Shopping for Residential Solar —How to Shop for Home Improvement Projects

By Vernon Trollinger, May 1, 2017, Energy Efficiency, Green, Home Improvement, Save Money

While most homeowners love their homes, not every home is perfect. There are one or two things the homeowner would like to change, such as an outdated bathtub for a new walk-in shower or updating the look of their kitchen. And then there’s occasional “uh-oh” of the unexpected repair. We’re going to identify several home improvement projects and some of the ins and outs of what you can expect.

How to Shop for Residential Solar

When it comes to residential solar panels, most homeowners love the idea of being able to make their own electricity and sell part of it to their local utility. As long as the sun shines, you don’t need to worry about having a high electric bill. While home solar’s past costs made it prohibitive, new materials and processes have drastically reduced the price of solar panels and inverters to the point where the average 5,000 watt array (installed) costs $15,000 (before tax credits). And even if you set up a system that only partly covers your electricity consumption, the amount of solar power you generate will offset what you would have normally purchased from your utility. The energy those panels will pay for themselves sooner.

But don’t start ordering a stack of solar panels just yet or sign up with the first installer you see. Going solar isn’t all that simple and you could easily wind up paying thousands of dollars more than you need to. That’s why were going to cover all of those important things you need to know before you start shopping for a residential solar installation.

Shopping for Residential Solar —How to Shop for Home Improvement Projects | Bounce Energy Blog

Is My House Ready for Solar?

How well a photovoltaic (PV) system performs is directly related to how much sunlight it receives. Solar radiation that area receives is measured in watt/square meter (W/m2). Factoring in the amount of time it’s available, the ratio becomes kilowatt-hours per square meter per day (kW·h/(m2·day). This ratio is called “insolation”. The more direct and uninterrupted a region’s solar radiation is, the higher the amount of insolation. Not surprisingly, insolation is highest in dry regions close to the equator, such as the southwestern US, than it is in rainy northern climates.

Of course, Texas is one the best places to live if you’re going to install solar onto your home since both the eastern and western parts of the state have high insolation ratios, averaging from 5.0 in the east to over 6.5 in the far west for the year. However, there are several other factors that effect insolation at your home:

  • Your roof— the direction it faces and its pitch. A roof facing towards the south west with panels tilted so sunlight strikes it close to 90° will make more electricity longer during the day.
  • Local weather —cloudiness and temperature. Clouds block the sun and heat reduces a panel’s efficiency.
  • Shade — trees and neighboring buildings that reduce sunlight.
  • Soiling —the amount of dirt and dust that can accumulate on the panels.

If you can’t use your roof, you can build a frame to hold the panels. While frames add to the cost of building, they reduce the labor cost because they are lower to the ground and make maintenance easier.

You can calculate your areas’ specific monthly insolation values throughout the year and get a better of its potential output and value by using NREL’s free tool.

Shopping for Residential Solar —How to Shop for Home Improvement Projects | Bounce Energy Blog

How Many Panels Do I Need?

For a rough estimate, you can multiply your home’s square footage by 2 watts per square foot. For example, the average square footage of a US home for the past 10 years has been 2,400 to 2,600 square feet. Divide 5,000 by 200 watts (DC panel wattage) and you get 25.

Again, that’s a rough estimate. Different houses and different occupants use energy in different ways. For that reason, the most cost effective way to find out how many panels you need is to calculate your total electrical usage in watts by adding up the wattage of all your appliances and electronics. It can get a little complicated but there’s two basic ways of doing this:

  • Use last year’s electric bills. The amount is shown in monthly kilowatts/hours (kWh) but you’ll need to convert that down to watts per hour to get a more accurate estimate. The reason is that appliances need a certain amount of power to run or they just won’t work. For example, if you’ve got a refrigerator that is rated to use 700 watts AC, then that’s how much power it needs to run every second. A solar array must be able to put out more than 700 watts every second to run that refrigerator. To find your average hourly load usage, find your average monthly electrical load. Divide that number by 30 days and then by 24 hours and you’ll have an average watt usage per hour. You can also track your usage on-line through your Bounce Energy Account.
  • If you don’t have your old bills, you can still calculate the electrical load of your home by adding up the usage specs of all your appliances and electronics from either their nameplates (usually found in the back), in their manuals, or from their manufacturers’ websites. Some appliances may only show their amperage. Although calculating wattage for AC is a little different than DC, you can still use the same formula to calculate the wattage. Multiply the standard household AC voltage (120 volts) by the appliance’s amperage to get a good approximation of the wattage. For example, a 10 amp vacuum cleaner running on 120 volts AC uses about 1200 watts.

