Last episode, we explored the various methods of abusing electrons in the pursuit of making light. While there is no limit to the ways of consuming power, it is helpful to have some idea of which loads will drain our batteries fastest, which will draw a small amount of current over a long period of time, and which are completely inappropriate for use in a Renewable Energy system.
Some appliances consume large amounts of power, but are used only for a few minutes at a time, perhaps only once a day. A hair dryer, water pump, or microwave oven are good examples. Other loads may draw only a small amount of power, but are used over the course of many hours, or are left powered up continuously. For example, a cellular telephone may be left on all day and turned off at night. Since the current draw is very small when the phone is not being used to make a call, only a small total drain is presented to the batteries. Another example would be a digital battery system monitor, using an LED display which runs 24 hours a day.
Still other devices may draw a considerable amount of power, and be needed for extended periods. The circulating fan in an RV-type LPG-fired furnace, or a full-sized personal computer with a CRT monitor are possible in live-aboard vehicles.
Whatever the loads combinations, it is essential to calculate carefully to avoid constructing a system that is too small to successfully power all necessary appliances and devices. The nuts and bolts of these calculations is not difficult, but beyond the scope of this article. This is where you are best off finding someone who has installed renewable energy power systems to assist in your system's design. It is also possible to learn to design your own system, many books have been written, and a wealth of information is available from Home Power magazine.
Now, about things you are NOT going to be able to use on a battery-powered system. Forget about air conditioning, electric space heaters, most forms of conventional refrigeration, electric cook stoves and water heaters. Unless you have a very sizeable battery system with adequate charging sources, you may find it difficult to use appliances such as waffle irons, crock pots, toasters and toaster ovens, etc. Blenders, vacuums, coffee grinders (!!!) and mixers all are possible in your bus or truck, as are radios, CD players, tape machines and television/VCR's. While most stationary tools such as table and radial-arm saws, planers, air compressors and the like draw too much current for the average vehicle-sized system, most powered hand tools can be utilized, including drills, circular saws, grinders and sanders, electronic soldering tools, etc. AC powered welders are out of the question, but it is quite possible to weld directly from a battery bank, using the proper conditioning and control equipment.
A good use of your renewable energy power system is to recharge small batteries like the ones in cordless tools, radios, flashlights and the like. It is not practical, nor is it desirable to recharge large storage cells such as vehicle starting batteries from your system. These batteries should be recharged from another source, possibly the same one which charges your 'house' system, although through alternate wiring and controls, so as to protect the house batteries from discharge.
A few words about "phantom loads", devices which continue to draw current while giving the appearance of being turned off. In all cases, these must be detected and accounted for. Any device that uses a "wall cube" power supply, or has a display or indicator which remains on after the switch has been cut off will slowly drain the batteries while producing no usable work. Such appliances will require an external on-off switch to completely remove all power when they are not being used. Similarly, electric clocks, VCR's, many consumer radios, and a good few laptop computers will fall into this category. Unplug them completely, or put them on a 'plug strip' outlet bar to allow you to turn them off for real when you are done using them.
Many of you will note that quite a few of the loads mentioned are conventional utility grid powered devices, which brings us to next issue's subject, inverters. Changing low-voltage DC battery power to utility line-level AC power needn't be expensive or difficult, and can make living with renewable energy much more enjoyable and convenient.