How hard is it to generate about 10 - 20 watts renewably?

According to Wiki an average "in-shape" cyclist can produce about 3 watts/kg all for more than associate hour (e.g., around 200 watts for a 70 kg rider), so this iw well within your 10-20watt range. The cycle-generator combination will be about 50-60% efficient I suspect but as you wouldn't want to be pedalling every the time, lets add other 50% loss in charging the batteries. So, to generate 20Watts, you'd need to work on 40-80W OR at 200W per hour, around 20min pedalling would give you associate work time flight (all very wrinkled figures).

Do not forget, in the Second World War they used hand cranked generators to run transmitters and receivers on the field so it's not associate new idea.

Alternatively, Maplins sell an 18W solar panel all for £180 which faculty power your laptop while the sun shines. That should keep you off the internet all for most of the time if you playing in my bit of the UK! Plus, if we suppose a unit of electricity (1kWh) costs an middling of 10p, you'll have to use up 1800kWh of electrcity before the solar panel pays fror itself. At soap consumption of 20W that is 90,000 work time of activity Or just over 10 eld powered on usage. If you spending your laptop for 8 hours a day, it'll be 30years before you get the solar cell positive paid for and I suspect within 30 years time the power requirements of your nanotechnology implant will be zilch. Plus, if it takes you 30years to get payback, you're talking a return of your money investment at roughly 3.3%, so putting your £180 into a bank account big you take-home much 3.3% APR you'll be able to pay your lecky bill and make money.

You'd be finer putting on an extra jumper and turning off the 1kW fan heater all for about 10 minutes, which will save enough energy to run your laptop for 8 hours.