Prince Charles's income – including funding from the taxpayer for his official duties – rose by nearly £1m last year, according to figures published in the annual review of his activities. His aides insisted that the increases were either not rises at all, or reflected an increase in official visits undertaken at the government's behest.

The most obvious saving highlighted by the report. It has shrunk from 56 pages of cheery photographs of the prince and his wife, the Duchess of Cornwall, going about their official duties, to 24, demonstrating the household's mastery of new technology by placing many of the details on the web, including videos and details of gas emissions and energy usage. Sir Michael Peat, the prince's soon-to-retire private secretary, insisted the move had the prince's personal support as a saving in costs and paper.

Remarkably, although the review indicates the prince travelled 34,000 miles on royal duties in the past year, to the end of this March – 9,000 fewer than the previous year – and halved the amount of foreign travel he undertook, the cost rose by £388,000, to £1,080,000. On a simple cost basis that represents £31.50 a mile, compared with £16.13 the previous year.

Prince Charles's income from grants-in-aid, to subsidise his royal duties, and from government departments, rose by £298,000 to £1.962m. His main income, which comes from the duchy of Cornwall – the ancestral estates of princes of Wales – was up by nearly 4% last year to £17,796,000, owing to profits from his bonds portfolio. Peat described the latter as "in the circumstances a very creditable performance", though he added it was a fall in real terms.

The prince's tax bill – paid on the duchy's surpluses at 50% – plus VAT, national insurance contributions for his employees and council tax payments, increased by £900,000 to nearly £4.4m.

The size of the household – 132.8 members of staff compared with 124 the previous year – increased slightly because five new aides were taken on: three to work for princes William and Harry, one to assist with their father's website and another as an agricultural worker for the Highgrove estate.

Peat said that expenditure had increased in three areas: "Overseas travel is nothing to do with us. The prince and duchess have no say in that. They go where the Foreign Office and the government chooses to send them. The prince's tax is up by 26% and his own expenditure has increased almost entirely because His Royal Highness increased his personal donations to charity."

As in previous years, the review stressed the prince's charitable works, claiming that he had helped to raise £123m directly or indirectly for his 20 core charities, and also the household's continuing commitment to the use of environmentally friendly energy sources. It claims that total carbon emissions fell by 22% and that nearly a third of the energy used comes from renewable sources. Solar photovoltaic panels have been installed on the roof of Clarence House in London and on barn roofs around the farms on the prince's Gloucestershire estate at Highgrove.

An electrically powered Mini intended for use as a staff pool car in London, announced in last year's review, was not, however, a success: it was too small. Peat said: "It was not particularly capacious. We are trying cars the whole time."

One item of conspicuous expenditure not listed in this year's review is the cost to the family of the royal wedding at the end of April and is unlikely to be detailed next year either. Peat said: "What really counted was the happiness of the occasion. I am not going to say how much money was spent. Obviously, the Prince of Wales spent the majority of the costs but I don't think generally people say how much weddings cost do they?"