Being Grounded Dear Home Power, Enclosed is my renewal for 1991 (the first one, mailed on Jan. 28, seems to have become lost in space or wherever). The magazine keeps looking better and better! I am glad to see that you are branching out into electric vehicles, I think this will generate a lot of interest among "grid folks"; please send me the OOZIE Design Newsletter. A question for the resident geniuses. A friend of mine has an array of PV panels about 200 ft. from his house, where the battery bank is located. Calculations show that #000 wire is indicated. My friend and I have kicked around a couple of, what we think, are novel ways to reduce the cost of this very long wire run. a: Use only one run of #000 wire, grounding the other side of the PV array and the matching side of the battery bank and use the earth as one conductor; much as high voltage transmission lines do. Is the voltage (approximately 14 VDC) too low?, is the distributed resistance of the earth too high??, will this work only with high voltage AC, but not with low voltage DC??? b: Use one run of #000 wire pulled through a run of copper pipe buried in the ground; using the wire as one conductor and the copper pipe/conduit as the other conductor, an impromptu coaxial cable! Must the cross sectional area of the pipe/conduit be considered alone or can the current carrying capacity of the earth, with which it is in contact, be considered? What is the current carrying of earth??, is it a constant???, or does it vary with the particular local soil???? Anyway, can some of your resident experts kick this around or just tell us why it won't work. Keep up the good work and try to move toward the mainstream; there is more interest in alternative energy among us "grid folks" than you may think. After all, sooner or later the oil will run out and there will be no more "safe" places to store the nuclear wastes. Sincerely, Edward Read If the power utilities used the earth as a conductor for their 69Kvac and up transmission lines, anyone living remotely close to a power tower could just stick a couple of copper rods in the ground, run the current thru a rectifier, and charge your batteries-forget the PVs! 'Course, taking a wizz out on the back forty might get a bit dicey... No, one of the 3 conductors on a HV line is the neutral line. The resistivity of earth runs from a couple of K½s to near infinity depending on soil type, mineral content, moisture level, and a pack of other stuff. Using copper pipe as a conductor will actually work, assuming all the joints are soldered, BUT the current carrying ability is the same as if you melted the pipe down into a solid wire. I have no idea what that would be for 1/2", 3/4", etc. Using 400' (round trip) of 3/0 copper wire will carry about 30 Amps @ 14.5VDC with just a hair over 5% acceptable wire loss. Are you tied to a 12V system for some reason? Going to a 24VDC system will allow you to cut down to 1/0 wire for the same # of PVs with only a 4% wire loss. Bob-O Getting Wired Our PV site is 200' from batteries. What size wire should be used? At present we have 4 panels that produce between 7-10 amps. But we wish to expand to 20-30 amps, should we get wire for our future use or can the wire size we use today be incorporated to accept four more panels? Actually I'm guessing at our present amps but have four Arco panels and wish to go to eight panels. Good magazine. Joey Coccia, POB 18, Dillard, OR 97432 Joey, you don't say whether you are running a 12VDC or higher voltage system. It makes a big difference. If your PV site is 200' from your batts (400' round trip) and you are sizing it for 30 Amps, you will need at least 3/0 copper wire for a 12V system and 1/0 copper for a 24VDC system. For an 8 PV array, (±24A @12VDC or 12A @ 24VDC) you would need at least 2/0 or #1AWG respectively. Bob-O Three Way Fridge To answer Richard Cameron, Dillard, OK (p. 88 HP#22) on 3-way refrigerators: By all means increase the insulation. I have just 1" Thermax on the top, sides and freezer door and it uses noticeably less gas. However, they (ammonia absorption refrigerators) are still WAY too inefficient to run on a battery. They operate on heat, so the AC, DC and gas all have the same equivalent efficiency (1 watt= 3.412 BTU). You'd be ahead if you could get direct solar heat into the boiler with some kind of concentrator oven, but it's not very accessible. Most 3-way models I've seen have the same BTU on gas or 120VAC. The 12 VDC heater is proportioned to only 2/3 of the BTU. This is just to avoid the cost of a 15A DC thermostat - on 12V it just stays on continuously to approximately maintain temperature. If you have a large enough PV system (20A +), you can use the heater in the refrigerator as a shunt load or diversion load when you have a surplus of power and no more storage capacity. This way your surplus offsets your use of propane fuel. I've had mine that way 7 1/2 years and it uses very little gas in the summer. Just be SURE the gas valve goes off when the heater is on, otherwise you'll overheat and waste gas. Do not exceed 15 volts on the 12v heater. Also be aware the 12v- operated gas valve (Norcold) consumes 250 ma from the battery just to keep the gas on. Keep cool, S Marshall, RD3 BOX 30-A, Dover-Foxcroft, ME 04426 Cool Fridge Dear Home Power Crew, Please renew my subscription to this excellent magazine. I enclose $40 US. Perhaps the extra $6 can extend my entitlement from 6 to 7 issues, starting with #23. Our system in brief: 6 PV panels (2 x Kyocera, 2 x 45w BP, 2 x 58w Solarex) charging 2 x 200 AH battery banks at 24V. A Heliotrope 2324 inverter (sold here as "Solartronics", producing 240 VAC. This powers a small auto washing machine, a wide range of power tools including a 9 1/4" saw (I'm building our home) numerous compact fluoros, bench grinder, W M motor powered air compressor, vacuum cleaner, TV (14" colour Panasonic gave best results of 3 brands tried), video, and kitchen appliances. I have Danfoss 24V refrigerator components but this is not set up yet. In the meantime I am running an old refrigerator from the inverter as an experiment. This refrigerator has 2 variations from newer types: 1. Thicker insulation 2. A condenser in the form of a pressed steel duct which draws air over the motor, thus avoiding heat from the motor rising up beneath the cabinet. The steel duct also acts as a reservoir of "cool" into which the piped refrigerant can quickly shed its heat. I have further improved efficiency by insulating the duct from the cabinet using heavy cardboard