The idea is ingenious and simple, and while industry has been familiar with it for some time, the idea of a block of ice as a storage battery is just starting to gain public attention.
The concept is startling: solar energy generated during the day powers a freezer, creating an enormous slab of ice. The system cycles water through the block and into the air-conditioning unit, which blows cool air throughout the building, skipping the need for the compressor. As the ice slowly melts through the afternoon, the solar-powered freezer replaces it.
Most electricity consumption is air-conditioning, particularly in hot, humid climates like the Cayman Islands: Estimates range upward of 60 percent of all the power used in a day. Institutions like hospitals or IT offices can demand more, as much as 80 percent of power.
The “CleanTechnica” website likened ice storage to a backyard barbeque:
“Most would agree that it is a bad idea to wait to start making ice cubes until the guests start walking through the door,” author Mark MacCracken observes. “It turns out you need about one pound of ice per person for the party to keep drinks cold …”
A giant refrigerator would be needed to meet the demands, so, MacCracken says, “most people would create ice the night before. To cool an office space for that same person it takes the equivalent cooling of 150-300lbs of ice per person,” and, “as ludicrous as it sounds,” most buildings do not store their own cooling, meaning they generate instantaneous cooling each day, placing enormous – and increasingly expensive – demands on the local electricity grid.
A building, however, “can reduce peak demand by making ice using excess grid energy generated during cheaper, off-peak hours when electricity is plentiful, or when the building has excess solar energy. The ice can then be melted the next day to cool building occupants during expensive peak periods, if the cooling demand cannot be met by onsite generation,” he says.
Next month, Cayman’s first experiment with ice storage starts as Ryan Smith, construction and facilities manager at Health City Cayman Islands, breaks ground on a four-acre, 1 megawatt solar array that will help power the East End hospital’s operations. An ice storage unit inside a 40-foot shipping container is part of the plan.
“The physical work will probably get started at the end of May and be operational by September,” he said. The array, comprising “thousands of panels,” is oversize to meet Health City’s “critical capacity,” leaving nearly half the single megawatt generation to help power the container-based ice storage.
The scheme, he says, essentially “a solar-powered heating/ventilation/air-conditioning system,” will cost between $2 million and $5 million to build, but will save 30 percent of Health City’s power consumption and pay itself off “after about seven years.”
Smith pegs the costs of one kilowatt hour of electricity “close to 20 cents,” considerably less than charged by Caribbean Utilities Corporation, and rejected the idea of selling his solar power to the utility as part of its Consumer Owned Renewable Energy (CORE) program.
CORE program hits a rough patch
The CORE scheme, he said, was “extremely limited for commercial customers,” making it unsuitable for Health City, although Smith said he “would participate if we could.”
CORE itself has run into headwinds as CUC is almost a victim of its own success. Started in 2009, CORE encouraged individuals and businesses to generate their own renewable energy, selling it to CUC, then buying it back at reduced costs as necessary.
The program has gone through several revisions as the limits on the amount of power CUC accepted from CORE were reached, then raised, then raised again.
The price CUC paid to CORE participants for their power declined from an initial 38 cents per kilowatt hour to 30 cents today, some say in discouragement of consumer participation, and prolonging payback periods for investments in solar-generating systems.
CUC now limits CORE to a 4 megawatt aggregate contribution from all sources, but faces a growing clamor to raise the limits again. The program has grown faster than anticipated and the utility fears the transmission and distribution grid cannot safely manage greater renewable contributions.
Critics reject the claim, pointing to systems around the world that routinely accept far more. CUC, they say, seeks to discourage the program, underlining its resistance to alternative energy – they are contractually forbidden to profit from it – and the employment and economic activity the nascent industry generates.
A decision about raising the limit to 5MW was due Feb. 1, but has been delayed.
“The 4MW limit is close to being fully subscribed,” said CUC President Richard Hew. “CUC and [industry overseer] the Electricity Regulatory Authority are currently reviewing the program to determine if there should be a further extension to the available capacity.
“The uptake for CORE has certainly been very positive since its introduction. CUC remains committed to promoting and developing renewable energy as a source of electricity generation,” he said.
James Whittaker, chairman of the Cayman Islands Renewable Energy Association, was modest in his dissent.
“The ERA and CREA have been in consultation, looking at the long-term future, analyzing the cost-benefit of CORE,” he said, describing as dubious CUC’s claim that the grid can handle only minimum renewable contributions.
The CORE cap “is frozen at the moment, but we are thrashing it out. We are trying to get CORE to raise the limit by 1MW for another year.”
He also worries that the imminent start of utility-scale solar generation on a 5MW solar farm in Bodden Town may work against expanding “distributed generation,” small rooftop solar arrays for individual homes and businesses.
