Buying cheap, storing intelligently and selling high
This installation demonstrates how a Sigenergy DC-coupled battery system can materially change the economics of a home energy setup.
The property combines 9.02 kWp of solar PV, approximately 18.1 kWh of usable stationary battery storage, a bidirectional EV connection, and a 10 kW Sigenergy hybrid inverter/controller.
While solar generation contributes substantially to the household’s energy economics, one of the most impressive elements of the system is something different: energy arbitrage.
Instead of relying solely on sunshine to charge the batteries, the system can take advantage of very cheap overnight electricity. Energy is purchased from the grid at around 4.99p/kWh, stored in the battery/EV system, and subsequently exported when electricity is worth considerably more.
During August 2026, the average export price actually achieved was approximately 17.98p/kWh
That is the fundamental opportunity:
Buy at 4.99p → store → sell at an average 17.98p.
Even after allowing for energy lost during charging and discharging, there is a substantial spread between the purchase and sale prices. The scale of energy being moved through the installation is significant
August 2026 result
Grid electricity imported 1,744.52 kWh
Grid electricity exported 1,649.55 kWh
Solar generation 906.94 kWh
House consumption 526.60 kWh
Stationary battery charged 793.41 kWh
Stationary battery discharged 761.03 kWh
EV/DC system charged ~1,390 kWh
EV/DC system discharged 953.84 kWh
Electricity import bill £106.73
Export income £296.59
Net electricity cash position +£189.86
Perhaps the most striking figure is that the household exported almost as much electricity as it imported, yet because imports were concentrated into inexpensive periods while exports achieved much higher prices, the financial position was strongly positive.
For the month, export income of £296.59 exceeded the entire electricity import bill of £106.73, leaving a positive electricity cash position of £189.86.
How much came from energy arbitrage?
It is important not to attribute the whole £189.86 to battery arbitrage.
The monthly data does not identify the source of every individual exported kWh, so the analysis uses a conservative lower bound and a practical working estimate.
August solar production was 906.94 kWh, while total exports were 1,649.55 kWh.
Even in the extreme assumption that every single kWh of solar generation had been exported, exports still exceeded solar generation by:
1,649.55 − 906.94 = 742.61 kWh
So at least 742.61 kWh of export must have originated from stored/non-solar energy or energy already held in storage at the beginning of the period.
A more practical estimate assumes that solar first supplied the home’s 526.60 kWh consumption.
That leaves:
906.94 − 526.60 = 380.34 kWh of potential solar surplus.
Subtracting this from total exports gives: 1,649.55 − 380.34 = 1,269.21 kWh
This produces a working estimate of approximately 1.27 MWh of August export associated with stored/grid-derived energy.
Approximately £160 gross arbitrage margin in one month
Using the 1,269.21 kWh working estimate and allowing for a 93% round-trip efficiency, approximately 1,364.74 kWh of cheap electricity would have been required to deliver that exported energy.
At the overnight rate of 4.99p/kWh, the estimated charging cost is: £68.10
The 1,269.21 kWh exported at the achieved average export price of 17.98p/kWh generated approximately: £228.20
That produces an estimated gross energy-arbitrage margin of:
£160.10 for August alone
The calculation is:
£228.20 export value − £68.10 charging cost = £160.10 gross margin
Even using the much more conservative 742.61 kWh lower-bound calculation, the implied gross margin is approximately £93.68.
So the evidence supports a range rather than pretending every exported unit can be precisely attributed: approximately £94–£160 of August gross margin from the storage/arbitrage element, with around £160 representing the working estimate.
Why the Sigenergy system makes this particularly powerful
A conventional solar-and-battery installation is often thought of primarily as a way of storing excess daytime solar for use later in the house.
This installation demonstrates a broader opportunity.
With suitable tariffs and permissions, storage capacity itself can become economically productive. The system can deliberately charge during periods when grid electricity is exceptionally inexpensive and retain that energy until export prices become attractive.
The Sigenergy DC-coupled architecture, combined with the stationary battery and bidirectional EV capability, means a comparatively large volume of energy can be shifted. And volume matters.
A few pence of profit on one kWh is not particularly exciting. Repeating that spread across hundreds or thousands of kWh every month is where the economics become much more interesting.
In August, approximately 1.65 MWh was exported.
That scale is what turns a relatively simple price difference into a meaningful financial result.
The effect on return on investment
Strictly speaking, this strategy does not reduce ROI — it can increase the return on investment and reduce the payback period.
A battery purchased solely to increase solar self-consumption has a limited number of opportunities each day to generate financial value.
A battery capable of participating in electricity-price arbitrage potentially has another revenue stream:
solar saving + avoided peak imports + cheap-rate charging + high-value exports.
Based on the August working estimate, the arbitrage component generated approximately £160.10 of additional gross economic value in one month.
If — purely for illustration — an equivalent margin could be achieved in every month, that would equate to approximately:
£1,921 per year of gross arbitrage margin
That should not be treated as an annual forecast because export prices, weather, available charging periods, battery utilisation and tariffs will change throughout the year.
But it illustrates why arbitrage can have such a significant impact on payback.
For example, if a battery installation had £10,000 of capital cost to recover, an additional £1,000 a year of sustainable net value from arbitrage would shorten its simple payback materially compared with an installation earning value only through solar self-consumption.
The exact payback improvement for this installation requires the original installed cost of the Sigenergy equipment, together with battery degradation, financing and other running-cost assumptions.
A different way to think about home batteries
This case study changes the traditional battery proposition. The question is no longer simply: “How much of my solar can I store?”
It becomes:
“How much energy can my system intelligently move from low-value periods into high-value periods?”
That distinction is important.
During August, the installation bought much of its imported electricity for approximately 4.99p/kWh and achieved an average export price of 17.98p/kWh.
Despite conversion losses, that price spread was sufficiently large to create an estimated £160 gross arbitrage margin, alongside the wider benefits of the property’s solar generation.
The result
For this household, the Sigenergy battery has effectively become far more than emergency storage or a place to put excess solar.
It is an active part of the home’s energy economics
Cheap electricity can be purchased overnight, stored efficiently and sold back when it is worth considerably more.
August 2026 provides a particularly compelling example:
1.745 MWh imported.
1.650 MWh exported.
£296.59 export income.
£106.73 total import bill.
£189.86 positive electricity cash position.
Approximately £160 estimated gross battery/grid-arbitrage margin.
That additional earning potential can materially improve the economics of owning battery storage and, where similar opportunities are available consistently, shorten the time required for the original Sigenergy investment to pay for itself.
Important qualification: the ~£160 figure is a modelled estimate rather than a separately metered arbitrage value. August monthly data does not identify the source of every exported half-hour. The calculation also excludes equipment cost, financing, battery/EV degradation, tax and tariff-specific restrictions. Annual performance should therefore be based on a full year of data rather than multiplying one particularly successful month by twelve.