How Can I Have Battery Backup for My Whole Home?

Posted by Kenneth Scott on

Your at home and your power shut's off; however your laptop stayed on because of the long lasting built in battery, a UPS.  You than had one of those moments; I wonder if I could put my whole home on a UPS?

Well the answer to that is Yes You Can.  It might even be less expensive than you think but we’ll cover that in the basics. Remember, a system like this should be installed by a qualified electrician. Stay with us and we’ll see how you might be able to plan out such a system, and save some real money.
How Can I Have Battery Backup for My Whole Home

How Can I Have Battery Backup for My Whole Home?

The concept is simple.

  1. Collect several batteries connected together to form one big battery, we will it a  battery bank or a battery power generator.
  2. Have a way to connect that bank into your domestic power supply to keep the bank fully charged.
  3. Setup in a way to use the power from the bank when the power goes out. Simple yes. Yes it is simple, but is it easy?

What Do I Need?

What do you need to create this UPS backup isn’t a lot.

  1. You’ll need batteries
  2. Inverter/charger
  3. Battery cables
  4. Inline fuse, a battery rack, and some electrical wire.
  5. You will need other bits and pieces, but this is an introduction to how to make such a system.

You’re need a qualified electrician to connect to the power grid.

When it comes to finding an electrician, try to find one with plenty of experience in installing UPS power systems. Battery backups and grid-tied power systems is a specialist task, In fact, see if you can find someone who is a certified Clean Energy Council installer who is  trained to ensure your system meets industry best practice standards and all relevant Australian Standards.    Click Here to see a list of all Accredited Installers near you:  Don’t be afraid to ask for references and go see some of their other work.

If this looks like something you want to do, the next thing to do is figure out is the specifications of all the parts needed. This depends on the appliances you use in your home. It also depends on how you currently use electricity. The final piece is how long you want backup when the power goes down.

How Do I Size Equipment for my Home Battery Backup?

  • You need to figure out some things about how your home and appliances use electricity.
  • You need to work out is what kilowatt hours (kWh), watts (W), and amp's (A) are been used from the appliances and devices in your home.
  • Start writing these numbers down now as you work through your house. This will help you a lot when you start this project and will be very useful latter for other energy saving projects.
Homes vary widely across the world, let’s base the calculations in this article on my sample home. Lets use a 150m/2 home located somewhere in the northeast of Queensland where power usage is highest in February. The easiest way to figure out how many kWh your home uses in a day is to look at your power bills. Find the bill that has the most electricity usage. If you’re in the north, it’ll probably be from the first three months of the year. If you’re in the south it will probably be from the peak months of the winter. Your bill should tell you what your average daily electricity usage is for that period. That will be in kWh and is a key number for this project. The average daily electricity usage for this home January is 42kWh.

You’ll also want to know how many watts your appliances use at one time. There are a few ways to work this out. You could get the information from the nameplates of your devices, write that all down, and then add it up. But many devices don’t have a proper nameplate with all the information. The most accurate would be to get a device like the Kill A Watt EZ Electricity Usage Monitor. The example home’s appliances and devices would draw about 4400W (or 4.4kW).

How Do I Size an Inverter/Charger for My Battery Backup?

The inverter is the device that will take direct current [DC] electricity from your batterie bank and convert it to the alternating current [AC] that your house appliances use. It’s capacity is measured in watts [W] and volts [V]. You will need an inverter that has the ability to charge your batteries as well. Your home is still connected to a power grid and your inverter needs to be safely tied in to the grid. This type of inverter has the ability to automatically detect when the grid power drops and an AC auto-transfer switch commences recharging the batterie bank.

The inverter is the device that will take direct current (DC) electricity from your batteries and convert it to the alternating current (AC) that your home’s appliances use. It’s capacity is measured in watts and volts. You’ll want an inverter that has the ability to charge your batteries too. Because your home is still tied to grid power, your inverter needs to be able to safely tie in to the grid. These types of inverters have the ability to automatically detect when the grid power drops and switch you to the batteries. That function is known as an AC auto-transfer switch.

Sumry Power ~ Big Power Inverter/Charger  PSW7 Series [4Kw~4000w] 12/24/48v Dc to 240v Ac should work.

How Do I Size My Battery Bank?

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A battery bank is just a collection of batteries that are connected together. It’s the battery bank that will determine how long you can run your house while the grid power is down. So you need to figure out how long you want that to be.

