navitron
 
Renewable Energy and Sustainability Forum
Welcome, Guest. Please login or register.

Login with username, password and session length
News: Anyone wishing to register as a new member on the forum is strongly recommended to use a "proper" email address. Following continuous spam/hack attempts on the forum, "disposable" email addresses like Gmail, Yahoo and Hotmail tend to be viewed with suspicion, and the application rejected if there is any doubt whatsoever
 
Recent Articles: Navitron Partners With Solax to Help Create A More Sustainable Future | Navitron Calls for Increased Carbon Footprint Reduction In Light of Earth Overshoot Day | A plea from The David School - Issue 18
   Home   Help Search Login Register  
Pages: [1] 2   Go Down
  Print  
Author Topic: Solar powered computer  (Read 9140 times)
dtww
Newbie
*
Offline Offline

Posts: 4


« on: August 15, 2012, 02:36:30 PM »

Hi all

I'd like to build a solar power computer, hopefully this is the right place to ask for ideas!

I am fine with building computers. What I want to do is to set up a home server that is always on. It is for file copying and archiving rather than anything exotic like video streaming. It will have several hard disks which adds to the power needs. Other than that I intend to use as few components as possible to maintain low power consumption. So, apart from the power supply unit, I will have a motherboard that has its own monitor output and LAN network port, 1 or 2 RAM, 1 or 2 SSD and probably 6 hard disks, and if required, fan(s). A monitor is used very rarely.

My plan is to build the computer, and deal with the solar power separately. I know you can use DC to power the computer, but my electronics knowledge is nil. So I thought what I'll do is to find a good solar solution that gives me enough 'power' to power the PC. Because the computer is always on, the system ought to be able to charge the battery while the battery is also powering the computer.

Using Maplin as a reference with regard to what kits are available and price, I have the following and wonder if anyone thinks this is a possible set-up.

12V 85W Solar Panel Kit    --- £179.99
12V 100Ah Solar Battery --- £159.99
Solar Battery Box --- £62.99
600W 12V Inverter --- £59.99
12Ah Regulator --- £71.99
Multimeter --- probably about £25.00
plus various other bits, cables etc., totalling probably £650


I have thought about the UPS route, but this is likely to involve having to modify the UPS to either connect to the solar source and/or replace the battery with a deep cycle. My plan is to go off grid (as far as this computer goes, not the whole house!), but the AC-DC PSU will still allow me to plug it to the mains. That type of PSU is not really a get-out back to using mains, but more because - as I understand it - this stuff is robust enough to cope with the varying voltage with the computer components. I don't want to find myself having to tweak the electronics stuff (not knowing what I am doing in the first place) just to get more power if I add more components to the computer. So, if the list of kits above is a workable solution, I appreciate if anyone who has done this to let me know if there's are better ways / components.

Many thanks

David
« Last Edit: August 15, 2012, 02:38:20 PM by dtww » Logged
Justme
Hero Member
*****
Offline Offline

Posts: 3562


« Reply #1 on: August 15, 2012, 02:56:19 PM »


1, 12V 85W Solar Panel Kit    --- £179.99
2, 12V 100Ah Solar Battery --- £159.99
3, Solar Battery Box --- £62.99





First off all of the above are well over priced.

1, think less than 80p per watt
2, think less than £1 per 1ah
3, really? for a plastic box? check out caravan battery boxes, more like £10



Now the worse news.

1, There is no way that 85watts of solar is going to power a standard consumption PC with one hard drive never mind 6 even in the hight of summer. The most energy you will ever see from that is 680wh (that is 28 watts you now have to play with) & in winter more like 40wh (so less than 2 watts) .

2, Your 100ah battery only has a usable portion of about 50% to prevent serious battery life reduction. As the battery would be supplying 42ah per day outside of the solar day you are very close to the max & it will only take a few days of bad weather to deplete the battery. You really need at least 3 to 5 days autonomy from the battery & still be above the 50% discharge level. So think about increasing your bank by a factor of 5.

You need to approach this from the other end. First design the pc to be as low consumption as possible then make it even more efficient & then design a system to cope with that amount (after reducing the consumption even more).

