Category Renewable Energy Technology Characterizations

System O&M Costs

Operation & maintenance costs consist of fixed and variable costs. Fixed costs include cooling and genera l maintenance at the site. Variable costs include recharging the batteries and periodically replacing the batteries. These O&M costs are presented as annual expenses in the prior table. The cooling charge is based on a power managemen t system which consists of eight modules, each one of which is the same size as the system being characterized here [18]. The unit must be installed in an air-conditioned room [4], and thus, the parasitic load for the cooling fans is quite small at 1.25 kW. At a peak or shoulder rate of 50/kWh, the annual cost of the cooling load for the 30 kW system is $548...

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System Capital Costs

The cost of an energy storage system is affected primarily by four drivers: (a) the initial cost of the storage subsystem, (b) the cost of the power converter, (c) the cost of the balance of system, and (d) the need to design, engineer, procure, and construct one-of-a-kind systems. The capacity of the plant as well as the discharging profile impact both capita l and O&M costs. At present, flooded lead-acid batteries are the dominant choice for many utility applications. Flooded lead-acid batteries have been in widespread production and use for so long that further reductions in costs are unlikely [7]. Industry and government have been working to develop improved VRLA batteries and advanced batteries tha t offer potentially lower costs and longer cycle lives.

The 1997 cost estimates for the...

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Performance Indicators

The assumed economic life of the battery system is 30 years, requiring battery component replacements at appropriate intervals. The structure and power conditioning system are expected to last 30 years [18]. Battery replacement charges vary by the type of the battery and the number of years until replacement. One manufacturer claims that the type o f flooded lead-acid batteries they use should be replaced every three years [25]. When VRLA batteries are used mor e widely for renewable applications in 2005, they initially are replaced at 5-year intervals, improving to 10-year intervals in 2010. Advanced batteries are assumed to require replacement once every 10 years when incorporated into the PV – battery system in 2020 [3,19]...

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Performance and Cost Discussion

The most productive hours of sunlight for PV systems are from 9 AM to 3 PM. Before and after these times, electricity is generated, but at much lower levels [8]. In addition, an afternoon thunderstorm will severely reduce local PV output before it will indirectly reduce the load by cooling ambient temperatures and suppressing solar heat gains. This ha s profound technical impacts that can negate some of the benefits associated with distributed, grid-connected PV. A n hour of energy storage can alleviate this problem [9].

INDICATOR

NAME

UNITS

Base Case 1997

| +/- %

2000

| +/- %

2005

| +/- %

2010

| +/- %

2020

| +/- %

2030

| +/- %

Plant Size

kW

30

30

30

30

30

30

Battery Subsystem

Type

Lead-acid

Lead-acid

VRLA

VRLA

Adv. Battery

Adv. Battery

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Performance and Cost

Table 1 summarizes the performance and cost indicators for the storage portion of the system being characterized i n this report.

4.0 Evolution Overview

The 1997 30 kW baseline system is based on a commercially-available 31 kW PV/flooded lead-acid battery system. The battery subsystem is assumed to improve and transition in technology type, changing from flooded lead-acid i n 1997 and 2000 to VRLA beyond 2005. Advanced batteries are anticipated in 2020. These technology changes slo w the cost reduction path for the battery subsystem. The PCS and max power tracker are expected to be integrated, so significant cost reductions are expected as modular design and factory-assembly become the norm and productio n volumes increase substantially...

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Battery Operation

The life of a b attery and its energy delivery capability are highly dependent on the manner in which it is operated. Many deep discharges (above 70-80%) reduce the life of lead-acid batteries. High rates of discharge reduce the energy delivery potential of lead-acid batteries. Batteries also have shelf-life limitations.

Poor charging practices are responsible for short battery life more than any other cause. A number of methods exis t for charging batteries used in stationary utility applications. Optimum life and energy output from batteries, but no t efficiency, are best achieved when depth of discharge (low, e. g., 40%) and time for recharge are predetermined and repetitive, a condition not always achievable in PV applications...

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Battery Technologies

This appendix assumes that current R&D activities will lead to significant improvements in the cost and performanc e of battery storage systems. As these improvements take place, battery storage systems will compete with conventional sources of peak electric power generation, such as gas turbines, diesel generators, or uninterruptible power supply units. Flooded lead-acid and VRLA batteries are commercially available today, although not in designs wholly suited to utility applications. Zinc/bromine and lithium batteries are two advanced batteries under development. Each of thes e technologies has particular strengths and weaknesses.

Lead-Acid Batteries: Basically, flooded lead-acid battery technology for renewable energy storage systems is th e large-scale application of a technology simil...

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System Application, Benefits, and Impacts

Application: This document describes the use of a battery storage system in conjunction with a PV system to avoi d or reduce the purchase of more costly on-peak power. However, energy storage systems can also play a flexible, multi­function role in an electric supply network to manage resources effectively. Battery energy storage systems are use d for a variety of applications, such as: power quality assurance, transmission and distribution (T&D) facility deferral, voltage regulation, spinning reserve, load leveling, peak shaving, and integration with renewable energy generatio n plants [6]. Battery systems appear to offer the most benefits for utilities when providing power management suppor t (i. e...

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