Solar panel design for homes/off-grid settlements

Solar energy is one of the reliable energy forms; among renewable energies. Due to its abundancy and predictable characters, have gained ground for off-grid applications and energy storages.

The role of solar panels is to absorb the energy of sun`s radiation and converting it to electrical current through photovoltaic reaction. Installed solar panel system should be well calculated and well designed to meet the power requirement.

Parts of solar panel system

Solar energy design is made of; solar panel, charge controller, battery tank, inverter, distribution panel (AC and/or DC).

Charge controller adjust the unstable voltage and current coming from solar panel and prevents battery tank to overcharge. Battery plays to role of storing energy. In order to use stored energy in battery, the inverter is needed. Basic function of inverter is to convert DC to AC to use in home appliances which mostly work with AC. If there is any DC load in design, an extra DC distribution panel should be placed.

Placement of solar panel

Generated output by PV panel varies on the geographical location and time. For that; the placement of the PV panel should be away from any obstacles and installed direct to sun light at peak time of the sun. In additionally, the surface area of PV panels should be chosen based on calculated total loads. The design of PV system components should be in compact in order to prevent voltage loses in the cables.

Size of PV system

The size of PV system determines undertaken power load in the design. Therefore; it is important to calculate power load in the system. The energy consumed by a device can be calculated like below;

Energy = Power x Time

Thus;

Required energy = Watt of device x number of hours of operation.

When required energy is calculated, it should be calculated for the most active time of the day, which is during the day light. Be careful; designing the system for peak demand will increase the cost of the system.

The design of the PV system begins with calculating number of solar panel. Assuming a house having;

A LED lamp of 15 watts in operation for 8 hours per day

TV 58 watts for 3 hours per day

A water pump 150 watts for 3 hours per day

We can now calculate number of solar panels, charge controller, inverter etc.

Total load of energy = (15 W x 8 hours) + (58 W x 3 hours) + (150 W x 3 hours) = 744 Wh/Day

Required total load of energy = Total load of energy x 1.3 (energy loss factor)

Required total load of energy = 967 Wh/day

Now we can calculate size and number of solar panels

Peak Watt of PV system = PV System Watt / Number of peak sunshine hours (assuming it`s 4 hours)

Peak Watt of PV System = 967 / 4 = 241.75 Watt

Considering 100-Watt panel chosen for our system, now we can calculate the number of solar panel; No. Panel = 241.75 / 100 Watt = 2.41 (Taking it 3 pcs of solar panel) = 3 pcs of 100-Watt Solar Panel

Now we should calculate size of inverter

Total required watt = 223 Watt

Rating = 223 Watt x 1.25 = 278.25 Watt Inverter Required (Minimum)

Now we can find battery specifications

Battery Capacity (Ampere Hour, Ah) = (Total Wh per day used by devices x days of unexpected use of battery) / (0.85 x 0.6 x Nominal Battery Voltage)

Unexpected used days assuming is 2 days

Battery Capacity = (967 Wh x 2 days) / (0.85 x 0.6 x 12 Volt) = 316 Ah (Considering it is 400 Ah)

We need 400 Ah deep cycle 12 V battery for 2 days of use

However; we will parallel connect 4 pcs of 100 Ah 12 V to achieve reliable design, but you might want to use single 400 Ah 12V battery if you want.

Now let`s find charge controller details

To find rating of charge controller; we need to know specification of Solar PV panel`s short circuit current (ISC) value. Let`s assume it is 5.45 Ampere.

The required solar charge controller = number of solar panel x ISC x 1.25 The required rating solar charge controller = 4 x 5.45 Amper x 1.25 = 27.25 Ampere (However, we cannot use this method to find exact rating of solar charge controller)