If you already have solar panels, the most valuable thing you can do this month costs nothing and takes five minutes: find out exactly what electricity tariff you are on.
This matters because almost everything below only works on a tariff with more than one rate, or a tariff that pays you for what you export. If you are on a single flat-rate tariff, with one price for every unit you import and no meaningful separate export payment, most of the advice in this article does not apply to you. The arithmetic below all depends on there being a gap between two numbers: what you pay to import, what you are paid to export, and, if your tariff has one, what you pay at different times of day. No gap, no saving.
So before doing anything else, check your tariff’s structure. Log into your supplier account or read your latest bill, and confirm whether you are on a flat rate, a time-of-use rate with a cheaper off-peak period, or an export tariff that pays a different rate to your import rate.
The two ways to save
Once you know your tariff has a gap to exploit, there are two distinct things you can do with a load you control, such as a dishwasher, washing machine or immersion heater.
Shift the load into your own generation. If you run an appliance while your panels are generating more than the house is using, you consume electricity you would otherwise have exported. You save the price you would have paid to import that unit, but you give up the payment you would have received for exporting it.
The value of doing this is the difference between your import rate and your export rate, not the full import rate. That distinction matters more than it sounds. People assume that using their own solar saves them the whole cost of a unit of electricity, and it does not, because the unit was worth something already. Look up your own two rates, subtract one from the other, and that is what one shifted unit is worth to you. We are not going to publish an illustrative figure here, because a made-up pair of rates would tell you nothing about your own.
Shift the load to an off-peak period. If your tariff has a cheaper off-peak window, for example overnight, running an appliance then instead of during the day saves the difference between your normal day rate and your off-peak rate. The mechanism is the same subtraction, just with two import rates instead of an import and an export rate.
Where your panels are actually generating, daytime self-consumption is usually the stronger move of the two, because it captures its saving immediately, from generation you already have, rather than requiring you to wait for an off-peak window. Once the sun goes down, the off-peak comparison becomes the relevant one instead.
Timers, and the safety line that matters more than the saving
Most modern washing machines, dishwashers and some tumble dryers have a delay-start function, which lets you set an appliance to begin its cycle at a chosen time rather than immediately. This is the practical tool for acting on either calculation above.
There is a firm safety limit on how you use it. UK fire services advise against running washing machines or tumble dryers overnight or while a property is unattended. Dorset and Wiltshire Fire and Rescue Service states plainly: “Never leave your appliance unattended or running overnight”, and that the advice is to never use tumble dryers and washing machines overnight, because there is a risk of fire if these appliances develop a fault, and if that happens when people are sleeping the risk to life is far greater.
Source: Dorset and Wiltshire Fire and Rescue Service, “Tumble dryers and washing machines”, checked 25 August 2026. https://www.dwfire.org.uk/safety/safety-at-home/causes-of-fires/tumble-dryers-washing-machines/
That advice should set the boundary of your timer settings, not the tariff arithmetic. Set a delay-start so the cycle finishes while someone is awake and in the property: a morning generation window that finishes by mid-afternoon, or an off-peak slot timed to end shortly after you wake rather than running unattended for hours. Do not set a cycle to run through the night while you sleep, and do not set one to run for the full working day while the house is empty.
On how much energy a single wash or dry actually uses, so you can judge what a shift is worth in practice, we are not giving a figure. The number that matters is the one on your own appliance’s energy label or in its manual, given per cycle for the programme you actually use, and it varies more between machines and programmes than any average would suggest.
If your system is on a legacy Feed-in Tariff and you have roof space left, adding panels is less risky than most owners assume, but there is one metering decision that quietly costs money. Adding panels when you are on a legacy Feed-in Tariff sets it out.
What this article does not cover
This is about the arithmetic and timing decisions for a household that already has solar, whether or not it also has a battery.
It does not cover what happens to generation you neither use nor shift, which is whether your system is quietly wasting generation. It does not cover battery charge scheduling, which is when your battery should actually charge. And if you are deciding whether to add solar or a battery in the first place, that is the solar and battery storage guides, not this one.
Correct as of 27 August 2026. Tariff structures, rates and appliance features change; check your supplier’s current terms before acting on the arithmetic above.
