The Solar page
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. Soon to be revived an made part of my energy gathering system
My home heating system comprised of an air to air heat pump with an electric furnace back up. The system was designed with eventual solar input in mind.
Life was busy, and I did not progress much beyond that stage except for refining my coal and wood heating which has been the deep winter core heat for our home.
This year 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 in harsh New England winter conditions. The amazing tubes are made of stress relieved borosilicate glass (Pyrex), with the two tubes only attached at the top, and supported at the bottom by three stainless steel springs. The outer surface of the inner tube is sputtered with a 98% absorptive 2% emissive selective surface to optimize the gathering and retaining of the radiation from the sun. The space between the glass tubes is a high vacuum, with a barium getter just like CRT's. The tubes have the advantage of having the collection surface insulated from wind and outdoor temperatures, and the selective surface which is stable up to the stagnation temperatures exceeding 450 F is in the vacuum for long life. The collected heat is brought to the top header/manifold for extraction by the flowing water in solar loop. By a heat pipe. The collectors are mounted on a stainless steel rack so that the angle can be changed for optimization at different times of the year. Once the drums were filled and the plumbing was done, I turned on the pump and installed the heat pipes and collector tubes. I climbed the ladder more than 88 times twice for each of the 44 tubes.
I next needed a heat storage tank, and to my dismay the tank cost more than the collector. An 80 gallon tank with two heat exchanger coils cost over $1000, and a whole house storage with 1000 gal of capacity was going to cost $12-15K. Being a yankee inventor, I figured there was a cheaper way. I designed modular solar heat storage system that could be expanded to any size in 55 gal increments. The tank is non corroding HDPE that is rated for stacking at 150F and gets soft at 253F. The removable cover is stiffened with thoroughly painted plywood, and has an upper 30 foot of 1/2"OD copper tube heat exchanger, and an identical lower coil. The coils are fed with 3/4" copper tube and coupled with a custom copper fitting that I made. The drums were filled with 53 gallons of water and 2 gallons of EV anti freeze. The drums are connected in series with unions for easy maintenance if replacement is needed. The two coils position on the cover is alternated to simplify piping. Since the collector stagnation temp is over 212F, pressure relief valve and expansion tank were needed to protect the solar loop from explosion. The drums are sitting on an insulated base , and are surrounded by a thermomax aluminum faced insulation . The air space between and around the drums is filled with celulose attic insulation. The addition of flow control valves allows me to select the size of the storage, and heat 1, 2, or 4 of the drums. This allows me to get one drum very hot quickly, or more drums heated to a lower temp.
To
control and monitor the performance of the collector and storage system, I wrote
a program in Labview that uses a data acquisition card in my notebook computer.
Click on picture to see full size screen dump.The screen can be scrolled to see
more graphs, showing the hot water tank
and all important data graphically.The linked photo is a solar startup. Data on the system is logged to a
file on the hard disk every 2 minutes. A new file is generated each day. The
file can be displayed on an excel spread sheet or graph.
The small collector and the cloudy overcast days that we have had this
winter both contributed to limited heating of the drums. During the winter my
coal stove usually runs constantly, so I decided to extend the heat gathering
circuit to include a stove top heat
exchanger. I was pleased by the heat output of the exchanger, as it was able
to heat and maintain all 4 drums at over 150 F. I can now heat my hot water, and
also preheat the cold well water that flows into it to replace the water
that we use from the hot water tank. I bought a new electric hot water heater,
and modified it with a side mounted heat
exchanger. As the hot return water from the coal stove or collector flow
back to the drums, I can route it through this heat exchanger, and keep the tank
at well over the 125 F setting of the thermostat, so the electric never comes
on, and we have a huge supply of hot water available.
Sue and I only use a relatively small amount of hot water, so I added a second
circulator to the fresh water circuit. The circulator can run the hot water
through a surplus radiator in a
box under the floor in our family room variable
speed computer fans complete the heater. A second heat extraction radiator in the whole house air
handler can distribute heat through out the house. A freon / water heat
exchanger in the heat pump circuit is a third heat extraction method. Click the schematic to see the full size
schematic.
The control of the new system is more complex, as the glycol circulator is always running, and only through the adjustment of the flow mixing valve can the water be directed through the solar collector and stove in the correct proportions. I built a servo attachment to the valve to allow computer control. An inexpensive water meter was added to the return line and a laser/detector was added to generate pulses that represent flow. The pulses are counted by the acquisition card and the labview software allows me to determine total water pumped, flow rate, and to compute btu/min output of the system. The plumbing and control system has gradually become more complex, but I will design an automatic system that does not need the computer, that is powered by a UPS power supply so that we do not have to be here to adjust the system. The pipes and valves are in an insulated box with extensions to the valves to allow adjustment.
The distributor of the collectors Sunwise Solar in Portland ME was nice enough to give me a short 18" demo tube which I made a parabolic reflector for the next day. I added a tracking system, and proceeded to test the tube. I was able to just barely run the little steam engine that I had ran with my earlier fresnel collector. I was able to take 650ml of 55F water to boiling in under one hour. Great potential for other uses like cooking, canning, and water disinfecting.
All of my research was done out in the sun, so I made a fan cooled solar sombrero to keep me cool.
Contact me: genesis1@snet.net
