How to design a residential solar system
The cost of solar panels is decreasing daily. The purchase or self-assembly and installation of stand-alone solar systems has become affordable to ordinary consumers. We decided to create this guide so that consumers can understand the necessary components, and be able to assemble a solar power plant for the home with their own hands.
Where do we start?
To independently design an autonomous system, you need a knowledge of the basics of electrical engineering and a certain knowledge of mathematics. To assemble, the simplest solar power plant requires 4 components:
- Solar panel (PV panel);
- Charge controller;
In addition to the above components, you will need copper cable, connectors, protection devices and some small things. Below, we explain step by step how you can choose components just for your needs.
Calculating the load
Before you choose components, you need to calculate the load of the devices that will be connected to your solar power plant and how long they will run. To do this, you need to do the following:
- Determine what appliances (lights, fan, TV, pump, etc.) you will connect and how long (hours) they will run;
- Read the specifications of your appliances to determine their wattage;
- Calculate the amount of electricity you will use in watt-hours (Watt*h), which is equal to the product of the power rating of your appliances (W) divided by the operating time (h).
When you’ve finished calculating the load, it’s time to start selecting components to meet your load requirement.
Selecting the batteries
All solar panels are direct current sources. They only generate electricity during the day. If there is a desire to connect a DC load during the day, there is no problem with that, you can connect directly from the panels. But doing this is not a good solution because:
- Most appliances need a constant rated voltage to work effectively. The voltage and current transmitted by solar panels are not constant. They change depending on the intensity of sunlight; overcast weather is “not good.”
- If you want to turn something on at night, it simply will not turn on.
This problem is solved by using rechargeable batteries to store energy during the day and use it at night. There are many kinds of batteries. Open-type batteries with liquid electrolyte, which include car batteries, are designed to deliver high current for a short period of time. They are not designed for deep discharge, they have other tasks. Batteries for solar panels are deep cycle batteries, they can easily tolerate partial discharges and are designed for deep slow discharges. Gel and lithium batteries are well suited for solar power plants.
Selecting the panels
We will consider only monocrystalline or poly crystalline panels, and will not consider amorphous and other thin-film panels, due to their rapid degradation – loss of power.
The main differences between mono and poly:
Monocrystalline panels are more expensive and more efficient than poly crystalline panels. But in general, the efficiency is not much different, it depends not only on the type of cell, but also on the quality of the cells themselves and the integrity of the manufacturer.
Choosing a solar charge controller
A controller is a device that fits between the solar panel and the battery. It regulates the voltage and current coming from the solar panels to keep the batteries properly charged.
12-volt batteries are most often used, but solar panels can produce much higher voltages than are needed to charge the batteries. The charge controller actually converts the excess voltage into current, thereby reducing the time it takes to fully charge the batteries. This allows the solar panels to be quite efficient at any point in the day.
Choosing an inverter
Solar panels take the sun’s rays and convert them into electricity, they are direct current (DC) sources, just like a battery pack, and we need 220V AC to plug in our outlets. The direct current (DC) is converted to alternating current (AC) through a device called an inverter.
Types of AC waves at the output of an inverter:
- Rectangular wave – meander;
- Modified sine wave;
- Pure sine wave.
The rectangular wave inverter is the cheapest, but it is not suitable for all appliances. A modified sine wave inverter is also not designed to provide electricity to appliances with electromagnetic or capacitive components, such as: microwave ovens; refrigerators; and various types of electric motors. Modified sine wave inverters are less efficient than pure sine wave inverters.
Mounting the solar modules
Once everything is calculated and all the components have been purchased, it’s time to install the solar power plant with your own hands. First, choose a suitable place on the roof, where there are no obstacles to sunlight – no shade from trees and other buildings.
Angle of inclination of solar panels
To get the most out of a solar power plant for your home or cottage, you need to install them in a direction that will capture the most sunlight. The longer the panel is perpendicular to the sun, the more electricity it will generate.
With the angle of inclination figured out, the orientation of the same panels should be to the south, if not, then south-east or south-west, but it should be understood that in this case, the output will be less. There are systems with variable position of the panels (solar tracker), but it will not be considered in this article because of the high cost of implementation and the presence of friction parts.
A rack or fixture for the roof of solar panels can be bought or make your own hands, even from wood, even from metal. The main thing is that it must be reliable, because the panel has a great sailing, plus you need to consider the distance between the panel and the roof – a tight fit is unacceptable. We use and recommend you to use special fasteners just for solar panels.