A residential grid-tie solar PV system will be disconnected during a power outage. This is to stop the solar panels feeding back into the grid and presenting a safety hazard to workmen who may be repairing the line. This phenomenon is called ‘islanding’ and modern inverters incorporate anti-islanding circuitry.
What happens to solar when power goes out?
As usual within the solar PV subject, it’s a bit of a trick question. Of course, they’ll work. As long as their is sunshine, solar panels will convert the sun’s energy to electrical power. Unfortunately, under normal circumstances the system will be disconnected from the grid and from your home’s electrical system.
If you have solar panels do you need a generator?
The motivation for many people when considering solar is providing the security of an electrical supply during power outage. In this case home energy storage in the form of batteries is required. The only other alternative is to use a backup generator.
How to store solar energy at home
There is a lot of interest in home energy storage, particularly after thousands of people in Texas recently found themselves without electricity after storms. No matter if it’s winter or summer, it’s very difficult to live comfortably without electrical power.
The best known example of home batteries is the Tesla Powerwall. This compact battery bank consists of multiple rows of small lithium-ion cells and an inverter to convert the DC battery voltage to AC power. It sits on an internal wall, such as inside a garage, and looks like an electrical storage heater.
How does a Tesla Powerwall work?
Essentially, the Tesla Powerwall is a smart device, that is, it can be monitored and controlled at a distance. It charges up by solar, or from the grid, if solar isn’t available and can supply power to the home at night-time, or when there is a power outage.
Do solar panels work automatically?
Multiple Powerwalls (up to 10) can be connected together, so it’s possible to have home energy storage for several days, if care is taken with energy consumption. It will simply detect when there is an outage and switch into ‘supply’ mode. In order to maximize the time that power can be supplied, it’s normally necessary to reduce energy consumption i.e. minimize heating and air conditioning as much as possible.
Although an individual Powerwall has a capacity of 7.5kW, the device cuts out when there is 10% capacity left in the battery. Lithium-ion batteries have a charge/discharge cycle life of 2000 at 90% discharge, which is optimum for long battery life.
Will solar panels work on cloudy days?
It isn’t only power outages that can send solar panel output plummeting – thick clouds can also severely reduce output. Passing clouds that obscure the panels every now and again will reduce system output by between 10% to 25%, while total cloud cover has a much bigger effect.
Research to determine how solar panels work on cloudy days shows that it’s very difficult to quantify solar power reduction due to clouds because there are so many variables involved:
- how high are the clouds?
- what type of clouds are they – cirrus, cumulus, cumulo-nimbus, etc
- are the clouds white, dark or in-between?
It’s generally agree that full, low, dark cloud cover affects how well solar panels work the most. In this case an installation might only generate 10% of its capacity. If the clouds are lighter, then more diffuse light will seep through and there will be more production.
By far the biggest factor affecting how well a solar system works is the insolation or peak-sun-hours in a particular location. This can easily be found for your home by going to globalsolaratlas.info and entering your town in the search box at the top of the page.
The image below shows the results for Tampa, Florida. The circled value is termed the irradiation or amount of sunshine for that location, which 4.846 kWh/m2/day. It can be toggled from day to a yearly historical reading.
The number is also known as Peak-Sun-Hours and can be directly used to determine how much energy a solar installation will produce by multiplying it by the installed solar panel capacity in kilowatts.
Example for Tampa, Florida:
- Installed kW of solar power = 5 kW
- Peak sun hours (irradiance) = 4.846 kWh/m2/day
- Energy produced per day = 4.846 x 5 = 24.23 kWh (kilowatt-hours)
Will solar panels work after an EMP?
EMP is short for Electro Magnetic Pulse and can occur in 3 ways:
- as a result of a nuclear explosion
- as a result of a solar flare from the sun
- deliberate generation by a device called an NNEMP. (Non-nuclear electromagnetic pulse)
Wherever or however an EMP comes from, depending on the size of it, the effect on electrical and electronic equipment is devastating, basically destroying it.
The solar cells themselves are in fact semi-conductor device, that is, it’s basically a P-N junction and so will be affected. However, scientists estimate that the actual production capacity of solar panel would only reduce by up to 10%, which is encouraging.
Now for the bad news – depending on the EMP proximity, the electronic control equipment and associated cabling would most probably be fried.
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How to protect electronic equipment from an EMP
Solar panels should be disconnected from each other and any junction boxes. Everything should be disconnected from the grid and put inside a Faraday cage, or bag for smaller devices. A Faraday cage shields devices from electromagnetic fields and is the quickest way to protect your solar inverter and other essential equipment.
Once the EMP danger is past, you should be able to re-connect your system and enjoy up to 90% of the previous capacity. Those around you with no solar, or unprotected solar, will have no electricity.
Would solar panels work with snow on them?
Solar panels don’t work at all if covered with snow. However, all solar arrays should be mounted at an angle, an angle which is normally steep enough for snow to slide off. Solar cells absorb heat as they are generating electricity and tend to retain it. This helps to melt any accumulating snow, encouraging it to slide off.
Do solar panels work when covered with ice?
A thin veneer of clear ice may not affect solar panel production very much, but there are several kinds of ice. It’s rare to have a completely clear type. Normally, ice contains small bubbles which can either block or deflect light. Even clear ice will refract, reflect or diffuse the sun’s energy, thereby reducing a solar panel’s output.
Will solar panels work through glass?
Solar panels will work through glass but at a reduced efficiency. The tempered glass used for rigid solar panels has a non-reflective coating to minimize the amount of light energy lost that way, but some is also lost as it passes through the glass, through diffusion and absorption.
Ordinary ‘float glass‘ used in most domestic homes doesn’t have anti-reflective coatings and so will lose a significant amount of the energy shining on it. Depending on the quality of the glass and the angle at which the sun’s rays hit the glass, up to 5% of a solar panel’s output may be lost.
Can solar panels freeze?
Freezing temperatures cannot damage a solar panel and doesn’t inhibit their ability to generate electricity. In fact, heat is one of the main enemies for solar production. The STC standard solar panels specification cites a stated output at a temperature of 77°F (25°C). For every degree over this value, the efficiency drops by 0.5%.
Can solar panels withstand hail?
Commercially available solar panels are certified to withstand the impact of a 1 inch (25mm) hailstone falling at 23 mts/sec (about 50 mph). In practice, many solar installations have withstood hail-storms with much greater size ice-balls without breakages.
Do solar panels work with moonlight?
Solar panels cannot work with moonlight. The energy level is much too low. Moonlight is 10 million times weaker than bright sunlight. A candle at a distance of 1 meter would be 10 000 times stronger than moonlight.