INSTALLATION & ELECTRICAL DISTRIBUTION PARTS
Power panels provide a central location for mounting inverters and charge controllers in battery systems and include enclosures for wiring, over-current protection, ground-fault and surge protection, bypasses and related hardware.
FUSES AND BREAKERS
Fuses and breakers are designed to prevent excessive current from overheating conductors or devices by opening the circuit. Specialized breakers can also be deployed to open the circuit in case of arc-fault conditions. Fuses and breakers should be sized according to NEC and/or manufacturer guidelines to ensure that they open the circuit before conductors or equipment can become damaged.
Photovoltaic, wind, and hydroelectric systems usually have long runs of exposed wire that can pick up surges from lightning, even if the lightning strike is only nearby. These power surges can damage sensitive electronic components in meters, charge controllers, and inverters. Surges can also damage telephone, audio, and video equipment connected to the power system. It is a good idea to install surge protection on all incoming wires in the system, including incoming photovoltaic, wind, or hydroelectric power lines; AC generator lines; and telephone and antenna leads. Proper grounding is absolutely necessary for lightning protection to be effective. In the event of a direct strike, damage may occur, even with surge protectors installed. Type 1 heavy duty surge protectors are recommended when a direct lightning strike is possible on the installation.
Proper equipment grounding helps to ensure that any electrical faults that may develop in a PV system have minimal opportunities to cause fires or electrical shocks. It is just as important to be familiar with NEC 250’s general grounding requirements when installing PV as it is to know 690. Jurisdictions and inspectors may vary on the grounding equipment and techniques they consider acceptable, so it is also important to know what your inspector will be looking for.
SnapNrack, as well as some other mounting system brands, now offer UL 2703 listed racking packages that incorporate much of the equipment grounding by bonding modules and related gear to the rails. However, not all equipment is considered compatible or likely to be accepted by a particular inspector, so it’s important to have some other options like those offered here.
Array combiners are used to electrically combine the output of multiple series strings of PV modules into a single wire to simplify the connection to an inverter or charge controller. They typically include string-level overcurrent protection and sometimes host other functions such as monitoring, a disconnect, or even AFCI and remote shutdown. It is important that the combiner used be rated for the worst-case voltage and current the array can output.
Disconnect switches provide a means for safely opening a circuit between the power supply and any loads that may be present. Some disconnects also offer fusing, remotely-actuated contactors or other specialized functions. The NEC requires listed disconnects in a variety of situations. Be sure to choose a disconnect that is rated for the AC or DC voltage and current that may be present on the circuit.
Load centers provide a central location for mounting busses and breakers to feed multiple load circuits from a single power supply such as a utility service or inverter output. The NEC requires NRTL-listed load centers for most applications. Be sure to choose a load center that is rated for the AC or DC voltage and current supplied as well as any application-specific requirements.
Low-voltage power systems with inverters can have very high current through the cables that connect the inverter to the batteries. Large AC loads like microwave ovens, toasters, irons, and washers can cause an inverter operating on a 12 VDC battery system to draw over 100 A. Large motors may draw 300 to 500 A during startup. When cables between batteries, and from the battery bank to the inverter, are too small, the current available to the inverter is limited and it may fail to supply larger loads. Properly sized cables also impose less resistance and thereby help maximize system efficiency. Use this chart to find typical ampacity limits by wire size.
ARRAY CABLES AND CONNECTORS
Grid-tie modules generally ship with attached cables that are listed to UL 1703 with the module. The cable connectors on these are fully waterproof when connected, touch-protected and designed for up to 1,000 VDC and 30 A, but cannot be safely disconnected under load.
Our output cables are made with 10 AWG PV Wire and Amphenol H4 connectors, and can be used in solar arrays up to 1,000 VDC. All of our array output cables are made with PV wire that is listed to UL 854, which is required by the NEC for use with transformerless inverters.
Additionally, we stock the common styles of crimp-on connectors for use with 10 AWG PV stranded wire. Proper crimping to the wire and insulator assembly requires special tools.
