What Do I Need to Know for Roof Top Solar? | The Light Lab

What to Know Before Installing Roof Top Solar

Thinking about some Do-It-Yourself (DIY) home improvement projects for your Texas home, but you’re not really sure about what to do or where to start? You’ve come to the right place! Welcome to the DIY Energy Efficiency Tips series from First Choice Power. We’ll show you how to improve the energy efficiency of your home, including hints that make the jobs easier.

What Do I Need to Know for Roof Top Solar? | The Light Lab

What do I need to know for roof top solar?

With solar photovoltaic (PV) panels getting cheaper and cheaper in recent years, more Texas homeowners are thinking about installing solar power arrays. Many have already found out there is a LOT of hype that winds up raising more questions than answers. Because deciding about installing a solar array for your home is complicated, we’re going to unpack this complicated and confusing process to help you better understand the costs and benefits.

Finances and Incentives

The big reason for getting into residential solar is generating your own energy to bring down your monthly energy bill. After all, if you can make even a portion of your own energy, you’ll not only avoid the cost of energy from your provider but also be more likely to use a little less energy. For years, it’s been known that home solar panels also enhance the value of your home. A study by Lawrence Berkeley National Laboratory found that home buyers were willing to pay $15,000 more for a house equipped with a mid-sized 3.6 kilowatts (kW) solar array versus a similar home without one.

Paying for a solar array, however, is another thing. While prices have dropped dramatically by 29% since 2015, they still cost thousands of dollars. Fortunately, there’s a federal tax credit that will give you a 30% tax break on solar systems placed into operation by 2019. Factoring that into the cost pulls the price of a 10 kW system to an affordable range of $19,700 – $25,600.

Another important financial consideration for a residential solar is system payback, which depends on several factors:

  • The energy your system actually generates.
  • The price of electricity in your area.
  • The total cost of your installation.
  • How you choose to pay for your solar installation.

Apart from the federal tax credit, Texas hosts many other incentives that also bring down the cost of installing solar. For example, in current Texas property tax code, the value that a solar-power or other renewable-energy installation adds to the value of the property is exempt from tax. Variations of this are also available for businesses, too. Many cities in Texas still have incentive programs. Lastly, the Texas PUC’s Energy Efficiency Rule requires TDUs to offer energy efficiency programs to customers within their respective service territories. Currently, only two TDUs are offering solar incentive programs:

Oncor— ​Solar Photovoltaic Program

AEP Texas— SMART Source Solar PV Program

Leasing a solar array is another financial means to reducing cost. Solar leases are available from third party owners through a traditional lease agreement or through a power purchase agreement:

  • Traditional lease —the third party builds the array on the house and the customer pays for the use of the solar system over many years.
  • Power purchase agreement —the third party builds the array on the house and the customer pays a specific rate for the electricity generated each month.

Can I sell my extra electricity back to the utility?

Known in other states as “net metering”, Texas does not have state-wide net metering. The PUC prohibits single meters that subtract out-flow from in-flow within the meter. Instead, meters use two separate channels to measure the in-flow and out-flow energy. These amounts are reported to your TDU every 15 minutes and sent onto to your REP. REPs are not required to purchase your surplus and currently only a few Texas REPs offer surplus power purchase programs. Be sure you keep this in mind when deciding on the size of your solar array. Unless you intend to include battery storage, any excess power you generate without being able to sell it will just be wasted.

Decisions, Decisions

You also need to decide on your power needs, your goals, and your plans.

  • How much electricity do you use each day? How likely is it that your power needs will change over time, especially if you are raising a family?
  • Off the grid with batteries or grid-tie? Grid tie with batteries? Having a grid tie is a convenience but some TDUs plan to charge solar array owners extra fees for grid-tie service. Batteries are also convenient in grid-tie set ups but significantly add on to the cost.
  • Is your goal a zero-energy home? Zero-energy homes make as much energy as they consume while producing no carbon emissions.
  • How long do you plan on staying in your home? Average lifespan (capacity declines to 80%) of a solar panel is 20 years. (NOTE— Remember, this could be offset by swapping in newer, more efficient, and probably cheaper panels as they come to market over time.)

