What to Know Before Installing Solar at Home
Looking into home solar can be exciting but also a bit daunting. Below, we outline a few areas worth knowing about, including components, characteristics, locations, sizing, layout, orientation and additional costs of installing a solar photovoltaic (PV) system.
A typical solar PV system consists of a solar array installed with other components, such as an inverter. An array contains many solar modules wired together, and each module is composed of individual solar cells within an aluminum frame. All of these cells are wired together to give the module its electrical characteristics when struck by a photon of sunlight.
Solar arrays can take many forms, incorporating multiple technologies to create a system that fits specific needs, price ranges and site conditions. Ultimately, what equipment is included will depend on the type of system and where it is located, but here are some potential pieces:
- Inverter: A critical component that turns the direct current (DC) from the solar modules into alternating current (AC), which is used to power loads in a home or building (i.e., appliances, lights and electronics).
- Combiner box or junction box: Typically found on larger systems, a combiner box combines multiple module strings into one pair of conductors to run to the inverter.
- Module optimizer: A small box installed on or near a module that optimizes the power output of that module. It can also isolate a module from the array if it is shaded or has a problem, so total output is only minimally affected.
- Battery bank: In some cases, a battery bank is added for storage. (An inverter that can pull DC energy from both a battery bank and solar array is required.) The batteries are charged with DC energy from the solar array, and potentially from the inverter.
- Charge controller: A charge controller is used to prevent overcharging and over-discharging of the battery bank.
Various solar setups exist, each with its own pros and cons, costs, maintenance needs and use cases. For all types, however, it is useful to ensure that your home is energy efficient. This will help reduce costs and save money when purchasing the array, and may allow you to go with a smaller array size.
Grid-connected Systems: Grid-connected systems are the most common arrangement and are cheapest to install. With this setup, the energy produced from the solar inverter is either used in the home or captured by your electric utility through a meter before it goes onto the grid. Because your home is still connected to the grid, if the solar array does not cover 100% of your energy needs (such as at night), the grid is there to fill in. If, on the other hand, your array produces more energy than you need, you may receive a credit from your utility that can be applied later (see System Sizing section for more information). A downside is that during a power outage, when the utility has to disconnect power, you will lose power as well. For the safety of electrical workers, your array is not allowed to produce if the grid is down. There are, however, some inverters that can power a single outlet, wired into the inverter, during an outage (if it is sunny and your array can produce enough power). Typically, the power output is limited to 1,500 to 2,000 watts, which should support several lights, a refrigerator, phone chargers and computers. It is not enough power, however, to run air conditioning. ProsConsCheapest system typeOffers least amount of energy independenceHome will always have power when the grid is onlineHome will not have power during an outage*Does not take up a lot of spaceRequires minimal maintenanceReduces monthly energy bill
Hybrid Grid-connected Systems with Battery Backup: This design is similar to a grid-connected system, but a small battery bank can be called upon to power your home or critical appliances when your array is not producing, like during an outage. Typically, a hybrid grid-tied inverter is required, which is able to take power from your array and either power your home, sell power to the grid or charge the battery bank. In addition, it can call on energy stored in the battery bank if your home is using more energy than your array can provide or when your array is not producing. How long the inverter keeps your appliances, or entire home, powered depends on the size of your battery bank. Batteries come in many different configurations, and some require maintenance. ProsConsOffers some energy independenceMore expensive upfront than grid-connected systemHome will have energy for a short period during an outageBatteries take up some spaceAble to use or sell stored energy at nightBatteries may require maintenance depending on their chemical compositionLittle to no monthly energy billSmaller and cheaper battery bank than off-grid system
Off-grid Systems: As their name sounds, these systems are completely independent from the grid. In other words, even if there were a citywide outage, your home would still have power. Off-grid systems are the most expensive but offer complete energy independence. A larger battery bank — taking up considerable space — is needed that is typically able to completely power your home for 3-5 days and meet your energy demands through nights, cloudy days and storms. With this type of system, the solar inverter sends energy straight to the loads in your home. If there are none, there is no complete circuit and no energy will flow, but the system will charge up the battery bank until it is full. ProsConsComplete energy independenceVery expensive upfrontHome will always have power if system is sized properlyBatteries may require maintenance depending on their chemical compositionNo monthly energy billHaving an energy efficient home is critical and may add to costsLarger battery bank footprint
You have a few possibilities for locating your solar array. No matter which location you are considering, though, it is helpful to reach out to current solar owners to learn about their experiences and get advice and references for solar installers.
Rooftop: This is the most common placement. Because roof space is typically not used for anything else, locating the array here leaves valuable real estate open for other purposes. There is also generally less shading to worry about and minimal aesthetic impact, as most people install the array flush with their roof. However, your roof may not be strong enough to support the weight of an array and may need repairs or replacement. Though rare, if the array is installed incorrectly, it can cause issues with roof leakage. Most solar arrays last at least 20 years, so it is beneficial to ask current rooftop customers how their situation is holding up post-installation.
