Looking to add Solar to your caravan and need the basics?
Before you get started make sure all the appliances, lighting, and anything electrical used is as efficient as possible. This may include changing the lighting to LED, replacing the Fridge to a more efficient one, charging the laptop during sunlight hours and unplugged at night while in use. List each item, the number of Amps each item uses, and how many hours per day on average those items are used for.
Now that you have added up the number of amps used in a day, you can look at how much storage is required. Lithium batteries are becoming more popular in recreational vehicles due to depth of discharge, size and weight - but the cost is still relatively high. Although worth the extra cost, for this example we will use AGM Technology since we are keeping it simple. A good quality AGM battery can discharge up to 50% of its rated capacity, it is not recommended to discharge to these maximums so if your daily consumption for example is 30 Amps then a 100Ah (50Ah usable) capacity will be the minimum in this example. From a system design perspective, the minimum is not what we would call ideal as we are not going to go into days of autonomy and sustainable off-grid living in this write up.
Now we have a battery sized up for the system it is time to decide how much solar is needed. A quick way to figure this out is decide the minimum hours required to charge the battery bank (2-3 hours per day is a general rule). In this example to recharge the battery we need 30A / 2 Hours = 15A (per hour) then multiply that number by the voltage of the Battery e.g., 15A x 12.8V = 192W. So, at a minimum we can put a 195W solar panel on the roof.
These are not "Real World" performance calculations as the panels on a caravan are typically installed sitting flat which is far from the optimal position. Controller type, efficiencies and general losses are also not factored in. It may come as a surprise that you can lose up to 30-40% of the solar panel output if the panel is flat and sun is not at an optimal position.
Now we have the Battery and Panel sized up we need to use a Solar Regulator to make sure the battery is getting the right amount of voltage and charge into the battery. The two common types of Solar Regulators are PWM (Pulse Width Modulation) and MPPT (Maximum Power Point Tracking). We won’t dive into the technical differences here but the PWM is a cheaper regulator that just clips the voltage of the panel and delivers the right amount of current based on the charge mode at the time, where the MPPT is more expensive and uses the full voltage curve of the panel to maximize the amount of current being delivered to the battery – this essentially boosts the current required to achieve these maximums rather than throwing away "clipping" that much needed voltage like the cheaper PWM Regulators (expect to lose up to 25% of the panels rated Wattage if using PWM).
Because we can only deliver 15A of charge from the Solar Panel obviously a 15A Solar regulator will be a good choice for this system. However, because we are always adding new devices and the winter months is always where trouble begins, you may want to think about future proofing your system. So if you have the roof space make sure you leave room for another equivalent size panel and the solar regulator you put in is big enough to handle the increase in solar energy - e.g. Use 30A regulator to allow for another 195W panel.
These are just the basics when sizing a system and is more complex when all the components are designed in, especially with safety in mind. So, If you are thinking about installing solar or looking to use your caravan off-grid for days on end, get in contact and we can put you in touch with one of our recommended installers near by.