How to Size An Off-grid Solar System? Sizing Guide

How to Size An Off-grid Solar System? Sizing Guide

This blog post will provide a step-by-step guide to help you size an off-grid solar system so you can produce electricity even if you’re miles away from a power line.

  • Step 1: Determine Energy Requirements
  • Step 2: Evaluate the Site Location
  • Step 3: Calculate Battery Bank Size
  • Step 4: Figure Out How Many Solar Panels You Need

Off-grid solar power system sizing can be challenging because you need to consider a variety of factors to ensure that you never run out of power. Along with determining the size of the battery storage system, you’ll need, you also need to determine how many solar panels will be required to power your application while also keeping off-grid solar system costs low.

Don’t worry. Here are the steps to sizing your off-grid system.

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Step 1: Determine Energy Requirements

You must first be aware of how much energy the equipment consumes on a daily basis. This is expressed in watt-hours or kilowatt-hours per day. For example, let’s assume the equipment consumes 10 watts of power and operates 24 hours a day:

10 Watts x 24 hours = 240 watt-hours per day or .24 kWh per day

Where did you discover this data? To determine your equipment’s power consumption (in Watts), consult the datasheet or manual, and then multiply the result by the number of operating hours per day. If at all possible, measure the power consumption with a meter for a precise reflection of real-world usage.

Remember to factor in the inverter’s self-consumption and efficiency losses if you’re using it to generate AC power for a load. Inverters consume a small amount of power while they are operating. Referring to the inverter spec sheet, include the self-consumption in your daily calculation. Depending on the inverter, inverter self-consumption typically ranges between zero and thirty watts.

How to Size An Off-grid Solar System? Sizing Guide

Depending on the inverter and how much it’s loaded, efficiency losses range from 5% to 15%. This will be accounted for when sizing the batteries. It’s crucial to spend money on a high-quality inverter.

Step 2: Evaluate the Site Location

Next, choose the location of the system to gauge the solar energy that will be available. Use a solar insolation map, also known as a “sun hours map,” to determine the amount of PV capacity that is available. The system’s size should be determined by the month with the highest electricity use and/or the lowest solar resource, usually December or January.

The National Renewable Energy Laboratory (NREL) has an online resource for mapping available solar radiation. Most of the US has fairly low solar insolation in January. Generally speaking, 2.5 sun hours is a good estimate, but depending on your location, it could be lower or higher. For our example, we’ll use 2.5 minimum hours of sunlight.

Solar panels should be mounted in direct sunlight. Shade is going to impact performance. It makes a big difference if one panel is even partially shaded. Inspect the site to make sure your solar array will be exposed to full sun during daily peak sun hours. Throughout the year, keep in mind that the sun’s angle will change.

Step 3: Calculate Battery Bank Size

The standard practice is to size your battery bank for a one-day cycle. By doing this, your battery bank will receive sufficient maintenance and you will have enough charging amps.

How to Size An Off-grid Solar System? Sizing Guide

There will typically be 10 to 15 charging amps per 100 amp hours of storage capacity for lead-acid batteries, including AGM types. For instance, if you have an 80 amp charge controller maxed out with solar on a 48-volt system, that equates to about 4,000 watts of solar power.

A battery bank with a capacity of up to 800 amp hours can be reliably charged by this size solar array during a single charge cycle (under ideal circumstances with a 5-hour sun window and a 50% depth of discharge).

Depth of discharge is always a factor, as well as the number of good sun hours in your area. If your solar power supply is insufficient, you can also rely on a generator and an inverter charger to keep the battery bank charged as needed. Plan to use about 30% of your battery bank’s total capacity for a longer life expectancy.

Overall, a lead-acid (flooded or sealed) battery bank has a lifespan of 3 to 10 years. With proper care and minimal usage, these batteries will last longer. Keep in mind that lithium batteries operate differently from lead-acid batteries and must abide by different regulations.

Step 4: Figure Out How Many Solar Panels You Need

We can size the charging system now that the battery capacity has been established. Normally we use solar panels, but a combination of wind and solar might make sense for areas with good wind resources, or for systems requiring more autonomy. The charging system needs to produce enough to fully replace the energy drawn out of the battery while accounting for all efficiency losses.

How to Size An Off-grid Solar System? Sizing Guide

Lead-acid batteries need to be fully charged on a regular basis, which is another issue that needs to be addressed. For optimum battery life, they need a charge current of at least 10 amps per 100 amp hours of battery capacity. Lead-acid batteries will most likely stop working if they are not recharged frequently; this typically happens within the first year of use.

The ideal charge current for lead acid batteries is between this range (10–20 amps per 100 ah), which is between the maximum charge current for lead acid batteries of around 20 amps per 100 Ah (C/5 charge rate, or battery capacity in amp hours divided by 5).

To confirm the recommended minimum and maximum charging levels, consult the battery’s specifications and user manual. Your battery warranty will likely be voided if you don’t follow these recommendations, and you run the risk of battery failure before its time.

Conclusion: Size An Off-grid Solar System

That’s pretty much it. You have now completed all the steps required to size your off-grid battery bank system.

Your system won’t run out of power and will function reliably for years if you ensure that you have enough solar to supply energy every day and a battery system that can store at least five times your daily load. Best of all, there is little to no maintenance on these types of systems.


How Much Solar Power Do I Need to Go Off the Grid?

Firstly, you’ll need about 20 solar panels, but those can easily go on the roof. To store the batteries, you’ll also need room inside. Up to 30 batteries might be required for your installation, depending on its size.

How Much is a 10kW Off-grid Solar System?

10kW off-grid solar system or stand-alone solar system can cost from $28,000 to $35,000 depending on the type of off-grid solar equipment and the complexity of the installation site.

Is 10kW Solar Too Much?

10kW solar systems are on the large side for residential installations (where 5kW to 6.6kW is much more common). So as mentioned above, 10kW systems tend to be most appropriate for homes or businesses with significant amounts of daytime electricity consumption above 40kWh per day.

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