How Much Power Do You Need to go Off-grid?

Actually, the question should be, how much money do you want to spend to live off-grid comfortably to meet your basic energy requirements?

Through trial and error, scary times when the monitoring system indicated we were stuffed, lots of reading, and talking to those in the solar game, the following is a brief summary that may assist those considering living off-grid. For those that currently live off-grid, I would never profess to tell you anything, but encourage you to continue reading, even just for a chuckle, raised eyebrow, or even for a disapproving shake of the head.

All off-grid systems have pro's and con's, and which one you end up choosing to start will depend on need and financial resources. This article is not a comparison on which is the better system, but rather a novices view of how to wade through the myriad of information available, mostly designed to confuse and complicate what should be a very simple decision. Anyone reading this has probably read other articles about calculating energy needs, ohms law, lithium, gel, lead acid batteries, and DC and AC coupled off-grid battery systems etc etc.

So we're not going to revisit that detailed information here. If you aren't up to speed, then google your heart out. From here on we're going to talk in layman's terms. And we are talking from a specific point of view (ours), which is based on the fact that technology relating to off-grid power is about to change significantly over the next 5 - 10 years. Hence you need to ask yourself when you are about to part with your money, is it really beneficial to spend money on something that's going to last 15 - 20 years but be outdated in 5 years' time. Because that's our experience. Everyone appears to be trying to sell you the latest and greatest now, whilst acknowledging that new tech is just around the corner. Reminds me of the Betamax, VHS, DVD, USB to download world journey.

So let's look at need to cost, rather than cost to need to start.

Firstly, forget about the size of the building and usage. Look at what appliances, lights and other power-sucking toys you'll need. Stressing the need, not the want. You can look at the 'want' later when you have more knowledge.

Let's start small with some basics that a couple may need.

Off-grid system used to power the following:

  • Fridge
  • Lights x 10 (not all of them at the same time of course)
  • Computers x 2 (12/24 hours a day)
  • Mobile broadband modem (if you are lucky enough to be in a spot to have access to mobile reception)
  • Fans x 2 (for those days when you need them)
  • Battery charges for power-tools (most days for a few hours)

Gas used to power the following:

  • Hot water
  • Cooking

Our above configuration requires a 48V x 900Ah battery system (or 43.2kwh-24 x 2V batteries), 3kw off-grid inverter, and a total of 3kwh on the roof in solar panels (very old panels-120W). But this gives us reliable power and can sustain 5 days without sun before we need to kick-in the generator. We tried to add a freezer recently, but the combination of that power, a longer than ususal period of rain, and a guest or two just tipped the balance to depending on the generator for the first time in three years. All hail the fossil fuel tech here as it remains the only truly dependable life saver now, and into the future until renewables become truly self sufficient, and reliable in all conditions.

For those who like figures we generally average 50Ah overnight and rarely does the battery system drop below 90%. This has meant that our 12 year-old lead acid battery system is still going strong, but starting to show some wear-and-tear physically. As we know our system is coming to the end of its life, we've been researching how much to spend on an upgrade to;

  • Similar size system, or
  • Larger system

Upgrade To Similar System

The reality is a 3kw system suits the two of us, but has shown to not quite able to handle anything more. So we've decided to go larger. But for those who would like a cost effective reliable system for two people, our advice is that this size is more than adequate so supply our off-grid needs. No matter what size you decide on, you will need a generator to top up your batteries. You just can't get away from it unless you spend a small fortune on a huge battery bank.

Our suggestions , which may go against a lot of other mainstream advice at present is the following:

Battery system

Seriouly consider lead acid and even consider traction batteries (used for forklifts). A 48V 800/1000ah bank will cost approximately AU$5,000 to $7,000 new, comes with a warrantee and be the most reliable you can get. You can get them second hand for about 3k but for me, new is the way to go. You can also fork out 12 to 20k plus for a similar size
"solar" battery bank.

