Why LED lighting is the choice for solar power systems

In an off-grid solar system every watt means panel area and battery capacity. Here is why LED lighting decides how big the whole system has to be.

Solar panels are no longer a rare sight on village houses, summer pastures, farms or garden plots beyond the reach of the grid. Anyone who builds such a system quickly faces one fact: unlike the grid, the energy here is not unlimited. You can only use in the evening what the panels collected during the day. In those conditions the type of lighting stops being a matter of the bill and becomes a factor that sets the size of the whole system.

Thinking in an energy budget

An off-grid solar system should be thought of as a daily budget rather than a monthly bill. The panels produce a certain number of watt-hours during the day, the battery stores them, and appliances spend that reserve in the evening and at night. Overspend and the battery is deeply discharged, the system shuts down or the battery's life is shortened.

Lighting holds a special place in that budget because it runs precisely when there is no sun. A pump or fridge working in daytime can take part of its energy straight from the panels; a lamp lit in the evening runs entirely off the battery. So every watt of lighting is paid for twice: in panel capacity and in battery capacity.

A simple comparison

Say a house has lights on in six rooms for five hours each evening. With a 60-watt incandescent bulb in each room, daily demand is 6 × 60 × 5 = 1,800 watt-hours. With an 8-watt LED bulb in each room, the same sum gives 240 watt-hours.

The effect on the system is large. A battery bank that stores 1,800 watt-hours has to be more than seven times the size of one that stores 240. Panel power, the charge controller and cable sizes grow in the same proportion. In other words, running a solar system on incandescent bulbs means enlarging equipment that costs far more than the lighting itself. The 8 watts here is simply a figure for the example; when choosing a real lamp, look at its light output.

Direct current or an inverter

There are two main layouts in solar systems, and the choice of lamp changes with them.

In the first, lights run straight from the battery on 12 or 24 volts DC. You then need LED lamps or strips designed specifically for low voltage. The advantage is that there are no inverter losses, and the lights stay on even if the inverter shuts down. The drawback is that at low voltage the current is high, so voltage drops over long cable runs and thicker wire is needed.

In the second, an inverter turns battery power into ordinary 230 volts and the house uses standard holders with normal E27 and E14 LED bulbs. That is convenient, since bulbs are easy to find and the house wiring stays as it is. But the inverter uses energy itself, and its idle consumption can be noticeable next to a small lighting load. If only one or two lamps are on at night, that loss looks large in percentage terms.

What to check when choosing

• The inverter type. With cheap inverters that do not produce a pure sine wave, some LED bulbs flicker, buzz or fail early. Test the lamps together with the inverter when setting up.
• The lamp's stability. As the battery discharges its voltage falls. An LED bulb with a good driver copes with that without a sharp loss of brightness.
• How much light each place needs. Rather than fitting the same powerful bulb everywhere, plan dim light for corridors and stores and stronger light for the kitchen and work areas.
• Motion sensors. In the yard, toilet or hallway a sensor light cuts the consumption of an all-night lamp to almost nothing.
• Winter operation. Days are short and the sun weak in winter, while evenings are long. Size the system for the shortest days, not for summer.

Practical advice

When planning, first list every light point: where, how many lamps, roughly how many hours a day. Note the LED wattage for each and add up the watt-hours. Add other loads such as the fridge, TV and phone charging, then put a safety margin on top. Figures like these also make the conversation with the installer much easier.

If a solar system is being added to an existing house, the first step should not be buying panels but replacing old bulbs. Often that step alone shrinks the required system size several times over.

Where the solar system feeds 230 V sockets through an inverter, standard E27 and E14 Zəfər İşığı LED bulbs can be used; questions about compatibility with a particular system can be put to the company.