Today's residential solar power systems can take many forms and functions, from a single purpose application such as heating water or cooling attic space to broad application, whole-home total grid power replacement.
Assuming you are relatively new to the solar power game, if you are anything like me you will want to start small, get comfortable with the concepts and products on a manageable scale, then perhaps ramp up with add ons or otherwise larger systems down the road.
Heck, you may even have a skeptical wife, husband, significant other….. for whom you have the need to demonstrate the economics and utility of a limited residential solar power system before scaling up to the 20-acre solar farm you have living in your head.
But enough about me ! Let's continue, shall we?
How To Plan Your Residential Solar Power System
First off, let me just say that if you are new to solar, you will want to focus on the most common residential solar power system in use today; the Grid-Tied system. Period.
The grid-tied system uses the national power grid to store any excess energy you might manage to produce, rather than requiring you to house and manage your own energy storage locally inside a battery bank. More important even, with a grid-tied system, you have total flexibility regarding the size of your solar panel (PV Module) array, its position, and its output, which is much less critical to the overall success of your system than it would be were you planning a total off-grid power system.
The totally off-grid solar power system produces and stores locally 100 percent of all the power you will use on any given day. When your stored power runs out, and, lacking the necessary cooperation from mother-nature, your electric appliance use will be abruptly curtailed for the day.
The off-grid system requires careful planning, unless space and money are irrelevant to you, to ensure that you are producing enough PV module output (enough DC electrical current), to satisfy your household's demand for power.
Planning the off-grid system requires more attention to detail, because it is a self-contained, closed system, and it adds the additional dimension of the battery bank for onsite power storage. Batteries are the heart of this system and are worked hard, and continuously which necessitates diligence in attention and maintenance.
Batteries are expensive, heavy and highly caustic. Batteries can explode, short circuit and prematurely fail. They represent a commitment and may be fine for an experienced individual, but could also be an expensive trial and error, especially the error part, for the un (or under) initiated.
Let me say here that obviously, if you are working on powering a remote cabin, or a boat or anything where tying to the grid is just not an option, then sure, learn about batteries and incorporating them and their required supporting hardware into your system. The main thrust of this article is about planning a residential solar power system, and so I am making a broad assumption that you are in an area within reach of the national grid.
This is the easiest and least expensive way forward with solar power. The grid-tied system connects your solar array to the power grid, and uses the grid to store the power you produce when it exceeds what you use. Since your grid connection is maintained, this system also draws power from the grid when your solar production is not adequate to meet your power demand. Pretty neat.
There is, however, one big disadvantage with a grid-tied system. When the grid goes down, you are just as much ‘in the dark' as you were before you bought those shiny solar panels.
This is due to the grid-tied system safety requirement referred to as self-islanding. When the grid is down, your system will go into its own automatic disconnect so that you are not back-feeding dangerous amounts of power through the power lines and potentially harming power company workers.
Now, you can of course add a battery bank to your grid-tied system and use that as an emergency back up, and even a primary power source, with the grid still available when the PV module as well as battery bank power is insufficient. This is really the ultimate system in terms of flexibility and thrift, however, the cost to implement and maintain a grid-tied with battery backup system is high. This is a highly sophisticated system that is best left to a professional installer, and is more advanced than most DIYer's should take on.
Stuff to Consider
First, you want to look at your power bills for the last year or two and specifically your KWh usage. My power company's website allows me to log in and see a graph of my power usage over time. This is handy when contemplating a system sufficient to reduce or replace this consumption. Knowing what the numbers are is a big first step.
Second, determine the size of the system you need in terms of producing sufficient power to satisfy all, or whatever part of your historical usage you want to replace. Knowing how much power you want to produce allows you to be thinking about where your PV module array will be located. This might be the roof of your residence, roof of an outbuilding, or ground mounted system.
Typically, PV Modules produce about 15 watts per square foot of area. So for every 1000 watts (1kW) of power, you need a 10-foot by 10 foot (100 square feet) of open area, preferably (but not mandatory) facing south.
Your panels need open sky, but they also need open ground! Other words, you cannot mount your panels too close to roof features such as vents and chimneys and other protrusions. Your ground-mounted system also needs to be located away from wells, tanks and other ground-level systems.
How old is your roof? You definitely don't want to invest in a big PV module array and install it on a 30-year old shingled roof. That would be analogous to putting a $3000 paint job on an old Ford Pinto. Sure, it would look all flashy and be an obvious chick-magnet, but, like many things that feel right, it just makes little economic sense.
Removing a year old 600 or 700 square foot solar array, re roofing, then replacing the panels is an unnecessary waste of time, money and effort. If you roof is getting long in the tooth, consider replacing it before tackling the solar project, or, go with a ground mounted array.
