Solar Electricity and the Grid

For grid-connected domestic PV systems, there are three main economic considerations which are closely linked :

1. Is there a payment available for excess electricity fed to the grid and if so, what is it?
2. Will the PV installation produce enough electricity above and beyond the demand of the building to be able to export, and what is the value of this electricity over a year based on the likely number of units exported?
3. How much electricity is the PV installation likely to produce over the year, and for electricity used directly in the building, what is the value of this electricity offset (i.e. how much would have been paid to purchase this amount of electricity?

Feed-in-tariffs

Some countries in Europe offer elevated payments for PV generated electricity. These elevated payments (called feed-in tariffs) assist projects to be financially viable and are created and legislated for by Governments rather than electricity companies and all electricity consumers have to subsidise these tariffs.

As we know from the Solar electricity applications section, the way in which the electricity is used will determine the profitability and viability of a PV installation.

• Domestic PV installations below 6kW (single phase) and 11kW (3-phase) in domestic settings, fall into the microgeneration scale category :
• How do I go about organising a tie-in/connection to the grid?
• As a domestic producer of electricity, Will I get paid for electricity exported to the grid?
• With regard to the grid connection process itself, ESB Networks should be contacted, in particular, see the following section of their website: http://www.esb.ie/esbnetworks/en/generator-connections/gen_connection_export.jsp

For further information on microgeneration, please see the Solar electricity : Microgeneration section.

• Non-domestic PV installations or installations not falling into the microgeneration category (i.e. above 11 kW) should be planned with the following in mind :

With regard to getting payment for power supplied, then electricity suppliers should be contacted to see if any of them will offer a power purchase agreement (i.e. to see if they are prepared to buy the electricity produced by the generator) notice that the grid connection and electricity payments are separate items.

REFIT is a scheme which assures long term security for electricity suppliers when purchasing power. This has not been formalised yet for this year, but suppliers are more likely to buy power from renewable generators when it is in place. For more information on REFIT, contact Department of Energy, Communications and NaturalResources.

The design and sizing of a grid-tied PV system is based around the following considerations :

• Available roof space, orientation of roof and the angle of inclination
• Possible sources of shading of the PV modules (which will reduce their electricity output)
• Economics: Incentives, payments, initial cost of system, payback times.
• Geographical location (which has a bearing on the solar resource available)

The available roof space, or else the available spending budget are typically the two limiting factors regarding the size of system to be installed. Solar PV requires significant surface area to produce a reasonable amount of electrical power.