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7 Things to Know About Off-Grid Solar Power Systems

Installing an off-grid solar system is exciting for many reasons. You will no longer remain dependent on your grid electricity; the soaring energy prices no longer bother you. And to top it off, you are not contributing any CO2 to the environment.

But is going off-grid as simple as it seems? Unfortunately, not really. There are many things you need to know about off-grid solar power systems before installing one.

In this blog, we will discuss the most pressing questions solar shoppers usually ask from our energy advisors. For instance,

  • Can an off-grid solar system work without batteries?
  • How many batteries do I need for off-grid solar?
  • How many solar panels do I need to run a house off-grid?
  • What happens to excess solar power generated off-grid?
  • Do you need a permit for off-grid solar?
  • Which is better? On-grid or off-grid solar?
  • How much does an off-grid solar system cost?

These are only a few questions we come across. Let’s discuss them, one at a time.

1. Can an off-grid solar system work without batteries?

No, an off-grid solar power system cannot work without batteries. Batteries are the very soul of any off-grid solar system, without which the system cannot function. You will have a steady power supply when the sun shines in full bloom. But there will be no power for your night needs, or the sun goes away for a day.

If you want to cut yourself off from the grid, you must have batteries as part of your system. Batteries store energy that you can use at night and during cloudy weather without utility electricity. So, how many batteries do you need to go off-grid?

2. How many batteries do I need for off-grid solar?

There is rarely an absolute answer to this question. Not all homes are equal in their size and needs. Needless to say, large homes would need more batteries than smaller homes. Similarly, if you just want to save more money with solar but still decide to stay connected to the grid, you would need fewer batteries. Merely 2-3 average lithium-ion batteries would suffice.

Also, most homeowners install batteries for resilience—that is, to have access to power when the grid goes down. If that’s the case, only a single average lithium-ion battery, such as Tesla Powerwall, could keep you powered during your emergency hours. 

Want to be completely off-grid?

You would need about 7-14 lithium-ion batteries.

But how much exactly you need could only be calculated after analyzing your needs and which type of batteries you prefer.

For example, if you use 500kWh power a month, you would need a 21kWh battery bank. That roughly means two Tesla Powerwall batteries—one Tesla Powerwall has 14kWh total energy.

This is just a ballpark estimate and not a final number. You can only get a definite answer after your solar installer analyzes your power needs and goals in detail.

3. How many solar panels are needed to run a house off-grid?

Like the question above, we cannot precisely pinpoint the number of solar panels you would need. But what we can tell you with certainty is that you would need more solar panels to go off-grid than you would need for a grid-tied solar system. This is due to the extra energy you would need for your batteries. In grid-tied systems, you just need power during the day, but for an off-grid system, you will need more panels to ensure your batteries get enough charge.

To be a little specific, let’s do some math. An average American home uses 10,632 kWh a year—that is about 886 kWh per month. There are many types of solar panels, but for the sake of simplicity, let’s assume you install 300-watt solar panels. Your home may get varied sun exposure but let’s keep it 7 hours a day. That means you get 2.1kWh (7 x 300 watts) power per day from one panel—or 63kWh monthly from one panel. Your consumption is 886kWh a month. So, you would need 14 solar panels (886/63~14).

But this may still not be enough, as we have not factored in power needed by batteries. However, you got a rough estimate. For batteries, you may need six additional solar panels, though it depends on the size of your battery bank. So, to go completely off-grid, you may need 20 solar panels, each 300-watt.

4. What happens to excess solar power generated off-grid?

An off-grid solar system is usually designed to match the power needed during the day’s peak hours and also to charge batteries. But there still could be excess power. What happens to that?

It goes wasted. Since you are not connected to the grid, you cannot utilize net metering, through which you can import any excess power to the grid. Also, the batteries are full, and overcharging them would damage them. You don’t have any other option than wasting it.

This job is done by inverters and charge controllers (charge controllers regulate and monitor energy flow to batteries). When inverters and charge controllers sense that the incoming power is more than needed, they activate a function called “Active Power Curtailment.” This function deliberately limits the flow of energy to the home and batteries, letting any excess power goes to waste.

5. Do you need a permit for off-grid solar?

Yes, you will likely need a permit to install an off-grid solar system.

The rules may vary based on the state or county you live in and the building codes there, but generally, a permit is required for safety purposes. We recommend checking with your local or state administration to confirm the requirement.

That said, you won’t need an interconnection agreement, as you will not be connected to the grid. An interconnection agreement is only required for grid-tied and hybrid systems, where you are actively connected to the grid.

6. Which is better? On-grid or off-grid solar?

Both are better. An off-grid system will be more financially feasible if you live in a remote area, where running power lines would cost more. Even in an urban center, an off-grid system may save you a little more than a grid-tied system.

But there are some cons of off-grid solar systems.

  • One, they have higher initial investment than grid-tied systems.
  • Two, they demand major lifestyle changes from homeowners.
  • Three, batteries require regular maintenance and replacement after some years—which is going to cost more in the long run.
  • Lastly, you can still run out of power. For example, if the weather stays cloudy for more than three days, you may experience a blackout.

Based on the above, a grid-tied system would make more sense, especially if you live in an urban center.

You will still save a significant amount on your electricity bills, but you will have ready access to backup power—your grid.

7. How much does an off-grid solar system cost?

Every home would need a bit different system, so pinpointing the exact cost could be difficult.

However, an off-grid solar system that could power an entire home costs between $15,000 to $50,000. Some systems may even cost more, up to $60,000.

For an off-grid system, you need solar panels (which can cost between $6,000 to $30,000); inverters (can cost up to $14,000); charge controllers (usually cost up to $1,000), and a battery bank (which can cost between $10,000 to $40,000). If we do the math, the cost of a larger system with a suitable battery bank could be in the vicinity of $40,000. But as mentioned earlier, the precise costs could only be determined after assessing your regular energy consumption, goals, lifestyle, etc.

Note that these costs are before claiming any incentives, such as the Federal Income Tax Credit, which could reduce the cost by a flat 30%.

Above were a few things to know about off-grid solar power systems. We hope this article cleared some of your confusions and gave you insights you needed to know.

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