What Types Of Solar Power Systems Are There?

Solar power systems are classified by how they connect to the utility grid and how the electricity is used. There are four main types: grid-tied systems, off-grid systems, hybrid systems and pure DC systems.

All four use essentially the same solar panels. What differs is whether there is a grid connection, whether there is a battery, and whether the power is delivered as AC or DC. Which one is right for you depends on whether the grid is available where you are, how electricity is priced, and how much a power outage would hurt.
 

Here is a side-by-side comparison first, followed by a closer look at each type.
 

1. Grid-Tied Solar Systems: Feed Electricity Directly into the Grid

How it works

During the day, the panels produce DC electricity. A grid-tied inverter converts it to AC that matches the grid's frequency and phase. The power first supplies your own loads, and any surplus is sold to the grid. At night or on overcast days, when the panels cannot cover your demand, you buy power from the grid. No battery is involved.

What it consists of

Solar panels and mounting structure: the panels turn sunlight into electricity, and the mounting structure sets the tilt angle and wind resistance.

Grid-tied inverter: the heart of the system. It performs maximum power point tracking (MPPT), converts DC to AC, and provides grid-interconnection protection.

DC-side protection: DC cables, DC switches and a combiner box (small string-type systems often omit the combiner box).

AC distribution box: contains circuit breakers and a surge protection device.

Meter: a generation meter or bidirectional meter used to settle the electricity exported to the grid.

Lightning protection, grounding and monitoring: these keep the system safe and let you check generation data remotely.

Where it fits

It works best where daytime electricity use is high and the grid is stable: self-built houses and villas with usable roof space, and factories, warehouses, supermarkets and schools that operate during the day. It has the lowest investment and the simplest structure, and it is the type with the largest installed capacity worldwide.

Examples and recommendations

Self-built rural house: with roughly 60 to 80 square meters of roof area, you can install about 8 to 10 kW. Choose a single-phase or three-phase string inverter. Annual generation depends on local sunshine, so estimate it using local irradiation data.

Factory building: a large roof and high daytime load suit a 300 kW to 1 MW system, used mainly for self-consumption with surplus exported to the grid. Payback is usually shorter than for residential systems.

One thing to keep in mind

A grid-tied system shuts down automatically when the grid goes down (anti-islanding protection). That means a house with a grid-tied system still has no power during an outage.
 

2. Off-Grid Solar Systems: Completely Independent of the Grid

How it works

Power from the panels charges the battery first. When loads draw power, the battery supplies them through the inverter. The system is self-contained and has no connection to the utility grid.

What it consists of

Solar panels and mounting structure

Solar charge controller: charges the battery and protects it, usually an MPPT type.

Battery bank: lithium iron phosphate, lead-carbon and gel lead-acid batteries are all used. Battery capacity determines how long the system can run without sun.

Off-grid inverter: converts the battery's DC power to AC. Many products combine the controller and inverter in a single unit.

Distribution and protection equipment

Backup generator (optional): an additional source during long spells of cloudy or rainy weather.

Where it fits

Places with no grid, or where connecting to the grid costs too much: islands, grazing land, border outposts, mountain homes, remote research stations and telecom base stations.

Examples and recommendations

Herder's home: with daily consumption of about 5 to 8 kWh, a setup of around 3 kW of panels, about 10 kWh of battery storage and a 3 kW off-grid all-in-one unit can run a refrigerator, a TV and lighting. Stagger the use of high-power appliances.

Sizing tip: size the battery by the number of consecutive cloudy days you want to cover. Reserve 2 to 3 days as a rule, and more where sunshine is unreliable.

Most of an off-grid system's cost goes into the battery. Battery lifespan has a large effect on total cost, so do not judge by upfront price alone.
 

3. Hybrid Solar Systems: Grid-Tied Plus Storage, with Grid Power and Backup

In the industry, this type is more often called a hybrid grid-tied/off-grid system or a solar-plus-storage hybrid system. It adds a battery to a grid-tied system, so it can interact with the grid and also supply power on its own during an outage.

