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Standard net metered grid interactive solar system

Solar panels and the DC danger zone – reducing risk factors – Part 1

The growth of solar photovoltaic (PV) systems has been exponential for the past two decades. In the last 10 years especially, the world has seen solar PV evolve from a pure niche market of small scale applications towards becoming a genuine mainstream electricity source.

This has been driven by a number of factors. When solar photovoltaic (PV) systems were first recognized as a promising renewable energy technology, governments started implementing programs such as feed-in tariffs to provide economic incentives to invest in solar projects. As a consequence, cost of solar declined due to improvements in technology and economies of scale, even more so when widespread production ramped up in China. Another factor has been the rising cost of grid electricity in first world countries and the lack of reliable grid electricity in third world countries. In conjunction with these trends, popular sentiment has shifted towards finding clean, sustainable and affordable energy sources for the future wellbeing of the planet.

Deployment of photovoltaics will continue to gain momentum on a global scale and solar PV is set to become an increasingly popular competitor to conventional energy sources. In fact, grid parity has now been reached in around 30 countries with predictions that 80% of countries will be at parity by the end of 2017. To quantify this in numerical terms, cumulative PV power capacity is nearing 200GW (gigawatts) which is the equivalent of nearly 1 billion solar panels installed globally. A figure that is forecast to reach 2.5 billion solar panels by the end of 2017.

Legislation, safety and training

Due to the exponential growth of the solar industry globally and its rapidly evolving technology, standards and legislation have not been able to keep pace with solar innovation. There are very few true experts in this new frontier and it is becoming increasingly obvious that there is a significant gap in the safety protocols surrounding the use of solar. There is an urgent need for better training programs to educate the various industries that are impacted by the increasing popularity of solar.

The knowledge gap

Firefighter awareness of solar PV systems, being able to identify the different types of solar PV systems and gaining a basic operating knowledge of these systems are paramount to effectively mitigating a fire event involving solar PV systems. Taking this back one step further, it is also essential that firefighters are aware of both Direct Current (DC) electricity and Alternating Current (AC) and the differences between the two electricity types.

Training objectives

Firefighters cannot be expected to be electrical engineers, so a training program needs to be tailored to equip firefighters with the necessary tools to make accurate and informed decisions when dealing with incidents that involve solar PV systems. So what information do firefighters require and what are typical questions that are asked?

Firefighters need to understand the different types of electricity, the nature of DC electricity and how it works in solar PV systems. Why would you want to turn solar systems off? How do you turn one off? What goes wrong with them? How does presence of a solar PV system impact your first response procedure? These are just a few of the questions that need to be answered.

Physiological Effects of DC Electricity Table of the physiological effects of DC electricity taken from the AS/NZ Standard

Physiological Effects of DC Electricity Table of the physiological effects of DC electricity taken from the AS/NZ Standard

Understanding the animal

Let’s start with electricity basics; Watts = Volts x Amps. A Watt is a unit of power, this is the indicator of how much power is available (or how badly it can hurt/injure you). Remove either Volts or Amps and you have no Watts (meaning no power/electricity).

Alternating Current (AC) is created by a rotary alternator. Electrons flow and vibrate backwards and forwards creating a frequency. The voltage and frequency varies from country to country, but in most regions the voltage is typically either 220- 240 Volts – AC (220V-240V) or 110 Volts – AC (110V). Frequency is typically 50Hz (50 cycles per second) or 60Hz (60 cycles per second). Because of this positive and negative alternating frequency, if you come into direct contact with the electrical current your muscles will contract and release, potentially allowing you to break free of the electrical current.

Direct Current (DC) is the type of electricity that is generated by all solar PV systems. The electrons only flow in one direction and so do not produce a frequency. Direct Current (DC) travels in one direction only, from the source to the load. Due to this, if you come into direct contact with the electrical current your muscles will contract and lock, there is no opportunity to break free of the electrical current. If you do try to break the load (wire short circuit, switch or even your skin) from the source, the current arcs very badly, either setting fire to or burning the load. From a physiological perspective, given the same voltage and amperage, Direct Current (DC) will not allow you to break contact and will cause much worse deep cell damage than Alternating Current (AC) (excluding high voltage/high amperage equipment which is just plain deadly from either an AC or DC source).

