Batteries for Stationary Use and Grid Storage
Stationary Batteries
Stationary batteries are almost always lead acid. Size and weight is of lesser concern. The limited cycle count does not pose a major problem because the batteries are seldom deep discharged. Large stationary systems are mostly mature flooded systems that provide a reliable and economical service, but they need regular maintenance in form of checking the electrolyte level and adding water. Automatic watering reduces some of this routine maintenance work.
Valve-regulated lead acid (VRLA) offers a lower-cost alternative to flooded lead acid. Being maintenance-free, the battery can be installed and forgotten. This benefit is often taken to the extreme in that the batteries are neglected. In the absence of adding water, maintenance comes in the form of checking the voltage, internal resistance and verifying capacity.
Flooded nickel-cadmium batteries are used in applications that need regular deep cycling or are exposed to hot and cold temperatures. NiCd for stationary applications is about four times the price of lead acid; however, the vendors say that improved longevity will make up for the higher cost. Flooded nickel-cadmium batteries are non-sintered and don’t have memory.
Battery manufacturers are introducing NiMH and Li-ion batteries for stationary uses. The advantages are wide temperature range and the ability to deep cycle and fast charge. These batteries have a small footprint, need minimal ventilation and have a long life. When storing energy from renewable sources, such as from solar cells, NiMH and Li-ion do not suffer from sulfation as lead acid does when not fully charged. Li-ion has the added benefit of being light. It can be made semi-portable for temporary systems and remote installations.
NiMH and Li-ion are more expensive than lead acid and the industry will continue to rely on lead acid batteries for common UPS systems. Experts predict that alternate chemistries will find market acceptance for general use once the price can be lowered to $200/kWh, the cost of a lead acid system. Lithium-based stationary batteries cost as much as $1,500/kWh.
Grid Storage Batteries
Renewable energy sources such as wind and sun do not provide a steady stream of power, nor do they harmonize with user demand. Large energy storage batteries called load leveling or grid storage batteries are needed to provide a seamless service.
Storing energy when the demand is low is not new. Hydroelectric power stations use excess electricity to pump water back up to the reservoir at night for use the next day. With an efficiency factor of 70–85 percent, pumped hydro is easier to manage than adjusting the generators to the exact power need. Flywheels also serve as energy storage. Large electric motors spin up one-ton flywheels when excess energy is available to supply brief energy deficiencies. Flywheels are the most expensive energy storing media, followed by Li-ion. Pumping compressed air into underground cavities is another way to store energy, but load leveling batteries are the most practical for wind farms and solar installations.
A wind turbine generates between 900kW and 4MW of power and a typical wind farm produces 30–300 megawatts (MW) in total. To get a better idea of electric mega-power, 1MW feeds 50 houses or a super Walmart store. A 30MW wind farm uses a storage battery of about 15MW. This is the equivalent of 20,000 starter batteries and costs about $10 million. Besides wattage, the battery industry also uses Volt-amps (VA) to specify battery capacity. Read more about Watts and Volt-amps.
Most energy storage batteries are lead acid; newer systems lower than 1MW include sodium-sulfur and Li-ion. The battery management system (BMS) keeps the battery at 50 percent charge to allow absorbing energy on wind gusts and delivering on high load demands. Modern BMS can switch from charge to discharge in less than a second. This helps stabilize the voltage on transmission lines.
Comments
A typical wind turbine is not 30 kV. That was 20-30 years ago. New wind turbines are typically 3-4 MW, old ones around 2 MW.
If one turbine should be 30 kW you will need 1 000 turbines to make 30 MW, and 10 000 to make 300 MW. That would have been a GIGANTIC wind farm.
How is it possible that Sealed Lead-Acid manufacturers claim that their battery life expectancy is 5-10 years when used in Solar or Wind powered Systems and on the other hand they claim that Designated cycle life is around 500 cycles. (500 charging cycles + 500 discharging cycles). If we assume that Sealed Lead-Acid battery will be charged during day and discharged during night it come that 500/365 days will give me 1,36 years of life. When i take in consider that 500 cycles is at 20 degrees Celsius (which is almost never) it come to conclusion that Sealed Lead-Acid will run approximately 1 year… which is i must admit to low comparing to some older chemistries in use. I agree that without particular maintenance such system is very good but on the other hand such system is usually installed far away and on inaccessible terrain and with 1 year of life time it rises a lot of price of such system…
Regards,
Darth
Hi there, I’ll try to enlighten you - I work for a Battery manufacturer and I’m involved with solar installs as well.
A VRLA may have a 15yrs ‘design’ life in normal applications, but only 8 in a solar application due to the cycling and loading.
For life cycle and discharge - Normally a cycle, is 1 full discharge and 1 full charge. Which shouldnt be 24hrs. If it is, yes your 1.36 life is correct.
In remote application a 3, 5 or 7 day backup on a single charge is normally the design factor. And so batterys should be sized accordingly.
I have seen batterys in remote places that are as good as new, many years later.
Also I have seen some allot of batterys exhausted early in their life.
Battery quality and the system design are very critical, to ensuring a long life and care free installation.
If using lead flooded batterys (wet), they must be normalised very month, to maintain the system.
Hope this helps
Does anybody know where can I find the schematic of an electronics circuit to measure the conductivity of a VRLA battery?
I have been looking for on the internet but have not found anything relevant.
I’m trying to build my own batter analyzer.
Merry Christmas!
Concern about storage batteries within residences and industrial/institutional buildings when solar or wind energy conversion systems have been installed. Where can the batteries for a building be safely stored - protected from fire, water, gas release, etc. The use of small WECS or Solar Panels require batteries to level the power. We need to determine the hazard of various storage locations.