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Solar Powered Laptop
6th July
Its been on my "to do" list for a while, and in April I finally managed to build my Solar Laptop project. The goal was to power an energy efficient laptop without using mains electricity. The laptop is used for around an hour in the day, and around 3-4 hours in the evening. The solution was to install a 60w BP Solarex Solar Panel, and hook this up to a 100ah of batteries and use a Kensington DC-DC converter to power the laptop.... and its a good success with some learning. Since installing I've been happily running mains free and feeling good about it. However, I've learnt that your battery bank needs to be in good condition and you need the most efficient DC-DC you can get. I've also learnt that you need to overspec your panel and batteries. Anyway, here's a nice picture of the solar panel gracing the corner of our flower bed.
The laptop is a Dell D420. This is a 'dual core' laptop running Vista and has a 68w extended battery in it giving around 5 hours usage when fully charged. This is using Wireless and normal activity. This means that it uses around 13watts per hour (68wh divided by 5). Switching to an EeePC or similar would allow a smaller panel and batteries as its more energy efficient still, but I didn't want to compromise too much. My solar battery bank has around 100ah, so thats around 1200wh capacity -or if I only drain the batteries to 50% capacity to maximise their life it has 600wh of useable capacity. When the sun is shining, the main batteries are charged, so that I have a constant store of energy to charge the laptop up. Even on a sunny day, I'm usually charging the large 12volt 100ah batteries and not the laptop directly. Only when I plug the laptop power lead does the laptop get charged, and then its from the 100ah batteries. If its cloudy for a while, I still have enough juice to last several day to recharge the internal battery several times over. If I know its going to be sunny, I'll leave the laptop charger plugged in and on knowing that the sun will bring the batteries back up to full in a day.
The panel is capable of putting out 60w an hour in ideal conditions(thats around 4ah -5ah per hour, so on a sunny day I'm getting enough juice to power the laptop for a few cloudy days.
This project required the following (prices are the prices I paid):
1 Energy efficient laptop (the more efficient the smaller solar panel needed)
1 Solar Panel 60watts (£120)
1 100ah battery bank (£35)
1 length of cable (£120) (If distance is short 2.5mm cable is sufficient, but 150metres required heavier duty to minimise energy loss)
1 Charge controller (£20) to prevent frying your batteries
1 Fuse (£8)
1 Laptop Car Charger (£12)
1 Car lighter socket with USB port (£10)
The cable is the shocking part of the list, and is one area where I was unsure whether to go with a thinner wire or not. The issue is that 12volts doesn't carry well over long distances and thin wire. There are lots of calculators on the web that will explain the exact drop in volts given a certain distance, but lets just say that having a distance of 150ft compromised me from using cheaper cable. In the end I 'overspecced' by buying some serious cable, but I fully expect that as I move house, or upgrade my system that it will prove to be worth the investment. The cable is fully armoured 4 core, and 10mm per core, so can meet a number of uses in the future!
My old laptop power supply used 7 watts when not even plugged in to the laptop, so wasted 61Kwh a year!! Thats around £6 using 10p per Kwh which is about our current rate. It also uses over 100 watts when its charging for around 3 hours a day, so that is a further 100Kwh. That means I'm spending about £15 a year to run the laptop from the mains. As a comparison, a Kensington 120w DC-DC auto converter uses 70ma an hour on idle and not plugged in. Thats under 1 watt an hour. The iGO Juice 70 uses slightly less at 50ma an hour but is more bulky. Either way, it will take this project decades to pay for itself if I want to recoup ALL my costs. However, I'm looking at everything except the batteries as 'capital outlay' so in my twisted mind I figure I need to pay for the batteries out of the running of this system as its a 'consumable' part of the system and will need replacing every 5 year. So long as I cover that cost and 'chip away' at paying for the rest then I'm happy. On this basis I need to use this for 2 years without further expenditure. We shall see.
One more thing to note is that now that I have a 12v 'Free Energy' socket in the kitchen, I can use it to charge mobile phones and other small electronics, so I'm hoping this will speed up the payback.
Heres the schematic. See the 'Media Showcase' for further pictures.
Ideally these would have been 1 100ah battery, but I had to take what was available. Make sure you pick up good batteries that haven't been sat around for a while.
Newspaper Bricks
6th July
Given the current oil crisis, it seems only sensible to make use of the twice week free newspapers that get dropped through our letterbox. In the winter we tend to just put these straight onto the wood burner. This works very well after you've cleaned it out. We just lay half a dozen or so newspapers straight onto the bottom of the woodburner. Then we just light our normal fire. This seems to minimise the ash. As we are now in summer, we have a pretty large build up of papers, cardboard boxes and a few other bits and pieces waiting for winter. In the meantime, I will press the current crop of papers into briquettes using the paper brick maker we picked up from CAT (Centre for Alternate Technology) which incidentally was a great day out a few years back.
To make the bricks, you just tear the paper into strips and leave soak for a few hours before using the brick maker to squash the water out and then leave to dry. I have to admit the brick maker takes a bit of pressure, but at least it keeps you in shape ;-) Once they have dried they burn amazing slowly and with virtually no ash.
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