Last September we energized a small solar setup at the house: twelve panels on the roof, a battery in the corner, a hybrid inverter on the wall. Total damage (capital expenditures) was ₱325,000 installed. I now have ten months of inverter telemetry, which is enough data to stop guessing. So this post is me marking the system to market the way I would to a stock: real cash flows, real depreciation, no vendor math.

The system

Component	Spec	Cost (₱)
Panels	12 × 585 W (7.02 kWp)	~125,604
Battery	Dyness 200 Ah LFP (~14 kWh)	~100,000
Inverter	Deye 6 kW hybrid	~56,650
Mounting, wiring, installation		~42,746
Total		325,000

No net metering. Anything the house doesn't use in the moment charges the battery, and anything beyond that simply doesn't get made. Keep that constraint in mind, because it shapes everything below.

What ten months of data looks like

September 1, 2025 through July 2, 2026, which is 305 days:

Metric	Value
Produced	4,870 kWh
Consumed	7,160 kWh
Bought from Meralco	2,660 kWh
Battery charged / discharged	2,480 / 2,110 kWh
Exported	0 kWh
Self-sufficiency	63%

Counting savings without lying to yourself

The number every solar seller quotes is production times tariff: 4,870 kWh × ₱15 = ₱73,050. That is the wrong number.

The system's value is the electricity I didn't buy, which is direct self-consumption plus battery discharge: 4,500 kWh, or ₱67,500. The ₱5,550 gap is 370 kWh that died inside the battery. My observed round-trip efficiency is about 85%, which is normal for an LFP hybrid setup. Normal or not, energy that evaporates in conversion is not savings.

₱67,500 over 305 days is ₱221 a day. Annualized naively, that's ₱80,800. But the two months missing from my data are July and August, peak habagat, so an honest full-year figure is closer to ₱78,000.

One more caveat: I priced everything at today's ₱15/kWh even though the tariff floated month to month, so treat every peso figure here as a close approximation rather than an audit.

The shading tax

Here is the embarrassing part. The system is 12 × 585 W, or 7.02 kWp. Unfortunately, there's a bigger house facing our system on the east. My 4,870 kWh in ten months annualizes to about 830 kWh per kWp per year. A well-oriented, unshaded array in Luzon does 1,400 to 1,500. I knew this before installing. The alternative was not a better roof, it was no solar, and 830 shaded kilowatt-hours per installed kilowatt still beat zero.

The grid-tie detour

I spent an evening modeling what happens if I flip the system to export. Philippine net metering credits exports at roughly the generation charge only, historically about half the retail rate, so call it ₱7.50. That gives every kilowatt-hour leaving the panels a strict value hierarchy:

Where the kWh goes	Value (₱)
Straight into a load	~15.00
Through the battery, out at night	~12.76
Exported to Meralco	~7.50
Nowhere	0.00

The battery line is retail times my observed round-trip efficiency, and it is the whole analysis. Every kWh diverted from the battery to the meter earns ₱7.50 but forfeits ₱12.76 of avoided night purchases, losing ₱5.26. Applied to my actual battery flows, going grid-tie would have made the ten months ₱13,056 worse, about ₱15,600 a year.

The general result is cleaner than the specific one: exporting beats storing exactly when the buyback rate exceeds your round-trip efficiency times the retail rate. Meralco would have to credit me 85% of retail before the meter beats the battery, and they pay about 50%. That gap is structural, not situational.

Battery wear doesn't rescue the export case either. Cycling costs me roughly ₱2 per kWh of throughput, and at 0.86 cycles a day, calendar aging will retire this pack long before cycle count does. So the counterintuitive punchline: in a zero-export system, the battery is not a luxury bolted onto solar. It is the only thing standing between my midday surplus and a value of zero.

Running it like a business

Cash yield is ₱78,000 a year on ₱325,000, about 24%, with simple payback in a little over four years, around late 2029.

But cash yield flatters any machine that wears out, so I keep a second set of books. PFRS straight-line, with installation capitalized into the components: panels over 25 years, battery and inverter over 10. That works out to about ₱24,200 a year of depreciation for the first decade, and it is not an accounting fiction. The battery and inverter really will be scrap around 2035, and the replacement money has to come from somewhere.

Component	Years	Annual depreciation (₱)
Panels	1-25	5,785
Battery	1-10	11,514
Inverter	1-10	6,523
Total, years 1-10		23,822
Total, years 11-25		5,785

Subtract it and the system's owner earnings are about ₱53,800 a year, a 16.6% return on invested capital. I use gross cost as the denominator on purpose. Return on net book value looks better every single year as depreciation melts the base toward zero while the cash keeps coming, which is the classic depreciated-base mirage. A wasting asset gets judged on what it cost, not on what's left of it.

What kind of 16.6% this is

Avoided expense is untaxed, so the fair comparisons are after-tax: PSE dividends net of the 10% final withholding, time deposits net of the 20% final tax. The revenue is indexed one-for-one to Meralco tariffs, so it is inflation-linked. It has zero market beta, and it hedges a liability my household already carried.

The battery also throws in brownout insurance, which the arbitrage math never sees but which is worth real pesos in this country. Against all that: single-site hardware risk, total illiquidity, and a hard cap on the upside. It is a strange little bond, but I don't know where else to buy one like it.

Where the next peso goes

The headline ROIC is not the rate I can reinvest at, which is the part most solar ROI posts skip. Ranked by marginal return: shifting load into the solar window is free money at ₱15 per kWh. Restringing or optimizing the shaded panels is cheap and attacks the actual constraint. A second battery earns approximately nothing, because the first one isn't saturating. And the net-metering meter only becomes worth its fee if I ever see sustained curtailment of a couple of kWh a day, which so far I have not.

The system will never make anyone rich. It just quietly deletes most of an electric bill for the next 25 years, and I get to watch it do that from the other side of the planet. I've made worse trades.

NB: This blog was written with the assistance of a LLM. The ideas, analysis, conclusions, and interpretations are my own, and I reviewed and verified the content for accuracy before publication.