Whichever solar panels or shingles you choose, your solar electric installations will fall into one of three categories: grid-connected, grid-connected with battery back-up, and stand-alone (off-grid). Read on to learn which is best for you.
Table of Contents
Most types of solar installations involve solar (photovoltaic) panels connected to racks connected to a roof. Some solar installations are freestanding, however, with panels mounted on angled racks placed in a field or yard that gets lots of sun exposure. Solar shingles are another type of solar installation and are sometimes referred to as a solar roof.
Solar panels or shingles are just one kind of solar installation. Solar power can also be gathered in the form of concentrated solar power, or as part of a solar hot water or heating system. When we talk about types of solar installations, however, we most often mean a rooftop solar array or stand-alone solar panels.
Whichever panels or shingles you choose, and wherever you choose to locate them, your solar electric installations will fall into one of three categories:
- grid-connected,
- grid-connected with battery back-up,
- and stand-alone (off-grid).
Grid-connected solar electrical systems
A grid-connected system typically consists of a solar module (i.e., panels), an inverter, and the main service panel. The solar module converts energy from the sun into electricity (direct current, DC), which travels to the inverter for conversion to alternating current (AC). Most household appliances run on AC, hence the need for the inverter.
The inverter also boosts the voltage from 12, 24, or 48 volts to 120 or 240 volts, which then travels to your home’s main electrical service panel. From there, your solar-generated electricity runs into the circuits around your home, and any excess electricity is diverted automatically to the electrical grid. If you have a meter measuring electricity delivered to your home, any surplus electricity sent into the grid will make the meter run backwards.
Most code-compliant systems require a meter to measure electricity production and consumption. This meter may be part of the inverter and can measure in either amperes or kilowatt hours (helping to track production and consumption over time). If an inverter doesn’t have an in-built meter, you can buy a separate unit to add to the system.
If your solar installation is connected to the grid, your utility company may require one or two standard utility meters. These are typically large, tamper-proof, glass-encased meters that track electricity used and consumed, so the company can bill you accurately each month. If you have just one meter, chances are your utility company uses net metering to work out your bill each month.
Some utilities insist on a more onerous two-meter system that allows them to buy your surplus electricity at a discounted rate and sell it back to you at a higher price later.
For safety, most grid-connected systems also require two ‘disconnects’. These are safety switches that can be flipped to prevent electrical shocks when homeowners or service personnel are working on the solar electrical system. One disconnect is located between the solar array and the inverter. The other cuts the flow of current between the inverter and the main service panel.
In grid-connected systems, the main electrical grid serves as an outsourced back-up battery.
Grid-connected systems with battery back-up
With the costs of solar battery storage now lower than ever, many more homeowners are choosing solar installations with battery back-up. A grid-connected solar electrical system with battery back-up is very similar to the system outlined above. The difference is that this system includes battery storage and a charge controller between the inverter and the DC disconnect.
Charge controllers are essential if you have a solar installation with battery storage. These devices monitor battery voltage and use that information to protect the batteries from overcharging. A charge controller is also known as a high-voltage disconnector because it can interrupt the flow of electricity from your PV array if it detects that the battery is fully charged.
How battery backup works
While the sun is shining and your solar panels are producing electricity, the current flows through the system to the inverter and into the main service panel to reach the circuits in your home. Any excess electricity is stored in the batteries. Then, when needed, the system can draw stored energy from the battery to power your home.
This kind of system has two main advantages. The first is that you still have a source of power (assuming your battery is charged) when the sun isn’t shining, overnight, and if the main electrical grid goes down.
The second benefit is that you can use your batteries to avoid feeding (much, if any) surplus electricity into the grid only to buy it back later. Why does this matter? Because most utilities pay less for the electricity they buy from homeowners than they charge for supplying electricity to the same homeowners.
In most cases, however, a grid-connected system will still draw power from the grid overnight, rather than drawing it from the battery. There are ways around this, for savvy homeowners wanting to go a step beyond a standard installation. We discuss that in more detail here.
Stand-alone solar installations
Stand-alone solar installations are very similar to grid-connected systems with battery backup. The main difference is that there is no connection to the grid from the main service panel. Many stand-alone systems also include a backup generator that connects to the battery bank. This can be run to charge batteries when they are low. It’s also a good idea to have a backup generator in order to perform routine battery maintenance (notably, equalization).
In some cases, off-grid solar installations might also include wind turbines or microhydro systems as secondary power sources. These can provide additional electricity when the sun isn’t shining.
As with a grid-connected system with battery back-up, a stand-alone system also features a charge controller to prevent overcharging and battery damage. Unlike with a grid-connected system, an off-grid system draws on the battery during the day and night, whenever energy is needed and is not being provided directly from the PV panels (or wind turbine or microhydro system).
