Solar panel : Powering the world
A solar cell panel, solar electric panel, photo-voltaic (PV) module or solar panel is an
assembly of photo-voltaic cells mounted in a framework for installation. Solar panels use
sunlight as a source of energy to generate direct current electricity. A collection of PV
modules is called a PV panel, and a system of PV panels is called an array. Arrays of a
photo voltaic system supply solar electricity to electrical equipment.
Solar trackers increase the energy produced per module at the cost of mechanical
complexity and increased need for maintenance. They sense the direction of the Sun and
tilt or rotate the modules as needed for maximum exposure to the light.
Alternatively, fixed racks can hold modules stationary throughout the day at a given tilt
and facing a given direction . Tilt angles equivalent to an installation’s latitude are
common. Some systems may also adjust the tilt angle based on the time of year.
On the other hand, east- and west-facing arrays (covering an east–west facing roof, for
example) are commonly deployed. Even though such installations will not produce the
maximum possible average power from the individual solar panels, the cost of the panels
is now usually cheaper than the tracking mechanism and they can provided more
economically valuable power during morning and evening peak demands than north or
south facing systems.
In general with solar panels, if not enough current is taken from PVs, then power isn’t maximised. If too much current is taken then the voltage collapses. The optimum current draw depends on the amount of sunlight striking the panel. Solar panel capacity is specified by the MPP (maximum power point) value of solar panels in full sunlight.
- Solar inverters convert the DC power to AC power by performing the process of maximum power point tracking (MPPT): solar inverter samples the output Power (I-V curve) from the solar cell and applies the proper resistance (load) to solar cells to obtain maximum power.
- MPP (Maximum power point) of the solar panel consists of MPP voltage (V mpp) and MPP current (I mpp): it is a capacity of the solar panel and the higher value can make higher MPP.
Solar panels are wired to inverters in parallel or sereis (a ‘string’). In string connections the voltages of the modules add, but the current is determined by the lowest performing panel. This is known as the “Christmas light effect”. In parallel connections the voltages must be the same to work, but currents add. Arrays are connected up to meet the voltage requirements of the inverters and to not greatly exceed the current limits.
Micro-inverters work independently to enable each panel to contribute its maximum possible output for a given amount of sunlight, but can be more expensive.
For optimum performance, a solar panel needs to be made of similar modules oriented in the same direction perpendicular to direct sunlight. Bypass diodes are used to circumvent broken or shaded panels and optimize output. These bypass diodes are usually placed along groups of solar cells to create a continuous flow.
Leftover PV panels can contaminate soil, as it happened in 2013 when US-based Solyndra solar farm bankrupted leaving broken panels on site. IRENA 2016 study estimated the amount of PV waste at 78 millions tons by 2050.Most parts of a solar module can be recycled including up to 95% of certain semiconductor materials or the glass as well as large amounts of ferrous and non-ferrous metals. Some private companies and non-profit organizations are currently engaged in take-back and recycling operations for end-of-life modules. EU law requires manufacturers to ensure their solar panels are recycled properly. Similar legislation is underway in Japan, India, and Australia.
The price of solar electrical power has continued to fall so that in many countries it has become cheaper than ordinary fossil fuel electricity from the electricity gridsince 2012, a phenomenon known as grid parity.
Average pricing information divides in three pricing categories: those buying small quantities (modules of all sizes in the kilowatt range annually), mid-range buyers (typically up to 10 MWp annually), and large quantity buyers (self-explanatory—and with access to the lowest prices). Over the long term there is clearly a systematic reduction in the price of cells and modules. For example, in 2012 it was estimated that the quantity cost per watt was about US$0.60, which was 250 times lower than the cost in 1970 of US$150. A 2015 study shows price/kWh dropping by 10% per year since 1980, and predicts that solar could contribute 20% of total electricity consumption by 2030, whereas the International Energy Agency predicts 16% by 2050. Some photovoltaic systems, such as rooftop installations, can supply power directly to an electricity user. In these cases, the installation can be competitive when the output cost matches the price at which the user pays for their electricity consumption. This situation is sometimes called ‘retail grid parity’, ‘socket parity’ or ‘dynamic grid parity’. Research carried out by UN-energy in 2012 suggests areas of sunny countries with high electricity prices, such as Italy, Spain and Australia, and areas using diesel generators, have reached retail grid parity.
Impact on electricity network
With the increasing levels of rooftop photovoltaic systems, the energy flow becomes 2-way. When there is more local generation than consumption, electricity is exported to the grid. However, an electricity network traditionally is not designed to deal with the 2- way energy transfer. Therefore, some technical issues may occur. For example, in Queensland Australia, more than 30% of households used rooftop PV by the end of 2017. The famous Californian 2020 duck curve appeared often for a lot of communities from 2015 onwards. An over-voltage issue may result as the electricity flows from PV households back to the network. There are solutions to manage the over voltage issue, such as regulating PV inverter power factor, new voltage and energy control equipment at the electricity distributor level, re-conducting the electricity wires, demand side management, etc. There are often limitations and costs related to these solutions.
When electric networks are down, such as during the October 2019 California power shuttoff, solar panels are often insufficient to fully provide power to a house or other structure, because they are designed to supply power to the grid, not directly to homes.
Implication onto electricity bill management and energy investment
There is no silver bullet in electricity or energy demand and bill management, because customers (sites) have different specific situations, e.g. different comfort/convenience needs, different electricity tariffs, or different usage patterns. Electricity tariff may have a few elements, such as daily access and metering charge, energy charge (based on kWh, MWh) or peak demand charge (e.g. a price for the highest 30min energy consumption in a month). PV is a promising option for reducing energy charge when electricity price is reasonably high and continuously increasing, such as in Australia and Germany. However, for sites with peak demand charge in place, PV may be less attractive if peak demands mostly occur in the late afternoon to early evening, for example residential communities. Overall, energy investment is largely an economical decision and it is better to make investment decisions based on systematically evaluation of options in operational improvement, energy efficiency, onsite generation and energy storage.