Battery Price Break-Even (Sezibwa)

[!info] Conservative, bank-facing basis (revised after independent review) Turnkey installed capex and real day-to-day weather. Independent of the other docs because it rests on a battery-price assumption rather than a fixed quote.

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?

It takes Aaron's framing as the base case: net metering is not the play (best value is selling onsite, not feeding a grid that already has a generation surplus). So this 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, real weather, battery aging to 50 percent by year 20, turnkey solar, 15 percent discount) but with the battery price swept as a variable. At each price the model re-finds the best allocation and compares its NPV against the best allocation that adds no battery. Today's price: SR-SE10B is 5,568,000 UGX for 8.9 kWh usable, about 626,000 UGX per kWh.

Result

The break-even is anchor-dependent (it depends how much solar you already have, because a bigger array spills more surplus that a battery could soak up):

At the 5 kWp optimum, battery must fall to about 410,000 UGX/kWh (about a third cheaper than today) before the first extra unit pays. Below that, the gain grows.

Investment metrics (15 percent cost of capital)

Findings

1. Break-even at the 5 kWp optimum is about 410,000 UGX/kWh, roughly a third below today. Higher if you have already scaled solar to 6 kWp, lower at 4 kWp.
2. For material value you want battery well below break-even, toward 200,000 UGX/kWh or less (6 kWp + 1 unit gives about 13.2M NPV at that price).
3. At a cheap or free source the storage-heavy model wins outright: recycled cells give 6 kWp plus three units, about 17.6M NPV and a 54 percent IRR, better than solar-only.
4. This validates the recycled-battery strategy. Second-life cells (discarded by cars while still holding 60 to 80 percent) are the path into the price range where expansion pays. Aim for roughly 200,000 UGX/kWh or below.

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 raises the price target (makes it stricter). This prices energy value only; battery also buys backup, which has its own value not counted here.

Related

Builds on Optimal Solar and Battery Allocation. Companion cases: Battery Arbitrage (alone) and Solar Plus Battery.