Here Comes The Sun!

My mobile knife sharpening business is entirely solar powered.

Mobile Knife Sharpening Booth with Solar Panel

I have a small folding portable 80 watt solar panel which I adjust to exactly face the sun throughout my work day. The picture above shows the panel facing the morning sun in San Jose.

I adjust the tilt so that the solar panel is perpendicular to the sun, and I adjust the direction that they face to track the sun across the sky during my work day.

This system works quite well — quiet clean power that meets all my needs. The panel's 80 watts is less than my knife sharpening needs — which is 180 watts — the battery in the circuit is the magic that allows this system to work.

The battery accepts a charge from the solar panels while my knife sharpening equipment is not running, and sends power to the machines when they are turned on. I carefully designed this system, factoring in the output of different sized solar panels, the size of the battery, the access to the sun at all locations, and the exact quantity of knives and garden tools that I would receive to sharpen during the work day.

Or you could say I guessed.

Being a mobile knife sharpener I wanted to keep the size and weight of each component as small and light as possible. I estimated the resting time of the machines and designed from there. The run time of the knife sharpening machine is never anywhere near 100%. Even during my busiest days the sharpener is off while the knife is inspected or the machine is adjusted, while I am wrapping up the knives, talking to the customers and such. Not to mention the time I am between jobs waiting.

Reading, Waiting for some Knife Sharpening Business

The winter seems to be season that stresses the system the most. I believe — since I can aim the panels exactly at the sun at all times — that I am capturing just as much sun in the winter as the summer, so that's not the problem. 

What winter throws at me that is hard to deal with is long shadows, shorter days and rain. 

With the sun lower in the horizon, buildings and trees cast a much longer shadow — and it gets harder to find a spot for the solar panels that is sunny and that is safe from Granny parking her SUV.

Shorter days means I miss perhaps an hour or so of direct sun during the day — especially since this combines with the long shadows.

Here in Northern California we get all of our rain in winter, so if it is raining, its winter — with the long shadows and short days.

Knife Sharpening Booth Suffering A Northern California Winter Rain Storm

Now — this being the ides of March — the sun is coming back!

Knife Sharpening Solar Panels Aimed at the Sun

I took the photograph above about a week ago. This photograph shows the panels tilted up with the attached legs so that they are aimed square on to the sun. I have the legs positioned so that the panels are tilted as high as possible, and during winter I cannot raise the panels quite high enough to be exactly perpendicular to the sun. With the sun inching up in the sky — last week was the first day of the winter that the panels were truly perpendicular to the sun! From now on I will adjust them down slightly, that is until the winter solstice.

My system has a battery, and this battery protects me from most of these variables. Just not quite. I now have a second battery which I keep charged and with me. If the operating battery is run down I can operate from this spare. I have had to do that twice this winter. Once the main battery is run down and I am operating on the spare then I will charge them at night using a AC powered battery charger. I believe I have done this three times this winter.

With the sun coming back I probably won't have to worry about the power so much. Spring around here usually brings high winds, and summer brings heat, but that is another blog post.

That is to say while I am out on the job I am solar powered