What Do I Need to Know for Roof Top Solar? | The Light Lab

Knowing What’s Watt—Figure Your Usage

In order to understand how big a solar array you’re going to need, you’ll have to know how much energy you use. To do that, you need to list all the electric appliances you use (such as HVAC system, electric water heaters, washers, dryers, ranges, microwaves, fans, etc) and add all that power usage together. Calculating usage can be tricky. One common misconception is that home size is a factor. The fact is, the square footage of your home is irrelevant. A 1,500 square foot home doesn’t use any energy; it’s the people living inside that do.

To figure your energy usage, you need to know how many watts your appliances use. The power (watts) required to use an appliance in your house is not measured the same way as your utility bills, which show watt-hours. The wattage of an appliance is how much energy it uses during any given moment it’s being used. For example, if you’ve got a refrigerator that rated to use 700 watts AC, then that’s how much power it needs to run. If you have a solar panel array that can only supply 100 watts, then the refrigerator will not work.

Watt-hours measures the use of energy over time. In the case of our refrigerator, it uses 700 watts per hour. That means during a full 24-hour day, it roughly consumes 16,800 watt-hours or 16.8 kWh.

With that in mind, the best way to determine your electrical usage is to review your monthly utility bills because they summarize your usage over time. For example, let’s say you use an average of 1000 kWh per month. That divides out to 33.33 kWh per day. The next step is to find out what electrical appliances and devices are being used, how many watts they consume, and how long you use them. To compute kWh of a device or appliance, multiply the watts times the hours it runs during the day — such as our refrigerator above. For smaller appliances (such as a vacuum cleaner), you can approximate their wattage by multiplying their volts by their amps.

Knowing What’s Watt—How Much Capacity

Once you know how big your usage load is you can then calculate how much power you’ll need to generate. Most residential systems are rated at less than 50 kilowatts (kW). There are two things to remember:

First, you can have the best, most efficient solar panels on earth but if they are in an area that gets very little direct sunlight for only a few hours a day, they won’t perform well. That’s because the amount of power that a system can generate during a day depends on its physical location on the planet. Called “insolation”, it is a ratio of the kWh per square meter per day that is determined by the angle of the sun, the weather, atmosphere, elevation, and location on the globe. The intensity of power and the length of time it’s available drops the further north or south you go from the equator. Insolation in Texas is among the best, ranging from 6 in the west to 4.5 in the east.

With that in mind, take a critical look at your roof. Your solar array’s effectiveness will depend on:

  • The roof’s area, because it could limit the number of panels you can put in place. You may find that your roof space is inadequate. If that’s the case, there are plenty of other ways, such as free-standing frames, to support solar panels.
  • The roof’s orientation. Roofs facing towards the south/southwest have optimum insolation, especially during late summer afternoons during peak usage hours.
  • Roof shading. Is the roof shaded at any point during the day? Trees and shrubs may be cut down but neighboring buildings can be problem.

Second, the efficiency of a solar array depends on the efficiency of the hardware handling the electrical current:

  • The solar panel outputs electricity in Direct Current (DC). The average energy efficiency of a solar panel is 14 to 17%. Higher-end panels have reached over 20%. The better your solar panels are at converting sunlight to electricity, the more power you’ll have to use.
  • An inverter converts and conditions the DC current into AC for use in your home. Some of the power is lost as heat during the conversion. A 5% loss may sound small but when it’s coming from a 5000 watt array, that means it’s losing up to 250 watts. While efficiencies on most inverters are now in the high 90s, settling for a cheap inverter may wind up costing you a lot of energy.

Texas Interconnection Rules —Paperwork, Inspections, and Fees

For the experienced DIY person, installing solar panels on to a roof isn’t too complicated. Many Texas cities and towns do require inspections as part of the building permit process but this is alone doesn’t clear your solar installation to begin generating electricity.

All homeowners with solar arrays must go through the interconnection application and inspection process with their TDU. Even if your array is small and will not be sending out electricity onto the grid, it must meet interconnection requirements and be certified to be safely connected. The interconnection process will include a study and a fee (though some fees are waived depending on the size of solar installation), plus specific system requirements, so it pays to get familiar with this process while you’re in the planning stage. Specific information about application requirements and fees is all available from your TDU:

CenterPoint Energy
AEP Texas
Texas-New Mexico Power (TNMP)


Vernon Trollinger is a writer with a background in home improvement, electronics, fiction writing, and archaeology. He now writes about green energy technology, home energy efficiency, the natural gas industry, and the electrical grid.