A cost comparison of battery storage at a glance

How much is a kilowatt-hour of lithium-ion, lead or salt water batteries?

What should be considered for a cost comparison of batteries?

Comparing cost of a battery / storage system is a science in itself. On the one hand, many parameters must be taken into account, on the other hand, many assumptions must be made, such as the ambient temperature. Then there is an additional topic. At first glance every power storage shows fantastic values ​​on the data sheet. Whether these values ​​from the data sheets are consistent and the assumptions fit, is another matter. This also includes the issue of whether the values given ​​in the data sheet comply with guarantee and warranty provisions? After all, what use are 6,000 cycles on the data sheet if there is no guarantee for them? A cost comparison of battery storage is therefore an extensive matter.

A simple way of Cost comparison of Battery storage: Costs / kWh

Because of that many different factors it is hard for customers to make an objective cost comparison. There is nobody to blame for still using the old and simple formula: cost / kWh instead of digging through the bump on datasheets and warranty terms. We from BlueSky Energy did the work and analysed four practical examples in detail. We have carried out an analysis in order to better understand where we stand today (August 2018) regarding costs in relation to our market companions. We looked at two common lead acid batteries and one common lithium product in detail and compared them to our saltwater power storage. The aim of the analysis is taking into account data sheets and warranty conditions and find out the costs per kilowatt hour of each of the four listed products.

Results of simple cost comparison battery storage

At the first quick glance, the lithium product wins with 0.099 Euro / kWh before salt water with 0.11 Euro / kWh and the two lead products with 0.14 and 0.17 Euro / kWh. Anyone who checks the analysis in greater detail recognizes that the price advantage of the lithium product is primarily due to the high number of cycles of 6,000 specified cycles. These cycles are not guaranteed in the warranty terms. So the question arises, what are 6,000 cycles good for if the manufacturer does not guarantee for them? An analysis conducted by cleanergyreviews rates the lithium product at 3,650 cycles. Here is the link to the cleanergyreviews. New data sheets state 4,500 cycles for this product. Just to get a sense of the complexity of costing battery storage, the cost of the same lithium power storage would be  0.16 EURO / kWh for 3,650 cycles and 0.12 EURO / kWh for 4,500 cycles.

Cost comparison of Battery storage including the number of cycles according to the guarantee regulations

Accurate calculations will use for their cost comparison only the number of cycles covered by the warranty provisions. The two lead batteries offered clear indications. Also the saltwater battery states clear rules of warranty. In contrary the lithium-ion battery has very special warranty conditions. There are five years guaranteed to be free from defects. That’s – assuming 1 cycle a day – 1,825 cycles. Although there is a 15-year warranty, this only applies to self-discharge degradation. No number of cycles are guaranteed. The replacement of defective products is guaranteed up to 10 years, but considering a degressive time scale. In other words, 1,825 cycles are guaranteed with time value and then another 1,825 cycles with a reduced time value. Although it is not entirely true, we have used 4,500 cycles of battery storage for the lithium-ion product for cost comparison purposes. With strict judgment, we would expect only 1,825 cycles. The following overview shows a cost comparison / kWh of battery storage without inverter but including installation.

table cost calculation

Effective cost comparison and important parameters for comparing battery storage

  1. Usable capacity. How many kWh per cycle can be used by the battery? Meaning how many kWh can be discharged from the storage. The usable capacity of the battery storage degrades (decreases) the more frequently the battery is used. Depending on the number of cycles, degradation is between 2% and 4% per year. The usable capacity differs from the nominal capacity or gross capacity because depht of discharge (DoD) limits the nominal capacity. You can calculate the usable capacity by multiplying the nominal capacity and discharching depth (in%).
  2. Number of cycles. How often you can use the battery until reaching a remaining capacity of 70% (see point 1 above)
  3. Efficiency. How much of the energy charged into the power storage can then be taken out as usable energy again. The efficiency is given in%.

Calculation of effective costs of battery storage

In the first step you can calculate the energy throughput with the parameters of usable capacity, number of cycles and efficiency.

Usable capacity x number of cycles x efficiency = energy throughput in kWh

In the second step we set into relation the initial costs or investment costs (for the electricity storage, transport, installation) to the energy throughput.

Initial costs, investment in EUR / energy throughput in kWh = cost of electricity storage / kWh

If the electricity storage requires ongoing support or maintenance, these costs are to be summed over the number of cycles and added to the investment costs.

energy throughput

The table above shows the calculation of energy throughput in kWh based on the data of the product data sheets.

Now the cost / kWh per electricity storage can be calculated by setting the initial costs in relation to the energy throughput.

table EURO_kWh

The table above shows cost comparison of battery storage at initial costs in EURO. The initial costs are set in relation to the usable kWh.

Comparison shows that lead products have the lowest initial costs. Due to low number of cycles and low depth of discharge, lead-acid batteries have increased costs per kWh over time. In the test, lithium-ion batteries and saltwater electricity storage compared to lead acid batteries have an advantage.

Increased ambient temperatures and consequences for cost comparison of batteries

Temperature is a very important factor in the performance of batteries or power storage. Narrow temperature windows for lead batteries described in this study of +15 ° to + 25 ° Celsius or + 10 ° to + 30 ° Celsius limit the performance.  As the temperatures get cooler, the capacity of the power storage decreases. This is well known. But what happens when temperatures are elevated? A study by PowerThru shows that lead-acid battery life is reduced by 50% when the temperature is 8.3 ° C above the specification level. Here is the link to the study PowerTrhu. There are serious increasments in costs if the battery is working in high temperature ranges. The costs per kilowatt hour in EUR increase for the two lead products to 0.29 Euro / kWh or 0.23 Euro / kWh. Coming to a conclusion, if you expect increased temperatures then lead batteries will be more expensive to lithium or salt water batteries. Although at first glance the initial costs are low the effective costs are higher than at other products.

Generally lithium products are also sensitive in terms of temperature. The analysed lithium product has an active cooling and is therefore specified at 0 ° Celsius to 50 ° Celsius. When working with active cooling, the values ​​given in the data sheet are unlikely to be effective in terms of efficiency (94%) because cooling requires further energy.

This again proves how difficult it is to evaluate and compare batteries and above all to calculate the right costs.

Summary Cost Comparison Battery Storage

One thing is clear, the perfect power storage for all applications does not exist! In the cost comparison of power storage technologies, saltwater beats lithium. If we are strictly evaluating the warranty of the lithium product salt water beats lead and lithium.

Is Saltwater Power Storage Technology the New Non-Plus Ultra on the Storage Market? No, it depends on the field of application. But if the weaknesses of salt water technology (space requirements and C-rate) do not play a critical role, the saltwater electricity storage technology offers a cost-effective alternative. Saltwater energy storage systems also score points alongside the core advantages in terms of safety, freedom from maintenance and environmental friendliness. Learn more about the saltwater technology and GREENROCK saltwater energy storage.