There are many ways to use solar panels, and the best option will depend on your energy consumption habits and electricity tariffs. You can have a grid-tied installation that only reduces your power bills when the sun is shining, or you can install a solar battery system that can be used after sunset. It’s also possible to design an off-grid solar power system that is fully independent from external energy sources besides the sun.
However, keep in mind that the design and installation process changes depending on the type of solar system you’re looking for. To make sure you get the best possible results, your requirements and expectations should be explained clearly to solar installers before asking for quotes.
As you might expect, the price of solar power systems changes depending on their complexity and features. A basic grid-tied system with a 10-kilowatt capacity is much more affordable than a 10-kilowatt system with a home battery and smart energy monitoring, even when the solar panel capacity is equal in both cases.
There are three important differences between off-grid and grid-tied solar power systems, which are summarized in the following table:
|Solar PV System Features||Grid-Tied System||Off-Grid System|
|Energy Storage||Energy storage is optional since you can rely on the power grid during nights and cloudy days.||Energy storage is necessary since your solar panels are only productive during daytime hours.|
|Solar Power Capacity||You have more flexibility when sizing your system. If you consume more electricity than what your solar panels produce, the rest can come from the grid.||Your solar panel system must generate enough electricity to cover 100% of your needs, and your battery must have some extra capacity in case of cloudy weather.|
|Type of Inverter||There are several options: you can use traditional grid-tied inverters for solar panels only, or hybrid inverters for both solar panels and batteries.||You must use a multi-mode inverter, which is designed for off-grid operation 24/7. Without the right inverter, even a solar system without batteries cannot go off-grid.|
In a few words, an off-grid solar system can power more devices on its own, while having more functions. However, a grid-tied solar system will normally have a lower price and quicker payback, since the inverter is simpler and energy storage is optional.
Here we will discuss the main points to consider when going off-grid with solar panels, and when it makes sense to install this type of system.
How Many Solar Panels Do I Need to Go Off-Grid?
Before you can off-grid with solar panels, there are two important questions to answer:
- How much electricity does my home use each year? This determines how many kilowatt-hours must be generated by solar panels.
- How much electricity does my home use each night? This determines the energy storage capacity needed for the hours when solar panels are not productive.
Look for your location on the map and click on it, and you will get several values about solar irradiation on the point of interest. Here we will use the specific photovoltaic power output, which is measured in kWh/kWp (kilowatt-hours produced annually, for each kilowatt of peak solar capacity).
For example, if your location shows 1500 kWh/kWp and you install a 10-kW solar system, you can expect to produce 15,000 kWh per year. However, here we need to follow the opposite procedure: look for your last 12 power bills, add the kilowatt-hours, and divide that value by the specific PV power output for your location:
- Assume your last 12 power bills show a total consumption of 12,000 kWh.
- In a spot with 1,500 kWh/kWp, you need an 8-kW system to generate 12,000 kWh.
- 12,000 kWh ÷ 1,500 kWh/kWp = 8 kWp
If the PV system in this example uses a 340W solar panel model, you need 24 of them to reach 8 kW. Using a larger solar panel rated at 400W, you would only need 20 to reach the target.
We also need to determine how much of that electricity goes into the battery system for nighttime consumption. If a home uses 6,000 kWh when solar panels are generating power and 6,000 kWh after sunset, you need a battery that stores 6,000 kWh throughout the year. This means you will be storing 16.44 kWh of solar electricity each day, on average.
Designing an Off-Grid Solar System: Importance of Seasonal Variation
The procedure explained above can give you a general estimate of the solar and battery capacity needed to go off-grid. However, you also need to consider that solar panels are more productive during summer, and less productive during winter.
via Off-Grid Cabin
Your system must be designed to generate enough kilowatt-hours during winter, even if that means having extra production during summer. Since you’re going off-grid, the solar power system must be designed for the least favorable scenarios.
A qualified solar company will consider your power bills throughout the year, ensuring that solar panels generate enough electricity on a monthly basis. Using this information, they can provide a customized solar design that meets the energy needs of your home.
Generally, you will need a larger solar system to go off-grid if your home location has a hot climate. This means you need more air conditioning during the summer, and all that electricity must come from solar panels.
Using the Right Inverter for an Off-Grid Solar System
The main function of an inverter is converting DC power into AC power. When used with solar panels, an inverter makes their electricity output usable by home appliances and compatible with the grid. However, the inverter type changes depending on the features of your solar power system.
- Traditional solar inverters are designed to operate only when connected to a larger power system like the grid, and they are used with solar panels alone. These inverters are not designed for batteries.
- Hybrid inverters can handle electricity for solar panels and batteries operating together. Some models are designed for off-grid operation during short periods, such as blackouts, but others can only operate when connected to the grid.
- Multi-mode inverters are similar to hybrid inverters, since they manage solar panels and batteries simultaneously. However, multi-mode inverters are designed for permanent off-grid use, while hybrid inverters are generally designed to operate off-grid during short periods such as blackouts.
Having a multi-mode inverter is fundamental for an off-grid solar system, since it meets the electricity needs of larger devices that normally run with the grid. However, once you have an off-grid installation with a multi-mode inverter, you can easily expand it with traditional and hybrid inverters.
Using Off-Grid Solar Batteries with Enough Capacity
As mentioned above, a grid-tied solar power system gives you the option of falling back to the grid when batteries are depleted, and solar panels are not productive. Unfortunately, you don’t have this option with an off-grid solar system. This means both the solar panels and the battery must have a high enough capacity for all your energy needs. Off-grid solar systems are generally larger for this reason, and this means they are more expensive.
Each home is unique, and an off-grid solar system needs a customized design based on your energy needs. However, as a rule of thumb you can expect to pay 2-3 times more for an off-grid solar panel system, compared with a grid-tied of the same capacity.
- For example, an 8-kW solar system will cost around $24,000, before accounting for incentives like the 26% federal tax credit.
- However, you can expect to pay over $50,000 for an off-grid solar system of the same capacity, considering the specialized inverter and the energy storage capacity needed.
When Does an Off-Grid Solar Power System Make Sense?
Many electricity providers now offer net metering, which means you get full credit for all the kilowatt-hours that are produced by solar panels and exported to the grid. In other words, you save the full value of each kWh, even when it was sent to the grid and consumed by someone else. When this benefit is available, you can achieve an excellent return on investment with grid-tied solar panels.
However, net metering is not available everywhere. There are electricity providers that only pay a small tariff for surplus solar energy, and some of them pay no tariff at all, which means you’re giving away your electricity for free.
The ideal scenario for an off-grid solar power system is when you don’t have net metering, and your electricity tariff is very high. There is no way to offset your nighttime consumption with solar power produced during the day, and the only option is storing it in a battery system.
Keep in mind that you can size a solar battery system for 100% of your energy needs and remain connected to the grid in case of emergencies. This configuration offers the best of both system types, since your power bills are reduced to a minimum, but the grid is there for cloudy days and nights when you deplete the battery.
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