Ferry wrote: ↑23 Nov 2020, 23:17
If you spend 60 kWh/day you drive quite a lot. My i3 can drive 500 km with that amount of energy. Let's say a bigger car can drive 300 km. Still a lot. Around 4-5 hours of driving around here. Way too much every day. 69.000 km/year with 230 working days.
Remember, you only have to charge up what you will be missing on you next trip. And the battery is seldom empty when you start charging. Your math is correct, but it's not a realistic scenario.
Ideally the car should be charged at work, where it's stationary for 8-10 hours during daylight.
For three years I used to do at least 150 miles (240km) a day. These days I do some longer days (I've done 200 miles in a day for work in the last few months) but often 100 miles (160km) and I'm often out on the road visiting clients for the day, with 3 or 4 hours of the day actually driving the car). I've just put tomorrow's itinerary in Google Map and it's saying tomorrow is 120 miles (c.190km) and just over 3 hours driving. That's a typical day at the moment.
Not a typical usage for many, admittedly, but also not unusual. In the UK there are still a good number of people that commute 200 mile (320km) round trips (100 miles each way). If they can find somewhere to charge when at work, that's ok. If not, they'd be charging the car entirely at home. Of course, in an i3 they wouldn't get home unless they'd found a charger at work as it doesn't have a 200 mile range.
For lots of people that only do a few dozen miles a day, they'd probably be able to charge some of that from their PV and a battery storage but they'd still then not be able to use the PV / battery storage for running household items.
If someone wants to charge a car from domestic PV alone, they either need a lot of PV or they need to be doing a very small number of miles each trip. In which case they'd be better off using a different form of transport in the first place (from an environmental perspective).
We're looking at adding PV here along with a solar thermal panel to heat some water. I reckon doing that and having a battery is the better option. We can then use some of the PV-derived electricity during the day (base load such as fridge, freezer, etc. plus my home office) with excess going in to a battery to use in the evening. Just checked our smart meter and we're currently using about 400W (about 300W during the day) - lights, TV, base load, my home office - and will have used about 9kWh over the whole 24 hour period. This is about the median figure for the UK and equates to about 3,000kWh per year. It'll be a bit less over the year than 9 x 365 because 9kWh / day is our "winter" figure - the sun set at about 4pm today so we've had lights on for a good while now. In summer, lights might not go on until 9pm or even later. Even though we're an LED household, the lights still add up over time.
Anyway, all of that means that I reckon we can run a reasonable portion of the year near enough "off grid" for electrical demand (that is, the summer months). Luckily, we're not hugely greedy with our electricity and generally only have things on that need to be on - no kids here leaving everything switched on!
What's interesting playing around with the figures is data sources. I've revisited a site I referenced in an earlier post and followed the link for the daily sunshine hours they quote. And unsurprisingly, they've picked a sunny year for their figures (I wondered why an article written this month used 2018's sunny day figures rather than 2019). 2018 was a good year if you're selling PV. 2019 a less good year, 2017 a rubbish year. Playing with the figures in a spreadsheet, the difference between using the 2018 figures quoted in the article and the average figures for 2001-2020 is notable. For example, they quote July as being 8.7 hours/day of sun. The average over 2001-2020 is 6.45 hours/day of sun. That gives you 16kWh for the day instead of the 22kWh they suggest. That's a big difference, especially if someone is wanting to use PV to help charge a car, for example.
Of course, one would hope that people looking to do this wouldn't take the word of one web site, but even so, it's a bit naughty and doesn't, in my opinion, help the cause of encouraging PV uptake.
As mentioned previously, I think using PV and a battery to run the house with car charged from the grid overnight is the best balance. At least it means that if there's a power cut you've got the option of using the battery to run the house rather than having Joules locked up in the car battery and being unable to access them whilst you sit in the dark.
If you are more fortunate than others, build a larger table not a taller fence.
