“Line Loss” is often mentioned when discussing alternative energy systems, but that is just one of several significant losses. This article will describe five distinct types of losses.
In an alternative energy system that incorporates a battery or battery bank, the first electrical loss is within the batteries themselves as they discharge, this is called the Puekert exponent. This loss increases with the aging of the batteries. Look at it this way: If you had a 500 gallon tank of water and you used 200 gallon a day you would have to replace 200 gallons every day or 400 gallons every other day. If this tank had a half inch hole it could lose say 50 gallons a day. That means you would have to put 250 gallons back in every day to keep it full. The erosion on that hole would increase the size of the hole and the loss as time goes on. Whether you used water or not you would have to replace this loss or the tank would be empty when you wanted to use the water. Like that tank of water, a battery has the same type of loss every day, whether it is used or not.
Second is line loss, which increases with line distance, especially in direct current low voltage applications. This is why higher voltages are becoming popular. The lower voltage’s lose efficiency and can become dangerous if wire sizing isn’t given special attention. On the other hand the higher the voltage the less choices of direct current appliances (12 volt) you will have. The lower the voltage the larger the wire must be to maintain a safe system. It also needs to be multi stranded. Multi-strand cabling increases the surface area. This can’t be overstated.
The following table shows the Voltage Drop Index (VDI) per foot of various sizes of copper and aluminum cabling.
VDI = Amps times Feet divided by (% volt drop times voltage)
Wire Size – Copper Wire Wire size – Aluminum Wire
AGW VDI Ampacity VDI Ampacity
0000 99 260 62 205
000 78 225 49 175
00 62 195 39 150
0 49 170 31 135
2 31 130 20 100
4 20 95 12 75
6 12 75
8 8 55
10 5 30
12 3 20
14 2 15
16 1
Determine the appropriate wire size from chart above.
A) Take the VDI number you just calculated and find the nearest number in the VDI column, then read to the left for AWG wire gauge size. B) Be sure that your circuit amperage does not exceed the figure in the Ampacity column for that wire size. (This is not usually a problem in low-voltage circuits.)
Example: A photovoltaic (PV) array consisting of four Sharp 80-watt modules is 60 feet from your 12-volt battery. This is actual wiring distance, up pole mounts, around obstacles, etc. These modules are rated at 4.63 amps X 4 modules = 18.5 amps maximum. We’ll shoot for a 3% voltage drop. So our formula looks like:
VDI = (18.5 A a 60 ft.)divided by (3% x 12 V) = 30.8
Looking at our chart a VDI of 31 means we’d better use #2 gauge wire in copper, or #0 gauge aluminum wire. Hmmm. That is fat wire.
What if this system was instead 24 volt? The modules would be wired in series, so each pair of modules would produce 4.4 amps. Two pairs 4.63 amps = 9.3 amps, Max.
VDI = ( 9.3 x 60 ft.) Divided by ( 3% x 24 V) = 7.8
What a difference! At 24 volts you could wire your array with # 8 gauge copper wire.
[JWR Adds: Up until the 1980s, residential aluminum AC wiring was allowed in new construction by the U.S. National Electrical Code (NEC), in branch circuits (inside walls.) But because of a higher incidence of house fires caused by overloaded circuits, beginning in the 1980s nearly all state building codes were updated to ban aluminum wiring in branch circuits, for new construction. Typically, these laws grandfathered aluminum wiring it in existing houses.]
Next, I’ll discuss inverters. Losses within inverters are the third types of loss. Converting direct current (DC) to 110 or 220-volt alternating current (AC) creates another electrical loss. Inverters are an electrical appliance and use electricity (3 to 40 watts) to run. The better inverters have a “search mode” using from 3 to 5 watts when no loads are detected. When operating an appliance they may use from 25 to 40 watts plus the appliance load. This can be anywhere from minutes to 24 hours a day, depending how long the inverter needs to be on to operate the appliances needed. The cheaper inverters do not have a search mode and must run 24 hours a day unless turned off and on mechanically. This usage can use up to 1,000 watts a day. This amount of electrical usage is equivalent to having two 100-watt panels in direct sunlight for 5 hours just for ability to use electricity if you want to, or three 100-watt panels if there are clouds passing by from time to time. It is much wiser to have an inverter with a search (sleep) mode especially if you have a load that needs to have access to electricity on a non continues basis, like a refrigerator or furnace. If the electrical system has one 110 Volt inverter and 220 Volts are needed the transformer uses electricity (25 to 35 watt range) just like any other appliance.
Phantom loads are the fourth loss. Phantom loads are created by appliances that have been designed to still need electricity while nominally switched “off”. The is often the greatest loss, especially in 110-volt AC systems. These are a serious problem in smaller systems. These can be voltage converters that convert a/c back to a variety of lower voltages both AC and DC (wall warts). Clocks, timers, remotes, smoke alarms, and even ground fault interrupt (GFI) outlets are all culprits. (It is noteworthy that GFI outlets are required by the electrical code for bathrooms and kitchens and can use as much as 5 watts per 24 hours.) Appliances with timers and clocks like microwaves and stoves also create phantom loads. Remote controlled appliances like televisions and stereos are the biggest users of electricity while off, some using as much as 80% as much electricity while off as when switched on. All so you can turn them on without going over and using physical force. If industry were to eliminate these phantom loads in their appliances we could close several power plants and save our environment and resources, as well as reducing heart attacks (exercise walking to the television and back to the chair) but people and industry would rather talk than do. These combined phantom loads often exceed the electrical consumption of the necessary household appliances like refrigerators and furnaces. Simple switching could save thousands of watts per household. These phantom loads would save enough electricity to eliminate the need for rolling blackouts in the cities, like happened in Texas.