Logged

Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
2 x Victron Multiplus II 48/5000/70
Cerbo GX & GX 50 touch
BMV 700
6kva genny
48v 1000ah
Grid Possibly coming soon
dhaslam
Hero Member
*****
Offline Offline

Posts: 6775



« Reply #2 on: August 15, 2012, 03:00:01 PM »

The problem  with  your suggested system is that the scale out output  compared to cost isn't very good.  

I was  recently looking at a  small system  using  4X Yingli  220 watt panels at £178 each  that would be mostly used  for day time use, with minimal battery storage,  and mostly  on sunny days for fans  and pumps.   On that scale the output would be  somewhere  around daytime electricity cost  over ten years.        It would cost about twice your figure  but with ten times more output.        
  
Logged

DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
w0067814
Full Member
***
Offline Offline

Posts: 239


« Reply #3 on: August 15, 2012, 06:13:36 PM »

Given the specification on the number of hard drive you need to hold, you're unlikely to be looking at one of the purpose built Mini-ITX based systems as few of they have the capability for that many hard disk, and lack things such as RAID.

I would suggest that you look into your choice of motherboard very carefully. It is the chipset which can draw significant power even if the processor is low power. A good example of this is the Intel Atom which can draw just a couple of watts, but the chipset they shackle it with can draw 20+ watts!

I would recommend that you look at the Intel i5 processors, and choose one with a low clock speed, paying close attention to the TDP, and measurements from others that have looked to build low power servers. www.tomshardware.com has several articles on building low power servers / NAS devices.

A well chosen Intel i5 based server and motherboard combination can idle at just 23w of power, but still have the grunt you may need to serve files fast, or for transcoding video etc.

Beware that each of your HDDs can draw 5 watts - with 6 HDDs you'll be burning 30 watts idle, plus the ~23 watts for the CPU / MB, plus a watt or two for the SSDs. Let's call it 60w average idle draw.

Yes you will be able to spin down the hard drive, but it depends on how often you access things - if you use the server for torrents, then it shall be active most of the time.


Now let's do some maths.

Assume 60w constant draw from the computer.

60w * 24 hours = 1.44kWh usage per day.

Assume effiecncy of inverter is 90%, we can add that into the energy usage caclulation.

1.44kWh / 90% = 1.6kWh.

Assuming you are centrally located in the UK, in winter the length of the day can be as short as 7 hours. This means that for 17 hours of the day, you shall need to supply the power from batteries.

1.6kWh / (17h/24h) = 1.13kWh used from the batteries over night.

Now, you shall need to put that amount of energy back into the batteries to recharge them, and you shall need to account for the losses in battery charging. Lead Acid charging is about 70% efficient. So for every Amp-Hour you take out, you need to put 1.42 back in.

1.13kWh / 70% = 1.61kWh power used to recharge the battery during the day.

Of course you still need to power the computer during the day, so we need to add the powers of both the PC and the computer together to find out how much power we need.

Still assuming the 7 hour shortest day. Within that time we need to generate

1) 1.61kWh to recharge the battery.
2) 60w * 7 hours = 0.42kWh to run the computer.

Thus your total energy usage per day is 2.03kWh.

Using PVGIS (http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php) we can estiamte our solar panel requirements.

In putting Cambridge location, with a south facing set of panels at 35 degree angle and 0% inverter losses (we've already calculated our losses), I can see that we need at least 2.5kWp system to deliver our required daily usage in December. I' would allow a but of extra, so would look to install at least 3kw. If your system was critical, I would look to install double this. Wilst batteries can provide several days of hold-up time, you shall then have to put in proportionally more power to recharge them once bad weather clears!

Two factors determine the battery size. The amount of current we need to put into them during charging, and the energy we wish to take out of them per cycle.
Draining a battery deeply dramatically reduces its life span. 50% discharge would kill a battery pretty quickly. 20% target is much better. The second factor is the recharge current as a proportion of the capacity. Typically this is 10%, but some batteries can be higher.

1.13kWh / 20% = 5.65kWh recommended battery capacity.

At 12 volts...

