DIRECT CURRENT ELECTRIC POWER

TO THE SRI LANKAN AC. POWER GRID

BASICS 1: The Power Grid Infrastructure:

The electrical power grid transmits HIGH Voltage AC long distances to substations around the country. This HIGH voltage is transformed to a lower voltage of around 220 to 250 volts. (in the US 110v.ac.) for the end user. This high voltage system is needed as a way to minimize power loss in transmission. This is because electricity travelling through wire heats the wire as it travels, thus incurring power loss. This is considered wasteful – a costly waste of a valuable resource – electric power. It is more efficient if electric power travels at a high voltage so the energy loss is much reduced.

This high voltage system is needed as most consumers of electricity are remote from the source of power generation. It is a tested and working system, it works. The same cannot be done efficiently with DC. power as produced by Solar panels and stored in batteries.

BASICS 2: Electric power is produced by rotating electric generators.  These are driven using coal–fired steam boilers or using hydro power.  This is how 3-Phase AC electricity is generated.

Therefore power from Solar cannot be fed directly into just one phase but has to be fed equally to all three phases to avoid unbalance, or overload in any one arm of the system. To feed DC current into this system needs specialized equipment for all to work well.

BASICS 3: Power from large installations of Solar panels

I read Sri Lanka is planning a 500Mw Solar installation. The power from Solar Panels is received as direct current or, DC. Therefore, the DC. power from solar panels needs to be transformed to AC at high voltage in order to travel any long distance to the nearest sub-power station or other consumer.

Because the grid operates in three-phase, therefore a single supply of DC needs to have equipment specially designed to connect up to these three phases, in addition to its conversion to AC with a converter as required in smaller or domestic installations.

Note the way solar panels work. Power output throughout the day varies from a minimum, rising to a maximum at midday and then, falling back down as the sun moves away to the horizon. Output rises and falls during the day light hours and is not constant and cannot be commanded to supply on demand, just as the customer requires. Maximum is available only for around four hours per day. Batteries are needed to store whatever energy is received and then supply the grid at a steady rate, any surge to meet demand would drain the battery!  Battery technology must be developed as it is not fully satisfactory at present. Therefore, this Solar form of power can only supplement power from conventional sources such as coal or Nuclear.

BASICS 4: POWER GRID SAFETY

Occasionally, the Power Grid “goes down” or fails. This requires engineers to do repair work on it. Thus, all sources of input power to the grid need to be switched off for obvious safety reasons. Great care is needed to control inputs when dealing with private owners and multiple sources of power input to the grid.

Therefore, all power inputs to the grid must have isolators or switching yards installed to isolate (= to switch off) the power being supplied to the power grid.

ELECTRIC ENERGY FROM SOLAR PANELS

– SOLAR PANELS – PLUS ADDITIONAL EQUIPMENT REQUIREMENTS

The fact is, any large Solar Power installation requires a considerable amount of equipment, simply to make the system work at all. Therefore, firstly, a substation and surrounding fence is required to house this equipment. The list of equipment is: batteries, solar charge controller, specialized equipment such as inverters (creating AC), step up transformers, special equipment to synchronize to the 3-phase electricity of the grid, switchgear and even a computerised monitoring and reporting unit which is connected to the remote CEB control centre. And also required, of course, are transmission lines from the project site to the nearest power grid point.

For a large solar power installation this equipment mentioned above may double or triple the cost of the total project, just as the chief of Russian Rosatom says. He is in a position to know. This information given above, all or in part, is what the CEB engineers are failing to explain to you. The salesmen are enthusiastic about profiting from a simple sale, but they must also sell highly technical power control equipment for it to work at all. The advocates for Solar power are not qualified persons in electrical power engineering..   PH.

Re-submited by R.O.S