Solar power gets a ton of attention as one possible answer to our energy needs. The fact is that using the sun's energy just makes sense for our future. But utilizing solar power is still out of reach for most homes and businesses, and probably will be for a couple more years. One great application for photovoltaics right now: remote power. There is no better option for powering electronics in a location with little or no access to traditional power sources. Let's talk about what goes into system design and applications for photovoltaics in far off locales.
As with any electrical installation, you first need to decide just how much power is needed. This is especially critical with PV since it most likely will be the only power source. We'll need a conservative estimate of the amperage, voltage, and the time of usage to size the system. When doing this, don't forget that most devices have a spike in the amperage upon start-up. Some devices use five times their operating amperage briefly when starting.
AC, DC or Both?
Most electronic devices are built to take AC power since that is what our grid provides. Since solar generates DC power, we often need to use an inverter to convert DC to AC. If we can avoid this, we'll save both the expense of the inverter and anywhere from 5-20% of the power that we would lose in inversion. Often times the expense of using DC devices is offset by the savings on an inverter and reducing the wattage of solar power kit. Using AC and DC electronics increases the complexity of the install but can be accomplished with proper design.
Critical or Non-Critical?
When designing a system one of the most critical factors is what we call 'days of autonomy'. This translates to how long the system would run if there was no sunshine. This is important because going from one day of autonomy to three days of autonomy would triple the size and expense of the system. Usually the days of autonomy depends on whether the system is critical or non critical. An example of a critical application might be a traffic warning light or a communications system.
For either case, you must take into account local weather patterns and determine what a likely scenario is for days without sunshine. For critical applications we might double or triple that time. In non-critical instances we might not add any days of autonomy depending on budget. For most part of the US, in semi-critical applications (ie lighting, security, signage) we would plan for 3-4 days of autonomy.
Mounting and Enclosures
How the system is installed is important since most of these systems will need to operate with minimal maintenance. Generally smaller systems need pole mounts and battery enclosures to keep the weather out. Sealed or AGM batteries are preferred in these systems since they don't require maintenance or ventilation. Another design consideration is wind load, snow load, and hail damage, since the remote locations are often exposed to extreme weather. Many remote solar power kits now come with the electronics, solar panels, and enclosures in one complete unit that can be transported to the site ready and set up in very short amount of time.
You can size a solar power system to match any application. That's one of the great things about solar is that it can be scaled for any project. But for most part there are some good ways to use the sun for your remote power needs. Here are a few:
- Electronic Monitoring. Weather stations and water monitoring stations are perfect uses for PV and usually can be powered cheaply and reliably. Oil field monitoring is another area that is perfectly suited for remote power solutions.
- Lighting. With the advances in LED and CFL lighting fixtures nearly any lighting setup can be powered with solar now. More and more we will see traffic, parking lot, and street lights powered with PV.
- Small Moving Parts. Smaller moving parts that have intermittent use such as gate and garage openers can be powered by the sun. It is advisable to have a manual override so in case of power failure you can still get in or out.
- Communications. Cell phone and communications repeaters are increasingly using PV as systems they are being installed in more and more remote locations. These can often be coupled with wind generators since they tend to be installed in high places.
- Computers and Modems. Most computers and modems now use very low wattage and can be custom made for DC systems.
- Small Volume Pumping. A 'direct solar' system can be designed to pump during sunny hours and then store the water using tanks, instead of storing the electricity with batteries.
- Security Cameras and Recording Devices. If you've ever though about putting a camera in a far corner of your lot to monitor those pesky prowlers, you've no doubt wondered how you would get power to the spot. Now with a simple pole mounted panel and battery box you can power the camera, motor, and recoding device.
- Cabins and Cottages. Remote homes can now be powered fairly easily with solar. The system should be designed for the owners usage patterns, but its best if heating, cooling, and refrigeration can kept out of the electrical circuit. Propane refrigerators, wood stoves, and natural cooling techniques will keep power systems simple and affordable. These system almost always need a backup as well, such as a gas generator.