7.53kWh / 12v = 470 Amp-Hours (remember energy (kWh) is voltage * current * time)

In terms of MPPT Charger capacity, you need to put 1.61kWh into the battery in 7 hours. If this was done at a constant rate you would need 230wH per hour, or to put it another way 230 watts of recharge power (hours / hours cancels out). Of course peak the recharge power shall come when the sun is highest in the day. The graph would look like the "normal distribution". Someone cleverer than me could tell you how much peak power that would produce. For now I'm going to guess that most of the charging occurs in the middle 1/3rd of the day.

This 230 / 33% = 690w of recharging power peak. 690w / 12v = 57.5 amps. This is about 12.2% of the battery capacity, so is a good fit for the size bank recommended above.

Add in the 60w draw of the PC, and we arive at 750w maximum draw from the solar panels, or 62.5 amps to be provided by MPPT.


So there you have it. For a PC drawing 60w 24 hours per day, running through winter you need:

* 2.5kWp of Solar Panels

* 470 Amp-Hours or battery capacity at 12v.

* A MPPT charger capable of 62.5 Amps.

* An inverter capable of handling the in rush of a PC starting up, and peak load when all hard disks spin up. I'd recommend at least 150w.

I'd also recommend a pure sine wave inverter as your PC power supply effeicieny may drop with a modified sine wave feeding it. Victron Energy do a nice small inverter which would suit this application nicely.

Hope this helps - Hope my logic & calculations are all right too. <Hoping to avoid egg on my face>

-Tim
Logged
dtww
Newbie
*
Offline Offline

Posts: 4


« Reply #4 on: August 15, 2012, 06:47:25 PM »

Thanks for all the replies.

Indeed I started off by trying to find the right balance between what solar power can generate and what watt output I can get; but at the end I decided to build spec a PC with very low consumption (because I know what I am doing with building PCs) and then spec the solar source + battery to match it, bearing in mind I won't get a lot of W with solar.

I think my message title is slightly misleading, solar charged battery powered always on home file server... Shocked

While, mini-itx keeps power consumption and footprint low, they can't cope with several disks. You could get an external enclosure / NAS box but wait... you need to power that one too!

I have started looking at component power consumption and estimate daily usage, turning Ah x V into watt etc. and all the rest. I come up with something like 3.6kwh. It looks like I need to get some 'large capacity' (?) batteries, of over 200Ah. Tim's calculation is useful, at least I am sort of in the same direction! Justme, once I am clearly what I need, I'll make sure I go elsewhere for the kit for better price! Though have to wait for delivery, while M is a few miles away.

The reason for the hard disks is for redundancies but I won't use RAID, more likely rsync (linux) or Goodsync (M$). I could step it down to use 2 x 2 3.5 disks, + 1 operating system on ssd.

It won't do torrent, purely 'files' (documents) serving within LAN and external access; any calculating stuff is done on other PCs, and when backing up, I save them to the server. So it might only be at load for about 30 minutes a day on average. Most transactions will be via GUI rather than command line e.g. scp so there's a bit of power draw there. Wake on lan will be useful.

David

Logged
martin
Hero Member
*****
Offline Offline

Posts: 15733



WWW
« Reply #5 on: August 15, 2012, 07:27:42 PM »

3.6kWh per day......... lawks!  - Looking at midwinter, you'd need about a 4kW array to feed the batteries, and a simply ginormous battery bank........
Logged

Unpaid volunteer administrator and moderator (not employed by Navitron) - Views expressed are my own - curmudgeonly babyboomer! - http://www.farmco.co.uk
Justme
Hero Member
*****
Offline Offline

Posts: 3562


« Reply #6 on: August 15, 2012, 08:57:02 PM »

Why do you want to do this?

You could be better off powering the PC from the grid & using the solar to power something that is only on during daylight hours that closer matches the available power / energy profile.
Logged

Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
2 x Victron Multiplus II 48/5000/70
Cerbo GX & GX 50 touch
BMV 700
6kva genny
48v 1000ah
Grid Possibly coming soon
clivejo
Hero Member
*****
Offline Offline

Posts: 1609



« Reply #7 on: August 15, 2012, 09:29:27 PM »

Do you really need it on 24/7?  Surely there are times when the system could shut down to conserve power.  For example between 3am - 8am do you really need it powered?

