WHY GO SOLAR
Over 80% of Americans live in urban areas, with many residing in multifamily buildings. New York City has the highest concentration of condominium and co-op owners, and City residents pay the highest energy prices in the continental United States. In recent years the availability of new forms of financing has greatly increased the ability of multifamily buildings, particularly co-ops and condos, to pay for solar incrementally over time, rather than all at once. These new financing options makes solar much more affordable, as it can be treated more like an operating expense than a capital investment. Popular financing mechanisms include third-party ownership via solar leases and power purchase agreements (“PPAs”), with private loan options increasing as well. In most cases, solar systems on multifamily buildings that are purchased outright can pay for themselves in 5-10 years at 2015 prices and incentive levels. Start by checking the solar potential of your roof or property on the NY Solar Map. If your roof is not suitable, learn about 'Community Shared Solar' options.
HOW SOLAR WORKS
There are a variety of solar PV and solar thermal technologies available for your home or business. Read below to learn more.
Solar electric systems, otherwise known as photovoltaic (PV) systems, convert sunlight into electricity. Solar cells, the basic building blocks of a PV system, consist of semiconductor materials. When sunlight is absorbed by these materials, the solar energy knocks electrons loose from their atoms. This phenomenon is called the "photoelectric effect." These free electrons then travel into a circuit built into the solar cell to form electrical current. Multiple solar cells are included in solar modules, which are wired together into an array that will generate electricity for your home. Only sunlight of certain wavelengths will work efficiently to create electricity. PV systems can still produce electricity on cloudy days, but not as much as on a sunny day. For more about the basics of PV, visit the Department of Energy,EIA, and Solar Technologies Program websites for more solar energy resources.
Most PV systems today connect to the local utility system so the consumer can still receive electricity from the grid to power their home at night. Net Metering allows the consumer to send any excess electricity generated during the day from the consumer's solar system back out to the grid in exchange for credits. Using the free electricity from your solar system will lower your electric bills and decrease your carbon footprint.
PV panels produce DC electricity, which is converted into AC power by an inverter. Generally there is only one inverter for an entire array of panels, but some systems have a newer technology called micro-inverters where each solar panel feeds into a small inverter. Micro-inverters are more efficient, although they can also be more expensive. A similar new technology is ‘DC optimizers’, which provide similar efficiencies and panel-level monitoring but are connected to a central inverter. Appropriate technologies vary depending on the application, and you should consult with a certified solar installer to decide what is right for your needs.
The performance of a solar cell is measured in terms of its efficiency at converting sunlight into electricity. There are a variety of solar cell materials available, which vary in conversion efficiency.
A solar cell consists of semiconductor materials. Silicon remains the most popular material for solar cells, including these types:
* Monocrystalline or single crystal silicon
* Multicrystalline silicon
* Polycrystalline silicon
* Amorphous silicon
The absorption coefficient of a material indicates how far light with a specific wavelength (or energy) can penetrate the material before being absorbed. A small absorption coefficient means that light is not readily absorbed by the material. Again, the absorption coefficient of a solar cell depends on two factors: the material making up the cell, and the wavelength or energy of the light being absorbed.
Thin film solar cells use layers of semiconductor materials only a few micrometers thick. Thin film technology has made it possible for solar cells to now double as these materials:
* Rooftop or solar shingles
* Roof tiles
* Building facades
* Glazing for skylights or atria.
Thin-film rooftop or solar shingles, made with various non-crystalline materials, are just now starting to enter the residential market. The following are benefits of these solar shingles:
* Attractive integration into homes
* Dual purpose: serves as both roofing material and electricity generator
Commercially-available solar shingles generally have lower efficiencies and greater expense compared with the standard small solar electric system.
ENERGY EFFICIENCY AND SOLAR
It is generally recommended that you start looking at energy efficiency first as a way to save money before installing solar. Certification that an energy assessment has been completed must be indicated on project application to NYSERDA at time of submission. You can find information on ENERGY STAR’s Portfolio Manager Benchmarking Tool or other equivalent tool. If requested by the building owner, the participating Solar Contractor can assist with entering utility bill information into the Tool in order to produce a EUI (Energy Use Index) and, where applicable, an ENERGY STAR score. NYSERDA also offers the Multifamily Performance Program: Existing Building
In hot and sunny regions, solar thermal systems can be a great decision. But even in New York's relatively cold climate, solar water heaters can provide year-round hot water for homes and swimming pools.
The economics of solar water heaters depend largely on the available incentives and on the type of fuel being displaced. For example, a customer that has an expensive source of energy to heat their water, such as electricity or propane, will receive greater benefits from going solar than a customer using relatively lower cost natural gas. For more information on Multifamily buildings and solar thermal in NYC see this Clean Heat presentation.
HOW THEY WORK
Solar water heating systems include storage tanks and solar collectors. There are two types of solar water heating systems: active, which have circulating pumps and controls, and passive, which don't.
Most solar water heaters require a well-insulated storage tank. Solar storage tanks have an additional outlet and inlet connected to and from the collector. In two-tank systems, the solar water heater preheats water before it enters the conventional water heater. In one-tank systems, the back-up heater is combined with the solar storage in one tank.
Three types of solar collectors are used for residential applications:
Glazed flat-plate collectors are insulated, weatherproofed boxes that contain a dark absorber plate under one or more glass or plastic (polymer) covers. Unglazed flat-plate collectors (typically used for solar pool heating) have a dark absorber plate, made of metal or polymer, without a cover or enclosure.
Integral collector-storage systems
Also known as ICS or batch systems, they feature one or more black tanks or tubes in an insulated, glazed box. Cold water first passes through the solar collector, which preheats the water. The water then continues on to the conventional backup water heater, providing a reliable source of hot water. They should be installed only in mild-freeze climates because the outdoor pipes could freeze in severe, cold weather.
Evacuated-tube solar collectors
These feature parallel rows of transparent glass tubes. Each tube contains a glass outer tube and metal absorber tube attached to a fin. The fin's coating absorbs solar energy but inhibits radiative heat loss. These collectors are used more frequently for commercial applications.
For more information on solar thermal systems, please visit the Department of Energy website.
SOLAR THERMAL APPLICATIONS
Low Temperature (> 30C)
–Swimming pool heating
–Ventilation air preheating
Medium Temperature (30C – 100C)
–Domestic water and space heating
–Commercial cafeterias, laundries, hotels
–Industrial process heating
High Temperature (> 100C)
–Industrial process heating
Solar thermal and photovoltaics working together
For more information on Solar Thermal Applications, visit the NREL website.
KEY CONSIDERATIONS FOR MULTIFAMILY/CONDOS IN GOING SOLAR