Yes, you will need to check and top-up batteries regularly with distilled water and perform basic maintenance, but this is incredibly simple. Again, google your heart out.

You can go for gel, but from what we've found gel-batteries appear to be old-tech already, so we've been advised multiple times to either go for lead-acid or lithium. There appears to be quite a lot of second hand, old Telstra backup ones as an example that can be obtained from recyclers or ebay. Buyer beware.

Lithium of course is the buzword in batteries. So is lead-carbon, so is super-capasitors, and probably other tech options we're not aware of. But like any new tech they are all expensive and have really not been tested over time. Hence the risk factor will be a bit higher when parting with your cash. Remember we are just talking about a small system here. So, the focus is on a reliable cost-effective system to get you started with confidence.

Inverters, Regulators and Chargers

No need to waffle on too much here. Google, Google, Google.

Advice is to buy quality and don't skimp. A 3 - 5kw inverter with a seperate MPPT will set you back AU$3,000 - 5,000. Buy Chinese and you can get that down to under AU$2,000. The reality is you will probably regret that decision in a year or 4. But more and more feedback appears to indicate that there are some better brands than others. Do your research.

We also suggest that you look at buying a made-up board with the system completely wired. One where all you would have to do is connect your panels and connect your batteries (using a qualified electrician of course).

The Panels

So this is where it gets interesting. It can be tough trying to find a solar installer to put panels on your roof for a reasonable cost in a remote area. The moment you say 'off-grid' the phone seems to hang up. So don't say 'off-grid', just say you want panels on your roof with no inverter. You may then be lucky enough to get the rebated price. other than that it will most likrley be up to you to install. general feedback is that there is no need to pay through the nose for a good roof system. being off gris space shouls not be an issue so less powerful panels are fine. Suggest you don't get caught up in the bigger is best when it comes to watts. Just get a decent brand above 250w per panel.

We've found if you choose to buy new panels for a 3-6 to 6kw system on the roof you are looking at around AU$2,000 - 4,000. We suggest that bigger is better as a whole as the bigger system will charge the batteries far quicker in less time on cloudy days ensuring the battery system remains at an optimal level.

This is an area you can go second hand though. We have, and found 1-2 year old panels (6.6kw) for around AU$1,000 with plenty of life left in them.

So there you have it. System for around AU$15,000 and depending on where you look, closer to 10K.

Now of course you will find cheaper, and you will find dearer, whether it be buying individually and installing yourself, or the multitude of packaged deals you'll find on the internet. The problem we found was trying to get the combination of what we wanted, lead acid batteries, good inverters, and mid-range panels installed on our property. Everyone wanted to sell us their products, naturally, and of course they were the best. So for us it looks like we will be doing a DYI with a sparky to sign off on the final system.

Upgrade to Bigger System

For us as we are upgrading, we have decided to go for a bigger system to accomodate a larger expected power consumption and doing some of the work ourselves. not through choice mind you. As such we are tripling our system in regards to the roof and inverter, but not battery. As our location gives us on average 300 plus sunny days per year we are going to spend money on a decent generator rather than a larger battery bank.

We are anticipating installing 10kw of solar panels, a 10 -15kw inverter, 2-3 MPPTs, and a 48V 1000Ah battery bank. The generator system supporting this will be critical in ensuring reliable power through wet and cloudy weather.

So we are at the point where we need to raise Depths of Discharge (DoD) of battery systems. This becomes very imporant as different battery systems have different DoD's which need to be considered when you want to compare let's say lithium batteries with lead batteries.

Our first decision is whether we make the leap to lithium? We like the aspect of being able to use 60-80% of the battery capacity, but still remain slightly unconvinced that the expenditure is worth it just now as the cost would be approximately AU$15,000 - 20,000 at the time of writing.

