Remote communities in the wintry northern US state of Alaska have “an unusual concentration” of renewables-based microgrids operating in challenging climatic conditions, new research has found.
A collection of nine research papers, collectively titled Technology and cost reviews for renewable energy in Alaska: Sharing our experience and know-how, was published this week in the Journal of Renewable and Sustainable Energy by the Alaska Center for Energy and Power (ACEP) at the University of Alaska, Fairbanks. Erin Whitney, ACEP’s data collection and management programme manager, said her state is home to “a substantial fraction of the developed microgrids in the world” and that microgrids provide up to 2 MW for many of the state’s more than 200 remote communities.
The collection of papers is comprised of technology and cost reviews for Alaskan decentralized power systems including wind, energy storage, diesel gensets, biomass, solar PV, heat pump and organic Rankine cycle (ORC) technologies.
According to the researchers, diesel gensets are the main source of power in remote Alaskan communities. Analysis of key performance metrics found that the size of a diesel power system directly affects capital costs, with larger systems being more cost-effective per kW.
However, sizing a system appropriately for a community is more cost-effective than significantly oversizing the system, the researchers found. Capacity factors range from below 5 per cent to over 25 per cent, with the low values typically being for hybrid diesel-hydropower systems.
In addition, rural diesel-fired power plants, which can feature three to four gensets, can have low capacity factors since several will likely be used just for backup power. With good maintenance, a diesel genset that operates for 35 per cent of the time will have a lifespan of around 20 years or 60,000 hours, but the researchers said this level of maintenance is often difficult to achieve, and SCADA systems with remote control capabilities require an uninterrupted internet connection that is not always available.
Solar PV is “a nascent but promising energy option” for remote Alaskan microgrids, the researchers found. Their study looked at community-scale PV installations between 2.2 kW to 50 kW, concluding that total installed costs “arguably show a trend toward lower values with larger installation sizes”, although costs are still higher than in the rest of the US. Capacity factors range from 6-15 per cent.
Costs for biomass boilers are higher than for other types of boiler, the researchers found. Capital and O&M costs vary with boiler type and location, and system efficiencies vary with the system type, installation protocol, O&M protocols, piping distance, thermal storage and wood moisture content. Sizing biomass units to meet approximately 80 per cent of peak required heat load means the boiler will run at the maximum heat output, the researchers said.
Heat pumps are being increasingly used in Alaska after improvements in their low-temperature performance, the researchers said, with air source heat pumps in the state found to operate successfully in temperatures as low as -15°C.
For the study, 17 installed heat pumps including air-, ground- and seawater-source systems were analyzed, showing that the average installed cost per kW was $5579. The minimum cost was just over $700/kW for a small air source minisplit system and over $12,000 for a complex vertical loop ground source heat pump.
Organic Rankine cycle (ORC) systems appropriate for small-scale generation are still new to the market or at the prototype stage, the study found, with “many villages … being approached by product developers to invest in this new technology”.
Analysis of ORC installations across Alaska showed that capacity factors ranged from 33 to 52 per cent, due in several cases to insufficient waste heat resources or higher-than-expected maintenance costs. However, annual fuel savings between $70,000 and a predicted $300,000 have been seen.
“Some [ORC] systems have been highly reliable and cost-effective, while other installations have been neither,” the study said. The smallest reliable system has a 50 kW nameplate capacity and requires 500 kW of waste heat. The researchers concluded that ORC technology is best suited for communities featuring 1 MW or more of diesel generation.
According to the study, data “do not show any difference in the cost of energy storage in Alaska compared to such costs in the rest of the nation or world”; but it noted that storage is “often difficult to justify economically based on fuel savings alone”, and that “significant work remains to quantify other possible cost savings”, such as lower fuel consumption and reduced stress on diesel gensets.
According to Whitney, the biggest driver for renewables-based microgrids in Alaska is lowering the cost of energy, but the region is also experiencing the effects of climate change. For icebound Alaska, this could mean growth in economic activity and growing demand for energy.
“Understanding the potential to tap local energy resources to support both communities and industry is important to enable sustainable development across the region,” the study said.
Source: Decentralised Energy