How much solar do I need?

One of the most challenging parts of building an off-grid electrical system is determining how much solar you need. This is because there are so many factors that influence solar power generation and off-grid power consumption. While this article will not be able to definitively tell you how much solar you need, it will help set you in the right direction by telling you the questions you need to ask yourself and the factors that you need to consider.

How long will you be off-grid?

The more time you spend away from charging sources, the more solar you will need. Users that spend most of their time moving between powered campsites and caravan parks will barely need solar at all, especially if they are using a DC2DC to charge from their vehicle while driving. If you plan on spending most of your time on-road, you will likely fall into this category. The solar needs of on-road users can often be met with the single 150W panel that is installed by most caravan manufacturers these days. If you plan to spend more time in the bush or at the beach, then more panels will be a necessity.

What other charging sources do you have?

For those who plan to stay off-grid, determine how many days you plan to stay away from your AC power. Do you plan on running a generator? If the answer is yes, then your solar panels can play more of a supplemental role rather than a critical part of your recharging system. Do you plan on driving a lot during this period? If you do, a DC2DC will play an important role in recharging your battery. It is often the case that a DC2DC and a single roof mounted or folding solar panel will often be enough for smaller vehicle-only setups.

How much power do I consume?

The most important factor in determining the number of panels is your power consumption. If you only plan on running a fridge and couple of small loads, such as lights or phone chargers, then one or two panels will probably suffice. If you have an off-road caravan, then there is a good chance that these have already been installed by the manufacturer.

If you will be using an inverter to run power hungry appliances, such as coffee makers, induction cook tops, or air conditioners, then you will want to fit as many panels as your roof space and budget will allow. Devices like these will quickly drain your battery banks, making solar a necessity. If roof space is limited, consider adding folding solar panels to your setup.

What is the weather like?

Unfortunately, solar power generation is often dictated by circumstances outside of our control. The number of peak sun hours available for solar charging will vary depending on where you are and what the weather is like. What will you do if the weather overcast or rainy? Having extra panels can help sustain you when solar conditions are not at their peak. Even during sunny days, high temperatures will cause you panels to lose some efficiency. None of these things are changeable by you, but you can take them into account when calculating your solar needs.

How are my panels mounted?

Caravan solar panel installations are almost always flat mounted against the roof. While this might be the most space efficient way to mount your panels, it is not the most energy efficient. Panels can output can fall by as much as 40% when they are not mounted at an optimal angle. While this is unavoidable when during many installations, it should be considered when determining how much solar your system will need. More information on panel mounting can be found here.

How big is my battery bank?

Along with your solar panels, the size of your battery bank will help determine how long you can stay off-grid. A larger battery bank can help you when the weather conditions are not in your favour, although even the largest battery banks can only go without recharging for so long. While it might be tempting to simply add more battery capacity to your system, it can sometimes be far more cost-effective to add a couple of extra panels to your system instead. For example, adding a 160W folding solar panel would give you an additional 35Ah or more per day. Over the course of five days, that panel would produce power equal the amount of usable capacity in a 200Ah B-TEC (based on 80% depth of discharge) for a fraction of the price (even if an additional solar controller must be purchased). While the gains from solar seem small, they can add up to a substantial amount of power over time.

Conclusion

For off-grid setups that rely on solar as their primary recharge source, you can never have too much solar. If you have an off-road caravan and budget allows, fitting as many panels as the roof will allow is the best option being able to stay off-grid for longer. Even if you don't have the luxury of free roof space, purchasing a folding panel or two can add a lot to you the capability of your system.