  • Take note of the number of power cuts you have had in your area over the last few years.
  • What’s the longest perioud of time you have been without power?
  • Was it like a few weeks due to a cyclone?
    • Try not to count that in to your calculations. Battery backup for a few weeks will require charging from solar panels, wind turbines, generators or a combination of those.
    • At that point, just consider going off-grid.

Most people only have an outage for a few hours but maybe you’re in a very rural area where it routinely takes a day or two for the service crews to arrive, or you live in the city and you’ve never had an outage longer than 4 hours, because events like a cyclone hitting your city are rare.

To have a backup that will cover you for a couple weeks would be expensive and will need to be reexamined as a off-grid system. Try not to count exceptions like that into your estimate unless you know that you are in a high risk area of been disconnected from the grid for long periods of time.

My sample home is in a rural city, so let’s say you’re never without power more than 4 hours. But you’re cautious, so let’s use 6 hours to build in a safety margin. Now let’s figure out how many kWh you need to cover 6 hours of disruption to your power supply.

  1. Divide the daily kWh used by 24 to get the hourly kWh used.
  2. Then multiply that by the number of hours you need backup.
  3. 38kWh divided by 24 gives us 1.58 kWh.
  4. Multiplied by 6 hours gives us 6.33kWh.

(Daily kWh / 24h) / Backup Need in Hours = Total kWh Needed

  • Lead-acid batteries should not be drained more than 50% to avoid permeant damage to the battery. This means you will need twice as many kWh, to safely protect the lead-acid battery, now this has become a 12.7kWh battery bank.
  • Inverters are not 100% efficient, so you will lose a small percentage of this 12.7kWh to the inverter. Inverter efficiencies vary but 85% efficiency is a reasonable number to work with.
  • To workout your final kWh, add the inverter 15% inefficiency to your 12.7kWh to get 14.9 kWh. Call it 15kWh for the sake of easier maths.

Here’s the whole formula for this calculation:

Minimum kWh X 1.15 = Total kWh

The final number we need is the Amp hours (Ah). To get that, you divide the total kWh (12.7kWh) by the voltage of the battery system that you want. You figured that out to be 48VDC.

Total kWh / VDC of Battery Bank = Ah

Your Amp hours are going to be 12700Wh divided by 48VDC. That gives you 265Ah. Now you know you need a battery bank that will give you 265Ah at 48V. So how many batteries will you need and how will they be configured? That depends on the voltage and amp hour ratings of the batteries you want to use. For this example, let’s use a 12V 100Ah deep cycle Lead-acid batteries. They’re common, easy to handle, and cost about $350 each.

Using this type of battery, you’ll need 12 of them, costing you at least $4,200. You’ll have 3 groups of 4 batteries wired in series. The 3 groups will then be wired in parallel. This will actually give you 48V and 300Ah. The diagram below shows what that will look like.

300Ah 48V Battery Bank

Can I Do This Less Expensively?

The system we’ve talked about above would be around $8500 to install using Lead-acid batteries. It can be done cheaper by been strict about what appliances and devices you really need during a power outage.

  • Eliminate non-essential loads can reduce your installation cost in half.
  • Replace high wattage appliances with new low watt appliances and lights. [LED lights].

You may consider getting a Solar system generator like a 3500 watt Solar Panels for around $4,300. The bonus with this system is that it can keep charging even when the power is out.

There are other more efficient batteries on the market now that can be run right down and can a fast charge with out damaging them.  It also means that you do not have to double up on the number of batteries to generate sufficient power for the same time period. Savings will also be made due to the longer working life of the battery even after 2,000 cycles [recharges]. 20 years can be expected out of this new battery range.  Pay more now; and save by not having to replace your short lived Lead-acid batteries.

Armed with what you’ve learned here, you can continue to research the best way for you with a greater degree of understanding. Be careful though! Once you realise you might be able to get off the grid altogether, you might just develop a whole new energy lifestyle!  The important point is that you can power your home with batteries during a power outage.

Energy saving technologies can be introduced into our homes to reduce our environmental impact and footprint on our small green planet. However not all renewable energy products are be affordable to all just yet, but hopefully they will all become the norm in the near future.

What do you think about building such a system in your own home? Will you hire an electrician to build one for you? Have you ever built one?

Share your own experiences in the comments section below!

Kenneth Scott

Founder | CEO

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