The same disconnects or safety switches are required in stand-alone systems, to allow for safe servicing. Some stand-alone systems also include a low-voltage disconnect (a second charge controller). This cuts the flow of electricity from the battery to the inverter if it detects low voltage in the battery. The reason for this is to prevent over-discharging, or draining the batteries to the point where they become damaged.
Using DC directly
If you’re looking for a straightforward solar installation, one of the systems above should satisfy your needs. However, if you’re game to MacGyver things a little, you might want to consider running some appliances with DC direct from your solar array, bypassing the inverter.
Why? Because inverters use energy when they’re running, and not all appliances require AC for operation. Converting 24-volt DC to 120-volt AC loses about 10% of the energy, which doesn’t sound like much but can really add up, especially if you’re trying to live off-grid and conserve energy.
Water pumps, some consumer electronics, and some refrigerators, ceiling fans, and other appliances can all run on DC. These sometimes cost a little more than those that run on AC, but are often far more energy-efficient overall.
Even if you don’t plan on running much on DC, it’s a good idea to install at least one DC circuit. Why? Because you can use this to power a lightbulb beside the inverter, just in case something goes wrong with the inverter itself or with the system beyond the inverter.
How to choose the right solar installation for your needs
For homeowners looking for the simplest and cheapest option, a grid-connected solar electrical system is the way to go. You can always rejig this system later to add battery storage, wind turbines, a generator, or a microhydro system, or take yourself off-grid entirely.
If you’re short on money or space, a grid-connected system without battery storage is also a smart choice. Batteries cost several hundred dollars and you might need a fair few of them, depending on your energy use and installation size. This can significantly increase your payback period.
Batteries also require quite a bit of maintenance, while a grid-connected solar installation without battery storage is much easier and cheaper to maintain. In most cases, all you need to do is keep the PV panels clean and free of snow.
All in all, a grid-connected system costs less, is far simpler to maintain, and can more easily satisfy local electrical codes.
When to go for backup batteries
If you live somewhere prone to blackouts or rolling brownouts, or you just want to future proof your solar installation, opt for a grid-connected system with storage. You might also want to do this if your utility company requires two meters and pays a lot less for your surplus power than it charges you to buy electricity.
Grid-connected systems with storage and battery banks are also a great choice for homeowners living in places with high electricity costs and those worried about rising prices.
Major solar installers, such as SunRun and SunPower, report dramatic increases in the demand for solar installations with battery storage. Sunrun expected battery installations to increase more than 100% in 2021 over 2020 levels, with around 4% of customers opting for storage.
SunPower reported 27% of its solar customers purchased battery storage directly through the company. And if you’re looking to install a Tesla roof, you probably already know that the company announced in 2021 that it would only sell solar paired with storage.
When to go off-grid
If you are installing a solar electrical system somewhere rural and are more than half a mile from the nearest power line, you might want to consider an off-grid system with battery storage. This is because many utility companies charge tens of thousands of dollars to run a power line to new homes. For the same cost, you could get a very fancy and powerful solar installation, plus a wind turbine or two.
If you do choose to go off-grid, consider sizing up both your solar array and your battery bank. This way, you’re less likely to end up using a generator (which typically means a diesel generator). With a bigger battery bank you’re also less likely to deep discharge the batteries, meaning you won’t have to equalize the batteries quite so often.
Final thoughts on types of solar installation
When choosing a solar installation, consider your future energy needs. Think about whether your family is likely to grow (or shrink!) and if you’ll be acquiring any energy-hungry appliances or installing a charger for an electric vehicle anytime soon. While you might not need to install a huge number of solar panels right away, you will want to get an oversized inverter to meet that future increase in demand.
If you are installing battery storage, consider whether you’ll want to add batteries in the future. Will your chosen storage location safely accommodate more batteries?
To make things simple for the average homeowner, an off-grid solar installation can be run using a power center. This connects all the wires from the solar array, inverter, and battery bank, and houses the charge controllers, disconnects, and meters. While such a center costs a bit more than the separate pieces, it is far easier to install and understand and is more likely to satisfy electrical codes. It also makes things much easier for electrical inspectors, so is a good investment if you’re planning to sell your home anytime soon.
Finally, before settling on a system of any kind, focus on energy efficiency. If you can make your home more energy-efficient, you won’t need as big a system, which will save money, space, and time. The general rule is that a dollar invested in efficiency measures (like insulation) will save you $3-$5 in system costs. That means $1000 in insulation batting for your roof could mean you save $3000-$5000 on your solar electrical system. Need more help sizing your system? We’ve got you covered.