PVWatts (PV What's?!)
The National Renewable Energy Laboratory provides a free online calculator: PVWatts, to help you determine the size of the solar array you will need for your location. If you know you must go with a roof-mounted system, it is very important that you determine your roof's pitch (slope) and orientation so you can provide adequate input.
Also, when considering usable area for your panels, panel shading is critical to your real-world power production. Other words, trees and surrounding structures will have a greater impact on your PV module output than their orientation or the direction they face. Its normally advisable to face your panels south, if you live in the northern hemisphere, but quite another if doing so points them straight at the canopy of the 60-foot live oak tree growing there. Better, in that case, to consider another location or point the panels west, or even straight up. Shading must be taken into account and avoided if possible.
PVWatts has a system info page with various design parameters to help you size your system. The calculator is deceptively simple and helpful, or incredibly complex should you want to drill down beneath the surface and tweak the input parameters.
What it allows you to do is change variables such as PV module type and rating, efficiency, location, position, tilt etc, and ultimately arrive at a panel array size whether roof top or ground mounted.
Ground mounted systems, if you have the room, afford the additional option of tracking. Tracking is the ability to point the solar panel array throughout the day at its optimal angle to the sun to maximize its electrical output.
Tracking adds a layer of potentially unwanted complexity to the system, especially with say a dual-axis, motorized tracking system. There are, however, simpler ways to go, specifically with a manually operated system, single axis or even the more common, fixed mount system.
Permits? Homeowners Association?
Once you know the size of the system you want, and where you need to put it, its time to map out a system plan and components and prepare for permitting. This is the time also to work with your homeowners association to clear any hurdles that might exist there as well.
This may also be the time to decide whether to go with a professional installer or if the DIY approach is best for you. You may live in a town that requires an architect or engineer as part of the permitting process. At minimum, even the DIY crowd will want an electrician with experience in residential PV installation to make the final connections and ultimately to help obtain a Permission To Operate (PTO) from power utility.
Doing all the work yourself, from planning and permitting to installing the panels and supporting hardware, can save you half the money you would otherwise spend by using a professional. A typical 5 kilowatt system at an average $2 per watt would, therefore, cost the do-it-yourselfer about ten grand to implement. This same system might run twenty thousand if you hire a contractor. The savings are substantial, but so is the research and the work.
In fact, hiring a pro, at least until 2021 because of the existing 30% federal tax credit for solar, may be the smart move. You want a solar installer who has a PV Professional Installation certification from the NABCEP (North American Board of Certified Energy Practitioners), and an experienced solar system electrician for final connections to the grid.
Going this route is expensive, but is also potentially much faster and, due to their combined experience with the product and installation process, may produce a better overall system. Sure, your ROI (Return on Investment) by going pro takes twice as long, but this is a very long term investment, possibly 30 years or more, so either way, hiring a professional makes sound, economic sense.
What Equipment Should I Use?
Putting thoughts to paper on a grid-tied system design will take some time and research, but there are a couple of things you should know to make better, informed choices.
You will no doubt read lots of material about series and parallel wiring as it relates to PV Modules, and the inverters these modules are wired to. Inverters are necessary because solar PV module output is always DC current and we need AC or grid power to make this system work.
Typically, what happens is that individual PV modules are wired together in series, called series strings, which multiplies the voltage, Groups of series strings are then wired in parallel, which multiplies the amperage.
This power is then routed to the string inverter which is located at or near your home's main breaker panel and electricity meter.
Manipulating the voltage and current from the PV modules is a clever way to modulate it for transmission through the connective wiring to the inverter. PV modules tend toward high current relative to pressure or voltage, so increasing the voltage by employing series strings, takes some of the load off of the string inverter.
Micro Inverters or String Inverter?
PV modules live in the world of DC current, and most residential systems, as well as the national grid, dwell in the AC world. As such, much effort and infrastructure is used to change the DC power your array will produce into the more accessible, AC current. This is the job for the inverter and is so fundamental to the design and implementation of your solar power system that I wanted to focus a little extra attention on it.
First the downside of the micro inverter, just to get that out of the way. It is more expensive to implement than a string inverter. That's it. It is really all upside from there.
Reason for this is that instead of one string inverter at the fuse panel, each and every panel has its own micro inverter with this implementation. So, the expense is significant, but you get what you pay for and with a micro inverter system, what you get is more power and greater efficiency.
Forget series strings and the art of properly grouping panels to maximize output and transmission. With micro inverters, you are working with parallel circuits, and the power from the array is transmitted as AC current, with its lower transmission resistance.
