Dear Editor,
President Granger has directed government ministries to incorporate “green technologies” into their operations. In addition, the US Ambassador has spoken favourably about selling surplus power to the utility grid. The push therefore is for the employment of renewable energy as an important part of Guyana’s development.
In an urban environment, such technologies are limited to photovoltaic and wind turbine generation. Photovoltaic generation is the production of electricity directly from sunlight whereas wind turbines convert kinetic energy from wind flow to electrical energy. However, because solar lumens and wind flow are uneven and unreliable, these technologies cannot stand on their own. They either need some sort of storage or support from a central utility to regulate supply to the load level. The former is accomplished through batteries, the current technology being lead acid, whereas the latter is through interconnection and synchronization with the electric utility system. The interconnection with the Utility requires costly on-grid inverters.
So, one can design a system incorporating storage batteries to serve all or part of the load. The problem with this approach is the battery is the weakest link in the system. Although heavy-duty in nature, they fail at a high rate due to maintenance required in wet batteries and control of electrical amperes entering and leaving their cells. Battery-systems design requires a controller to avoid over-charging, which is detrimental to the life of the battery, and hopefully the inverter, the device that converts dc power from the battery to ac power required by the load, is sophisticated enough to avoid over-discharging which also decreases battery life. For example, 12 v(dc) designs should not be charged above 14 v(dc) or experience voltage drops below 11.5 v(dc). Dry batteries require much less maintenance but suffer from the same control conditions as wet ones. New batteries from Tesla Motors using lithium ion technology avoid many of the lead acid technology problems but are super expensive.
Bottom line, battery storage systems should only be considered for remote areas where central utility power is not available.
That leaves the on-grid design. On-grid simply means interconnected to the utility power grid. Such interconnections come with great sophistication and responsibility. Here on in, I will refer to the interconnected party as an Independent Power Producer (IPP). When interconnected to the utility, the IPP’s system becomes part of the utility systems.
When there is an interruption by the utility on the IPP’s section of the distribution system, the IPP renewable generator must automatically disconnect or the consequence can be grave injury to utility workers. But more important, the IPP’s generator has to synchronize to the wave forms of the utility generation, or in technical terms, voltage and amperes have to be at the same phase angle and same points of the ac curve as the utility supply, to avoid shorting out the system. Fortunately, equipment on the market these days has all these safety capabilities built into it. The problem in Guyana is that the utility, GPL, is not ready for interconnections with IPPs.
GPL’s tariffs are very inefficiently designed and recover significant amounts of its fixed costs in variable energy rates. So, the utility does well when consumption exceeds the forecasts on which rates were designed, but will fail to collect all its fixed costs when usage falls below forecast.
Ideally, energy rates should only recover the fuel costs of generation adjusted for operating and maintenance costs, and line losses. Fixed costs should be recovered in demand and service charges. As a consequence of this inefficient rate design, an IPP interconnected to the utility system and supplying surplus power to the utility, will receive a benefit greater than the utility’s avoided cost due to net billing (ie, energy supplied by the utility less energy supplied by the IPP through the same meter), thus increasing its average cost. This increased cost is then borne by all other utility customers. To avoid this burden to other customers, and in the absence of efficient rate structures, the utility should offer a separate service for interconnected customers. This service is referred to as a ‘buy-back energy’ service where the utility is buying electric energy from the IPP at its true avoided energy cost. Again, in the absence of efficient rate structures, GPL would have to employ two meters with appropriate detents, one to measure supplemental and backup energy used by the IPP, and the other to measure energy supplied by the IPP to the utility grid.
In summary, the technology needed for the deployment of renewable energy technologies in urban settings is available and probably cost effective, given GPL’s high rate structures, but the major player, GPL, essential for on-grid interconnections, is far from ready. Unless it gets its act together in pricing and safety issues, such interconnections would have a deleterious effect for electricity consumers.
Yours faithfully,
Louis Holder