How to Calculate Your Off-Grid Solar System: A Step-by-Step Guide for Sheds, Campervan Conversions, and Off-Grid Properties

Welcome to the Off Grid Renewables blog! Whether you’re looking to power a garden shed, a campervan conversion, or a remote off-grid property, understanding how to calculate your solar power system requirements is essential. In this guide, we’ll walk you through the necessary calculations so you can confidently design your own off-grid solar setup, tailored to British conditions.

Step 1: Determine Your Energy Consumption

The first step in designing your off-grid solar system is to determine how much energy you need, measured in watt-hours (Wh) or kilowatt-hours (kWh).

To calculate your daily energy consumption:

1. List All Your Devices: Identify all the devices you plan to power, such as lights, a fridge, phone chargers, etc.
2. Find the Power Rating (Watts): Check each device for its power rating, usually indicated in watts (W).
3. Estimate Daily Usage (Hours): Estimate how many hours each device will be used per day.

Formula:

$$\text{Energy Consumption (Wh)}=\text{Device Power (W)}\times \text{Usage Time (hours/day)}$$

Example:

• LED Light: 10W × 5 hours = 50 Wh/day
• Mini Fridge: 60W × 24 hours = 1,440 Wh/day
• Phone Charger: 5W × 2 hours = 10 Wh/day

Total Daily Energy Consumption = 50 + 1,440 + 10 = 1,500 Wh/day (or 1.5 kWh/day)

Step 2: Calculate Your Solar Panel Requirements

Now that you know your daily energy consumption, the next step is to calculate the number of solar panels needed to generate that energy, taking into account the British climate.

To calculate the solar panel capacity:

1. Find Your Peak Sun Hours: This is the number of hours per day when sunlight is strong enough to produce the panel's maximum power. In the UK, peak sun hours typically range from 3 to 4 hours depending on the location and season.
2. Calculate the Required Solar Panel Capacity:

Formula:

$$\text{Total Solar Panel Capacity (W)}=\frac{\text{Total Daily Energy Consumption (Wh)}}{\text{Peak Sun Hours}}$$

Example:

• Total Daily Energy Consumption = 1,500 Wh/day
• Peak Sun Hours = 3.5 hours (UK average)

$$\text{Total Solar Panel Capacity}=\frac{1,500\text{ Wh}}{3.5\text{ hours}}=428\text{ W}$$

You will need at least 428W of solar panel capacity. Since panels are available in various sizes, you could use a single 450W panel or multiple smaller panels that add up to this capacity.

Step 3: Calculate Your Battery Storage

Since solar energy isn’t produced at night, you’ll need batteries to store the energy generated during the day for use at night or on cloudy days.

To calculate battery storage needs:

1. Decide on Days of Autonomy: Consider how many days you want your system to run without sunlight. In the UK, 2-3 days of autonomy is generally recommended due to the variable weather.
2. Account for Depth of Discharge (DoD): Batteries shouldn’t be fully discharged; aim for a 50% DoD to extend their lifespan.
3. Convert Wh to Battery Capacity (Ah): Batteries are typically rated in amp-hours (Ah).

Formula:

$$\text{Battery Capacity (Ah)}=\frac{\text{Total Daily Energy Consumption (Wh)}\times \text{Days of Autonomy}}{\text{Battery Voltage (V)}\times \text{DoD}}$$

Example:

• Total Daily Energy Consumption = 1,500 Wh/day
• Days of Autonomy = 2 days
• Battery Voltage = 12V
• Depth of Discharge = 50% (0.5)