WIRE MANAGEMENT HARDWARE
As most experienced PV installers will attest, good wire management is a hallmark of high-quality installations, and its lack can lead to inspectors and customers alike looking for other potential issues. Cables and wires should be kept off the roof or ground and water should not be allowed to pool at the entrances of enclosures, splices and junction boxes. Given that a solar PV system is designed to last for 25 years or more, it is vital to use wire management hardware that will hold up in the environment and allow deployment with minimal strain on the components.
PV CABLE ASSEMBLY TOOLS
Crimp-on PV cable connectors require special tools to properly attach the connectors. Single-purpose tools from Multi-Contact or Amphenol work with only that type of connector and are often the best option for installers who work only with modules that have that same connector type. For those who encounter several different types of connectors, one of the Rennsteig tool sets that have sets of dies and positioners can be more convenient and economical than carrying a different tool for each connector type.
SYSTEM SURVEY AND COMMISSIONING TOOLS
Surveying and commissioning a PV system are important steps in the installation process, and it’s worth doing properly and consistently. Commissioning standards, such as IEC 62446 and related NABCEP guidelines, provide visual and physical inspections as well as electrical tests that should be performed prior to activating a new PV system. Common electrical tests made during commissioning include: continuity, phasing, and voltage for AC circuits; continuity of grounding conductors; DC circuit polarity verification; string I-V curves; string open-circuit voltage; string short circuit current; insulation resistance testing of PV source and output circuits; and, finally, a full-up system functionality test. With proper documentation, these same tests can be repeated periodically as systems age to ensure that they are operating efficiently.
SOLAR SAFETY LABELS
The NEC and International Fire Code (IFC) require specific components of a PV system to be labeled for the safety of operators, maintenance, and emergency responder personnel. The Code also requires these labels to be appropriately weather resistant (IFC 605.11.1.1.3) and durable (NEC 110.21). These labels are UV and weather resistant and should meet Code requirements in most jurisdictions. Note that some jurisdictions may still require engraved placards. The labels are designed to permanently adhere to metallic, baked enamel, and powder-coated surfaces in most outdoor environments.
Local jurisdictions and company policies often call for unique language or types of labels that are not available in preprinted form. If this is a frequent requirement, a label printing system can be an economical way to get exactly what you need when you need it. The ability to produce custom labels also presents opportunities for branding as well as organization, theft prevention, and identification.
SOLAR WATER PUMPS
Solar pumps operate anywhere the sun shines, making them ideal for an independent water supply. While energy production from solar pumps is impacted by cloudy weather, having adequate water storage and decreasing water needs during cool or rainy weather mitigates these impacts.
Most solar water pumping systems operate on direct current (DC). The output of the solar power system varies throughout the day and with changes in sunlight intensity and weather conditions, requiring specialized pumps and controls that operate within a wider range of voltage and current compared to most AC pumps.
Conventional AC pumps are usually centrifugal pumps that spin at high speed to pump as many gallons per minute as possible. They also consume a large amount of power and their efficiency suffers at low speeds and when pumping against high pressure. If you run a centrifugal pump at half speed, it pumps one quarter of the volume.
To minimize the size of the solar PV system required, solar pumps generally use more efficient motors and pumping mechanisms. The most efficient pumps are “positive displacement” pumps, which pump a fixed amount of water with each rotation. If it is cloudy or early morning, the pump will receive less energy and run more slowly, but with no loss of efficiency—so at half speed, it simply pumps half the amount of water at the same pressure.
To use solar energy economically, solar pumping systems typically pump more slowly than conventional well pumps (many solar pumps are designed to produce less than 6 gallons per minute) and they don’t run at all between sunset and sunrise, so an adequately sized storage tank is usually required. Instead of pumping a large volume of water in a short time and then turning off, the solar water pump works slowly and efficiently all day to provide the same volume of water. Often, a solar pump can be used in a well with a recovery rate too slow for a conventional AC pump.
If your water sources are remote from power lines, compare the cost of a low-maintenance solar pumping system to what you would spend on a generator, with continual fuel and maintenance costs, or on a utility power-line extension. In most cases, a good solar pumping system is far more economical, which is why many non-profits and NGOs use solar pumping to provide clean water to remote villages around the world.