With a circuit wired in series, a poor performing panel, due to shade, dirt, bird dropping, etc, causes the entire string's power output to drop. If you do have space for a PV module array that is 100% in full sun and normal distance from array to panel, then you might even opt to save some money and go with a string inverter.
A micro inverter setup ignores the voltage variations between panels and thus does not lower or equalize output to the lowest common denominator. If your system is partially shaded, or different parts are shaded at different times of the day, or if some of the panels are oriented differently – perhaps on the other side of a roof peak, you will want micro inverters.
Plus, over longer distances, AC power is easier to transmit so this means smaller gauge wire with a micro-inverter system. Smaller wire is easier to work with, easier to sheathe and bury, plus, copper is expensive.
This is the hardware around which you will be designing your system:
- PV Modules – mono or polycrystalline, power output (watts, volts, amps), physical size ?
- PV Modules – how many will I require and how will they be mounted – rooftop or ground based?
- Inverter selection – properly sized to array output if a string inverter. Should be 20 – 30% higher wattage rated than array.
- Mounting hardware – rails, posts, frames, etc.
- Wire types and sizes
- PV wire, 10 AWG, stranded copper, single conductor, UV protective coating, open air connections, no conduit
- Insulated wire, 10 AWG, stranded, run in conduit, connects array to ground components
- Ground wire, stranded, green cover for use in conduits or solid bare copper wire for exposed circuit runs.
- UF Cable – 10 AWG, single pair plus ground wire, direct burial sheathing, used for the ground based array connection to residence hardware.
- DC Combiner – string inverter setup
- Rapid shutdown control – string inverter setup
- AC Junction box – micro inverter system
- AC Disconnect box – both string inverter and micro inverter system
The DIY'er will need a million other things to execute the installation of the array, from junction boxes and conduit, to sealant, connectors, clamps, disconnects, various tools etc, but these can, and should be sourced as locally as possible for convenience’s sake.
What is a Net Meter?
There are a couple of meters required by all grid-tied systems;
- PV Production Meter – used to track your Solar Renewable Energy Certificates (SRECs) for registered systems
- Net Meter – installed by the power company, replacing your original meter, which lacks the ability to run backward as you produce electric power.
The net meter represents the final link in the chain and follows successful final inspection by your permitting authorities, and is installed by the power company to connect your new power generating system to the grid.
Following this event, you must still wait for your PTO notice (Permission To Operate), which also comes from the power company.
With the PTO in hand you are finally, officially finished and ready to go!
Monitoring Your New Residential Solar Power System
It can be exciting waiting for the next power bill to see what savings have been achieved by your new power generating system. In the past, this was really the only way to go…… hook up and wait.
Instant gratification being what it is, (under-rated in my opinion), today's solar systems have many data monitoring system options available, from simple to complex, depending on your setup.
Your smartphone is potentially a brilliant monitoring device, especially when using applications that all you to tap into your micro-inverter output. This will allow you to check individual PV module output, real time and daily/monthly, overall system output – also real time and daily/monthly, and it opens up quite a lot of data recording and sharing capability that gives you insight about the health of your system, at any point in time.
Regardless of whether you opt for micro or string inverter setup, the manufacturer from which you buy your inverter(s) will likely include software you will use over your computer network, smartphone, or simply with its organic, system monitor.
The point here is that today's systems are put together with diverse monitoring capabilities. There is no more connecting and waiting to see what happens. These days, you will know right away how effective and efficiently your new system is operating.
Where To Go From Here?
This overview is designed to give you a birds-eye view of the grid-tied residential solar power system, and introduce you to many of the concepts, hardware and installation aspects with this type of system.
Building your own solar powered electrical system is a big project, but it is also within reach of the average homeowner. There is an abundance of information about this online, YouTube videos, eBooks etc, that will go into as much detail as needed to help get this project off the ground (and onto the roof!).
Here are a few resources you might find helpful, or even critical to your residential solar power project:
- Install Your Own Solar Panels \ Designing and Installing a Phtovoltaic System, Joe Burdick & Phillip Schmidt – eBook and paperback from Amazon.
- US Department of Energy Efficiency and Renewable Energy (NREL) – PVWatt's Calculator
- Planning a Home Solar Electric System – US Dept of Energy \ Energy.gov has some great info about setting up your system.
When all is said and done, whether you accomplish a total, off-grid system, grid-tied approach, or start with a solar attic fan or water heater, you are stepping into the world of self-reliant, unlimited energy and are learning the skills and products that will serve you well and return your investment in time and money over and over again.
Use the power for good! Enjoy the ride.