Setup factors for Off Grid Solar System

The hope of having energy independence: being able to power your home without a monthly utility payment and not be affected by blackouts or utility disruptions, is becoming more common place. The driving force behind this effort is the "off-grid" solar power system. Off-grid systems are not physically or otherwise dependent on the power company for operation as are grid-tied systems, but instead are a completely self-contained power generation, storage and distribution system. An off-grid solar power system is an example of a 'closed loop,' system, and will provide power to a cabin in the woods, camper or RV, or other remote locations that do not have access to a power grid.

The only way to achieve complete disconnection from the energy supplier is to have an independent solar energy system on your property. Installing just a couple of solar cells on your roof is not enough to do this; you must first decide how much electricity you use and then design an independent solar power system that can provide you with that amount of electricity. The solar energy system must also be appropriately sized for your specific energy consumption needs, as purchasing too many or too few solar electric panels will result in wasted energy as well as frequent battery depletion and almost no revenue from your installation. This article provides a comparison of some of the most important factors to consider when creating a solar power system with low operating costs and reliable long-term performance.

In order to perform calculations accurately, it is important to understand, first, the function of each of the four components that make up an off-grid (stand-alone) system.

Solar Panels (Photovoltaic): Virtually all photovoltaic systems are comprised of solar panels and their various technologies. The cells on the solar panel that convert light (solar radiation) into electricity (DC - direct current) are called photovoltaic cells and the process in which they convert light into electricity is called the photovoltaic effect.

DC Charge Controller (Regulation): The DC electricity flows from the solar panels into this device which is used as a gateway. The charge controller's primary responsibility is to regulate the voltage and amount of current coming from your solar panels so that you do not overcharge your batteries, thereby ensuring your batteries are not damaged.

For off-grid systems, the preferred choice of controller will be a Maximum Power Point Tracking (MPPT) controller over an older Pulse Width Modulated (PWM) model, as MPPT controllers track the maximum power point for photovoltaic panels, providing far greater efficiency than PWM controllers, and especially so in cold or overcast weather conditions.

Battery Bank (Storage): The battery bank is considered the heart of an off-grid solar system. Since 100% of solar photovoltaic energy generation does not occur at night, therefore it is necessary to have something in which to store all of the excess electrical energy produced during peak power production hours for use at night as well as on cloudy/rainy days.

Although flooded lead-acid batteries are cheaper in up-front cost; Lithium Iron Phosphate (LiFePO₄) batteries are becoming a new industry standard battery type for new installations due to their much longer lifespan, greater depths of discharge, and maintenance-free operation.

Inverter: The amount of energy stored in your batteries is low DC voltage. Most household appliances, however, use Alternating Current (AC) voltage to operate. In order to convert the low DC voltage from your batteries to usable AC voltage (usually either 120 volts or 240 volts) for your other appliances (lights, refrigerators etc.), you will need to purchase an inverter.

In order to operate sensitive equipment, you will need a pure sine wave inverter since it provides a smooth sine wave output (ideal for sensitive electronic equipment to operate properly).

You cannot choose any component until you know how much power you actually use. This process is called a load analysis or energy audit.

To determine how many watts consume your office or home on a daily basis (to perform this calculation), you need to know several pieces of information about any appliance that you use. Specifically, you need to know how much electricity is used by each of your appliances on a per-watt basis, how long the devices run each day, and how many watts are consumed per hour by your appliances. Another reason why off-grid systems fail to meet users' expectations is that few systems have been sized properly based on peak usage.

With your daily consumption known, you can size the battery bank. The key question here is "Days of Autonomy." This refers to how many days you want your system to run without any input from the sun (i.e., during a snowstorm or extended cloudy period).

Most off-grid system designers recommend a minimum of 2-3 days autonomy for their off-grid systems. Additionally, it is crucial to avoid excessive discharge of the batteries to prolong their lifespan. With Lithium Batteries, it may be acceptable to use 80-90%, but this will need to be considered in your capacity calculation.

The solar array must be powerful enough to recharge the battery bank while simultaneously powering your daily loads. The main variable here is Peak Sun Hours. This is not the same as total daylight hours; it is the number of hours per day when sunlight intensity averages 1,000 watts per square meter.

A location in Arizona might get 6 peak sun hours, while a location in Seattle might get only 3. To determine the size of your solar array, divide your daily consumption by your location's peak sun hours.

You will also need to select an inverter that can handle the power "surge" or maximum load. Even though your normal usage may be low, a water pump or refrigerator motor can use 3 to 5 times its normal draw when initially turned on. An inverter that cannot support this surge will trip.

The system voltage 12V, 24V, or 48V needs to be determined. Smaller systems (i.e. vans or small cabins) tend to use 12V so 24V or 48V systems are generally required in homes because of the increased distance between the batteries and the appliances. Higher voltage systems are advantageous because less expensive and thinner copper wiring is required, and power loss is less over distance.

Finally, technical specs aren't the only factors. The physical location of your panels is crucial. In the Northern Hemisphere, panels should ideally face south at a tilt angle equal to your latitude to maximize exposure.

Furthermore, recent academic research highlights the need for "adaptability factors" in off-grid design, particularly in developing areas. Factors such as the user's ability to pay for maintenance, the structural integrity of the roof, and even the ability to relocate the system are vital considerations that are often overlooked in standard sizing frameworks.

Consider the total energy requirements and the number of solar panels you can accommodate on the available roof or ground area. The only other consideration is choosing between Mono and Poly panels. It is a long and winding road strewn with science and mathematics. Yet the off-grid solar adventure culminates in self sufficiency – a profound reward. Apart from the significant threshold of knowledge to accurately predict system loads and minimize power losses, the ability to size storage batteries to achieve an autonomous state a requisite. The ability to match solar arrays to local sun hours and select appropriate inverters is also a prerequisite to building systems that produce clean power and operate in quiet solitude for years to come. Be it a DIY system or a Professional system, knowledge of these principles will make the sun work for you.