One of the biggest challenges facing those who wish to invest in, or otherwise work with, energy storage technologies is how to compare the costs and performance of different solutions.
Many (e.g. batteries) carefully select their data points to flatter both their capabilities and their costs. This checklist lists the best ways to compare efficiencies and costs on a like-for-like basis.
Over a 40-60 Year Life
Investors in Pumped Hydro (PHES) and Compressed Air (CAES) should know these technologies would require a mid-life overhaul/refurbishment. But, PHES reservoirs and the underground portion of CAES have potential lives in excess of 100 years; the best way to accommodate this may be to discount the cost of such assets, so only a proportion of them is included in the costs.
In the case of batteries, they require swap-outs of both cells and power electronic systems (e.g. inverters) every 8-10 years.
Other technologies (and other aspects of these technologies) would be treated in comparable ways.
Grid-to-Grid
Analysis of grid-to-grid should account for energy transformation, both into and out of the plant and substation, inverters, signal conditioning. An alternative figure should be given additionally for installations in which the input power is direct current, e.g. solar, wind, interconnectors.
Furthermore, heating, cooling and ancillary loads figures as well as capital costs of buildings, land, design, project development, planning should be made available.
Lifetime-average Efficiency
Lifetime-average efficiency should be calculated and a graph provided demonstrating how efficiency varies over time, which usually deteriorates until refurbishment or cell swap-out, in the case of batteries.
A new set of values should be available demonstrating efficiency after refurbishment and subsequent deteriorations.
Temperature and Humidity
In different environments, the performance of some technologies is more affected by ambient conditions than other technologies. Therefore, each climate’s cycles of temperature and humidity (and possibly other criteria) should be defined. Example climates are:
- Sub-Arctic, e.g. Scandinavia, much of Canada and Russia
- Temperate, e.g. United Kingdom, Netherlands, Germany, New England
- Continental: warm dry summers and cold winters
- Hot, e.g. southern central USA, Middle East, central India, most of Australia
- Monsoon season
Response Times
Investors should be alerted to response times for 10%, 50% and 100% delivery of output power. Figures should also be provided for response times at different points during power generation:
- From an “off” state
- From spinning / zero output power
- From delivering 10% output power
- On one full cycle per day
Self-discharge
Self-discharge figures should be provided over separate periods of 1 day, 1 week, 1 month and 1 year.
Different Size Specifications
All of the above should be evaluated for different size specifications, in a 3-dimensional matrix, because most technologies are affected strongly by size:
- Power in (standardised at 1, 10, 50, 200 and 1000 MW)
- Power out (standardised at 1, 10, 50, 200 and 1000 MW)
- Duration, measured as hours’ output at nameplate output power (at 0.25, 0.5, 1, 2, 5, 12, 24 and 168 hours)
Multi-Tasking Technologies
When considering different energy storage technologies, it is important to determine the number of services that the storage can deliver concurrently, using the same resources (i.e. not sub-dividing the plant’s output or storage capacity).
One of Storelectric’s plants can deliver concurrently a range of services that otherwise requires many same-sized batteries:
- Balancing services and arbitrage (based on power and duration);
- Ancillary services (based on speed of response);
- Inertial services (based on inertia, and including related services, such as phase-locked loops) –
- Distinguish between real and synthetic inertia, the former being best for preventing failures and the latter for recovering from them, as shown here;
- Reactive power and load;
- Voltage and frequency regulation;
- Black Start (without having to reserve capacity);
- Other services, e.g. constraint management, curtailment avoidance.