I've been looking into a similar project for data logging and control. (recording water temps, weather conditions, and deciding what to do about it)   In which I'm using a RaspberryPi to do the 24/7 data logging and control.  I then will have a PC which will power on for when I need it (Wake on LAN controlled by the RPi).

I am looking at a DC-DC PSU  (*coughs* something way cheaper) like this - www.amtrade.com/pc_power/dc_to_dc_power_supplies.htm to take my 48VDC directly from my batteries to power the 'server'. 

Maybe you could power directly via DC and cut out the inverter loses. Most HDD's only require a 12v and 5v supply and the Motherboards require more i.e. 3.3v
Logged



DISCLAIMER : Iím not responsible for anythingÖ for anything I say or do. Cos Iím a proud member of clan Eejit who once ruled Ireland.
Robl
Jr. Member
**
Offline Offline

Posts: 72


« Reply #8 on: August 15, 2012, 11:12:54 PM »

Key to this is has got to be keeping the power consumption down.  Every baseload Watt is precious.  The simplest off-the-shelf low power PC solutions will surely be based around a laptop or even a netbook.  You can get netbooks with an Atom processor running at <10W, and this would be fine for just moving data around.  Sure they don't have much storage, but external USB HDD's are cheap, and can auto-shutdown, adding an extra 10W each time one of them is accessed and 1W idle.  Or, as suggested, DIY using a laptop based motherboard chipset.

I'm with Justme on directly coupling this to solar though - sadly connecting a demand led load like this to solar will require an oversize array, and in summer the excess power will be wasted, whilst in winter you will struggle to keep it operating.  I appreciate it's "nice" to say that such and such is solar powered, but using the grid as a "battery" makes so much technical sense - in summer somebody else will use the power that you wouldn't, and in winter you can borrow some back - all without massive lead-acid batteries possibly venting* in your loft.

*I worry
Logged
dtww
Newbie
*
Offline Offline

Posts: 4


« Reply #9 on: August 15, 2012, 11:56:38 PM »

I am hearing what people are saying. So, now, I am thinking along the lines of:

- DC power supply e.g. http://linitx.com/category/157/149,157
- to work with its motherboard e.g. http://www.mini-itx.com/store/?c=2
- use ssd

I now need to figure out the calculations...! A bit lost there  Angry

plus a combination of ubuntu cron shutdown in the early morning, bios auto startup, wake on lan or just go press the power button. external access will have to rely on bios auto startup or wake on wan (soon on bt 'infinity' with home hub 3...)
Logged
w0067814
Full Member
***
Offline Offline

Posts: 239


« Reply #10 on: August 16, 2012, 10:21:24 AM »

No need to worry about the math - I've done that for you above. Just pop in the new power consumption figure and work through my steps.

Note: I made a typo. The line that reads:

7.53kWh / 12v = 470 Amp-Hours (remember energy (kWh) is voltage * current * time)

Should read:

5.65kWh / 12v = 470 Amp-Hours (remember energy (kWh) is voltage * current * time)

I was originally working on a 15% Depth of Discharge for the batteries, but revised this down to 20%, and missed updating this line fully.

Sorry.

In short if you are looking to run a load 24/7 throughout winter using batteries, then it's going to cost you a fortune. 3kWp of solar panels is about £2,250 worth, and then you have batteries on top. A decent sealed lead acid such as CSB Battery's TPL121500 costs about £221 + VAT each, and you would require three of them for 450Ah of capacity. Another £795.

So probably worth budgeting £3,500 for running your 60w computer.

Now, if you drop the battery thing and run grid connected, and be happy with "banking" electricity in the summer in the form of over supply to the grid (and thus your bank balance) then you can get away with a much smaller system and less cost.

An 880wp (4 off 220w solar panels) system would generate more than enough to cancel out the 60w 24/7 load over the course of a whole year. And you don't have to worry about battery maintenance, weight, chemicals etc.

