Battery Price Break-Even (Sezibwa)
The question
The optimal-allocation case found that at today's battery price, adding battery capacity lowers the return: the money is better spent on solar. But Aaron's point stands: the long-term microgrid model wants more storage, so the real question is a price one. How cheap does battery have to get before expanding it pays? This document answers that, and it is deliberately independent because it rests on a price assumption rather than a fixed quote.
It also takes Aaron's framing as the base case: net metering is not the play (the best value for onsite generation is selling it onsite to the consumer, not feeding it back to a grid that already has a generation surplus). So this analysis uses no feed-in and asks only what storage is worth for shifting onsite solar into the evening.
Method
The same 20-year model (real load, battery aging to 50 percent by year 20, 0.5 percent per year panel fade, 15 percent discount, solar about 990,000 UGX per kWp), but with the battery price swept as a variable instead of fixed. At each price the model re-finds the best allocation of solar and battery and compares its 20-year NPV against the best allocation that adds no battery.
Today's price for reference: the SR-SE10B is 5,568,000 UGX for 8.9 kWh usable, which is about 626,000 UGX per kWh.
Result
The line is the 20-year NPV gained by adding battery, as a function of battery price. Above the break-even it is zero or negative (spend on solar instead). Below it, battery starts to add value, and the gain grows as the price falls.
| Battery price | Best allocation | NPV gain vs no extra battery |
|---|---|---|
| 626,000 per kWh (today) | 5 kWp, no extra battery | 0 (battery does not pay) |
| about 575,000 per kWh (break-even) | 6 kWp, +1 unit | about 0 (marginal) |
| 200,000 per kWh | 6 kWp, +1 unit | about +3.3M |
| 100,000 per kWh | 6 kWp, +2 units | about +4.7M |
| near zero (recycled / free) | 6 kWp, +3 units | about +6.9M |
Findings
- Break-even is about 575,000 UGX per kWh, only about 8 percent below today's price. So battery is right at the edge: a modest price drop makes the first added unit marginally worthwhile.
- Marginal is not a business case. For battery expansion to deliver material value (a few million in NPV), the price needs to fall to roughly 200,000 UGX per kWh, about a third of today's price, or lower.
- At a cheap or free source, the storage-heavy microgrid model works. Near zero cost, the optimum becomes 6 kWp plus three battery units, adding about 6.9M UGX of NPV. This is where a battery-rich standalone system finally beats a solar-only one.
- This validates the recycled-battery strategy. Sourcing second-life cells (for example from cars, which discard packs while still holding 60 to 80 percent capacity) is exactly the path to the price range where expansion pays. The number to aim for is roughly 200,000 UGX per kWh or below; the closer to free, the stronger the case.
Caveats
- Second-life cells are already partly aged, so the "fade to 50 percent over 20 years" assumption is optimistic for them; a shorter effective life would raise the price target (make it stricter). The direction holds: cheap battery unlocks the case, but recycled cells should be de-rated for their remaining life.
- This prices energy value only. Battery also buys backup and autonomy, which has its own value not counted here; that argues for some battery regardless of the energy-only break-even.
Related
Builds on Optimal Solar and Battery Allocation. Companion cases: Battery Arbitrage (alone) and Solar Plus Battery.