In order for you to size the system correctly, you need to note the power rating of each appliance that will be drawing power from the system.
For this example, we will calculate the power requirements for a campervan with:
(Note that a 600W microwave will consume approximately 900W of power)
Total for AC and DC Loads = 841Wh per day
In Central to Northern NSW expect a usable average of around 5 peak sun hours per day.
Required solar panel input = (841Wh / 5h) * 1.4 = 235W
Note: The 1.4 used in this formula is a factor we have found that can be used to simplify the calculations for basic systems.
To ensure that adequate power is produced in the winter months, use a figure of around 4.0 to 4.5 peak sun hours per day instead of 5.
Select solar panels to provide a minimum of 235W. Always best to go bigger if possible:
The rated short circuit current of the 123W solar panels is 8.1 Amps each, giving a total of 16.2 Amps.
Select a solar regulator that is more than capable of handling the total short circuit current: 16.2 x 1.25 = 20.25 Amps
Note that, as described in the notes above, you must allow 25% extra capacity in the regulator rating as solar panels can exceed their rated output in particular cool sunny conditions. A 30A regulator will allow for an additional panel in the future.
Select an inverter that is more than capable of supplying the maximum anticipated combined AC load required. In this example, maximum load would occur if the microwave and TV were running at the same time. Load in this case would be 900W + 50W = 950W.
Note that this calculation assumes that the inverter selected has a suitable surge rating to cope with the start-up surges of the microwave or other loads. A 1000W inverter would appear to be suitable, but a 1200W - 1500W inverter would be recommended.
Note: A pure sinewave inverter is the preferred choice, but if the budget is tight, a modified sine wave unit could be used.
Select a battery, or a matched combination of batteries, that is capable of supplying the total power usage without being discharged more than 70%.
In most cases it is recommended that the batteries are sized such that they have around 3 to 4 days back-up capacity. This allows for days with low sunlight and reduces the daily depth of discharge resulting in longer battery life.
With 3 days storage capacity, the battery sizing would be as follows:
Note: The 1.1 is used in this formula as batteries are generally only about 90% efficient.
The appliance ratings used in the above examples may not be accurate. They have been used for example purposes only. Check the ratings on your appliances before performing any calculations.