A basic off-grid solar system needs four components: solar panels to generate power, a charge controller to regulate the charge going into the battery, a battery to store energy, and an inverter to convert stored DC power to AC for household appliances. Sizing depends on how much energy you consume daily.
Setting up your first off-grid solar system can feel daunting, but the fundamentals are straightforward. This guide walks through each component, explains how they connect and gives you a practical framework for sizing a system that matches your energy needs.
The Four Core Components
Solar panels
Solar panels convert sunlight into direct current (DC) electricity. For off-grid use, monocrystalline panels are the most efficient and are the standard choice. They are available in sizes ranging from 100W portable panels to 400W+ rigid roof-mounted units. The total panel wattage you need depends on your daily energy consumption and the number of usable sunlight hours at your location.
Charge controller
The charge controller sits between the panels and the battery. It prevents overcharging, which can damage or destroy a battery, and manages the charging profile to maximise battery life. There are two types: PWM (pulse-width modulation), which is simpler and cheaper, and MPPT (maximum power point tracking), which is more efficient and the right choice for larger systems or where efficiency matters. MPPT controllers can extract 20 to 30% more energy from the same panels, particularly on overcast days.
Battery
The battery stores the energy generated by your panels for use when the sun is not shining. Lead-acid batteries are cheap but heavy and require maintenance. Lithium iron phosphate (LFP) batteries cost more upfront but are lighter, cycle far more times (often 3000 to 6000 cycles), require no maintenance and can be discharged to a lower state of charge without damage. For any new off-grid build, LFP is the recommended choice.
Inverter
The inverter converts DC power from the battery into 230V AC power, which is what most household appliances use. A pure sine wave inverter is the right choice for sensitive electronics and most appliances. Modified sine wave inverters are cheaper but can cause problems with some motors, medical equipment and audio devices.
Sizing Your System
Step 1: Calculate your daily energy consumption
List every device you plan to run, its wattage and how many hours per day you use it. Multiply wattage by hours to get watt-hours (Wh). Add everything up to get your total daily consumption. For example: LED lighting (20W for 6 hours = 120Wh), laptop (45W for 5 hours = 225Wh), phone charging (10W for 2 hours = 20Wh). Total: 365Wh per day.
Step 2: Account for system losses
No system is 100% efficient. Battery charging losses, inverter losses and wiring losses typically mean you need to generate around 20 to 25% more than you plan to consume. Multiply your daily figure by 1.25 as a starting point.
Step 3: Determine your panel requirement
Divide your adjusted daily Wh requirement by the number of peak sun hours at your location. The UK averages around 2.5 to 3.5 peak sun hours per day depending on season and location. A 365Wh x 1.25 = 456Wh requirement, divided by 3 peak sun hours, means you need around 150W of panels as a minimum. Add a margin and round up to 200W to 250W for a comfortable result.
Step 4: Size your battery
Your battery needs to store enough energy for at least 1 to 2 days of autonomy without sun. For the example above (365Wh daily), a 730Wh to 1kWh battery is the minimum. With LFP batteries, a usable capacity of 80 to 90% of the rated capacity is realistic. Size accordingly.
Step 5: Choose your charge controller
The charge controller must handle the maximum current from your panels. Divide total panel wattage by battery voltage (usually 12V or 24V) to get the current. Add 25% safety margin. A 250W panel array on a 12V system produces around 20A, so a 30A MPPT controller is appropriate.
Basic Wiring Order
Always connect components in this order to avoid sparks or damage:
- Connect the battery to the charge controller first
- Connect the solar panels to the charge controller
- Connect the inverter directly to the battery with appropriately rated fuses
- Connect your loads to the inverter AC output or directly to the charge controller DC load terminals
Always disconnect in reverse order when servicing the system.
Safety Essentials
Use correctly rated fuses or circuit breakers between every component. Solar panels can generate dangerous voltages and batteries can deliver very high short-circuit currents. Use appropriately sized cables (undersized cables overheat and are a fire risk). If you are mounting panels on a structure or wiring inside a dwelling, consult a qualified electrician to ensure compliance with BS 7671 wiring regulations.
Expanding Your System Later
One of the advantages of off-grid solar is that it is modular. You can start with a small system and add panels, a second battery or a larger inverter as your needs grow. Plan the initial installation with expansion in mind, sizing the charge controller and battery bank to accommodate additional panels down the line.