How it works

Daytime generation serves the loads first. Surplus power charges the battery, and once the battery is full, the remainder is exported to the grid. At night the loads draw from the battery, and when the battery runs low, from the grid. When the grid goes down, the system switches to off-grid mode and keeps powering critical loads through its backup port.

What it consists of

Solar panels and mounting structure

Hybrid inverter: combines the functions of a grid-tied inverter and a battery inverter in one unit. It is the key piece of equipment that sets this system apart from the previous two.

Energy storage battery: residential systems currently rely mainly on lithium iron phosphate.

Smart meter or current transformer: measures household consumption and the power flowing to and from the grid, which the system uses to decide when to charge and discharge.

Energy management system (EMS): sets operating strategies, such as charging and discharging according to time-of-use electricity prices.

Backup load panel: critical loads such as the refrigerator, lighting and network equipment are wired to the backup port.

Where it fits

Areas with frequent outages or an unstable grid

Places with a large gap between peak and off-peak electricity prices, where you can charge when power is cheap and discharge when it is expensive

Users who are sensitive to power interruptions: home offices, livestock farms, cold storage and small clinics

Examples and recommendations

Villa household: 8 to 10 kW of panels with 10 to 20 kWh of battery storage. Connect the refrigerator, lighting, router and some outlets to the backup port. Whether heavy loads such as air conditioners can be included depends on the inverter's backup output power.

Livestock farm: install a grid-tied system with storage so ventilation, heating and drinking-water equipment keep running during an outage.

A hybrid system costs more than a grid-tied one. The extra money buys two capabilities: backup power during outages and price arbitrage. Whether it pays off depends on how often outages happen locally and on your electricity tariff.
 

4. Pure DC Solar Systems: DC Power Without Inversion

How it works

The DC electricity from the panels is not converted to AC. It goes straight to DC loads. Some systems include a battery and controller, and some have no battery at all: when the sun shines the load runs, and when it does not the load stops.

What it consists of

Solar panels

DC controller (only needed in systems with a battery)

Battery (optional)

DC loads: LED lights, DC water pumps, DC fans, cameras and similar equipment

Without an inverter, the structure is the simplest of the four, and there is one less conversion step where energy is lost.

Where it fits

Places where the load is itself DC, the power is small and the equipment is spread out: solar street lights, garden lights, solar water pumps, farm irrigation, traffic signals and surveillance equipment, and small communication devices.

Examples and recommendations

Solar street light: a common configuration is a panel of a few dozen watts, a lithium battery and a controller. The light turns on automatically at night, and no cabling is needed.

Solar water pump: the panels drive a DC pump directly. The stronger the sunshine during the day, the more water is pumped into a storage tank for later use. You can leave out the battery and save a major cost.

Its limits are clear. It cannot power ordinary household AC appliances directly, and the power level cannot be very large.

5. How to Choose Among the Four Systems

Work through these questions in order:

Is there a grid? If not, choose off-grid or pure DC. If so, go to the next question.

How much would an outage hurt? If a lot, choose a hybrid system. If not much, choose grid-tied.

Are your loads AC appliances or DC loads? If you only need to power DC loads such as street lights or pumps, pure DC is enough.

What is your budget? For the same solar capacity, grid-tied is the cheapest. Hybrid and off-grid systems add the cost of batteries.

FAQ

Q: Why does a grid-tied system not work during a power outage? Because the inverter has anti-islanding protection. If the system kept feeding power into a dead grid, it would endanger utility workers making repairs, so it must disconnect automatically. If you want power during outages, choose a hybrid system.

Q: Can an off-grid system be converted to a hybrid system later? Yes, but it depends on the existing equipment. If the original system uses an off-grid inverter, it usually has to be replaced with a hybrid inverter. The panels and mounting structure can generally be reused.

Q: Is a pure DC system more energy-efficient than an AC system? It loses less energy because there is no inversion step, but only if the load is already a DC device. Buying DC appliances just to save on conversion losses usually costs more than it saves.

Q: Which type is the best value for a home? If the grid is stable and someone is home using power during the day, grid-tied is the best value. If outages are frequent or the gap between peak and off-peak prices is large, consider a hybrid system. Payback depends on local electricity prices, incentive policies and your actual usage, so ask a qualified local installer for an estimate.