What size PanelTo start off with I worked out what power was needed by the two items. From the manuals: the wireless router needs 12V DC with a max consumption of 10W (0.83A) and the modem is 5V DC with a max of 6W (1.2A). So I need 16W for 24hrs, that's 384W per day. But with only 8hrs of light to generate that power 384W / 8hrs = 48W. So I need a 50 Watt panel! That should go for about $250. Pricey but less than I paid for the modem and router.
Store the powerI picked up a car battery for $35 which should do me for a few years and a $7.50 5Amp charge controller of EBay.
Use the PowerWe need a 12 volt and a 5 volt power supply. A 12 volt car battery is normally more than 12 volts so for both the 12 volt and 5 volt we will need to regulate the voltage. So we are going to have to either pay a bit of money or do it ourselves. And it's more fun to do it yourself.
This can be done pretty easily with a tiny bit of electronics, the main part being a regulator. I got a 5 Amp 1.2V-32V regulator (LM 338T) for about $5.
So you can see when need a few little items on top of the regulator. A 0.1uF capacitor, a 1uF capacitor, a 120 resistor and a 5k pot (variable resister), a fuse to match the max current for the device, some wire for in between and some plugs that match the power plugs on the device. All up it should come to around $20. Now all you need to do is put it all together like the diagram above. Once you have it together, grab a voltmeter and measure the voltage at Vout and adjust the pot higher or lower until Vout is the right voltage for you device (5 or 12 volts in my case).
And there you go. The panel charges the batteries, through the charge controller. And the modem and router run off the batteries through the voltage regulators and fuses.
SavingsSo your going to save 384W per day, that's 140kW each year. I was pretty impressed when I worked that out. However, it should only equate to about $15 off your power bill. And I don't know how they worked our the inspirational maths on this site but apparently that works out at about 380kg's of coal that is not burnt. Pretty cool. I'm off you find out what else round the house is plugged into transformers that I can move over to solar, you should too.