Solar PV (Photovoltaic) / Solar Electric Systems
A Solar PV (photovoltaic) system provides electricity when the sun shines on the solar array. This electricity is in the form of direct current (DC), which can be used to charge batteries or to power a DC appliance or device. To use it for house electricity it needs to be converted to 120V or 240V AC, alternating current.
The power from a typical Solar PV array is converted to AC power and fed into the electrical panel of a home or building and “tied to the grid”, which means any excess electricity generated can go back to the utility company where it is used for some other load (house or business) in the area. Less typically, in off-grid homes, the solar PV array and local batteries are the main power source for the home and there is no connection to a utility company.
Most states have Net Metering rules that require the utility company to accept extra electricity from a PV system and credit the owner for the extra kWh (kilowatt hours) generated. In this case, the utility is acting like a big battery for the home owner. When the house produces more electricity than it needs, it banks the extra at the utility. When the house uses more electricity than it is generating, the utility provides the credited kWhs back to the home owner.
PV modules consist of photovoltaic cells that are wired parallel to each other to achieve greater current, and bundled together in increasing series to gain higher voltage. The module, or panel, is sandwiched between tempered glass and protective waterproof material, and the edges are sealed to protect it from the elements. Modules are held in place with an aluminum frame. A junction box or wire leads provide electrical connections.
At Energy Emporium we can get modules that are made in the US, made in Europe or made in the Far East. The warranties for modules are almost all the same: 80% of the rated output power after 25 years. The efficiency of the module (number of watts per square foot) has increased quite a bit over the years. For most homeowners the difference in efficiency between modules that are available when they are ready to consider a solar array is not very significant.
Inverters convert the direct current (DC) power created by your PV panels into the alternating current (AC) power used by your home or office electronic devices. “String” or “Central” inverters are larger units usually mounted near the electrical panel or out at a pole or ground mount. For a home-sized solar array, one or two string inverters are usually installed and the solar modules are wired in series to the central inverter. “Micro” inverters are small enough to fit on or behind each solar module. Usually there is one microinverter for each module.
Microinverters can be more tolerant of shading on the array and they can report the output of each module. But there are more electronics being mounted outdoors, so there is more chance that something will fail. The labor costs are generally higher to replace parts on a roof than a ground mount.
At Energy Emporium we sell central inverters, microinverters and power optimizers (which is a combination of optimizing the power output of each module, fewer electronics on the roof, but still requires a central inverter). Some of the vendors we have worked with include SolarEdge, SMA, Fronius, Solectria, Kaco, Magnum, Outback, and Enphase.
For renewable energy systems that have a battery backup capability or are fully off-grid, we recommend renewable energy batteries over car batteries or other purposed batteries. Lead acid batteries (traditional chemistry) designed for charging and re-charging on a daily basis are created with deep-cycle cells that offer greater long-term energy and are constructed with thicker plates to prevent early degradation. The most common batteries used for off-grid applications are still wet-cell lead acid batteries. Lithium iron batteries are becoming more ubiquitous and prices should come down over the next few years. They can offer many benefits over traditional lead-acid including less maintenance, ability to increase capacity over time, and safer for home installations. There are also improvements to traditional lead-acid batteries and we may even see salt water batteries come into the market.
At Energy Emporium we can design with wet-cell lead acid, sealed lead acid (AGM, GEL), Nano carbon, lithium for low voltage, and lithium for high voltage applications. We also supply battery cables, fuses, breaker boxes, hydrometers, and battery monitoring equipment.
Charge controllers are used to maintain appropriate charging voltage to your storage batteries. When the voltage from your solar system rises, the charge controller prevents the batteries from becoming overcharged.
Charge controllers come in many different sizes for applications ranging from small solar projects to off-grid homes. It is important to understand the system voltages, currents, loads and battery capacities to choose the right charge controller for your application. At Energy Emporium we can help with the design for your own DIY project.