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First Year PV Basics

Richard Perez

The transition from grid power, generator power, or no power at all to solar power can be confusing. The user becomes his own power company and in the process inherits the responsibilities along with the Watt-hours. Fortunately, PV systems are ultrareliable, simple to size, install, and operate. The user only needs to know a few basics to get started on PV power. So, country folks and city dwellers, here's a guide to the basic concepts involved in a simple starter PV system.

The Need is for Electric Power

The size and success of your new PV system rests on you. What do you want to power with the system? What kinds of appliances will you power? How long will you power them? All of these considerations affect the design and size of the system. If you are considering putting your entire home on PV power, then you have two choices. One, learn to do the job right yourself. Two, hire a pro with the knowledge to do the job for you. The cost and complexity of a PV system increases with the amount of energy required from it.

If, however, you wish to replace the kerosene lights, or take a circuit in your home off of the grid, then this article, about simple and inexpensive systems, is for you.

Four Major Components

Every PV system has the same major components. The only difference is the quantity of hardware. This means you can get started with a small system, learn first-hand from that system, and expand it later.

The four major components in a PV system are: energy source (the PV modules), energy storage (battery), energy processing (inverters, controls, instruments, and such), and loads (appliances).

one person, one panel

Every system has these components; the only differences are in size and quantity. For our purposes here, consider a small system as one that uses between one and four PV modules. Such a system will use between two and four small lead-acid batteries like the Trojan T-105 (220 Ampere-hours at 6 VDC). Energy processing may or may not include an inverter (like the small Trace 612 or PowerStar models), a simple charge controller (like the Trace C30A), and a voltmeter. Typical loads appropriate to the small starter system are: lights (high-efficiency fluorescents), electronics (TV, stereo, VCR, computer, etc.), kitchen appliances (blenders, juicers, & mixers), and smaller workshop tools (like drills & saws).

A Starter System

I have written many articles detailing the mathematical approach to system sizing and design. This article is different. Here we are going to size and design the system with a nontechnical approach. We are going to design the system by the person. Sort of a "one person, one panel" approach to solar energy. This will work. It is based on my experiences in over one hundred small PV systems.

The starter system will use a 12 Volt battery. This keeps the system affordable to those now using kerosene lights. It also makes the system inexpensive enough that folks downtown can use it to gain experience in RE use. The system is designed to be expandable. It can grow about three times in capacity without requiring major component replacement.

Allow one 50 Watt PV module for each person in the household. This means that each person can use, each day, the energy produced by a single module— about 250 Watt-hours. While 250 Watt-hours may not sound like much electricity, it is more than enough for lighting, electronics, and conservative use of kitchen appliances and shop tools. Cost is about $370 per installed module.

Battery

Provide about 220 Ampere-hours of battery storage for each two people in the household. For example, this means two Trojan T105s (or equivalent) for a family of two and four T105s for a household of four. The resulting system is properly proportioned and will supply power for about four sunless days in a row. Battery cost will be about $170 for two batteries to $340 for four batteries. These "golf cart" batteries will last about five years and can then be replaced with higher quality storage.

Inverter

The use of an inverter is optional. In small systems, it is often much less expensive and less difficult to use the power exclusively as 12 VDC. Efficient low voltage DC lighting is readily available as are many varieties of low voltage electronics (stereos, TVs, and radios). The starter system is capable of supporting a small inverter. The Trace 612 and PowerStar UPG400 and 700 will function well and supply 120 vac for appliances like VCR, TV, and even compact fluorescent lighting. Using an inverter will add about $600 to the system's overall cost.

Controls

A control is not necessary if the system is continually occupied. If you go on vacation simply disconnect half of all of the PV modules. If you do wish to add a control, then keep it simple and inexpensive, like the Trace C30A for about$85.

Instruments

For economy and flexibility, buy a digital multimeter (DMM). The DMM can make most essential voltage and current measurements. An instrument provides you with the information required to operate and learn from your system. If bucks are tight, go to Radio Shack and spend about $60. If you can afford it, either a Fluke 77 ($130) or a Fluke 87 ($280) will accurately serve you for a lifetime.

Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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