Ground-mounted: Ground-mounted systems make it easier to perform maintenance or replace modules because they are more accessible. If there is a lot of shading around your house, the system can be installed in a location that captures more sunlight. However, the farther away the system is from the home, the greater the losses and the lower the performance. Ground-mounted systems also have a larger footprint than rooftop systems. They will likely be cheaper if your roof needs repairs, but more expensive if your roof is good to go.
Custom Design: Custom designs are least common but available to fit particular needs. The type of design can vary, from looking like a solar carport to a dual-use ground-mounted system with a partially shaded garden underneath to a vertical wall-mounted system that offers shade to your windows. The biggest downside to custom systems is price, as they will cost more than other systems.
Other Location-related Considerations
Are there trees, vegetation or other obstructions that will shade your array at certain times of the day? Obstacles like buildings, power line poles, or trees and vegetation that are not on your property are generally impossible to move. In these situations, it may be worthwhile to relocate your array to avoid shading. Obstacles that shade in the early morning or late afternoon are less detrimental to performance than obstacles that shade during peak sun hours, which are typically from 10 a.m. to 4 p.m.
Vegetation on your property that is obstructing the array is easier to manage. Think about whether the extra production you would get from your array makes it worth altering your landscape. If possible, remove trees or obstacles that will shade your array from 10 a.m. to 4 p.m. Early morning and late afternoon shading will not have as much of an impact.
System Layout and Orientation
The ideal orientation of a solar array is facing true south, which will allow the array to generate the most electricity throughout the day. Unlike magnetic south, which is the south on your compass or phone, true south takes into account magnetic declination from the Earth, which varies from year to year. However, orienting your array a couple of degrees off true south will not drastically affect performance, so if you have a building or tree that you cannot move, it may be beneficial to orient your array away from true south to try to maximize production. When performing a site assessment of your home, your solar installer can tell you the best orientation for your array and why. To learn more, check out this reference.
Considering the angle of the array is also important. Having an array angle that matches your location’s latitude is optimal for year-round performance, an angle 10-15 degrees closer to vertical is optimal for winter performance, and an angle 10-15 closer to parallel (flat) is optimal for summer performance.
For aesthetic and cost purposes, many people with rooftop systems choose to place their array at the same orientation and angle as their roof. However, this angle or pitch may not match your latitude, which will affect array performance. (This is not a concern for ground-mounted systems, which can be easily installed at any angle.) For example, North Carolina has an approximate latitude of 36 degrees. For optimal year-round production, you would want the tilt of the array to be 36 degrees from horizontal; however, if your roof is angled at 25 degrees from horizontal and you wish to install your array flush with the roof, it will be optimized for summer performance. In other words, compared to an array angled at 36 degrees, your array will produce more energy in the summer and less in the winter, so there is a balance to navigate between performance and aesthetics when installing a rooftop system.
Solmetric has a tool to visualize the performance of an array at a given orientation and angle. It can be valuable if you are installing a rooftop system on a roof that is not oriented to true south and you are trying to weigh aesthetic value against performance. It does not, however, take into account shading from obstructions.
Potential Additional Costs
As with any home improvement project, certain issues may come up that cost time and money. Here are some to be aware of.
You may need to install a subpanel or have your utility upgrade your electric service. If you do not have enough free circuit breaker slots to connect your inverter in your main breaker box, a subpanel will be needed to accommodate the additional breaker or breakers.
Most home main breakers are rated for 100 amps; however, with the addition of a solar array, this amount may not be sufficient to handle your normal loads and the production of the solar inverter. In this case, you will have to upgrade your utility service to a 200-amp breaker.
Both situations will require the help of an electrician or a solar installation company, and you will need to inform your utility that you are performing this work.
In addition, as mentioned earlier, you may look to clear branches or trees to improve system performance, which may require an arborist. It is important to cut only vegetation on your property or to obtain consent from your neighbors for anything on their property.
The first step to sizing your system is knowing your energy bill and past usage in monthly and annual kWh consumption. This information should be available on your utility’s account portal. It is useful for determining what percentage of your energy consumption you want to supplement with solar, and is handy for installers.
If your solar array produces more energy than you consume in a month, utilities and co-ops will typically either pay you for the difference or add a credit to your account, which can be used in the future if solar production does not meet consumption. However, utilities can have different restrictions on how these credits roll over, so check with yours for details.
Your utility’s credit policies will be useful to know when determining your desired array size. If your utility provides a credit that runs out at the end of the year, it may not be in your best interest to size an array that meets 100% of your energy needs, as any surplus or credit will not carry over to the next year. To save money on installation and material costs and take advantage of your utility’s payment/credit system, it may be wise to size an array that covers 50-80% of your energy needs. (In North Carolina, average residential electricity consumption is approximately 1,100 kWh per month.)
It is useful to have an idea of your preferred system size before talking to installation companies. They will be able to help you determine what size you ultimately need, but having this knowledge will allow you to better participate in the process.
Conclusion and Next Steps
There are a number of items to consider to ensure you end up with a PV system that meets your needs, but if you’ve gotten this far, you’re on your way. Whenever you’re ready to take next steps, check out our follow-up article on finding a solar installation company, navigating pricing and incentives, and reaching out to your utility.