Power Grab
Work is very quiet today, and I started looking at solar panels after reading some random comment online. They are, as I would have expected, still priced predatorily to capitalize on those who really want to try to do something good for the world’s energy progress, not just Netflix An Inconvenient Truth. They are also big and ugly.
But, while looking through the options I came across a 5 watt trickle charger intended for car and marine use. Not too expensive.
This is when I realized: LED Christmas lights are extremely low-power. Like, 2.4 W/string for a 17’ string.
Of course, lights need to be on at night, so a $60 marine battery is necessary.
The battery I found is capable of outputting 80 Ah at 12 V. That’s 0.96 kWh for those who use real-life measurements. Aside from being the unit upon which you are charged for electricity, a kWh in this case answers the question: how much power can I provide for a one-hour period? So, I can provide 960 W for 1 hour with this battery. For the coming calculations, it’s better to think of the total battery capacity as 960 Wh.
If I want to run 10 strings of lights (170’), I need about 24 W. Doing a brief algebriac flip, that means my marine battery can run this kit for 40 hours without any charging or external input. Not bad.
But, the bigger question is the sustainability question: how much energy is expended per night? My 24 W load will run from 6 PM to 2 AM, 8 hours. This means I will require 192 Wh per day.
From what I read in the reviews, 4 W is probably a reasonable expectation of the output from the solar panel. This means, per day, I need 48 charger-hours of energy. If we get an average 8 hours of good sunlight per day (in the winter), this implies a humming array of 6 trickle chargers to keep my ship afloat. You only eliminate one charger if you assume they run on spec (5 W) for the whole 8 hours. They don’t call them trickle chargers for nothing.
We have just arrived in Energy Policy Land: what now?
I can cut my load to 6 strings of lights, dropping my wattage to about 15 W. At my daily charge of 32 Wh per panel per day, I reduce my panel requirement to 4. If I cut my run time down to start from 7 PM and run to 11 PM, I only need 60 Wh per night, which can be provided by just a pair of solar panels running at my conservative 4 W rating. This sizing seems at least reasonable, but it’s a pity to start the lights so late and shut them off so early.
Pulling a move one might call the Pelosi, I could simply assume we will get more sunlight than originally planned.
Thinking outside of the box and definitely removing me from consideration for a cover feature in Martha Stewart Living, I think it would be awesome to install a manger scene yard decoration and put small solar panels on the roof. What a cool statement that would make!
The best idea is to upsize the equipment. The real weakness to the plan is the trickle charger.
I found this far superior device, but it’s also far larger. Definitely impossible to hide amid shrubbery.
To give us a pan-energy-source view of this load, let’s propose actually plugging the battery into an exterior AC outlet to charge. This still allows cord hiding during prime times (actually the main objective of the project) but is definitely a Peter-to-Paul situation energy-wise. The linked charger outputs 15 W, between three and four solar panels depending on how you calculate it.
Since we’re no longer dependent on sunlight, we could easily replenish the battery simply by leaving the charger plugged in for a while. The circuitry in this charger takes care that the battery does not overcharge. The circuitry may also slow down the overall charge rate, meaning lengthier plugins might be necessary.
As cool as the solar thing is, I think it’s an interesting illustration that the time is not yet ripe. I might actually consider the plug-in scenario just to avoid the cords.