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Why connect batteries to the grid?

We see an increasing number of articles about large battery installations in public power grids all over the world. However, it's a common misunderstanding that the batteries are there for power backup to bridge power outages and save us from potential blackouts.

This article explains why the batteries are being installed and how they can be used

High voltage posts

Power backup system

Power backup systems are widely used in data centres, telecom systems, hospitals and factories. Typically they have a battery that will run for a few minutes, just enough to start a diesel engine that will run until the power grid is restored. This solution is the standard for hospitals, data centres and even large hotels in areas with weak power grids.

Telecom systems usually are smaller in power, so installing a large diesel engine would be too costly. Instead, they rely on batteries with extended capacities, typically around 6-8 hours of backup power to keep the equipment running. This backup power means that your mobile phone would be able to work for several hours, even during a complete blackout.

In case of a large blackout, the amount of power needed to support the whole grid with batteries would be enormous. Today's battery costs make it financially impossible to install that many batteries to save us from blackouts.So we only use battery backup where it is absolutely needed.

Power generation today and tomorrow

Until just a few years ago, the power grid was primarily supplied with energy from huge power plants. Water power, nuclear and coal were the cheapest energy sources, and these plants were built everywhere. Environmental impacts such as CO2 emissions, nuclear waste, particles from smoke and wild river degradation were not the top priority.

Today it is challenging to gain support for new nuclear power plants in many countries, and very few are building them. At the same time, the maintenance costs of continuing to run the old nuclear power plants are increasing, and new coal-fired power plants are not only incredibly costly and possess a grim future as well.

The cheapest energy today comes from solar and wind. The number of these installations is growing fast, and depending on the location, wind power is sometimes cheaper than solar and vice versa. In Europe, large wind farms at sea are attracting an increasing number of investments, and the expansion has never been faster.

Solar panels in sunset

Grid monitoring and control

In order to keep the voltage and frequency stable on the power grid, the power production is monitored and controlled around the clock. When the demand goes up, more energy is pumped into the grid, and when the demand goes down, some power plants are required to limit their production. In the Nordics, all countries are connected to the same grid, and when one country lacks energy, another can fill in the required energy to keep the balance. Fine-tuning is typically done by altering the amount of water flowing in the turbines of the hydropower plants, which is much easier to do than slowing down a nuclear reaction or a coal fire.

The main problem for grid control today is that wind and solar power have large fluctuations due to natural variations in wind and sunshine. Additionally, solar power is only available during the daytime. These variations generate many problems for the power grid because the fluctuations in power production are much faster than they used to be. Previously the fluctuations were much slower when energy production was based on large, heavy, rotating generators in coal, nuclear or hydropower plants.

infographic of total export / imports

This is where batteries become interesting

The intermittency of renewable energy needs to be balanced. Still, variations are too fast to be fully compensated by old rotating generators. If they try, the generators tend to wear out more quickly because of the rapidness of the fluctuations.

A battery bank designed to help balance the power can be much faster as it doesn't involve any heavy mechanical parts that need to be controlled to increase or decrease power generation. When more power is required, the battery bank can discharge power, and when less power is required, the batteries will recharge.

Until today, most battery installations have been in the range of 30-100MW with a battery capacity of 30-100MWh (~1h at full power) but newer systems installed are rapidly increasing in size.

Battery energy storage
Battery energy storage

The main problem with batteries is high costs. Li-ion batteries are already expensive, and it is getting worse as demand is growing faster than supply. Even if large battery factories like Northvolt are being built worldwide, EV manufacturers are fighting to sign extended contracts with the battery manufacturers to secure their sourcing in the coming years. Currently, the batteries produced tend to go into EVs rather than into the power grid.

New battery chemistry

New battery technologies with lower prices and higher storage capacities are announced all the time, most of them aimed at the growing EV industry. A "solid-state" Li-ion battery without a wet electrolytic is one promising technology that Toyota is pushing for in their coming cars, and Tesla's Chinese-made Model 3 cars have started to use lower-cost LiFePo batteries.

One known battery technology that seems to be waking up again is the "flow battery", which is based on two liquids being mechanically pumped to a thin membrane that charges or discharges the energy stored in the liquids. The technology is cheaper than most Li-ion technologies. Still, the energy density is low, which means that it can be useful and competitive for stationary applications, but not in EVs as they would be too big.

Second-life batteries

Some reports say that the number of EV batteries coming out on the second-hand market for grid power applications will grow up to 200 GWh by the end of 2030 (McKinsey 2019). On the other hand, Tesla claims that their cars, including their batteries, will have longer service life than today's ICE cars, so this is a bit of a contradiction as most cars produced today will probably still be on the road in 2030.

Using second-life batteries from different vendors can be challenging as most vendors have proprietary communication protocols and different battery technologies. At Comsys, we have done installations using several different car and bus batteries. Through these installations, we have seen that the remaining capacity also varies significantly between different battery packs.

Fortunately, Comsys has learned how to handle all of these challenges, so if the reports on second-life predictions are correct, we will be able to build lower-cost installations using second-life battery packs. But if Tesla is correct, the second-life supply of batteries from EVs will be very limited.

Peak shaving

Peak shaving applications typically support intermittent loads and require a lot of energy in a short amount of time. A battery can supply the load during high peak demands and recharge again when the power need is low.

A typical application can be a bus stop where an electric bus stops to charge at very high power for a couple of minutes before continuing its journey. While waiting for the next bus, the roadside batteries can recharge, limiting the peak demand when a bus arrives to charge.

At Comsys, we recently did a project where we used a Li-ion battery together with our electronics to support a sawmill in Germany. The production line was located in a rural area where the available power from the grid was not enough to keep two production lines running simultaneously. After the battery installation, production increased 100% without any costly investments in new grid connections (read the article here).

sawmill and Comsys ADF

Power quality issues

Most new power sources, like wind, solar, etc., are based on electronic inverters that generate the frequency and voltage needed to fit into the grid at a given moment. The problem with the inverters is that they can also cause power quality issues. Overtones, phase imbalances, voltages sags, swells and transients are common problems that we at Comsys have been rectifying for many years with our main product ADF which stands for Active Dynamic Filter.

By adding large battery banks to the power grid, it is possible to tackle intermittent power generation problems from sources like solar and wind. Still, with more innovative electronics (like ADF), other power quality problems can also be solved using the same electronic modules, and this is where we have our core knowledge.

Electrical vehicles, problem or resource?

Today, most discussions about the transition to electric vehicles are about how to solve the increase in power demand and the distribution of power. And as explained above, batteries are being used as a solution in many countries.

electric vehicles loading

But what if we started to talk about evs as a resource in the grid instead of a problem?

Many GWh of "rolling batteries" could store and provide energy to compensate the grid when needed. Homeowners with a car could bridge a power outage by using the car battery as a power backup. They could also potentially make money by selling compensation power back to the grid while the car is parked and unused.

According to some research institutes, the daily use of a car is typically 30-50 km on average, but a standard electric vehicle has a battery range of 300-500 km. This means that the battery capacity is 10x greater than the average daily use. The stored energy could be used in V2G (vehicle to grid) applications as a resource in the grid rather than a problem.

However, V2G standards, compensation models, connecting points, etc., need to be put in place before we can truly see the EVs as valuable resources that could support the grid with compensation power.

Batteries, rolling or not, are here to stay and will play an essential role in the power grid for years to come.

Author: Stefan Lidström, Comsys AB

Stefan Lidström