Solar Power System Design

What is a solar power system?

A solar power system is made up of multiple photovoltaic (PV) panels, a Dc to AC power converter (called inverter) and a rack system that holds the PV panels in place.Solar Photovoltaic (PV) panels are generally fitted on the roof. They should face in an easterly, northerly or westerly direction. The panels should be tilted at particular angles to maximize the amount of sunlight that hits the panels.

Solar PV panels on the roofs of homes and businesses generate clean electricity by converting the energy in sunlight. This conversion takes place within solar panels of specially fabricated materials that make up the solar panels. It is a process that requires no moving parts. In most cases solar panels are connected to the mains power supply through a device called a solar power inverter.

System Components

 Basic components of grid-connected PV systems with and without batteries are:

 • Solar photovoltaic modules

 • Array mounting racks

 • Grounding equipment

 • Combiner box

• Inverter 

• Meters – system meter and kilowatt-hour meter 

• Disconnects:

                          - Array DC disconnect

                          - Inverter DC disconnect

                          - Inverter AC disconnect

                          - Exterior AC disconnect

 If the system includes batteries, it will also require:

 • Battery bank with cabling and housing structure

 • Charge controller

 • Battery disconnect 

Solar Power System Design

Solar Power System Design for the home.

The general layout of a residential solar power system design is shown in the image below (thanks to the Dept. of Energy). This article discusses the different components of designing a Solar Panel system for a home.

Solar Power System Design Step 1 - Solar Panels Capture the Sun's Energy

Solar panels on the house roof (or other area that isn't easily obstructed) capture and convert the sun's energy into electrical energy. Residential solar panels typically provide a voltage in the range of 12-48VDC. We discuss DC voltage in our DC vs AC post 

Solar Power System Design Step 2 - A Junction Box Combines the Solar Panels

A junction box is where the different solar panels are tied together - typically in parallel to provide more current. In the above solar power system design diagram, there are 6 panels tied together. If a junction box is used, the wire from the solar panel to the junction box can be a smaller gauge (actually a higher gauge number). If the solar panels were tied together on the roof, the wire would have to handle the combined current of all the solar panels. Also, if a solar panel had a problem, it could drain the energy that the other panels are providing. A good way to isolate each panel is to use a blocking diode on each solar panel string inside the junction box.

Solar Power System Design Step 3 - Storage Battery Bank

Although it is not shown in this solar power system diagram, the excess energy could be stored in storage batteries. The solar panels would keep the batteries charged. Typically a charge controller is used to maintain the battery bank at optimal charge and also prevent overcharging.

 If a battery bank is used, the battery bank would be connected to the solar panels in the junction box or a separate junction box. These batteries would attach to the solar panels on the wires before they feed into the DC disconnect and then the inverter.

Solar Power System Design Step 4 - The DC Disconnect

The DC disconnect is a safety device used to isolate the solar panels from the inverter. This is necessary for maintenance and troubleshooting of system problems. The DC disconnect typically consists of a breaker switch housed in a normal electrical junction box.

Solar Power System Design Step 5 - The Inverter Converts the DC to AC

An inverter converts the DC voltage into an AC voltage. Most houses and appliances use an AC voltage (that is what a standard outlet is). They will convert the 12 to 48VDC to 120VAC. If the homeowner is getting AC power from the power company (the grid), they will need a grid tie inverter. These inverters match the AC wave to the AC wave coming from the power company. If the house doesn't have AC power attached, a regular inverter can be used. For instance, a summer cabin in the mountains wouldn't require a grid-tie inverter. Grid tie inverters are typically more expensive than normal inverters.

Solar Power System Design Step 6 - AC Disconnect

This is where the Inverter connects to the house wiring and by extension, the power company's meter. Similar to the DC disconnect, this is used to isolate the solar power system from the house and/or the grid. This is useful for maintenance and troubleshooting as well as blackouts where we don't want to power the entire neighborhood - only our house.

In many cases AC disconnects are required by the utility company for their use and are typically located near the meter.

Solar Power System Design Step 7 - Power from the Utility Company

As you can see from the solar power system design diagram, electricity is also supplied by the power company via power lines. Their power goes through a power meter before entering the home. The power company checks this meter each month and bills the homeowner according to the amount of electricity used.

Solar Power System Design Integration - Solar Power Supplements Utility Company Power

In the above solar power system diagram, a double arrow is drawn between the inverter and the power meter. In theory, if the solar panels are supplying more electricity than is used, the meter will turn backward because the power will be sent back out on the power lines. Unfortunately, many newer power meters only turn in one direction - the direction that energy is consumed by the homeowner.

However, the solar panels do supplement the power used by the home. If a dryer is being used on a sunny day, the amount of power consumed is the same but a portion of the power is supplied by the solar panels so the meter will turn slower and indicate that less power is used.

Advantages to Solar Power Systems

It is apparent from the above picture and discussion that having solar panels will reduce the power supply burden that the power companies must supply and transfer on their transmission lines. In the future this will become more important. No one wants a repeat of the rolling blackouts, and this is a great solution.