-Tim
Logged
jonesy
Hero Member
*****
Offline Offline

Posts: 846



« Reply #11 on: August 16, 2012, 01:22:13 PM »

David,
You mentioned that you wanted hard drive for archive only.  You also mention NAS.  I guess I'm missing something here, but why not get a raid NAS and drop in on your network.  Depending on your brand of router, some come with USB built in, and will enumerate a port for any usb drive/key/disc.  As your router is on anyway, the extra power consumption won't notice.  My router runs off 12V (12W nom), so I could run it off batteries (I didnt as the battery bank size got silly, and, having recently gone off grid to on-grid, I am a strong advocate of using the grid as my battery)  Actually, not entirely true.  For 8 months (of 2 years) off grid, I ran the router off 24V via DC/DC converter.  24V/400Ah batteries.  When the weather (sun) was poor in December for charging (1.1kW array) and the battery pack was down to 24.5V in the morning, I did wonder about sense of leaving the router on at night.  A leech of 600mA adds up from sunset to sunrise.

Raspberry pi as clive says is a nice idea and really low power. 

I'm using a web server based on Microchip's TCP stack, to give me a basic web site, storage (SD card) and logging.  Not fast, but about 2W.  And it's not off the shelf.

Something else that could work is a media player.  I've also seen plenty of hacks for old routers, running linux.  All lower power solutions.
In the last few months I've started using idrive which is a backup and remote storage thingy.  15G for free if you give them your address book with 5 names in.  Always-on availability anywhere in the world!

I applaud the idea.  Anything that takes demand away from oil/gas/etc is great, but it has to be in perspective.  A 60W pc running 24/7 is about £60 per year.  Spending a rook of cash on gear which itself has used energy in its manufacture and logged air miles (and ultimately re-cycling energy) may not be the best solution.  It is, however, generally the right thing to do in the long term.
AB
Logged

1.1kWp PV & SB1700. 7kW log burner.
clivejo
Hero Member
*****
Offline Offline

Posts: 1609



« Reply #12 on: August 16, 2012, 03:13:50 PM »

I'm planning to install a 2wire network, over a Cat5 cable.  I'm hoping to create a 12-14v ring main with this cable using 2 x 2 cores, for example two wires for positive and two wires for negative.  The reason for this is to place some sealed lead acid batteries at specific points along the the ring main which would charge and discharge, depending on the voltage.  This is to power my router, cordless phone, RPi, control network etc and other low powered devices which combined cause a 'baseload' and prevent my inverter dropping into sleep/search mode.
Logged



DISCLAIMER : Iím not responsible for anythingÖ for anything I say or do. Cos Iím a proud member of clan Eejit who once ruled Ireland.
pj
Sr. Member
****
Offline Offline

Posts: 308

Nom de Plume


« Reply #13 on: August 16, 2012, 04:25:52 PM »

Clivejo,
I quick Wiki look for CAT5 shows a max current of 0.577A per conductor - you sure this is enough for your proposed loads?
Logged

North Hampshire
clivejo
Hero Member
*****
Offline Offline

Posts: 1609



« Reply #14 on: August 16, 2012, 04:55:02 PM »

I quick Wiki look for CAT5 shows a max current of 0.577A per conductor - you sure this is enough for your proposed loads?

0.5A x 2 (using two conductors) times two again as ring main, about 2A @ 14V as this should be the charging voltage on the circuit.  So say average load of 28w

My RPi draws about 2w when idle, Max about 10w when accessing SD-card, processing and Ethernet
Phone requires 6w according to base plate, but I reckon that depends on if its idle, making a call and when its charging the handset, so I reckon the same as the RPi 2-10w
Control circuits, switching 12v relays etc, if say 5 relays energised at once drawing 200mA each be another 12w

So in theory my max load would be 10+10+12 = 32w, which is why I wanted to use batteries at the 'control' stations, to provide extra power when needed. This same load using AC presents a continuous load of 40-50w, I hope to cut out a lot of timers and control equipment by using the RPi instead.
Logged



DISCLAIMER : Iím not responsible for anythingÖ for anything I say or do. Cos Iím a proud member of clan Eejit who once ruled Ireland.
Pages: [1] 2   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.20 | SMF © 2013, Simple Machines
SMFAds for Free Forums
Simple Audio Video Embedder
Valid XHTML 1.0! Valid CSS!