Solar Energy Systems Options
As you have probably discovered, installing solar power for your home is a great way to become energy independent, help the environment and save a lot of money. Now that you understand the benefits of solar energy and the potential your home has for the installation of solar panels; the next questions are: which type of system is best for you and what are the differences?
There are many different kinds of solar energy systems but all of them can be categorized in to three main categories: Grid-tied, Off-grid, and Hybrid.
Grid-Tied Solar Systems:
Grid-tied solar systems consist of PV (photovoltaic) panels, a DC-AC inverter and a net metering device to keep track of used and produced electricity purchased from or fed back to the utility company. Your solar panels collect photons from the sun in the form of DC (direct current) electricity and send that electricity to your inverter. Your inverter converts the electricity harnessed by your panels to AC (alternating current) electricity and sends that energy back to the utility grid. The energy sent back to the grid is then “stored” for you to use or as a credit. Essentially you are using the utility grid as a giant battery bank.
There are a few aspects of grid-tied solar you should be aware of. Grid-tied solar systems are exclusively dependent on the reliability and functionality of the grid. In most cases the energy produced by your solar panels is converted and put back on the grid by your inverter but does not actually supply your home with electricity.
Because of this correlation between the status and quality of your grid electricity and several safety reasons, when the grid power is down so is your solar system. You lose the ability to supply electricity back to the grid until the grid returns to a normal and consistent state.
It is legally required that all grid-tied solar systems in The United States shut down when the electricity from your utility company goes off. The workings of a grid-tied solar system require the inverter to “top” the flow of incoming electricity from the utility company in order to feed it back into the electrical line. Therefore, if your system were to remain on while an employee of the electric company where repairing a damaged power line near your home, you could very easily be pumping 1,000’s or tens of 1,000s of watts back into the line creating a dangerous scenario.
In summation, hands down grid-tied systems are the least expensive, the easiest to install and maintain and have the longest lifespan with no moving parts or components that need to be replaced during the effective lifespan of the system.
Off-Grid Solar Systems:
Off-grid solar systems mean just that. They are designed to run in isolated areas and function completely independent of the utility grid. Off-grid solar systems have several additional components necessary for the system to work. Solar power can only be produced during the day and when there is sun.
With an off-grid system the DC power collected by your solar panels is sent to a device called a charge controller. The charge controller takes the incoming power from the panels and sends it to a battery or bank of batteries in which the electricity is stored.
The charge controller is responsible for filling the batteries when they are low or stopping the electricity from the panels from reaching the batteries when they are full. The stored DC electricity in your batteries is then sent to an inverter, converted to AC electricity and sent throughout your property for use when you need it.
Off-grid systems are a lot more expensive than grid-tied systems due to the added cost of batteries, one or more charge controller as well as other protective devices and cabling. Typically an off-grid system is also designed with a slightly larger solar panel array than a standard grid-tied system to make sure you have enough power for your daily use and to keep your batteries full and prepare you for days without sun.
There are many benefits to having an off-grid system. Besides having power where there is otherwise no other available option (remote locations without access to the grid) the most attractive aspect of off-grid living is being 100% independent of utility electricity. You are harnessing, storing and using all of your electrical needs. Moreover, with a properly designed system, you won’t be running out of power for several years before you need to consider replacing your battery bank.
Hybrid Solar Systems:
The main distinguishing feature of a hybrid system is that it uses both DC electricity stored in your battery bank and AC electricity from the grid to make one seamless system. Hybrid solar systems take the luxury of having energy stored in batteries and make it available for your use when the grid-is down, during storms, natural disasters as well as any other situation in which you may lose electricity from the utility company.
The design of a hybrid system essentially makes your standard off-grid system limitless in the power it can provide. With a hybrid system your inverter uses electricity from your batteries (which charge from the charge controller and ultimately the panels and sun) and power from the utility company.
In a typical off-grid solar system you are limited by the power stored in your batteries and the maximum possible output of your inverter. In the above off-grid photo you can see there is a 3000 watt inverter being used. This means at any given time the customer cannot use more than 3000 watts. With a hybrid system you are only limited by the inverters rated output when you are using power stored in the batteries. This is because your inverter does not have to convert the connected grid AC electricity; it simply needs to pass it through to the loads in your house.
This type of system has become a lot more common in recent solar history due to the luxurious aspect of having electricity all of the time (even when the grid is down), taking advantage of tiered pricing from the utility company (only using grid electric when the rate is at its lowest during the day) and for the protective role it plays to prolong the life of appliances and electronics in your home.
As previously discussed, a strictly grid-tied inverter shuts off when the grid goes down or the grid input is above or below an acceptable voltage. These spikes and drops in incoming grid voltage can be detrimental to the lifespan of your electrical components; especially sensitive electronics and products with motors and compressors.
With a hybrid system, when the AC input to the inverter is above or below a certain threshold the inverter will switch to back-up battery mode automatically to provide the purest and most stable electricity possible. For restaurants, hotels and other service-based businesses in remote areas, the peace of mind associated with energy back-up and device over and under-voltage protection can be a nearly priceless commodity.
This holds especially true for hospitals and nursing homes where an electrical outage can create worse problems than a failing refrigerator compressor or a freezer of bad food after a day without power. The benefits of hybrid systems are most significantly acknowledged in the overall cost of the system. For this added luxury there is undoubtedly a significant price to pay.
So What System is Right for You?
Now that you understand the primary differences and benefits each system carries it is time to sit down with your installer and talk about which type of system best suits your needs. Is it simply a return on investment with a grid-tied system? The beauty of off-grid living and electrical independence by storing produced power in batteries? Or perhaps it is the best of both worlds, creating a seamless hybrid system to handle any blackout, natural disaster or power surge and keep you running clean and green.
If you're still not sure which system is right, get more information by reading our blog posts How to Assess Your Home's Potential for Grid-Tied Solar Energy and 6 Steps to Designing an Off-Grid Solar Power System.
This post was written by: Kyle Johnston
Originally from Easton PA, Kyle Johnston is a solar installer and owns and operates Lux Aeterna Solar Energy in Antigua, Guatemala. He provides system analytics, product comparisons, finance studies, energy audits and everything else to make the switch to renewable energy easy for his customers.