Scottish Elises

Anyone got one?
Worth the money? The car's not being driven much at the moment - sat for a month (flat battery) then driven for about 50 miles. Then used for 10-15miles a few times over the last couple of weeks.
This morning - just a few clicks.

I have no means of running a normal trickle charger from the mains.

So anyone..........?

From recent discussions on Solar Chargers on SELCO the small ones half A4 size barely keep up with the demands of the alarm system on a good day so your much better to go for the bigger one designed for boats and motor caravans and make sure it has a diode to prevent discharging when cloudy ? they go for about £44 on fleabay and weight 2.9 Kg or so

Get a 3KW halogen spot light pointed out of your flat window and align it with the solar panel - that should keep it going

Or get a small generator and leave it running inside the car?

I don't know how effective solar panels really are when stuck inside a car. For example, I have a 10W (max) rated A4 solar panel on my desk right now - it's pointing out the window towards today's gloomy sky. It's making so little power you would need 100 of them to make any difference on your car. Of course when the sun is shining it works a lot better, but the sun hasn't shone for more than 3 days in the last 3 months ...

The easiest thing to do, however, is to have a regime of starting it and running it for about 30 minutes a week ...

Cheers,
Robin

robin wrote:Get a 3KW halogen spot light pointed out of your flat window and align it with the solar panel - that should keep it going

Thanks Robin -I'll give that a go!

robin wrote:Or get a small generator and leave it running inside the car?

Or I could just leave the engine running?

robin wrote: I don't know how effective solar panels really are when stuck inside a car.

Thought you knew everything?

robin wrote: The easiest thing to do, however, is to have a regime of starting it and running it for about 30 minutes a week ...

Sounds like a plan

Thanks Robin

Had one on the side of the bike shed for N1 for years, but it did not seem to give any benefit.

No doubt a big one would, but the natural battery drainage was more than the output of the panel.

tut

RDH wrote:

robin wrote: I don't know how effective solar panels really are when stuck inside a car.

Thought you knew everything?

It is a known unknown (or perhaps a known unknowable). Without knowing which way your street faces, how wide the street is, how tall the buildings are, how dirty your windscreen is, etc., etc., it's impossible to calculate the angle of incidence and attenuation over time to get from the theoretical maximum (angle of incidence = 90 degrees, 0db attenuation) to what is actually achieved

Cheers,
Robin

robin wrote:
It is a known unknown (or perhaps a known unknowable). Without knowing which way your street faces, how wide the street is, how tall the buildings are, how dirty your windscreen is, etc., etc., it's impossible to calculate the angle of incidence and attenuation over time to get from the theoretical maximum (angle of incidence = 90 degrees, 0db attenuation) to what is actually achieved

Cheers,
Robin

I could park the car facing any way, the buildings are quite tall for Glasgow, and my windscreen is a bit dirty at the moment, but I could clean it...

At the moment the sun only makes ~22 degrees elevation above the horizon in Glasgow, with about 9.5 hours between sunrise and sunset (ignoring obstructions on the horizon).

Assuming the buildings to the south of your preferred parking position are either low enough or far enough away to obscure "only" 15 degrees above the horizon the the sun will be visible above those buildings for 5 hours in the day. The rest of the time your panel will make near-zero (they really only work in direct sunlight).

It's a bit of a simplification, but we can assume the average elevation of the sun during the 5 hours where it's above the building skyline is 15+(22-15)/2 = 18.5 degrees. So you would want to set the angle of your solar panel to 90-18.5 = 71.5 degrees to the horizontal (i.e. almost vertical). During the 5 hours where you can see the sun from your car windscreen, the sun sweeps through 360*5/24 = 75 degrees, centered on a perpendicular from your panel; again for simplification purposes we'll assume the average angle of incidence is reduced from 90 by half the worst case, i.e. about 19 degrees. Add to that the loss of about 2 degrees due to the change in elevation of the sun in this time and you get a typical angle of 90-22 = 68 degrees. The power is proportional to the sin of the angle of incidence, so that's about 90%.

We'll assume that your clean screen has almost no attenuation (what little it has is countered by the mild focusing effect it has).

But, the air path is much longer at these low elevations; also the lower atmosphere is much more attenuating than the upper atmosphere (more crap in the air at lower altitude, I believe) - 20 degrees above the horizon is approximately double the attenuation compared to overhead sun, 10 degrees approximately 3 times, 5 degrees approximately 6 times, etc.

So for your 15 degree to 22 degree sweep you're looking at a 2x to 3x attenuation. So 90% becomes 45% to 30%.

You can assume that a 10W peak power solar panel will make that at noon, on the equator, with not a cloud in the sky, lying flat on the ground.

So on a clear day in February with the panel perfectly aligned according to the above, I would estimate you'll make 3.75W in the 5 hour period. Spread across a whole day that's equal to 0.8W which is barely covering the immob/alarm/self discharge currents.

On a cloudy day, the output will be near zero - clouds provide huge attenuation. Most days in February have been cloudy, so far, I think ...


Cheers,
Robin

Not as much maths fun but you could get a spare battery on the trickle charger in the house...

btw if you have an Exige don't leave your jump leads in the boot (like I did).
I had to borrow a set to get enough power on the aux posts to power the central locking and get the doors open...to then open the boot and get at the battery.
I've taken the (teeny weeny carbon tat) battery out to charge it on the Accumate. Note, with the battery out you can leave it unlocked but disable the door catches with the key - a la 'ferry' mode.

Dunno how my insurance is covered as the alarm is not set but it's pretty well immobilised (no battery, brakes welded on and 8" snow piled up in front).

Simplified version is that the "angle of the dangle" equals the "heat of the beat."

tut

Mine makes a difference in the summer but is useless at this time of year (and a layer of snow does not help )

With our climate surely hydro rather than solar is the way forward? There must be some way to utilise all that water in the boot...





Ok, not helpful but it's friday night and I'm bored