Power Consumption Calculator - Excel - Have I Got This Right ?

[rcscs]

Hello MH People

Just thinking about doing a camper van conversion...
Reading lots and watching lots of youtube vids.

I do freelance software development and I'm wondering if I could do this 'on the road' - computer would be on a lot...

I'd be grateful if someone could take a look at my worksheet below - does this look correct ?

I assuming only 1 hour of 'peak' sun in this example - for worse case example in Winter.
Max 50% discharge on batteries, 10% efficiency loss from solar panels.
Any other losses I should be taking into account ?

So in the example shown - I'd have power for 33hrs.

If this worksheet is correct then 3 hours of Sun per day would give me 136hrs...

Regards.

R.

 

[tonka]

Winter sun wont get you anything like the figures you state.
More members will have better info and may be along soon.

 

[funflair]

I think you are overly optimistic with regard to Solar gain, I would halve that for safety, so 15 amp on average OK some days will be better some will be worse.

Martin

 

[meanders]

Running the fridge from gas will save a huge amount. I'd also look at either getting a new lower power PC and monitor, or move everything into the cloud so that you can get away with a laptop or similar. If you have a home base you can set up a virtual machine and connect to that. No network means its difficult to work, but you'd have the other problems anyway.

 

[Wissel]

As others have said, I think solar is a long way out. I'd use twice the solar and battery capacity listed to power the same, just for summer use.

Might be worth looking at this calculator to get a better idea:
https://www.bimblesolar.com/solarcalc

Can be done though. I have all that you want to power, powered (work online from van), plus more. I need a charge about once a week.

EDIT: In summer I'm totally self-sufficient. It's just with the weather as it is now and being parked largely in shade that means I need a weekly charge.

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[funflair]

Running the fridge from gas will save a huge amount. I'd also look at either getting a new lower power PC and monitor, or move everything into the cloud so that you can get away with a laptop or similar. If you have a home base you can set up a virtual machine and connect to that. No network means its difficult to work, but you'd have the other problems anyway.

I think that will be gas operation Robin as it's only 15w it must just be the control circuits.

Martin

 

[Wissel]

I think that will be gas operation Robin as it's only 15w it must just be the control circuits.

Martin

I use a 240v AA rated fridge, with a low-power Victron Eco inverter. It uses around 15w per hour.

 

[funflair]

I would also be tempted to look at Lithium batteries as they have a few advantages for big users, more capacity weight for weight vs lead acid, deeper discharge so you can use basically all your capacity if required and lastly I have read that they are more efficient at charging so you actually get more out of your solar.

Martin

 

[funflair]

I use a 240v AA rated fridge, with a low-power Victron Eco inverter. It uses around 15w per hour.

Fair point but if this is a Compressor fridge then it won't need full power for the full 24hr period, unless the OP has averaged it out.

Martin

 

[rcscs]

Thanks for all the (prompt!) replies

Martin - yes - I've averaged the fridge wattage out (based on Dometic CFX 35).

Meanders - I want to use a 'proper PC' not laptop - I can work on a laptop if necessary - but for productivity and lots of hours per day I want full size screen, keyboard etc. I found 24 inch monitor which only draws 16 watts , PC figure is based on Intel NUC running i5 processor.

So my calculations (i.e. formulas) look ok I think - thanks for the power calculator link (which seems to confirmed) - but my estimate of what the solar panels will input is very optomistic... I will take this into account.

I done some reading on Lithium vs AGM/wet batteries but i got the impression that AGM/wet were still the preferred option.

Research continues...

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[Burgo]

This is a good worked example, IMO (I saw it on a facebook posting this morning):

1. Calculate total power requirements for a 24h period.
Fridge requires 1.7a per hour. This is a manufacturer's figure and is supported by my measurements.
Phone charging requires 2a at 5v for 3 hours per device - for 2 devices this is ~1.5a at 14v for 3h. This averages at 0.2a per h over 24h
Each light requires 0.3a when on. We have multiple lights on in the evenings but not at other times.
Call it 0.3a per h over 24h on average.

1.7+0.2+0.3 = 2.3a per hour average load
Heater and other devices take more too.
Call it an average of 2.5a of average load over 24h.

2. Consider leisure battery
85ah as specified.
Lead acid batteries cannot be discharged >50%, so 42.5ah of useful capacity.
42.5ah capacity for a 2.5a load =17h of off grid camping.

3. Calculate size of solar system
Sustain 2.5a at 14v = 35W average load over 24h (2.5*14)
Solar only works about 5hrs a day (more in summer, less in winter).
(35w*24h)/5h = 168w per hour produced by solar system in 5h period will power the van for 24h

solar is rarely>60% efficient. 168W/0.6 = 280W rated solar system

4. Conclusions
- A 300W solar system is not crazy.

 

[rcscs]

Wissel - been reading your site myselfbuildcamper.co.uk - very useful (much similar to what I'm planning/wanting) - thanks

 

[Pausim]

I find the solar angle calculator here
http://solarelectricityhandbook.com/solar-angle-calculator.html
very helpful. It also demonstrates how little sun will fall on a horizontal solar panel in winter.

