Project Everest

Work Update

[Work Update]: Solar Consulting Malawi - Lead Acid vs Lithium-Ion: The Verdict - July 2018

Introduction

The energy team is currently using a proxy product to test various distribution methods and validate customer needs. While doing this, the team has identified areas of improvement when designing Project Everest’s solar product. Of these, the replacement of the lead acid battery in proxy with a lithium-ion battery with our product. This document aims to evaluate the pros and cons of each system and provide a recommendation to future teams.

Comparison

Lithium Ion

Pros

Cons

Ultralight

Expensive

High power

delicate

High capability

Can explode if misused

High cell voltage

 

126 Wh/kg for lithium-ion

185 Wh/kg for lithium polymer

86.4 Wh/kg for lithium iron phosphate

 

Lead Acid

Pros

Cons

Cheap

Very heavy

Powerful

Batteries are very large brinks

Easily rechargeable

Can produce noxious gases

Robust

Short cycle lifetime

 

Volatile chemicals at the end of lifetime

7 Wh/kg for lead acid

Wh/kg is the measure of energy density for batteries. Wh means Watt-hours; this is a product of the voltage, current and the time it takes to discharge. However, batteries charge and discharge according to a curve based on its chemical composition. So a battery rated at 5V will not discharge at 5V for its lifetime. Instead, it will discharge more like 5.1V, 5V for a majority of its lifetime, then 4.9V before being completely discharged. Especially prevalent in older battery types such as lead acid and alkaline. Discharge quality also changes over the lifetime of a battery, with older design batteries producing their rated voltages over shorter periods of time before not working at all.

Similar for current as a battery rated at 4Ah will produce 0.4 A in 10 hours, 0.04 A in 100 hours. For many batteries trying to draw the rated current in one go will fry the battery, so a factor of safety is required.

 

Lead Acid Downsides

  • Failure to fully charge ages battery prematurely
  • Up to 15% of energy wasted
  • Flooded batteries can cause noxious gases, harmful to health
  • The limited life cycle of 500 - 1000 cycles
  • Should only use ~50% of battery capacity to avoid premature ageing
  • Blocky construction, limits design
  • Requires maintenance to ensure consistent output
  • Heavy

 

Lithium Difference

  • Prone to thermal runaway, can lead to lithium fire
  • Can use over 85% of capacity
  • The life cycle of 2000 - 5000 cycles
  • Can be charged fast with no absorption phase
  • No need to fully charge the battery
  • Very little energy wasted, close to 100%
  • More suited to extreme temps
  • Fewer placement issues
  • Less maintenance
  • Voltage sag virtually non-existent
  • Weighs less

 

Solvable Problem

If fully discharged, the whole system can be rendered dead by using the lithium battery. Mitigated by including circuitry to prevent a full discharge.

Conclusion

From both the pros and cons of both batteries and the above notes of the characteristics of both batteries. The team has recommended Lithium-ion batteries to be implemented for all future product iterations due to the benefits of the improved life cycle, lack of maintenance needed, and improved efficiency. The negatives of being expensive and explosiveness are mitigated by removing the AC charger which adds unnecessary expense to the product and by using a Lithium Iron Phosphate (LiFePo4) battery which is not flammable.

 Useful Articles

Lead Acid vs Lithium Ion Batteries

https://www.linkedin.com/pulse/lead-acid-vs-l...ies-robert-bean

Battery Showdown: Lead Acid vs. Lithium-Ion -Solar Micro-Grid

https://medium.com/solar-microgrid/battery-sh...on-1d37a1998287

 

edited on 13th September 2018, 06:09 by Justin Hakeem

Scott Jucius Jul 9, 2018

If you are looking into using an established supply chain or importing from South Africa, then probably just ignore what I've written below.

If you are looking into importing lithium batteries from outside Africa, you will most likely not be able to ship the product via air due to safety concerns. Therefore, products would need to be transported via sea which would take time, and since Malawi is landlocked, the product would also need ground transportation. If shipping from China, this would most likely take roughly 40+ days. Therefore, you may need to potentially look into organising batteries in some capacity during this month, rather than leaving it for the next team.

Reply 0

Conna Sheedy Jul 10, 2018

We are currently looking into importation and what that would look like going forward. over the coming week or two there will be another post that will cover that.

Reply 0

Jimmy Menzies Jul 10, 2018

Based on the stats lithium batteries are definitely better. But I remember some of the locals mentioning that they associate bulkier heavier design with quality. So from a marketing perspective the more sleek, light-weight lithium battery might be a harder sell. And to counter the premature ageing of the lead-acid battery a 'control chip' could be introduced to the circuit, so even though it is still not as good as the lithium battery the lead-acid battery could still be a decent product.

I agree that lithium batteries are a better product in general, but are they necessary for Malawians who just need light for a couple of hours a night and, in a few cases, a mobile charged?

Reply 1

Conna Sheedy Jul 10, 2018

We will know more of what Malawians want from feedback from our proxy product. The main concern is how long we want our product to last, if we want it to last at least 2 years, lithium ion is probably the only way to go.

Reply 1

Wade Tink Jul 15, 2018

Product warranty is a consideration to make this a viable business. How long is viable to be able to guarantee the product at this point? Do you think the battery is the main obstacle to the longest warranty possible? If not, what else is the issue?

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Conna Sheedy Jul 16, 2018

I definitely think that the battery is the limiting factor. Most LEDs have a life time of at least 50,000 hours and solar panels have an average warranty of 25 years. Currently I see our product lasting maybe 1-2 years with the lead acid battery. A conservative estimate would be 5.5 years guaranteed lifetime if the battery is switched to lithium. This does assume the product is well looked after

Reply 0

Wade Tink Jul 15, 2018

Status label added: Work Update

Reply 0

Wade Tink Jul 15, 2018

As per Scott's post a proposal on solving this issue is needed. Particularly considering time in country and until next project.

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