Determine What Size Solar System Will Best Fit Your Energy Needs

How many solar panels do I need?

First determine what size solar system will best fit your energy needs to cut down the solar panel cost to the largest extend. Make a list of all the appliances and devices you plan on running. The main appliances taken into consideration when addressing energy needs may include a TV, lighting, water pump, laptop, fans, microwave, and refrigerator. We recommend inputting that information into the Renogy > solutions > calculator to help determine your specific solar panel needs. Renogy is a great place to shop and purchase solar equipment and products as well.

Solar panels in parallel operate independently of one another and therefore are the best option for mixed-light conditions. If shade covers one or two of your panels, the remaining panels in the array will continue to generate power as expected.

Parallel solar arrays are also ideal when you want a low voltage system using a lower-cost PWM controller. Again, wiring multiple solar panels in parallel doesn't change the total output voltage. So, if your panel output voltage matches your nominal battery charging voltage, a parallel array allows you to increase your output charging current without needing to regulate the voltage.

Connecting your solar panels in series is often preferred if you're able to spend most of your time in unshaded locations. The main reason for this is that your solar panel system will be more efficient and will perform better at the beginning and end of the day and when it's cloudy. Here's why.

Batteries require a higher voltage than their nominal voltage to charge. For example, our lithium batteries need 14.4 volts to start charging. Most solar panels in the 100-watt range have an output voltage between 18-20 volts. To reach the 14.4 volts required to charge your batteries, solar panels in parallel would need to be operating at 75% capacity or more.

However, if you were to wire three of these same panels in series, the maximum output voltage would be 54-60 volts. This would mean your panel array would only need to operate at around 25% capacity to provide a charge to your batteries. Operating at 25% capacity is much easier to achieve even late in the day or on cloudy days. It is important to remember that you will need an MPPT charge controller for a system like this to work.

What's The Difference Between Wiring Batteries in Series Vs. Parallel?

The main difference in wiring batteries in series vs. parallel is the impact on the output voltage and the capacity of the battery system. Batteries wired in series will have their voltages added together. Batteries wired in parallel will have their capacities (measured in amp-hours) added together. However, the total available energy (measured in watt-hours) in both configurations is the same.

For example, wiring two 12-volt batteries with 100 Ah capacities in series will output 24 volts with a 100 Ah capacity. Wiring the same two batteries in parallel will output 12 volts with a 200 Ah capacity. Thus, both systems have a total available energy of 2400 watt-hours (watt-hours = volts x amp-hours).

Additionally, batteries wired in series and parallel configurations should all have the same voltage and capacity rating. Mixing and matching voltages and capacities can lead to problems that may damage your batteries.

Disadvantages

In a battery system wired in series, you cannot get lower voltages off the battery bank without using a converter. Either all equipment needs to function at the higher voltage or an additional converter is needed to use 12V appliances on the system.

To wire multiple batteries in parallel, you connect all of the positive terminals together and all of the negative terminals together. Since all of the positive and negative terminals are connected, you can measure the system output voltage across any two positive and negative battery terminals.

The main advantage of wiring batteries in parallel is that you increase the available runtime of your system while maintaining the voltage. Since the amp-hour capacities are additive, two batteries in parallel double your runtime, three batteries triple it, and so on.

Another advantage to wiring batteries in parallel is that if one of your batteries dies or has an issue, the remaining batteries in the system can still provide power.

The main drawback to wiring batteries in parallel vs. series is that the system voltage will be lower, resulting in a higher current draw. Higher current means thicker cables and more voltage drop. Larger power appliances and generation are harder to operate and less efficient when operating at lower voltages.

The limit on how many batteries you can wire in series typically depends on the battery and manufacturer. For example, Battle Born allows up to four of their lithium batteries to be wired in series to create a 48-volt system. Always check with your battery manufacturer to ensure you do not exceed their recommended limit of batteries in series.

There is no limit to how many batteries you can wire in parallel. The more batteries you add in a parallel circuit, the more capacity and longer runtime you will have available. Keep in mind that the more batteries you have in parallel, the longer it will take to charge the system.

With very large parallel battery banks comes much higher current availability as well. This means the proper system fusing is critical to prevent accidental shorts that could have catastrophic consequences with so much current available.

Deciding between connecting your batteries in series vs. parallel is often dictated by the needs of the devices you're powering. For general boat and RV applications wiring batteries in parallel provides the simplest wiring and common voltage, however, for large applications beyond 3000 watts of power, using higher voltage series connections might be best. Now that you understand how each wiring configuration works, you can determine the best option for your needs and proceed with confidence.