Renewable energy systems can take a well-designed, energy-efficient home to net-zero energy status.
PRODUCTION OF ELECTRICITY AND HOT WATER AT HOME using natural energy from the sun is nothing new. But technologies have greatly improved over the past few years. Not only do they cost less to install, but they’re more reliable, more efficient—and simply a better deal. In addition, the supporting hardware is vastly superior to the old stuff. The politics of alternative energy is changing too, albeit more slowly than many would like. In many states, utilities are now required to buy back any “extra” electricity you produce. And both wind turbines and solar installations are eligible for 30% tax credits with no upper limit from the federal government, plus certain state and utility incentives. If you’re looking at alternative systems, here’s some essential information.
Wind Turbines: Lighter Wind Demands
Small-scale wind turbines that create electricity have always been a fairly specialized form of power generation—most valuable in mountainous and coastal regions. The challenge has been to build a turbine that produces adequate electricity, even in low wind, to make it worth the cost. We’re getting much closer. For example, both the Swift and the Skystream turbines begin producing power in winds of just 8 miles per hour.
The advantage of wind power over PV? The wind often blows when it’s dark outside. But before you buy, take a look at the national wind map published by the National Renewable Energy Laboratory (NREL). You’ll see that not every area of the United States is well suited for wind-powered living. In fact, if you live in any of the Southeast states—and you don’t have a place right on the water—wind is a long shot. You will make a lot more power with a good solar PV setup.
Photovoltaics: Looking Sharp
The race is on to build better PV cells that convert sunlight to electricity. New solar films and panels are being tested that are more efficient, less expensive and lighter than ever. The current challenge is to find a more affordable alternative to the polycrystalline silicon based panels that dominate the market. But while that R&D is going on, existing solar products are becoming more practical. For example, Sanyo recently came out with double-sided solar panels that can simultaneously provide shade (in the form of an awning), and take in sunlight on both the top and bottom surfaces.
At the same time, the range of building integrated photovoltaics (BIPV) has exploded. That’s good news for homeowners. It means you can now have a solar generating system built right into your roof that looks like asphalt shingles or architectural metal or even clay tiles. And, as we mentioned earlier, many states require utilities to buy any leftover electricity you generate. One of the key improvements in BIPV in recent years has been the way they connect to each other and your home’s power system. The early products were co-dependent. In other words, when the connection broke on a solar shingle, the whole roof stopped producing. Newer systems have built-in redundancy in their wiring, and most are more modular, making replacement of a single faulty tile or panel less of a hassle.
Third party-owned solar PV systems have made solar technology affordable to more people. Typically, a solar leasing company provides the array at a low (sometimes no) upfront cost. The leaser is guaranteed a fixed monthly rate for the term of the lease (often 20 years); in addition, the leasing company provides all maintenance of the array and often enables web-based monitoring of the system. Some companies offer a power purchase agreement instead of or in addition to a straight lease. In this arrangement, the customer pays for the energy produced by the panels, at a fixed and predetermined rate.
Is it better to lease or purchase a solar system? This often depends on your tax bracket. If you are unable to take advantage of the 30 percent federal tax credit, a third-party-owned system might be the way to go, as the solar provider can utilize the tax credit and pass on the savings.
Solar leasing programs are not available in every state (or in every region of a given state); however, the largest providers are continually expanding their territories. Companies that offer solar leases are SolarCity, SunPower, Sunrun, Sungevity, Real Goods Solar and NRG Home Solar (www.nrghomesolar.com).
Solar Hot Water: Smart Storage
The availability of extremely durable hot water storage tanks—which in some cases also serve as water heaters—has made solar hot water collection even more viable. Many tanks now include a separate closed loop of a freeze-resistant liquid. That extra loop is specifically for solar hot water—so that when the sun is shining, the solar panels on the roof heat the clean water in the tank. But when the sun is not sufficient (or you have teenagers using up the “free” hot water) an external boiler or heating system built into the tank kicks on to make up the difference.
One of the great advantages of a solar hot water system is the relatively rapid payback. In other words, if you install this year, it may pay for itself in less than three years, especially once you figure in the tax credits and rebates available.
Cogeneration: Waste Not
Cogeneration has been common at large factories for decades. It’s basically a way of squeezing more work out of fossil fuels. Also known as combined heat and power (CHP) generation systems, these mechanical wonders put the waste heat generated by a home furnace or boiler to work making electricity. By some estimates, they achieve 90% efficiency, compared with 30%–40% from your local power station. If you’re already replacing or installing a new boiler or furnace, why not take it to another level and try cogeneration?
Resilience: Back-Up Plan
A renewable energy system can be part of a strategy for keeping your home powered up during storms and power outages. Grid-tied solar PV systems aren’t available when the grid powers down, so it’s necessary to have a back-up plan. While gas- or propane-fired generators are a good conventional source of back-up power, other options are becoming available. Some inverter manufacturers are starting to build in a limited amount of storage into their products. Stand-alone solar panels can be used to power specific appliances. Battery banks have long been a staple of off-grid systems, but home batteries for grid-tied systems are just around the corner. Electric vehicle batteries paired with the right EV charger are another up-and-coming back-up power source. In this way, different power sources become part of a dynamic system that not only makes your home more resilient, but turns it into a dynamic participant in the grid rather than just an end user.
Solar Roof Area
There are a number of different things you need to know before calculating the roof area required for your solar panel installation:
1. The size of the system
2. The type and dimensions of the solar panels (You can get these from the solar panel datasheet.)
3. The spacing between solar panels
4. The orientation of the panels
Once you’ve gathered this information, here’s how to calculate the area required:
Size of the system (watts) ÷ Size of the solar panel (watts) = number of panels required.
Example: 5-kW system ÷ 250 W = 20 panels
Each panel measures 1,680 mm x 996 mm, or 1.68 m x 0.996 m = 1.67 m2
Total Area = 20 panels x 1.67 m2 = 33.40 m2
A little bit of space will also be needed between each panel for fixing the panels to the racks—this will depend on what type of racking system is used.
Orientation. If you don’t have enough roof space on a single roof face, consider splitting your system into two different orientations. The best orientation for panels (in the Northern Hemisphere) is south. East and west are slightly less efficient (around 9 percent less). If you split your panels between your south and west roofs evenly, you would only lose around 4.5 percent of your overall system capacity.