If you are pumping from a well, we have solar pumps that can deliver from 1 gallon per minute to over 75 gpm at peak output.
The SHURflo 9300 and Aquatec SWP pumps can be powered by a PV array as small as two 50 to 100 W solar modules, or a single larger 60-cell or 72-cell module, depending on the “head” (vertical distance or elevation change) they are pumping. They can pump 500 to 1,000 gallons per day and lift water up to 230 feet. These pumps require service every two to four years.
If you have a higher lift, need more water, or want a pump that does not require service for 15 to 20 years, the Grundfos SQFlex pumps are a good choice. These pumps can be used in wells up to 800 feet deep and can pump up to 20,000 gallons per day from shallower wells using solar modules, a fuel-powered generator, an inverter/battery system, the utility grid, or a combination of these power sources.
Surface pumps are typically less expensive than submersible pumps and can draw water from a spring, pond, river, or tank, and push it far uphill and through long pipes to fill a storage tank or to pressurize it for home use or for irrigation, livestock, etc. The pump may be placed at ground level, or suspended in a well in some cases.
All pumps are better at pushing than pulling, since the vacuum a pump can draw is limited to atmospheric pressure (about 14 psi). At sea level, a pump can be placed no higher than 10 or 20 feet, depending on the type of pump, above the surface of the water source (subtract one foot per 1,000 feet elevation). Most wells are much deeper than this and therefore require a submersible pump, which can push the water up to the surface.
Suction piping for surface-type pumps must be oversized a bit and not allow air entrapment (much like a drain line) and should be as short as possible.
Pumps can push water very long distances through a pipe. The vertical lift and flow rates are the primary factors that determine power requirements.
WATER STORAGE AND PRESSURIZATION
Many conventional AC-powered water systems pump from a well or other water source into a pressure tank that stores water and stabilizes the pressure for household use. When you turn on a tap in the house, an air-filled bladder in the tank forces the water into the pipes. When the pressure drops, a pressure switch turns on the pump, refilling and re-pressurizing the tank. This works because an AC pump delivers high volume and pressure on demand; however, this will not work with pumps operating directly from PV modules because the sun may not be shining when you want to take a long hot shower.
For pumps operating directly from PV modules, a non-pressurized water tank or cistern is used to store water for use during times when the sun is not shining. If the tank can be located above the house on a hill or on a tower, gravity can supply the water pressure. Gravity water pressure can be calculated in two ways:
PRESSURE (IN PSI) = HEAD (IN FEET) X 0.433, OR HEAD (IN FEET) = PRESSURE (IN PSI) X 2.31
For reasonable pressure, the tank needs to be at least 40 feet above the house, although to obtain a pressure of 30 psi will require about 70 feet of elevation.
Alternatively, a DC or AC pressure booster pump, powered from a battery or battery/inverter system, can be used to maintain a pressure tank as needed from a storage tank that is filled by a solar pump during the day. You must use a pressure pump that can deliver the maximum flow rate required by the house, or have a pressure tank that is large enough to make up the difference between what the pressure pump can deliver and what is required for as long as it may be required. This is called the “draw down volume” of the pressure tank.
CALCULATION OF SOLAR POWER NEEDS
If you are using a pump driven directly by PV modules, the array’s nameplate output should be at least 20% higher than the power required by the pump to achieve the desired head and flow rate. A larger array or a tracking system can maximize the amount of time each day that full rated power is available to the pump, providing more gallons per day.
Since the pump will only draw the power it needs, it will not be damaged by oversizing the array. A larger array will produce the needed power in less light, extending the pumping time and volume delivered in the morning, afternoon, and on cloudy days. For instance, a 1 kW array will produce 200 W in one fifth the amount of sunlight that you would get on a sunny day at noon.
DESIGNING A SOLAR PUMPING SYSTEM
Solar Gear Supply carries several types of pumps that can be used in a variety of applications. Which pump and related equipment are needed for a solar pumping system depends on many factors, including what the water source is, how much water is needed, when the water is needed, how far the water source is from another power source, etc.
