The firm also ran its coal-fired Rankine units more during dry periods at the start of the financial year and again over the summer.
It has a swaption agreement to cover Meridian Energy's output when that firm's South Island dams are low, and also uses the Rankine units to cap prices for other retailers and those of its industrial customers who buy power at spot rates.
"The result reflects strong performance as the integration between Kupe and the company's flexible generation portfolio delivered value in response to variable wholesale market conditions," chair Jenny Shipley said in a statement to the NZX.
"The customer segment performed well in a year of transition that included the integration of a new LPG operation, a billing system migration and a brand relaunch with the backdrop of increasing electricity market competition."
Genesis shares slipped 0.8 per cent to $2.545, having gained about 2 per cent this year.
Investors registered on October 5 will receive an 8.6 cent final dividend on October 19.
A year ago the company paid 8.4 cents.
Genesis had forecast full-year ebitdaf of $350m to $360 million.
It expects earnings of $350 million to $370 million in the current year, assuming a return to more normal hydrology, on-going customer growth, and allowing for a 50-day mid-life shut at its largest power station, the 400 MW gas-fired E3P plant at Huntly.
That work is expected to trim earnings by about $10m and could push capex $11m higher to $85m.
The company invested $80m last year, including upgrades at Tekapo, Tuai and Tokaanu, integrating the new LPG business and new digital retail products.
Net profit fell to $19.8 million, down 83 percent from $118.7 million the year before. The change reflects higher depreciation charges and a $100m swing in the value of the Rankine units.
Genesis has pledged to stop running the coal units routinely by 2025 and shut them entirely by 2030.
Having written up their value by $51.5m last year, it wrote them down by almost $49m this year.
The company said the lower valuation reflects lower price and generation volume assumptions for the units, offset by the life extension to 2030.
Kupe was the driver of the earnings improvement, with the increased holding – 46 per cent from 31 per cent previously – and higher oil prices lifting the division's earnings to $115m from $84mlast year.
While generation prices and volumes improved, margins were lower and the reduced output from the low-cost Tekapo plants trimmed earnings by about $5m.
Carbon costs also increased by about $6m.
After allowing for operating cost improvements and insurance received for the Tekapo fault, wholesale division earnings increased by only $2m to $178m.
Earnings from the customer division were unchanged at $110m.
While efficiency and mix improvements lifted margins by $11m, investments in new products and services and reduced volumes from customer losses reduced earnings by a matching amount.
Genesis is the country's biggest retailer by accounts.
While its digital Energy Online brand gained about 4,000 accounts during the past year, the firm's main Genesis brand dropped about 10,000 over the same period, according to Electricity Authority data.
It is working to get more power consumers to also buy gas and LPG from it. It has also used its dual-fuel capability to push aggressively into the industrial and commercial market.
New branding and better services saw the firm's customer losses slow during 2018.
Its brand reputation has also increased markedly, bad debts are down and customers carried out 1.3 million digital self-service interactions – 46 per cent more than the year before.
But those improvements came at a cost. Group operating costs increased by $21m to $305m, of which Genesis said about $12m was growth-related spending on brands and sales and technology staff.
Chief executive Marc England said the firm had spent the past year creating a multi-fuel, single service platform to support its yields and growth proposition.
"Genesis customers have more knowledge and visibility than they have ever had to help them monitor, predict and compare their energy spend. We are now also adding a holistic approach to sustainability as we demonstrate commitment to supporting New Zealand's transition to a low emissions economy," he said.