and PV panel packing (see broken line). INSERT DRAWING HERE. IT'S ON THE HARD COPY. This refrigerator motor is rated at 1.4 - 1.5 amps at 240V and the duty cycle seems to range between 11 and 19%. We place 4 litres of water in a plastic container in the freezer compartment. This turns to ice during the day. We switch the fridge off at night, the ice keeping the cabinet cold while switched off. Used this way, I estimate that refrigeration consumes 20 - 40 amps at 24V per day. In cool sunny weather, the PV panels can nearly keep up with this and the other demands. However, since I started experimenting with this refrigerator, I have made a practice of running the battery charging generator about 1 hour each day in the morning, when the fridge is switched on again, to provide for the initial daily cool down. This practice is essential in cloudy weather. The battery charging generator is a 1927 vintage (approx) 3 1/2 HP Lister petrol engine (water cooled) V-belt driving off one of the twin 18" flywheels to an ex work boat 24V generator estimated to put out 15 - 20 amp continuous. This system has several advantages. 1. Cost. An equivalent 240VAC generator powering a 20 amp 24 VDV battery charger would cost well in excess of $1000 whereas this cost less than $500. 2. East to live with. 600 RPM is much less stressful than 3600 RPM of modern motors. 3. Water heating. The water cooled motor provides an ideal opportunity to heat domestic hot water at the very time (cloudy weather) when solar heated water is in short supply. Use of this system thus fits in perfectly with prevailing weather conditions, being used most when PV panels are functioning way below their peak, and enables the maximum amount of energy to be extracted from the petrol that is used. Using only the cylinder head water jacket (no exhaust water jacket yet) we get about 30 litres (7 gallons Imperial) shower temperature plus. Thus; 1 litre petrol = approx 20 amp at 24V plus 30 litres hot water. I am looking forward to the time when a fully automatic system, similar to the above will be available, sensing low battery voltage, starting automatically, and switching off when the batteries are fully charged. I have several questions: 1. Is it normal for the voltage regulator of a generator (my reg. is Echlin) to run hot, and if so how hot? On mine, two of the three coils are blackened but the unit still performs okay. 2. Have you any info on using a water cooled heat exchanger for the fridge condenser. It seems to me, this would absorb the rejected heat more quickly and thus, cut down on motor running time, giving higher efficiency. The slightly heated water could be the first stage of the domestic water supply. 3. Have you a circuit diagram for a DC-DC voltage reducer 24 to 12 or 6 volt. This would be useful for powering certain appliances - radio, tapes, etc. 4. What are the best insulating materials for constructing refrigerator/freezer cabinets? Yours Sincerely, Jonathan Sutton, Bulga Rd., Bobin, Australia 2429 Hello, Jonathan. 1. Your regulator sounds like the electromechanical type. These types often use large power resistors which get very hot. Hot means that you can't hold your finger on the component for more than five seconds. I'd have a spare regulator around if I were youÉ 2. The concept of using water to remove heat from a refrigerator is sound. Any feedback from anyone who has tried this? 3. Diagram for a DC/DC power supply follows. This circuit uses either the LM 317 (1.5 Amps) or the LM 350 (3 Amps). Very simple and adjustable. INSERT SCHEMATIC 4. The most thermally efficient insulation is now a foam. A closed cell type is best, like PVC. Richard Ice Farm Dear Pinhead, Your article in Home Power #21 on Ice Farming got me to thinking. Way back when they didn't have refrigerators (or electricity, for that matter), the common solution to food preservation was the ice house, a year round cooling facility. I'm not sure about the construction details of these things, but around the turn of the century, in Nebraska, my grandfather (and practically everybody else around those parts) had one. It was apparently rather large (maybe 12-15 ft square) building filled with ice which was in turn packed around with hay or straw (not sure which) for insulation. Well, I am looking for land up here in the Northwest (a good ice farming country) on which to build an AE homestead. For a variety of reasons, electrical power will be a scarce commodity initially - probably only enough to run some lights. An ice house could be a good temporary solution to the refrigeration problem until the electricity production can be expected to handle refrigeration. Or maybe it could be a permanent solution. But I don't know of any sources of information on the construction of such things. I don't need general principles - what I need are construction details like, how big? How much ice is needed? How much and what type of insulation? Drainage problems? etc. So I thought I'd write to you in case you had any such information or could point me in the right direction. Perhaps a note in Home Power would turn up a reader with more specific and up to date information? Sincerely, Jim Perry, 3050 - 180th Ave. NE, Redmond, WA 98052 I was able to glean a few more details from my library but this is by no means all the information you want. The size of the ice blocks taken from the frozen ponds were two ft. square or more, and anywhere from nine inches to a foot thick. It was stored stacked in layers of sawdust. It was pulled up a long chute, by means of ice tongs and a rope, off the sleigh and into the ice house. They chopped a hole in the ice and then used a cross cut saw to saw the cakes out. A team of horses was used to pull the ice from the pond to the sleigh. All the men would work and fill a different farmer's ice house every day till everyone had ice. The ice house walls were about 7-13" thick and were without fire breaks. They were filled with sawdust. The attic was also filled with sawdust, in such a way that it continued to fill the walls as it settled down. Somewhere I read about an ice house that was built underground. There was some sort of hatch arrangement for opening to lower the ice blocks into it. Regular access was down a wooden ladder. Again, the ice blocks were packed into sawdust for insulation. I would be curious, also, to find out if there is a newer improved method of ice housing in the 90s. C'mon, you HPers, tell us what you know. There has to be someone who knows someone who grew up with an ice house. - Kathleen