 

[hilldweller]

As others have said, your solar is way optimistic. In the UK winter it's hopeless. You need to allow for the sun angle too if the panels are flat.

Don't overlook the other problems living and working in it, poo and water are even more tricky than solar to cope with. Where to park for days. Insurance.

Just before I retired I did use ours for on site software work, it was a real treat after years in hotels. This was in factories where I could hook up and dump the poo. It was great and no problem with insurance as long as I did not bring the customers in.

One enlightenment was the AMPS display, I could tell when the hard drive in my laptop fired up, a grim sight.

I worked on Deeside, Scotland in Feb once, my 11kg gas tank lasted 3 days at those temps.

 

[The Returnee]

As for the computer:

I had a problem with my seriously decent laptop and needed to replace it. I agonised for ages then bought an iPad Pro, with pen. All the MS Office programs are on it, as is One Drive, and I bought a case with keyboard for it. I do a lot of flying and feel liberated: battery lasts all day+, and so much easier going through airports. I like to think that I'm a decent photographer, so I've covered that base as well.

I do feel a bit of a hypocrite though. I used to preach about open computer systems and Apple isn't.

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[Wissel]

Meanders - I want to use a 'proper PC' not laptop - I can work on a laptop if necessary - but for productivity and lots of hours per day I want full size screen, keyboard etc. I found 24 inch monitor which only draws 16 watts , PC figure is based on Intel NUC running i5 processor.

Just in case your interested, I recently built a 12v PC that has a low power i5, 16gb DDR4, 3 x WD reds and a SSD. It uses a power supply that can take any voltage between 6-32v and runs on 24w.

Let me know if you want more details:

 

[Guigsy]

Just in case your interested, I recently built a 12v PC that has a low power i5, 16gb DDR4, 3 x WD reds and a SSD. It uses a power supply that can take any voltage between 6-32v and runs on 24w.

Is that peak 24w, or average/idle? Most electrical items only quote their peak power requirements, not the average. So @rcscs 's router probably only needs 15w while it's booting, after that it'll be significantly less.

 

[Wissel]

Is that peak 24w, or average/idle? Most electrical items only quote their peak power requirements, not the average. So @rcscs 's router probably only needs 15w while it's booting, after that it'll be significantly less.

That's the actual draw while in use, unless encoding video which takes it up to 30's.
It's not a quoted figure as I built the system, it's the measured current.

 

[rcscs]

Going off topic slightly here - but the 2x 2TB hard drives I can see in Wissel's build are probably pulling 3.5w each.
A 480Gb SSD will average about the same when reading/writing (i.e. 3.5w - probably a bit less) - but less than 1W when 'idle'.
I would plan a PC build with a SSD and a larger (say 2TB drive like the 2TB WD Red) - which would only be connected when required.
I reckon I can build a sub 20w (at idle) i5 PC without too much problem.

 

[Guigsy]

Going off topic slightly here - but the 2x 2TB hard drives I can see in Wissel's build are probably pulling 3.5w each.
A 480Gb SSD will average about the same when reading/writing (i.e. 3.5w - probably a bit less) - but less than 1W when 'idle'.
I would plan a PC build with a SSD and a larger (say 2TB drive like the 2TB WD Red) - which would only be connected when required.
I reckon I can build a sub 20w (at idle) i5 PC without too much problem.

I'm all for self build PCs, but for low power usage, it's going to be hard to beat a laptop.

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[Minxy]

@Gromett ... any advice you can give?

 

[Gromett]

@Gromett ... any advice you can give?

I wrote a big wall of text in response. Upon reading it back I realised that there was very little fact and lots of opinion (most from experience).
I decided against posting..

There is too much "well it depends on this or that" involved and no single set of advice is 100%...

However, for what it is worth and without getting into too much detail.

If it was me personally, and I do the same kind of work as the OP. I would aim for 400 Watts of solar and 400AH of battery. I would go with LiFePO4 batteries and a high quality MPPT charger such as the victron.

That said I would also plan for 3-4 months of being on hookup during the winter months as while at first you can deal with the hassles of occasional generator starts, being careful with power and being concerned about battery levels all the time. After a few years (6-7 in my case) it all gets to be a ballache and I now spend winters on hookup. At worst I will move every 28 days to stay within the rules and find a bunch of CL's that offer free (or cheap wifi) as well as a hookup with hard standing.

I am coming up on the 10th year of fulltiming. I initially ran a hosting company which I sold in early 2015. Since then I am a freelancer and vary the work I do. I do Server admin, including security, maintenance and install services. I also have a range of monthly services including server monitoring, updates and backups. I take on 1 big job each year which can be writing technical docs, or currently a very large programming job that has lasted 2 years. I got bored of dealing with power issues and trying to decide whether to prioritise fridge vs computer during long periods off hookup. I now do what is easiest...