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.
System Schematic and control program screen dump
National Instruments Labview with a small PCMCIA data acquisition card for my notebook is the control and monitoring system. The software graphs the data from the whole day, and adjust the flow control valves to provide the best mixing of flows for the heat sources that are active at the time. It is not uncommon for the 4 heat storage drums and the hot water tank to be at 150-170F all winter. Better photos of the heating schematic: heating schematic
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. The mixing of flows and control of the three heating loops is with a custom Labview program and servo controlled valves.The hot water tank is keep at the storage tank temperature with an attached tube in tube heat exchanger.
The Coal stove
Coal stove system
The core heat for the house during most of the winter is my trusty coal stove. The stove is in a parabolic shaped opening in the large stone and concrete chimney. At first I painted the enclosure flat black figuring that the stone would get hot and continue to radiate heat, but after several years,where the stone got to 100-120F, I took the opposite approach. The parabola is covered with a reflective aluminum sheet which reflects the IR back to the stove so it runs hotter, and heats the air better since it reaches a higher temperature for the same fuel use. The aluminum air director can be lowered which increases the "chimney" effect of the rising heated air, and creates a natural draft to suck in cold basement floor air, and direct it into the upstairs. The air handler can also be turned on to force circulate the air through out the house. The air director open, lets much of the heated air flow into the basement ceiling area, to warm the floors and keep the basement at a higher temperature. Combustion air from outdoors is drawn from the same manifold as the wood stove.The automatic inlet air bimetal thermostat needed to be modified to allow inlet air to be drawn from the manifold and still allow proper thermostatic control.Two loops of stainless steel tubing pass through the firebox, to heat my domestic hot water all winter.
The evacuated solar tubes
After a lot of research, I decided to get some evacuated tube hot water collectors. These tubes allow short wave IR and visible light to pass through the outer pyrex glass, to be converted to long wave IR (heat) on the selective absorber inner glass. This heats the air in the tube, which has a heat pipe to transfer the heat to a manifold at the top, where it heats the circulating water. I was impressed with how well it works. My 24" parabolic coffie pot will boil the water in less than 1/2 hour. I built a stainless steel tubular frame for the tubes so the angle could be adjusted for different times of year.
The wood stove
The wood system
After using an inefficient box type wood stove, for many years and burning about 2.5 cords of wood per winter, I bought an efficient Country Comfort fireplace insert. It was great. it has a catalytic combustor , and can burn dry wood like a gasification stove. All combustor stoves regardless of fuel, need air, and if that air comes from the house, cold air has to come in to replace it or the house would drop pressure and starve the fire of combustion air. When building the chimney, I put PVC ducts in the stonework so the air could be brought in from outside. What a difference that can make. The colder it is outside, the colder the replacement air will be, and if it has to pass through the house to get to the stove, you will have a drafty house.