Quite often in an off grid solar power system, the batteries are charged with solar panels. Sometimes solar power alone may not be enough to charge the battery, in these cases, an AC generator can be used to help keep the battery charged.
An inverter/charger would convert the AC power from the generator to charge the DC battery bank. An off grid inverter/charger would be converting the power in both directions, from AC to DC to charge the battery from the AC generator, and converting the DC power from the battery to AC for your appliances.
Power Inverters are Electronic gadgets that converts energy stored in a battery (or DC voltage) to AC voltage that will power your appliances. Their major selling points are their low noise and emission free operations as well as their convenience. This article will guide you on how to buy an inverter for backup power in the home.
Before you purchase an inverter you will want to take a piece of paper and a pen and write down all of the appliances that you feel are necessary to have during a power outage. After you write down all that, you need to go to each one of the appliances and look on the back or bottom for what is called the service tag. This tag will show you a few important specs that help with picking the correct size of the inverter. The first spec that you will most likely come across is the voltage; this will either be 110,115, or 120vac.
In some cases you may find that the voltage is between 205vac and 240vac. You will need a special inverter to run this appliance. We will get to that later.
The next spec you will find will be the Amps. For example this should read like this: 6.0a or 6.0 amps. What you will do now is take the volts–lets say 115–and multiply by amps 6.0 and this will give you 690 watts. The equation should look like this Volts x Amps = Watts or in this example 115 x 6.0 = 690. Ok, Now that we got that out of the way we can start sizing an inverter that is going to work well during a power outage.
The most common inverter sold for emergency home back-up power is a 1750 watt. The reason for this is that most people want to hook it up to their car, and the 1750 is perfect for most vehicles and will run most appliances. When you hook the inverter up to your vehicle, to run the inverter you will want to try to keep the inverter close to the battery, and out of any weather.
A lot of calls come through about why inverters sometimes won’t work when they are hooked to the vehicle this way. Most people hook these up with jumper cables. This is not the best way to do this. Jumper cables do not give a proper connection to the inverter. The best way to hook an inverter up is with a ring terminal that fits properly over the inverter post.
If you live in an area with less than 12 hours of public power supply, it will not make a lot of sense to buy an inverter, except you also have a power generator or you are willing to invest in a solar power system with solar panels.
It is also important to note that a power inverter is more suited for resistive loads like your household and office electronics like TVs, Computers, Printers, lights, etc.
Power Inverters are not best with inductive loads, so if you are going to be operating lots of machines with motors in them, a generator may be better, except you can find an industrial grade inverter.
Inductive loads like Refrigerators, Freezers, and Air conditioners can be powered by an inverter, just make sure you buy an inverter with high enough capacity and capable of handling their high start currents.
Power Needs
You can find the power rating on the back or side of the gadget. You can also check the manual of the gadget. For example for the load above, the rating could be:
- 1 TV set (100w)
- 1 Decoder (20w)
- 1 DVD Player (20w)
- 1 Electric Fan (70w)
- 1 Laptop (20w)
- 3 energy efficient light points (90w)
- Total Load = 320w
- The next step is to get a VA equivalent of the power, which if we assume a power factor of 0.8 gives 400 VA (i.e. 320/0.8)
After calculating your total load, the next step is to derate the power inverter to create some allowance for flexibility and to ensure it does not over work itself.
To derate, just multiply your total load by 2. In the example above 2 x 400 = 800VA. So, you will buy an inverter with a power rating of 800VA or higher like an 800VA Inverter.
Number of Batteries Required
The next option is for complete home back-up. This is the best option, but one of the most expensive. The system will require a large bank of batteries at a higher voltage, say 24 volt or 48 volt. They do make 12 volt systems, but they are less efficient. The best batteries to use in a large bank like this are the 6 volt batteries either made for solar or golf carts.
They have a much higher reserve time and are cost effective. The next component is an inverter/charger. These are great for home back-up. They have three key components: an inverter, a charger, and a transfer switch. Inverter-chargers come in sizes ranging from 1500 watts to 5500 watts.
The battery chargers that are included range from 70 amps to 150 amps and will charge the input DC voltage of the inverter (12V, 24V, or 48V). This system is a lot more complex than that of a inverter and battery. Most of the inverter/chargers do not have built in AC outlets and require an electrician or professional solar installer to hook them up.
An inverter is usually rated in this pattern X VA/Y V, where X is the rated power output and Y is the input voltage required.
For example an 800 VA/12 V inverter will give a maximum output power of up to 800 VA and require an input voltage of 12V. Similarly, a 1.5 KVA/24V inverter will output 1.5 KVA (1500 VA) and require 24V input.
Since batteries usually come in 12 volts voltage, the 800 VA/12 V will require a minimum of one 12V batteries, while the 1.5KVA/24V inverter will require a minimum of two 12V batteries connected in series.
What Battery Capacity
A very simple way to use an inverter for emergency power (such as during a power outage), is to use a car battery (with the vehicle running), and an extension cord running into the house, where you can then plug in electrical appliances.
Batteries come in different capacities. The higher the capacity, the longer a battery can last before getting discharged, given similar loading.
A 200 Ah (Ampere-Hour) battery is recommended though a 100 Ah or 150 Ah battery can be managed.
For example, for our example load above (400VA), a fully charged 200 Ah battery can theoretically deliver 6 hours of power while a fully charged 100 Ah battery can only manage 3 hours.
Solar Energy Support
Some inverters come with solar energy support. These inverters enable you connect solar panel(s) to your inverter and tap from the free energy of the Sun. This type of inverter is called a Solar Inverter.
The Solar Panel charges your battery ensuring you have enough energy when needed. Depending on the capacity of the Solar panel, it can charge the battery, while still providing power for your appliances. Solar inverters can also charge your batteries via generators or public power supply.
Inverter Installation
Except, you have above average electrical skills, you will need a technician to install your inverter. Thankfully, some retailers and online stores that sell inverters offer options with the installation kit, making installation easier for you or a trained technician.
The installation accessories come from the manufacturer of the inverter which ensures everything works well. When buying an inverter it is always advisable to take-up the installation kit.
The cost of the installation kit may be incorporated in the cost of the inverter or you will have to pay separately for it. Make sure you are present to inspect the installation.
Price Of Inverters
inverters price goes on sale for home and office ranges from around (NGN) 45,000 Naira to (NGN) 900,000 Naira depending on power output and level of sophistication.
This does not include the battery. A 12V 100 Ah SMF Battery costs around (NGN)55,000 Naira, while a 12V 200 Ah SMF battery starts at around (NGN) 102,000 Naira. You will need from one to more than eight depending on your setup.
Solar & Backup Batteries
This system allows you to enjoy uninterrupted power supply all the times and hence allow one to carry out daily functions without fearing for power cuts & trips.
They are noiseless and gives out back up power automatically without the input of a technician once installed. They’re suitable for domestic and medium to high commercial applications.