To dispel the myth that voltage alone is dangerous let’s use the example of a Taser. A Taser produces 50,000 volts, but only 0.0021 amps (105 Watts). Once contact with the body occurs the voltage drops, delivering an actual electrical charge to the body of between 7-26 watts. It will incapacitate an adult but causes no long term physiological effects. In contrast a typical domestic solar array will produce anywhere between 4kw (4000 watts) and 6kw (6000 watts) which is lethal.

Solar Power

Photovoltaic (PV) Photo = Light, Voltaic = Electricity

Photovoltaic = Light Electricity

Solar panels come in a huge variety of sizes and power outputs, anything from 1 watt through to modern panels of up to 315 watts.

A solar panel consists of many individual solar cells joined in series. Each solar cell produces 0.6 volts DC (at 25°c) no matter what size they are. The size of the solar cell determines the amperage that the solar cell produces. The larger the solar cell, the higher the amperage. The output of a typical modern solar panel is 250 watts.

These panels are then joined in series (also referred to as a string) to increase the voltage. Domestic solar panel strings are limited to an output of 600V and industrial/commercial strings are limited to 1000V , this is due to a number of factors such as the high cost of circuit breakers and isolators rated at over 1000W and also due to the potential problems associated with high voltage stress(HVS). Larger commercial and industrial solar PV Systems typically consist of multiple strings run in parallel to increase power output.

Types of solar systems

There are 3 types of solar PV systems. Firefighters need to be able to identify the three types of systems in order to determine the most appropriate risk assessment and isolation procedures (to be discussed in more detail shortly)

Grid Interactive System

A grid interactive system is a solar PV system that is connected to the utility grid. Any excess power that is produced beyond the consumption of the connected load (ie household usage) is fed/sold back to the utility grid. This allows the property owner the ability to earn feed-in tariff credits from the utility grid provider.

Standard net metered grid interactive solar system

Standard net metered grid interactive solar system

Off Grid System

An off grid system is a solar PV system that is not connected to the utility grid. An off grid system requires a number of additional components (compared to a grid interactive system) such as a battery storage system to store excess power, a regulator, a mains disconnect and a generator to support the system if power is depleted from the battery storage system.

Standard dc coupled off grid solar system

Standard dc coupled off grid solar system

Hybrid System

This third (and most recent) solar PV system type provides the best elements of both the grid interactive system and the off grid system. The convenience of a grid connected system, including the ability to earn feed in tariff credits with the extra flexibility of a battery storage system. This means that even during a power blackout, you still have electricity (more on the implications of this later). There is also a growing financial incentive; the ability to store your own power (through the battery storage system) and relying much less on the utility grid. In effect the utility grid adopts the function of the generator in the off grid system. Power from the utility grid is only utilized when power is depleted from the battery storage system.

Standard grid storage/hybrid solar power system

Standard grid storage/hybrid solar power system

The battery storage revolution

With the “best of both worlds” scenario that hybrid solar PV systems offer, virtually every grid interactive solar PV system currently installed will adopt a battery storage system within the next 5 to 10 years. According to studies by the CSIRO in Australia, it is forecast that up to half of all electricity generated will be on site (homes, businesses and communities) within the next few decades. These battery storage systems (or energy storage systems) will hold the same amount of potential energy as a 44 gallon drum of fuel. They will be mounted within garages next to normal household possessions, next to parked cars (many of which will have similar battery storage systems as well). They will not always be easily accessible and currently there is no legislation around the location, installation or signage of the mains disconnect. The implications for fire and emergency services personnel globally are significant!

In part 2 we will continue on to explain why solar PV systems fail, the DC Danger Zone, recent rules, regulations and technologies, and give you an overview of a new product PVStop which is designed to mitigate the dangers associated with the DC Danger Zone and offer first responders with a solution when encountering incidents involving solar PV systems.

For more information, go to www.pvstop.com.au

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Jim Foran is a Director of Solar Development Future Thinking and a partner in PVSTOP, protecting firefighters from the challenges of solar panels during a fire.