“The whole point is that the country needs both,” Whittaker says. “The 5MW give us scale and pricing, but the ‘distributed’ creates jobs and economic activity.”
The start of utility-scale generation has, however, been delayed, at least in the short term. David March is managing partner at Entropy Investment Management, the company building the solar project in Bodden Town. He is also Smith’s engineering partner in the Health City project.
The 22-acre 5MW, $18 million system was approved by the ERA on Oct. 30 after protracted talks among the three parties. Entropy later said it planned groundbreaking for the array in late February, a date the managing director said had slipped due to financing.
“These things always take longer than one thinks. We hope to have the ground breaking in the next few weeks.”
The project, he said, “should take about seven or eight months.”
Both ERA Managing Director Charles Farrington and CUC’s Hew said, however, they expected to commission the array on the original schedule.
“ERA was not given a firm groundbreaking date only a target commercial operation date of October 2016, which ERA understands has not been changed,” Farrington said.
Hew offered a little more insight, suggesting a delay in completion and hoping for a formal announcement this month: “The solar project is on schedule for end of 2016 completion,” he said. “An announcement on the ground breaking will be made in April.”
Similarly, a longstanding proposal for ocean thermal energy conversion appears to have hit another obstacle, throwing doubt on an already nebulous situation.
Baltimore-based OTEC International at least two years ago proposed a 140 feet by 200 feet floating platform one mile off the coast of North Side, exploiting temperature differences between warm surface water and deep-sea currents, driving an on-board turbine, producing between 6MW and 6.5MW of power, delivered to an onshore CUC interconnection.
The technology remains relatively unproven, however, and has not been commercially demonstrated.
OTEC International has missed a handful of local deadlines, most recently a promise to submit to the ERA by the end of March, an agreement with CUC to purchase OTEC-generated power.
In early February OTEC President Eileen O’Rourke told the Journal “significant progress” had been made with CUC, and that OTEC had “provided more data on the project” for an environmental impact assessment by the Department of Environment.
“The company,” she said, “plans to submit the information to DoE within 30 days after the [power purchase agreement]/[impact assessment] documents have been submitted to ERA.
“Ocean Thermal International hopes that all documents will be before the Cayman regulatory authorities in the first quarter of 2016.”
In mid-March, however, she indicated shifting dates: The company was “in the late stages of negotiations with CUC for the [power purchase agreement] and [impact assessment] with the goal of submitting to the ERA in the first or second quarter of 2016,” and pointed to the project’s “reliability, predictability, sustainability and flexibility,” saying “Cayman OTEC could initially provide 6.25MW of annually averaged wholesale electric power to CUC within the first year of operation.”
Farrington, however, said the ERA had seen nothing from the company and did not “have an expectation with a time frame attached.
“The ERA’s most recent information on this proposal as of last week of January 2016 was that OTI and CUC were continuing to discuss a potential PPA [power purchase agreement],” he said.
CUC was noncommittal: “OTEC is still proceeding. They are currently at the PPA and environmental impact assessment drafting stage. They will be presented to the ERA once completed.”
Smart meters and ‘time of use’
Elsewhere, the utility will complete installation of “smart meters” in all 28,000 customer premises by the end of July, enabling clients to micro-manage times and amounts of use.
Initially, episodes of overheating and even combustion occurred throughout the U.S. and Canada when smart meters first appeared prior to 2010, particularly with equipment from North Carolina manufacturer Sensus, which supplies much of CUC’s equipment.
Inaugurating the $5 million replacement program in 2011, CUC initially confronted similar setbacks, but appears to have resolved the problems, positioning the company to launch a much-rumored “time of use” scheme, in which customer costs are reduced during off-peak hours.
“TOU,” employed by utilities through North America, Europe and Australia, refers to cuts in the cost of electricity during non-peak hours. It enables customers to plan power consumption – such as doing laundry at 3:00 a.m. – reducing not only their own costs, but also relieving demand on the grid and enabling smoother load management.
CUC has been looking at a TOU scheme since at least 2015 – and probably earlier. The company has remained tight-lipped, however, saying last April that while its smart meters would enable the company to design a plan, “CUC does not offer time of use rates at this time. By changing its meters to the smart meter type, CUC will be able to consider the introduction of TOU rates in the future.”
In December, the company indicated the plan was moving ahead: “We are aware that some customers have expressed an interest in ‘Time of Use’ rates and we are reviewing.
“However, CUC is not about to make any announcement on the subject at this time.”
Finally, last week, the company reiterated its position, but did not deny plans for the scheme: “CUC is always exploring new rate structures. However, we do not have anything to report on this right now.”
One of the things a TOU scheme may boost is overnight charging of Cayman’s growing fleet of electric vehicles.