water impact of various foods to other activities like driving and flying.   You can try it here.
Eating 1 fast food burger a week for the year produces the equivalent quantity of green house gases as driving a car 1500 miles!

At this point we all know that flying and driving are completely horrible for the environment and we should try to reduce the amount of both we do.  Given the recent dire warning from the UN I started to think about this stuff again. 
There are calculators on line that will give estimates for emissions but the estimates vary wildly.  I'll let you do your own research here, but I've used a couple of average numbers here for my personal use.
As a guess:

• Nonstop return flight from San Francisco to London = 3.3t
• Average car use for a year = 4.6t

As I need to fly twice this year, the flights are my biggest impact. In fact I really don't drive that much at all these days. 

Just to muddy the waters further this is an interesting article about the time scales of various pollution sources.  

So there aren't easy answers but generally it's not rocket surgery, we should all try to fly and drive less.
​

Modern technology makes remote working not only viable but in many ways more productive and enjoyable that commuting or traveling to conferences.  I don't mean to minimize the importance of face to face contact, but if we don't change our ways we won't have a planet to live on in 50 years.
Virtual Reality, Augmented Reality and Tele-presence are all technologies that will allow us to interact with the world without the need to burn vast amounts of fossil fuels.  In my last year at NVIDIA I learned to work from home several days a week. It was an adjustment in style but I was definitely productive and less stressed. I also presented at an entirely virtual global conference which was a good experience, the audience seemed engaged and asked good questions at the end which is a good indicator of success in my opinion, so it can work.  
​

Soylent Green is the movie where people are eating people.. yeah right, but why are they eating people? Is it because of an environmental collapse caused by over population and resource exhaustion? The Solyent Corporation's Oceanographic survey (a big plot point in the movie) shows the oceans to be dying...  Our oceans are in trouble.