Medium to longer-term developments in the energy sector, and the risk / reward permutations offered by it, often appear attractive to many investors. However, at a time of market volatility, directly investing in energy equities may not be for everyone.

By that logic, a potentially less risky mode of exposure to the sector and the pursuit of a passive income may be via energy investment trusts. Typically listed on the UK and Japanese markets, investment trusts are public-listed pooled investment vehicles that generate income by investing in stocks of other companies, bonds (both corporate and government issued), real estate, infrastructure and privately held enterprises, etc.

They are closed-end entities, i.e., issuers of a fixed number of shares at any given time with their fund managers restricted from creating or redeeming shares continuously. When examining the performance of such trusts, two key figures to look at would be their net asset value (NAV) per share and dividend yield.

Starting with the former, NAV per share is a trust's total assets minus its liabilities, divided by the number of shares in issuance. If a trust’s shares are trading at a "discount", then it provides investors with an indication that its share price is lower than its NAV per share. A discount may offer an opportunity to profit because it suggests market sentiment at a given moment in time – for whatever reason (price of securities held, negative news-flow, etc.) – values the securities or assets in the fund to be below their comprehensive NAV value.

This may potentially offer an opportunity for a higher value realization at a later date in the trading cycle subject to market conditions often over a 3 to 5 year horizon. However, a trust's share price may also be higher than its NAV per share and trade at a premium. The second thing to consider is the dividend-yield or dividend-price ratio, especially in the pursuit of a passive income. It is a trust's dividend per share divided by its share price, expressed as a percentage to gauge returns. Be advised that not all trusts offer dividends.

Unsurprisingly, several energy investment trusts are on offer without having to undertake the risk of investing in specific equities. Many are easy to trade and provide exposure to energy exploration, infrastructure, storage and transmission. As with any asset, investors may need to do some background research and gauge their suitability in line with investment objectives and risk appetite.

Based on current dividend yields*, NAV discounts** and exchange rates***, the following two UK-listed energy investment trusts may be worth exploring:

Dividend Yield: 3.85%

NAV Discount: -9.71%

52-week high: 149.50p (Currency GBP / USD equivalent $1.95)

52-week low: 99p

Manged by BlackRock BLK , this specialist energy and mining investment trust has an objective of offering relatively stable quarterly dividends to set targets, as well as capital growth by investing primarily in the securities of companies operating in these sectors.

In its ambition of achieving long-term diversification of income and capital, BlackRock Energy and Resources Income (BERI) Trust currently allocates investment capital along three investment pathways – traditional energy (32%), energy transition (28%) and mining and resources (40%)****.

Listed on London's main market since December 2005, this trust's top 10 investment holdings include a veritable who's-who of global energy and mining namely – ExxonMobil XOM , Vale, Glencore, BHP, Teck Resources, Shell, BP, NextEra Energy NEE , Canadian Natural Resources and First Quantum Minerals.

Dividend Yield: 5.21%

NAV Discount: -13.62%

52-week high: 183.50p (Currency GBP / USD equivalent $2.39)

52-week low: 134.00p

As the world transitions to renewables, energy storage in general, and utility-scale battery energy storage systems (or "BESS") in particular, are incrementally entering both investors' conversations as well as their portfolios. Gresham House Energy Storage Fund plc (GRID) proactively holds and invests in precisely such assets by seeking to capitalize on the growing intraday supply and demand imbalances caused by increasing reliance on renewable energy in the UK and Ireland.

Its stated aim is to provide investors with an attractive and sustainable quarterly dividend by investing in a portfolio of British and Irish BESS that primarily use batteries to import and export power, and accessing the multiple revenue sources available in the power market.

As per the latest information*****, it has 590MW of operational portfolio holdings, as well as a further 700MW in pipeline portfolio holdings, lending credence to its managers' assertion of being constantly on the lookout for an "attractively priced pipeline".