[JWR Adds: The simple workaround to eliminate phantom loads is to put any identified culprit devices on power strips. When you’ve finished using the device, make sure that you turn off the entire power strip. The key here is to position the power strip in a convenient place on top of furniture, so that it doesn’t get overlooked. Granted, this approach detracts from your home’s decor.]
I was able to buy my second inverter and its accessories because of phantom loads. (These had soured their first owner on PV power.) Refrigerators are normally the largest users of electricity. Some have ice makers and need a “resistance heater” coil (in the freezer) to free the ice, automatically defrost, also using “resistance heating” and a “resistance heater” coil in the wall at the door to keep the magnets dry in humid climates because safe latches cost more to produce and diminish the manufacturer’s profits. These types of refrigerators can use 3.5 to 5 kWh per day. Short-term gain is certainly more important than efficiency or clean air. Some have a switch to disable this door feature for arid climates thus gaining the good ‘OLE’ Energy Star rating (most don’t). Another load can be a thermostat like all 120 VAC electric refrigerators and some gas heaters. When these are plugged into grid there is no load as the electric is available 24/7 (24 hours a day, 7 days a week) to the thermostat. Not so off grid. A cheap inverter has to run 24/7 to duplicate this feature, and can be using as high as 600 watts a day just to have your appliance off while allowing the capability for the appliance to come on. This usage can be eliminated by using an external thermostat with a plug system to plug into the wall and plug the refrigerator into the plug.
[JWR Adds: If you want to track down all of the phantom loads in a modern house, buying a Kill-A-Watt Meter
The better quality modified sine wave or pure sine wave inverters use a search mode and eliminate this problem, by allowing a mechanical device to be installed or the sensitivity to be lowered enough to sense the small voltage needed to make active the device. The lack of a search mode is the fifth potential loss. All this is before whatever appliance you intend to run can have electricity to do its intended job. Some pellet and gas stoves used instead of central heat have electronics that are two sensitive to run on modified sine wave (as are many other appliances). In some this will cause their “magic blue smoke” to appear. Most of the quote “real deals” on inverters are for inverters that use modified sine wave technology. Even better deals are on older square wave inverters (which may cause motors to show their “magic” abilities also). Many of these are sold in places like eBay and the tool magazines ‘you pay your money you take your chances. When shopping for an inverter a person needs to be aware of this fact. Many solar stores try to sell what they have in stock rather than what you need. As larger chains become involved in the sale of solar equipment misinformation will increase. Many factories offer incentives to their retailers to buy these older types of inverters, thus clearing old stock. Many foreign companies only make the older type of inverters. It is truly buyer beware! “Good information is the key” search it out whenever possible and you will be rewarded.
Many of the systems that I have built, modified, or altered and tested were on a small solar system by today’s standard. Thus teaching myself to conserve and question efficiencies. This was important to me. By this time I was completely off grid and had cut my electrical consumption to less than 6 kWh per day. This included using my shop welder (electric) that made many of the devices (photovoltaic trackers, etc) that I was using. Most all the systems herein were modified in this manner. I often had electrical components waiting for the remainder of the upgrades. The object was to use the old system as well as adding the new ones when they can be afforded. Mixing old but usable batteries with new will age the new making their capacity the same as the old, defeating the purpose of buying new. This is something that anyone who plans to become independent needs to learn while still living on grid. That way one knows how to deal with the quirks that arise without feeling the real discomfort that comes from not having put in the time to learn and understand. All of these remedies that I detail in my working for independence may not be the same avenues you wish to explore, but often the idea or the switching can be modified to be used in a different appliance or on a totally different project. Often just the idea will be the seed or the key leading to success, rather than “do it this way” I now live in an earth ship miles from utilities. I make my own or do without. I have almost every convince that I had before, like a dishwasher, trash compacter, microwave, bread maker and many other kitchen appliances that use electricity. Many I could do without ‘but’ I like them and have made room for them in my life. (Don’t we all.) Most people think this can’t be done. Not true! I have to be aware of my battery’s state of charge before using many of these appliances, but often I have spare electricity at the day’s end.
A Real World Perspective on Expense Paybacks
Many people ask me what is the payback time on all my solar power equipment? In reply, I ask them what is the payback on their electric bill, gas bill, water bill. Also, what is the pay back when the grid goes down and you lose everything in your freezer? I am helping the environment are you? I am not using alternative energy to make money; I am doing it for the independence that I gain! Look around you. How many power outages have there been lately? I haven’t had any. How about you? One question I never hear in the solar power industry is what is my payback on the grid-tie system that someone else put in and [for which they] only paid a portion of and then claimed their payback was just so many years, and I as a taxpayer had to pay the balance? I paid for my own [system] out of my pocket, with no help from any agency or deduction whatsoever.