You don’t have to be a Rhode’s Scholar to understand that solar is a natural, renewable power supply. It’s also a free energy source (following initial start-up costs) that is autonomous, flexible and silent. It’s therefore a perfect solution to the power needs of caravanners.
Quite simply, solar power is a maintenance-free process where the sun’s energy is converted to electricity (photovoltaic effect). But how can caravanners get the most out of this environmentally sustainable energy supply?
Use a MPPT regulator and connect panels in series
Maximum Power Point Tracking matches a solar regulator’s load to the voltage and current from the solar panel in order to achieve the greatest output power. It’s claimed many upmarket solar regulators with built-in MPPT technology can recover up to 20 per cent of otherwise non-accessible energy. When using a MPPT regulator, solar panels can actually be connected in series. Most MPPT regulators have a maximum input voltage of at least 75V. This means up to three of 18V (for a 12V system) can be connected in series (daisy-chained, 22V each and 66V in total). In this case there is no need for cable joiners, and the lower amps in the cable from solar panel to regulator results in less power loss. When charging your battery, the MPPT regulator will reduce the voltage and bump up the amps so there is no wattage loss from the solar panel. These days, a 15A branded MPPT solar regulator only costs around $150. Only identical panels should be connected in series.
Clean the solar panel
Solar panels should be cleaned periodically to ensure the solar cells are receiving maximum insolation (the solar radiation that reaches the earth) as anything blocking sunlight from the photovoltaic material will reduce the output of the panel. Most solar panels on a caravan sit nearly flat on the roof, which means dirt and dust builds up on their surface. A non-abrasive cloth will clean without scratching and consequently maintain the solar panel’s maximum performance.
Have a battery bank that is a bit larger than needed
Batteries can be damaged if they are overly discharged on a frequent basis. Ideally, a solar system should have sufficient panels to quickly charge the batteries to near full during the day so that they don’t run too far down overnight. Common lead acid AGM batteries have a rated cycle life of 500 at 50 per cent depth of discharge (DOD) and more than 1200 at 25 per cent DOD. This means, theoretically, when a battery bank is doubled in size, it will reduce the DOD from 50 per cent to 25 per cent and the lifespan of the batteries will extend more than twice!
So what do we get? A battery system that costs less money in the long term and that is also larger in capacity. Rule of thumb: If a battery bank goes down to 12V quite often, it’s time to consider increasing the capacity of the whole bank. Approximately 250W of solar per 100Ah battery capacity is considered a compatible ratio. This is because it’s recommended to draw up to 50Ah from a 100Ah battery (50 per cent discharge) and a proper setup of 250W solar panel will provide just about 50Ah during the day.
Be energy SMART
A battery monitor simply checks on the power stored – incoming and outgoing current and the state of charge for the battery. Without monitoring, batteries can be damaged through continual undercharging and/or over discharging. It’s highly recommended to install a battery monitor that displays not only the battery voltage but also the live current draw, amp hours charged and consumed, and the estimated state of charge of the battery. With these parameters, a good insight is gained of the operation of the energy system, thus enabling energy smart decisions such as turning off loads that are not in use or replacing devices that have high energy consumptions.
Minimise voltage drop
Wiring size is determined by the overall length of cable involved in the system and the amount of current drawn over that length of cable. A 12V system, especially from the panels to the regulator and batteries, needs 6mm2 internal wire. But a fundamental problem with 12V systems is voltage drop due to resistance in the wire, which is why short, very heavy wire is required. If there is 0.5V voltage drop from regulator to battery, a 14.4V charging voltage from the regulator will be received as 14.4V-0.5V=13.9V at the battery. On the other hand, a 12.5V battery will be read at the regulator as 12.5V+0.5V=13V, which is considered fully charged. A voltage drop will ‘mess up’ the communication between the regulator and the battery, and this is why a regulator should be positioned as close to the battery as possible with a decent sized cable used.