Solar Collectors


free solar charging

click to expand
juice box pro 40 evse
Have been living with a battery powered Micro grid now for three years.
The system works pretty well when the days are sunny and long and gets strained during cloudy weather when the output can be reduced by as much as 90%.
My Solar battery bank is ~ 48kwh of storage.
My solution is to switch back to the grid during those long cloudy spells in winter, and then back to the batteries when the output returns to normal.
I usually get the solar batteries fully charged during good weather by noon or slightly later.
This leaves the excess power to be simply wasted for the remainder of the day.
My Chevy Bolt has a 60KWH battery bank so I now have a place to dump the excess power.
Sounds good on paper but in reality it is not so simple.
Since the 48V solar battery bank charging needs to be highest priority , and the sun output is a variable, the best system would automatically adjust the EV charge rate to take max advantage of available solar output without exceeding it which would have to draw from the solar batteries.
My level 2 charger selection required an adjustable charge current the car would be allowed to draw.
After some research I got a Juice Box Pro 40 and installed it on the post right between my two garage bays.
The full solar charging current for the 48V solar storage bank is ~ 110Amps
The EV charger running at full output off my 9kw output outback inverter,can draw upwards of 145A from the batteries.
by adjusting the EV charging current I can allow between 1.4KW to the full output of ~7.5KW to be drawn, therefore keeping the solar bank charged while dumping most of the excess production into my car.
The EVSE has a network connection so I can set the max current on my cell phone.
while this works fine, it is a tricky thing to manage as a microwave oven turning on could exceed the solar charging ability.
Automating the load management is looking like a project that needs to be tackled.

Making a small solar concentrator

Making a small solar concentrator
turn old small dishes into solar concentrator
This blog will be about how I constructed a sun tracking solar concentrator from bathroom mirror tiles, and surplus small dishes that seem to be everywhere.
Thanks to Dan Dumas for donating the four dishes.
The bathroom tiles with silicone rubber adhesive will last for 20 or more years with no degradation, while aluminized mylar and other foils and tapes will deteriorate in months if left in the weather, so it is a bit more work, but the dish will work as good 10 years from now as it does today

Read More

Keeping Warm In New England

Keeping Warm In New England
My heat sources
My experiments with solar energy go back to my TV repairman days at Color TV & Stereo Clinic.

I built an exhibit for an energy fair at MIT in the 70's, where I built a sun tracking fresnel lens concentrating solar collector that ran a toy steam engine in February with the energy in one square foot of sunlight.

I also made, with the expenditure of lots of labor and beer, the 7 foot solar furnace that can melt aluminum. that is explained in the plugging into the sun page.

My home heating system is comprised of an air to air heat pump with an electric furnace back up. The system was designed with eventual solar input in mind, so I have both air to water and water to freon heat exchangers.
I invested in two solar hot water collectors made by the Apricus company in Taiwan. The evacuated tubes look to me like the best way to harvest the suns rays for water heating in harsh New England winter conditions.
I have a modified coal and wood stove that work alone or in parallel with the solar to store heat and heat my domestic hot water. My coal supply is a large cut off benzine tank with a slide back roof for loading. The coal is dispensed into 5 gal pails, via a surplus modified treadmill, that is driven through an old lawnmower transmission by my rechargeable drill.

Read More

C-band dish solar furnace

C-band dish solar furnace
Canning Tomatoes with the sun
Back in the 60's I was given a nice rugged parabolic dish, and had covered it with mirrors. It works pretty well. I have reached aluminum melting temperatures, and run a steam engine.
Old radar dishes are not readily available but old C band dishes are.
Start with an old C-band satellite dish. Cut Bathroom mirror tile into 2" or 3" inch squares.
Glue tiles to dish with silicone rubber,then glue aluminum foil to the back with a thin coating of silicone to seal out moisture, and protect the mirrors back.The small gap between the mirrors will allow eventual total curing of the silicone, but it takes several months for a full cure. The layer of aluminum foil stops the degradation of the mirrors rear surfaces. My dish has been outdoors for over 30 years and the mirrors are still like new.
The horizontal and vertical drives are run by a sun tracking servo amp that keeps it pointed at the sun.
A schematic of the basic tracker is available on the downloads page:Simple Tracker schematic
This generic servo will operate on 12-24VDC, and will run dc motors over the same voltage range. The power transistors need to be mounted on a good heatsink with electrical isolation between the collectors and the heatsink. The servo gain pot will want to be tuned for best accuracy of tracking without oscillation.
The sensing photo detectors are mounted at + and - 45 degrees to form a half bridge.The + of one detector connecting to the - of the other. This "shorted" connection forms a current bridge where the two photo diode currents cancel when evenly illuminated, and change polarity and amplitude of output when unbalanced. The idea is to have the servo always drive the dish to the null point.
I Canned some tomatoes this morning. The 8 quarts of water and tomatoes reached boiling in 6 minutes, but then it was boiling too fast. I had to drape news papers over the mirrors to turn down the heat. I will need to make an adjustable shade for the thing, so I can adjust the boil to a slow steady one. Tracker worked well.I need a steam engine for the thing, and I could make some electricity or pump water.
More information on this project:
Plugging into the sun blog