Solar Power—Is It Right For My Home and My Pocketbook?

Types of Residential Solar Power Systems

Sizing Equipment
Solar panels are also known as photovoltaic (PV) panels. Keep in mind that solar panels provide DC power and your appliances require AC power, typically 120 vac for most electrical equipment: lighting, washing machine, refrigerator, microwave ovens, etc. Your electric dryer and airconditioning equipment, other than window units, require 230 vac.

If you wish only to have photovoltaic power available during peak sunshine hours, you will need only PV panels sufficient for those hours. But, what do you do beyond peak solar hours? What about powering the home during nighttime hours?

The inverter converts DC power from your PV panels into AC power for your electrical appliances. The inverter also consumes electrical energy. In your load calculations include the power used by the inverter as an appliance load. Unlike your washing machine and your dishwasher, the inverter uses energy 24/7/365.

Your nearby PV systems vendor can usually help with the calculations. If you are uncomfortable with the vendor, look for a local electrical engineer to size the equipment.

If you are retrofitting your home and have owned it for a year or more and you have access to the total power (kWh) consumed in one year, follow the instructions provided by Solar Power Authority.

In the electrical energy business, wind and solar power are classified as intermittent energy sources for obvious reasons.

Peak Sunshine in Texas

Latitude and shading affect the voltage level and the hours of production of the solar panels. If your house is in a wooded area or in the shadow of a nearby tall structure, the output of the solar panels will be curtailed. This means you must know the actual hours of exposure to direct sunlight. At the equator, count on 12 hours per day. Peak sunshine diminishes with latitude. Clouds, altitude above MSL, and proximity to mountains all affect peak solar hours. Idaho, for example, has about the same peak hours as most of the state of Texas.

In metropolitan areas, solar panels are typically installed atop the roof of the house. Most city codes restrict solar panels. Know them before you begin your calculations and design. A major problem arises when the roofing must be repaired or replaced. If at all possible, mount the panels on a ground-based rack apart from the house. To maintain optimum solar gain, keep the glass surface of the solar panels clean. Doing this atop a roof can be hazardous to your health.

Latitude affects solar panel output. Stand-alone racks assure optimum angle. Do remember the sun’s angle continuously varies over twelve months. Can the mounting angle be permanent? Yes. If living on the equator the panels will mount horizontally at 0o. The angle is equal to the latitude of the location of the house or building.

Storage Equipment
Direct-current (DC) batteries must be sized to provide continuous operation of the inverter that converts DC power from solar panels into useful AC power for your appliances.

If your choice of battery is the lead-acid type, do not purchase automotive batteries. Purchase sealed lead-acid batteries that are made for inverters, golf carts, trolling motors, etc. The latter discharge slowly and will last a long time. Automotive batteries are manufactured to produce hundreds of amperes of current needed to start a car’s gasoline or Diesel engine. Why sealed batteries? Lead-acid batteries produce hydrogen gas (H2) while charging. Hydrogen gas and atmospheric oxygen (O2) are explosive, a fire hazard, and a death trap. The old-style lead-acid batteries with screwable filler caps on each cell serve to warn you to avoid them. Regardless of the type of lead-acid battery, the battery rack should be in a well-ventilated space isolated by a sealed doorway from the living spaces.

Off-Grid Solar Power
This is a must for remote properties not served by an electrical utility company or a rural co-op. When selecting your equipment keep in mind while the solar collector panels are weatherproof, the electronics and batteries are not. Delay designing your home until after a complete analysis of your power needs.

Grid-Residential Hybrid Solar Power

There are websites that succinctly explain these hybrid systems. The key thoughts are: “When the grid loses power, your solar panels will stop working too.

“This isn’t because your panels can’t generate power, but rather they are designed to automatically disconnect from the grid in a power failure. This is to prevent power lines from being energized when the utility company expects them to be off. Otherwise, utility workers repairing power lines could be electrocuted.

“Solar panels can continue working for you in a blackout, but it requires either a battery system or an inverter designed to supply emergency power to your home, such as the SMA Sunny Boy.” The Solar Nerd

We have on order a gas-powered Generac generator capable of powering the entire house under all conditions. Naturally, we do not require backup batteries. Think carefully and choose carefully.

John White
Rockwall, Texas

Published by John White

A lifetime (over 50 years) of experiences with automation and control systems ranging from aerospace navigation, radar, and ordinance delivery systems to the world's first robotic drilling machine for the oil patch, to process-control systems, energy management systems and general problem-solving. At present, my focus is on self-funding HVAC retrofit projects and indoor air quality with a view to preventing infections from airborne pathogens.

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