Just for kicks I decided to calculate the ROI on the 'solar investment' small as it may be. Thats not really the reason I'm doing this, but it I think the result is interesting.
First we have to figure out how much I spent on solarizing the clock. I'm not going to include the cost of the clock because I'd be buying a new one anyways. I'm also not going to include the rechargable battery cost because I'd be using these rechargable batteries anyways, just charging them with an AC powered battery charger. So, we really just have the cost of the solar panel and diode.
Solar panel: $7.99 shipped
Diode: $0.50 + $1.00 shipping
So, I have a solar investment of $9.49
Now, lets find out how much that old clock is costing me. Using my killawatt, I know my old clock pulls a continuous 3W of power (which is rediculous for what it actually does). So, lets calculate the cost.
3W * 24 hrs/day = 72 watt hours per day = 0.072 kWh per day
I pay an average of $0.17 per kWh (fees included so this is actual cost).
0.072 * 0.17 = $0.01224 per day = $0.37 per month = $4.47 per year
Wow, that dumb old alarm clock costs me just over 1 cent a day to sit there and show me the time.
Last calculation:
$9.49 investment / $0.01224 savings per day = 775 day ROI
So there we have it, a 775 day ROI. That is just a bit over two years for the solar stuff to pay for itself. That is probably the best ROI I've ever seen for a solar PV product. I honestly expected it to be more than that.