Whether you want to fight climate change by reducing your carbon footprint or have had enough of spiralling energy bills, or if you are living somewhere remote and not connected to grid electricity, investing in an off-grid solar system could be the answer.
An off-grid solar power system means you can be totally reliant on renewable energy, and are not beholden to the energy giants anymore. But just how many solar panels do you need for an off-grid solar system?
Calculate Your Energy Needs
To determine how many residential solar panels you will need to provide your home with enough off-grid solar energy, you will need to work out your monthly electricity usage.
An easy way to find out how much electricity you use is to check your energy bills. They should show how much energy in kilowatt-hours (kwh) you have used over the last year. You can divide this total by 365 to determine an average daily electricity consumption.
To give you an idea, according to Ofgem, an average-sized three-bedroom house will use around 2900 kWh per annum. This is around 8kwh per day.
Determining The Solar Panel Output
Once you know how much electricty you need your off-grid solar system to generate, you need to think about the output of your solar panels to detemine how many panels you need.
The output of a panel comes down to these 3 things:
- The power rating or wattage of the panel. The smallest solar panels start at 50w and standard panels range from 200w to 500w.
- How much solar power is there in your vicinity. This is affected by where you live. In the UK, there are not as many peak sunlight hours as there are in, for example, Spain or Australia. In the UK, there are on average 3 to 4 peak sunlight hours. If your roof is south facing and the panels are tilted, you will get more direct sunlight.
- How much power is likely to be lost in your solar panel system?
There are losses of between 20% and 30% in all off-grid solar systems from the following:
- The inverter.
- Direct current (DC) cable.
- Alternating current (AC) cable.
- Losses from high temperatures.
- Environmental losses such as dust, debris, snow etc.
Sizing Your Solar Panel System
As well as calculating the number of solar panels you will need when pricing up your off-grid systems, you will need to consider the other parts of the solar system such as the battery, inverter, cables and backup generator.
You will also need to consider the costs of having your panels installed. You might even want to think about having a grid-tied system where possible so you can sell any excess electricity back to the electric grid.
Factors To Consider When Sizing Your System
You will need to have ample battery storage to cover days, possibly even weeks, at a time when there will be minimal sun.
You will also need to weigh up how much solar panels cost depending on their power output and decide if you want more panels with less output or fewer panels with a higher output. The amount of roof space you have may make this less of a choice and more of a requirement.
How To Calculate The Number Of Solar Panels Needed
Multiply the power output in watts of one panel by the number of hours of sunlight where you live, multiplied by 0.75 to allow for losses. For example; panel output 250w x 4 sunlight hours x 0.75 (losses) = 750w.
This will give you the daily power output of one panel, then you just need to divide the total power required by this number to know how many panels you will need.
Using the example of an average three-bedroom house we used earlier, that would be over ten 250w solar panels.
Careful and thorough planning is essential before purchasing any off-grid solar systems. Although we’ve tried to make it simple for you to calculate how many solar panels to run a house off-grid in this article, we know that there are a lot of other things you’ll need to think about.
The good news is, we can help. Our team of solar professionals at Generator Pro can assist you every step of the way.