We found it difficult to find simple information that compared sizing of lithium battery banks to lead-acid battery banks. I.e. a 48kv lead-acid battery bank using 20% a day at a cost of AU$7,000 compared to a 48V x 4 x 3.55kwh lithium battery bank using 60-80% a day at a cost of AU$13,000. We have worked out that both essentially gives you access to around 10kwh daily usage but for different upfront costs. Lithium is supposed to last longer, give you more cycles etc but as stated at the start of this blurb, longevity of the tech is not that important as we assume we will be moving into a far more futureistic tech in 5 to 10 years.

Whatever size battery bank you choose you will be comparing the size of a lead-battery bank to a lithium-battery bank. A lithium-battery requirement is roughly half of a lead-battery due to DoD. When you start researching battery systems you are likely to get conflicting information on sizes of batteries and prices which makes it very confusing when you are not sure whether to buy lithium or lead batteries, and also if you don't know the difference between the two (which we personally didn't at the start of our journey and thus the reason for writing this post).

Below is alittle something for those a little more detail.

According to Solar Choice most people fit into one of three groups in terms of usage:

Group 1

Young adults or families that work. Their usage is higher in the mornings, evenings, and over weekends, but not during the day.

20kWh per day - 20 kilowatt hours per day

Requirement: Solar battery system (lithium) size of 3.5kWh according to Solar Choice

Requirement: Solar battery system (lithium) size of 25.2kWh according to Unbound Solar considering DoD of 80%.

Requirement: Solar battery system (lead) size of 48kWh according to Unbound Solar but becomes 96kWh when considering DoD of 25%.

Requirement: Solar system (panel) size of 5kW according to Solar Choice

Group 2

Retirees or young families where people are at home during the day and may use air-conditioning or heating depending on the season.

30kWh per day - 30 kilowatt hours per day

Requirement: Solar battery system (lithium) size of 6.5kWh according to Solar Choice

Requirement: Solar battery system (lithium) size of 37.8kWh according to Unbound Solar considering DoD of 80%.

Requirement: Solar battery system (lead) size of 72kWh according to Unbound Solar but becomes 144kWh when considering DoD of 25%.

Requirement: Solar system (panel) size of 6.6kW according to Solar Choice

Group 3

Big energy users who may have swimming pools, electric water heaters, 5 or more people in the home, air-conditioning or heating.

50kWh per day - 50 kilowatt hours per day

Requirement: Solar battery system (lithium) size of 13.5kWh according to Solar Choice

Requirement: Solar battery system (lithium) size of 63kWh according to Unbound Solar considering DoD of 80%.

Requirement: Solar battery system (battery) size of 120kWh according to Unbound Solar but becomes 240kWh when considering DoD of 25%.

Requirement: Solar system (panel) size of 13kW according to Solar Choice

We'll add in a Group 4...

Group 4

People who are completely off-grid, do not use washing machines, have TV's, etc. People who cook on gass and have gass-heating water systems, who only use electricity for lights, computers, fans, and charging batteries of equipment or phones.

People like us.

5kWh per day or less - 5 kilowatt hours per day

Requirement: Solar battery system (lithium) size of 5kWh accoring to Unbound Solar considering DoD of 80%.

Requirement: Solar battery system (lead) size of 10kWh according to Unbound Solar but becomes 20kWh when considering DoD of 25%.


Currently we have a 43kWh battery system and we use less than 5kWh per day which is about 10% of our DoD, which is likely why our system has lasted as long as it has. We are in the process of enlarging and upgrading to a new system and will keep you informed when we complete that task. Sure to be a learning curve.

So to finish off, it is important to understand what your needs are when choosing solar and battery systems more than the detail of power usage per appliance per hour. In our 3-year experience of living off-grid, people often get sold more than what they need because they don't want to be caught short, which can drive up the price. We suggest you do your research on what you need on a daily basis and how much energy it draws in general. It's as simple as checking your electrical meter. Make your calculations before talking to a battery or solar supplier so they can recommend an appropriate product for your needs. It could save you a lot of money, but more importantly a lot less headaches.

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