Three savings sources from your solar battery: self-consumption, arbitrage and grid services

Five years ago, a solar battery had one job: store the morning sun to spend it in the evening. Tariff savings, period. Today that view falls short. The same battery you own — or are evaluating — can do three jobs at once, and each pays separately.

This article is a practical guide, without complicated maths, to understand how a 2026 SolarBox battery can generate three different income streams that add up at the end of the year. We'll explain them one by one, put real numbers on a household and a small business, and see how payback changes with how many sources you have active.

The key idea: three floors of the same building

Picture your battery as a three-storey building. Each floor has a different function, each floor generates a different income, and — most importantly — the three don't get in each other's way. The same battery, the same stored kWh, work simultaneously for all three. You don't have to choose. You have all three.

Stream 1 — Solar self-consumption (what the battery already does today)

This is the classic function and probably what you have in mind when you think of a solar battery. The concept is simple: the sun rises and your installation produces energy, but you only consume part of it — the rest gets sold to the grid for four cents per kWh. With a battery, instead of selling it you store it. In the evening, when the sun is gone and you cook dinner, run the washer and charge the car, you draw from the battery instead of buying from the grid at 25 cents per kWh.

The gap between selling surplus at 4 cents and not having to buy it at 25 is the heart of the saving. Every kWh the battery lets you "move" from midday to evening is worth about 20 cents. Multiplied by hundreds of cycles a year, that's real money.

How much does Stream 1 contribute?

It depends heavily on your solar production and consumption pattern. For a typical Spanish household with a SolarBox SB30 (30 kWh) + 5 kWp of panels and annual consumption of 3,500 kWh, savings hover around €600-800 per year of pure tariff offset. For a small business or shop with a SB60 (60 kWh) + 15 kWp and 12,000 kWh/year consumption, the range is typically €1,800-2,400 per year.

Stream 2 — Hourly price arbitrage (buy low, sell high)

This stream is more recent and many customers don't even know it exists. The idea is as old as commerce: buy cheap, sell expensive. Applied to electricity: charge the battery at night (when kWh costs 7-9 cents) and discharge in the evening (when kWh costs 18-22 cents). That gap — 10 to 15 cents per kWh — is yours to keep.

What changed in 2026 to make this interesting is that the gap between cheap and expensive hours has widened enormously. Five years ago the peak/off-peak ratio was 1.8×. Today it often reaches 3×, and on days of heavy solar production climbs to 6-8×. The "renewable paradox" — daytime prices crashing to zero from solar excess while evening prices stay high because demand keeps going — has created a value pool your battery can capture.

When this stream works best:

• Low-sun days (winter, cloudy): no own production, but plenty of night-evening spread to arbitrage
• When you're away from home (holidays): you don't consume solar; the battery works alone
• Winter, when solar yields little but evening loads (lighting, heating) spike
• Weekends: whole day at off-peak rates (Spain's 3.0TD), allowing full cycles

Self-consumption and arbitrage complement each other perfectly: sunny days the battery does self-consumption; cloudy days it does arbitrage. Same battery, two strategies, two incomes.

How much does Stream 2 contribute?

For the same household (SB30, 3,500 kWh/year), well-managed automatic arbitrage adds around €150-300 extra per year. For the small business (SB60, 12,000 kWh/year), €400-600 extra. Businesses pull a premium because they have more constant consumption, sharper time-of-use rates, and operate all year in business hours where price peaks are most frequent.

Stream 3 — Grid services (the newest, still emerging)

This third stream is the most futuristic of the three, but it's not science fiction: it already exists in Germany, Belgium, the UK and California. In Spain it just took a major step: in February 2026 the Royal Decree 88/2026 formally created the independent aggregator figure. The legal framework is now in place; operational rollout is next. The idea: the grid operator (REE in Spain) leases your battery when it needs to balance the system.

Why does the grid need balancing? Because an electricity network works like a scale: generation and consumption must match within milliseconds. When a plant trips or a cloud crosses a solar farm, the system must correct instantly. Traditionally this is done with thermal or hydro backup — expensive and polluting. But thousands of aggregated home batteries can do the same job better, faster, and cheaper.

Key points to understand:

First: you don't lose control of your battery. You cede a portion — typically 30-50% of capacity — to the aggregator, but the rest is yours 100% for self-consumption and arbitrage. Stream 3 adds; it doesn't replace.

Second: this stream needs at least 1 MW of aggregated power to access the ancillary services market (REE sets this floor; RD 88/2026 regulates the aggregator). Note the common confusion: the threshold is in power (MW, instant push to grid), not in energy (MWh, what you've stored). A single home battery doesn't participate alone; it does so alongside hundreds of others coordinated by an independent aggregator. Since an SB30 cedes about 3 kW, it takes around 300 SB30 batteries — or about 167 SB60, which cede twice — to reach 1 MW.

For a household with an SB30, expected income — once the market is consolidated (2027-2030) and in a favourable scenario — sits around €200/year; in a cautious scenario closer to €100-130. For a small business with an SB60 and a larger inverter, around €400/year in the high case. Better viewed as a complement — a 15-25% top-up over self-consumption savings — rather than a second equivalent source.

The realistic calculation for the SB30 assumes: ceding 40% capacity (12 kWh), inverter limiting power to 3 kW, 6% of yearly hours actively dispatched (525 h), tariff net to client ~13 ¢/kWh after aggregator fees. Total: 525 × 3 kW × 0.13 ≈ €200/year.

The total: how much does a battery stack across all three?

For a household (SB30, 3,500 kWh/year, 5 kWp solar): €700-1,100/year combined (€700 Stream 1 only; €900 with Stream 2; €1,100 all three). Payback drops from 8.5 to 5.5 years.

For a small business (SB60, 12,000 kWh/year, 15 kWp solar): €2,400-3,300/year combined (€2,400 Stream 1 only; €2,900 with Stream 2; €3,300 all three). Payback drops from 5.0 to 3.7 years.

But does your battery actually do all three?

This is the least visible and most important aspect. The three streams only work if your battery has the right brain for each:

• Stream 1 (self-consumption): practically every solar battery today does this. Standard.
• Stream 2 (arbitrage): needs internet connection and a system reading prices hourly and deciding in real time. Some batteries do this; many don't.
• Stream 3 (grid services): needs real-time telemetry (latency <5 s), remote dispatch capability, unique battery ID (the EU Battery Passport mandatory from February 2027), and an aggregator contract.

At SolarBox we built our platform around these three streams from day one. Our fleet manager already collects real-time data per installed battery; firmware v3.10.13 already includes the passport_uid the future Stream 3 will need; and our management algorithms already arbitrage prices for customers on time-of-use tariffs. While many batteries bought in 2026 will be stuck on Stream 1 for their entire useful life, a SolarBox battery is ready for all three.

Why this matters beyond the money

The numbers are striking — €950-3,400/year combined is a lot — but the more interesting reading is another: the battery stops being an amortizable cost and becomes a revenue-generating asset. That's not a semantic difference. It changes how the investment should be framed entirely.

A battery understood only as "savings" has a closed horizon: past payback, you keep gaining but the conversation ends. A battery understood as a three-stream asset has a growing economic life: each year more services open at market, more remuneration modalities appear, more amortization paths exist. The same SB30 bought in 2026 could end up generating more income in 2030 than in 2026 with no hardware change — simply because the surrounding market will have matured.