The average Texas home uses 1,174 kilowatt-hours (kWh) of electricity per month, or 1.6 kWh of energy per hour.

Remember, your biggest appliances use the highest wattage. This includes central air conditioning (the biggest), laundry machines, water heaters, refrigerators, ovens, stoves, and dishwashers. Also keep in mind the number of appliances that are used or at least plugged in at the same time; such as the refrigerator and the TV, air conditioning, and WiFi. Add these wattages together. You want to have a solid idea of how much electricity you use all at once. If you know what appliances are used and how long they run each day, that gives you a more accurate picture of your electrical load. Also, be mindful that appliances with motors pull extra current when they start up. This in-rush amount should not be higher than the system’s inverter capacity.

Shopping for Residential Solar —How to Shop for Home Improvement Projects | Bounce Energy Blog


What Equipment Will I Need?

Solar Panels— These are composed of individual solar cells. Each is really a sandwich made from a polycrystalline silicon wafer. Now, each silicon atom has a swarm of electrons orbiting the nucleus. The electrons close to the nucleus are kept tightly nearby. But the electrons on the outer orbits yearn to fly off in search of a negatively-charged pole. When a photon of light enters the cell, one of the polycrystalline silicon cell’s electrons absorbs the photon’s energy. The extra burst of energy ejects the electron from the silicon atom and the electron joins other liberated electrons flowing toward the negatively charge pole. This flow of electrons forms the electrical current.

Solar cells individually produce very little electricity, about .5 volts. Wired up in a series to form panels, they can produce a lot of electricity, up to 12 to 17 volts at 200 to 400 watts. The amount of electricity produced per panel depends partly on how efficiently the panel can convert sunlight to electricity. The average energy efficiency of a solar panel is 14 to 17%. Higher-end, premium-priced panels can reach over 20%.

Inverter— Household current is alternating current (AC). That means, positive and negative switch 60 times a second. Solar panels, meanwhile, generate electricity in Direct Current (DC), which has a fixed positive and negative polarity. Inverters convert DC to AC for use in your home. Historically, inverters have been a single unit mounted near your fuse box. Newer solar panels now come with micro circuit inverters built onto each panel. Because inverters use a certain amount electricity to work, they aren’t 100% efficient. That said, efficiencies for most inverters are now in the high 90s.

Grid Tie? —Keeping a grid tie lets you continue buying electricity from your local utility. This way, you don’t need to buy expensive deep cycle batteries because you’ll be supplied with electricity from your utility when your solar panels aren’t producing as much — such as rainy days or nights. If you decide to stay connected to the grid, you’ll need an anti-islanding inverter that will shut down to prevent power crews from injury. There are also grid-interactive inverters that automatically disconnect the home from the grid during blackouts and supply a few thousand watts of electricity to the home.

What About Permits and Paperwork?

All Texas homeowners with solar must file an interconnection application and go through an inspection process with their TDU, no matter if the system sends power out onto the gird or not. All arrays must meet interconnection requirements and be certified to be safely connected. Interconnection includes a study and fee (usually waived for residential-sized projects). Specific information about application requirements and fees is all available from your TDU:

CenterPoint Energy
AEP Texas

Many Texas cities and towns do require inspections as part of the building permit process so it’s best to find out about local requirements well in advance so you’ll know exactly what to expect.

How Long is the Payback Period?

Residential solar does pay for itself over time. In years past, it could take over 20 years. Now with prices so low, the length of time is much shorter. For an average solar installation cost of $15,000, your system could save up to $2,500 a year. Assuming your home is also energy efficient, that payback period could be between 5 to 9 years. The Federal Renewable Energy Tax credit of 30% cuts the installation price further and also shortens your payback period.

How to Start Shopping

Most important is to do your research. Gather and compare installation bids from several solar installation contractors . Not all installers are alike, so don’t be dazzled by a flashy presentations or promises of how much money you’ll save. Get several bids from as many installers as possible and compare.

The U.S. National Renewable Energy Laboratory (NREL) issued a recent report that shows installation costs are still falling and are expected to fall. Who does the installation does matter. The difference in $/watt between small and large installation companies comes out to 33¢/watt (about 10%) MORE with a large company. With an average residential installation of 5,000 watts, choosing a large company could add another $1,600 to $2,000 to the project. Shop smart and compare bids carefully.

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A native of Wyomissing Hills, PA, Vernon Trollinger studied writing and film at the University of Iowa, later earning his MA in writing there as well. Following a decade of digging in CRM archaeology, he now writes about green energy technology, home energy efficiency, DIY projects, the natural gas industry, and the electrical grid.

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