The tragic disaster in Japan has captivated the country’s attention for the last two weeks but is also reminded us how quickly our lives can be changed. From someone who makes their living in the solar renewable energy industry, I could not help but reflect on how off-grid solar can help in emergency situations.
I live in California so it is not hard to imagine my town being rocked by an earthquake powerful enough to knock the town off-the-grid, stop communication and scatter enough debris to inhibit travel.
A portable solar emergency generator that can be rolled out and set up powering my refrigerator along with a few lights is a must. A solar emergency generator can also be used for a weekend camping trip allowing the guys to still catch the game on TV.
During emergencies, having the ability to power up a laptop with solar is also a must. A Wi-Fi signal may be hard to come by, but a maintaining a sense of normalcy is important in these types of situations.
The first step in choosing emergency power generator is to decide if solar is right for you. There are obvious advantages of solar over fossil fuel the first of which without electricity, you are not going to have access to gas. An emergency solar generator will cost around 4X what a gasoline generator costs, but the confidence knowing you have unlimited power has to give you some piece of mind.
When choosing an emergency solar generator starts before you even look for a product. You need to sit down with your spouse and choose which appliances and gadgets are critical and what you can do without.
The more power you require to power the critical loads in your home in an emergency, the more solar panels and battery backup you are going to need. Of course, that means more money. In this broken economy money is sometimes the key reason.
A list of electrical devices you may want to consider as critical to run off solar may be your refrigerator, radio and a few lights. We don’t recommend you start thinking about hot water unless you just won the lotto because they suck a lot of solar power from the battery bank.
The size of an off-grid emergency solar power system depends on the amount of power that is required (watts), the amount of time appliances and lights are used (hours) and the amount of energy available from the sun (sun-hours per day). The owner has control of the first two variables as well as the position of the solar panels; the third depends on the location.
Considering that plethora of information, sit down again and prioritize your list of must-haves and how long you have to run them then add up the combined power requirements. A cheap tool you can get to help you check your energy needs is a meter we use nearly every week sizing off-grid power is a “kill a watt meter”.
These simple devices can be connected to your appliance, and it will assess how efficient they really are. Large LCD display will count consumption by the kWh, same as your local utility. You can calculate your electrical expenses by the day, week, month, even an entire year. Handy item to have when considering how much emergency solar power you will need.
The next step is to compare your critical power list to the total wattage of the emergency solar generator you are considering. It is a good idea to allow for some wiggle room in your calculations. Emergency solar generators are usually rated by their STC watt number. STC in an acronym for “Standard Test Conditions”. All solar panels are rated in Watts. The watt rating is how much power (amps times volts) the panel will produce in full sunlight at 25 degrees C (77F). This is the industry standard (STC) for all PV panel ratings. Solar panel manufactures have long used this test standard which is 1,000 watts per square meter solar irradiance, 1.5 Air Mass and a 25 degrees C. cell temperature.
PTC is an acronym for “PV-USA”. The PV-USA test conditions was developed at the PV USA test site at the University of Davis, California. The PTC rating test is 1,000 watts per square meter solar irradiance, 1.5 Air Mass, and 20 degrees C. ambient temperature at 10 meters above ground level and wind speed of 1 meter per second.
The ambient temperature rating (PTC) is generally considered a better real world standard than factory conditions because silicon solar cells average about 20 degrees C. above ambient temperature in the real world, cell voltage drops as temperature increases. A module’s power output in real life conditions is lower than the power measured at the factory where cell temperature is maintained at a controlled 77 degrees F. (25 C).
STC Vs PTC Cell voltage drops about 0.08 volts per degree C. in environments which exceed 25 degrees C. That means an STC rating of 17 volts can actually become a PTC (PV-USA) rating of 15 or 16 volts. Using Ohm’s Law, volts time’s amps is equal to watts which equals power, so a reduced voltage, means reduced watts.
CEC is an acronym for the California Energy Commission. About 10 years ago the California Energy Commission drove the development of closer to real world standard that could be realistically used in their rebate program. It is common these days to see both STC and PTC power ratings measured in watts on most commonly accepted solar panels. The California Energy Commission also maintains a list of approved solar panels on its website for public viewing. In order for a rebate to qualify in California, the application must include the PTC standard rating not STC. More information can be found at NREL website.
Neither PTC nor STC account for all “real-world” losses. Actual solar systems will produce lower outputs due to soiling, shading, module mismatch, wire losses, inverter and transformer losses, shortfalls in actual nameplate ratings, panel degradation over time, and high-temperature losses for arrays mounted close to or integrated within a roofline. These loss factors can vary by season, geographic location, mounting technique, azimuth, and array tilt.
Choose the off-grid emergency solar generator that will meet your minimum needs. One more thing, don’t forget to test the equipment before the emergency.