If the well or other water source is close to an existing source of power, such as the utility grid or the power system of an off-grid house, it’s usually better to power the pump from that existing source rather than set up a dedicated PV array. If grid power is available, it can be used to power a water pump, and if desired, a grid-tied PV system can be installed to offset the grid power consumed.
In off-grid situations, if the well or other water source is close to the house’s off-grid power system, it’s usually easier to power the pump using the house’s power system, either directly from the battery bank with DC, or with AC from the inverter. Additional PV modules may be needed to accommodate the pump’s energy requirement, but they can be added to the house’s PV system and used to help charge the batteries when the pump isn’t running.
Solar Gear Supply is happy to help you design a pumping system, but please have the following information ready when you contact us:
- Total amount of water, on average, needed in gallons per day ( gpd). Because solar pumps deliver water in variable amounts due to the variable nature of sunlight, you will need to know the total daily water. Any seasonal changes in water requirements also need to be considered.
- Total head that the pump has to raise water to. This is the actual elevation difference between the water level in the well (or other water source) and the top of the storage tank. This is not just the length of the water line, although internal pipe friction needs to be considered if the distance is great or the pipe is small.
- Solar insolation at the site. Local insolation (how much sun is shining down at the site) data can be obtained using PV Watts (online). Any shading of the potential array needs to be taken into account, along with seasonal variations.
Additional information, such as well casing diameter, water quality, well regeneration capacity, etc., may also be needed, depending on the specific application.
WIND POWER SYSTEMS
Wind-power systems can be cost effective if the average wind speed is 9 mph or more at the location of the wind generator. Adding a secondary charging source, like wind power, to PV can make an off-grid power system more stable by increasing the amount of time that energy is being produced, reducing dependence on energy stored in the batteries. Using off-grid wind to supplement solar photovoltaic power can be cost effective even if good wind is only partially available throughout the year, especially if the solar potential is low at that time.
The amount of power generated by a wind turbine is dependent on wind turbulence, wind speed, and tower height. Like water, air is a fluid, and is subject to the same fluid dynamics principles, such as turbulence created by obstructions in the flow. A stream flowing over boulders becomes turbulent, creating wakes and eddies, and is robbed of much of its energy by friction.
Similarly, wind blowing over a landscape with trees and buildings obstructing its flow also becomes turbulent and loses energy to friction. Turbulence degrades the wind resource, both upwind and downwind of obstructions. Wind turbines placed in turbulent air wear out prematurely and produce little usable power.
To avoid air turbulence, wind turbines should be placed on a tower high enough that the bottom of the turbine rotor’s swept area is at least 20’ to 30’ higher than any buildings, trees, or other obstructions within a 300’ to 500’ radius. If the wind at the site primarily comes from a particular direction, and the obstructions are not in the wind path, then less clearance may be allowable as long as the flowing air is laminar. In the illustration below, a kite with long streamers tied to the line at 10’ intervals can be used to find the height above ground level where the air flow smooths out. Look for the first streamer to be fully furled out.
The power available in the wind increases with the cube of the wind speed. This means that there is nearly twice as much power available in a 10 mph wind as there is at an 8 mph wind. Wind speed increases as you get higher above the ground due to the loss of friction between the air and the ground. You can expect that the wind speed at 30’ above the ground will be about 25% greater than at eye level (at 60’, it’s about 37% greater; at 90’ about 45% greater; and at 120’, about 50% greater). And since power output increases exponentially with increases in wind speed, a turbine mounted on a 60’ tower can produce about 40% more power than the same turbine would on a 30’ tower (75% more power at 90’ and 100% more power at 120’ compared to 30’). Most wind generators are designed to deliver maximum power at a wind speed of 30 mph. At 15 mph, they will deliver about 1/8 their rated power. Therefore, increasing tower height is a cost effective way to get more power out of a wind turbine.
The power output of a wind generator decreases roughly 3% for every 1,000’ of elevation above sea level due to lower air pressure.