PV System and Installation Rules

Off grid installation

Historically, these were the first places in which photovoltaic systems were used, supplying telecommunication relay stations or remote settlements which were difficult to access and could not be connected to the network.
They remain one of the only means of supplying electricity to 2 billion people who currently do not have access to it.
In order to size these installations correctly, it is first necessary to identify the load curve required and the number of days where the installation will not be exposed to sunlight in order to identify how much energy needs to be stored in the batteries. This information is used to determine the size and type of batteries required.
Then, the surface area of the photovoltaic sensors must be calculated to ensure that the batteries can be recharged in the worst case scenario (shortest day of the year).

Specific issues

This method entails over-sizing the system to ensure continuity once or twice a year. As a result, this type of installation is very expensive!
It should be noted that according to the EPIA (European Photovoltaic Industry Association) this type of installation will account for 20% of the photovoltaic market in 2012 and 40% in 2030.

Storage

Storage is crucial to this type of installation.
Several types of batteries are available:

• Lead batteries

These batteries operate in cycles (charge/discharge). Open batteries are recommended to prevent inflating which may occur due to excessively rapid charging and large emissions of hydrogen.
Their purchase price is certainly their main advantage although they have short service lives. This is influenced by the depth of discharging but they last no more than 2 or 3 years at a discharging rate of 50% and above. Furthermore, deep discharging may “kill” the battery. Therefore, when operating such equipment at a remote site, the batteries should be changed on a regular basis to maintain their charging performance.

• Ni-Cd or Nickel Cadmium batteries

These batteries have the advantage of being much less sensitive to extreme temperature conditions and deep charging or discharging. They have a much longer service life (5 to 8 years) but are more expensive to purchase. However, the cost of the Wh stored over the service life of the installation is lower than that of lead batteries.

• Li-ion batteries

These are the batteries of the future for these types of operations. They are insensitive to deep discharging and have a service life of up to 20 years. At present, they are prohibitively expensive but prices are set to fall by 2012 with the start of mass production. They will therefore become the most economic variety for this type of usage.

Connected to the public network

Owners of power generation systems connected to the network have 2 options:

• Sell all the power they produce (option known as “total sale”). For this option, a separate connection must be established to the network, apart from the connection for consumption. This also requires an administrative declaration.
• Use the power they produce locally as required and only sell the excess (option known as “sale of excess”) which has two benefits:

  - The difference in the rates payable by the producer (purchase) and the consumer (sale)
  - It is not necessary to establish a new connection which may be expensive and requires an administrative declaration.
Since different rates are charged, a profitability analysis should be carried out to choose the best option.