Energy Storage costs

How much is a battery storage?

Calculation models and what you should check out when comparing different offers.

Read the guideline and get useful insights.

The simple approach:

retail price  / kWh = cost per kWh

Most times this is the calculation used for comparing costs. Simple and it seems an easy way to calculate costs of battery storage.


Hidden pitfalls

To ensure that you get a clear picture, you should consider the following points step by step.

What is included in your offer? Compare like with like.

Battery or energy storage system?

Buying the battery can be compared to buying an engine when buying a car. To get from A to B, you still need wheels, steering, bodywork, and some smart extras from the board computer would be nice. If you buy a battery, then your electrician has the job of making it into a working storage system. Lots of working hours for him and depending on experience, some trial and testing to make sure everything runs as desired. You will need battery inverters, controls, wiring and fuses, as well as a smart energy management system, for convenience and online access.

Therefore, compare whether you are offered a stand-alone battery (an engine in our example) or a ready-to-connect power storage system (a car).

With a ready-to-connect energy storage, the above topics are settled for you. Plug in and switch on is the motto. BlueSky Energy offers ready-to-connect storage systems. Easy and fast installation for our electrical partners is important to us.


What is included?

Coming back to the example of buying a car: You can choose a small car or the luxury sedan. Know your purpose and you can choose the right model.

Do you want to optimize your self-consumption in daily operation?

Do you additionally want to cover up in the event of a power outage?

What extras should be included in a back-up for blackouts?

When it comes to protection in the event of a power outage, terms such as emergency power, switching times, island or off-grid function, black start capability and DC coupling of photovoltaics are important topics.  In the blog article blackout we explain the terms and what to look for if your purpose is to provide power during a blackout. All of BlueSky Energy’s energy storage products offer these capabilities.


Depth of discharge (=DOD)

With some batteries you can use only part of the total capacity. Lead batteries are the best example for limited depth of discharge. In this type of battery up to 50% must be reserved. That means you buy a two-kWh battery but only use 1 kWh. Also, with lithium batteries usually 20 % residual capacity must remain in the battery. With the product family of BlueSky Energy (GREENROCK saltwater batteries, Vigos the outdoor power storage and CEL-3050) you can use 100% of the specified capacity.

Marketing versus Warranty

Marketing with beautiful pictures and excellent product features is one thing – but do these promises hold true in the application? First, take a close look at the data sheets and familiarize yourself with the technical features. Your electrician knows what to look out for. The next step is to check the warranty conditions. What good is information on the data sheet if it is not covered in the warranty data? You should take a close look at service life and number of cycles in particular.

Life time

Mostly the data sheets talk about cycles. e.g. 5,000 cycles – that’s how often you can completely charge and discharge the battery. Classic applications with PV installation make one cycle per day. With photovoltaic the battery is charged during the day and discharged at night. If you additionally integrated a combined heat and power plant or a wind turbine, several cycles per day may be possible.

There are differences in calculating cycles: Some models count for a full cycle, even if the battery was only charged to 30% on a bad weather day.

We at BlueSky Energy guarantee the energy throughput. That means we calculate exactly how much energy (kWh) will flow through your battery during its lifetime. With that method it doesn’t matter if you use 10% or 100% and when you use it. The exact values are added.

This  is how we calculate the energy throughput:

The battery has a lifetime of  … cycles  x  DOD in %  x  Efficiency in %  x  Nominal capacity of the battery x  degradation of capacity.

As you can see, the depth of discharge (DOD) is an essential parameter for calculating the energy throughput.

Area of application and temperature range

You know it from your cell phone: cold and heat affect the battery performance. Each battery has its comfort zone. If the battery is operating outside this temperature range, performance and usually lifetime suffer. Check out what is good for your battery. With our carbocap products Vigos and Cel-3050 we even more extended the temperature range. From -30 °C to +50 °C the battery feels comfortable. Cold cellars and garages cannot harm it, nor can poorly insulated rooms that heat up in the summer.


temperature range

Costs energy throughput/kWh

Comparing energy storage offers, we recommend comparing the energy throughput and to include extras such as comfort in your consideration.

This is how we calculate the energy throughput:

The battery has a lifetime of  … Cycles  x  DOD in % x Efficiency in %  x  Nominal capacity of the battery  x  degradation of capacity.

Just like buying a car, you make a conscious decision to buy or not buy certain extras. In the case of the purchasing of a storage system, the main issue is the back-up in case of a grid failure. Buying storage is also an emotional matter. You have made the right decision if you feel comfortable with your chosen solution.


EMS Energy management system and extras

The integrated energy management system offers further extras. Here we list some features offered by the integrated EMS of BlueSky Energy storage:

  • Access and data viewing via mobile app
  • Optimization of self-consumption with wireless sockets
  • Integration of different energy sources, such as PV, wind power, CHP, …
  • Integration and control of heating element or heat pump
  • E-charging and dynamic charging at multiple charging points
  • Load shedding
  • capping peak loads

Benchmark – Our long-life power storage compared with competitors

For comparison, we used a well-known, high-quality German product and a low-priced option from a supplier in China. Below is the breakdown of the 3 products. The Chinese storage in the example cannot cover a power failure. It only serves to optimize self-consumption.

Benchmark engl

BlueSky Energy storage solutions – positioning

GREENROCK – the saltwater battery is leading the ranking in aspects of safety and sustainability. Doing the calculation cost/kWh the system is leading. E.g. a 30 kWh GREENROCK is at 760 EURO /kWh.

GREENROCK Home from 5 to 30 kWh

GREENROCK Business from 30 to 270 kWh

Wherever saltwater batteries reach their limits and high performance is required, carbocap technology offers the suitable solution. Powerful and for even more extreme temperatures (from -30 °C to +50 °C)

Vigos – the outdoor power storage from 18 to 96 kWh for outdoor installations.

Cel-3050 the performance Battery from 6 to 20 kWh. The power solution or, the “little brother” of Vigos.


Cherry-picking. Pick out the best and combine for your own optimized solution. BlueSky Energy storage solutions are fit for combination within each other.