"We open the cafe when we have power and when the lights go out, we close it again,” he says. “It is difficult, because we cannot make our usual monthly plan. We don’t know when we will have customers or not.
"When we are open, though, we are busy with a lot of customers, because people want to come here to work. The power and the wifi is more reliable than in their apartments. We just try to run our business as normal.”
The Blue Cup is one of many cafes and other businesses still managing to operate amid rolling power blackouts and regular air raid alerts.
From the cafe’s social media pages, there is no sign that anything is unusual. The business is recruiting – advertising for a pastry chef with “experience and a great desire to create cool desserts”. Earlier this week, staff posted photographs of Facebook and Instagram of a tasty-looking breakfast special of “cheesecakes with strawberry jam and sour cream”.
Ukrainian president Volodymyr Zelensky has meanwhile accused Russia of engaging in "energy terrorism" after strikes on Ukraine's energy network left millions of residents without power. About 4.5 million people were without electricity across the country, Mr Zelensky said – many of them in the capital Kyiv.
Kyiv mayor Vitali Klitschko warned 450,000 apartments in the capital alone did not have power on Friday and urged residents to save as much electricity as possible.
Meanwhile, state-owned grid operator Ukrenergo reported that emergency blackouts would be taking place across Kyiv. Russia has carried out missile and drone attacks on Ukrainian power facilities, particularly in recent weeks.
Mr Fomenko’s own apartment is without power in the evenings. "We just light a candle and have dinner,” he says. “We have a gas stove, so when the electricity is off, that still works, we are cooking like that.”
Yuliia Pavytska, a researcher at the Kyiv School of Economics Institute, has prepared her office – and her team – for regular blackouts.
"Our institute bought a generator which powers the bomb shelter, so we can have some lights and wifi there,” she says. “It also has some stable electricity for wifi on some floors, so if we have an outage for three to four hours, we can still stay at the office and work. We have bought little battery-powered lanterns so we can have some light.”
She adds: "For the past eight months, Ukraine developed a high resistance to these new challenges and the ability to manage these new conditions we need to live in.
"A lot of my colleagues and friends have all bought products such as power packs and stocks of drinking water and basic food. We also have those at work.
"I am planning to go shopping this weekend to buy thermal underwear in case we have problems with heating. These are things I have never thought about in my normal life. This is the new reality.”
Ms Pavytska said she and her team had identified offline projects they could work on at times when they are without internet.
"We have a database which we have downloaded and can work on that when we have no wifi access,” she said. “We are lucky, because to do our work as a think-tank, we need just our minds and a laptop. It is harder for businesses which produce or sell something.”
She said there was little frustration among friends and colleagues over the blackouts. She lives alone on the outskirts of Kyiv, but plans to move in with her mother if the power outages become too difficult for both of them.
"It is inconvenient for us, but we’re fighting for our independence,” she said. “Having no light is the least we can suffer for now.”
In his address, Mr Zelensky described the targeting of energy infrastructure as a sign of weakness. "The very fact that Russia is resorting to energy terrorism shows the weakness of our enemy," he said. "They cannot beat Ukraine on the battlefield, so they try to break our people this way."
Mr Zelensky spoke soon after Moscow-appointed authorities in southern Ukraine's occupied Kherson region said Russian troops were likely to leave the city of Kherson – a claim that Ukrainian officials greeted with some scepticism.
The Kremlin-installed regional administration has already moved tens of thousands of civilians out of the city, citing the threat of increased shelling as Ukraine's army pursues a counter-offensive to reclaim the region. Authorities removed the Russian flag from the Kherson administration building on Thursday, a week after the regional government moved out.
Ukraine's southern military spokeswoman Natalia Humeniuk said the flag's removal could be a ruse "and we should not hurry to rejoice". She told Ukrainian television some Russian military personnel are disguising themselves as civilians. Neither side's claims could be independently verified.
Elsewhere, Ukrainian officials reported shooting down drones launched by Russian forces. Dnipropetrovsk governor Valentyn Reznichenko said eight drones were shot down in the Nikopol area, which was also subjected to artillery shelling.
Another drone was shot down over the western Lviv region, governor Maksym Kozytskyy said. Local Ukrainian officials said Russian forces shelled the regions of Mykolaiv in the south and Kharkiv in the north-east overnight, although no casualties were reported.
The commander of Ukraine's armed forces, Valeriy Zaluzhny, said on Thursday night Russian forces had "tripled the intensity of hostilities on certain areas of the front" and were carrying out "up to 80 attacks every day".
Mr Zelensky's office said at least nine civilians were killed and 16 injured in Ukraine over the previous 24 hours, while the Russian army attacked four cities close to the Zaporizhzhia nuclear power plant with drones and heavy artillery.