One kWh will power one 100W bulb for ten hours. A kettle typically has a power rating of between 2 and 3kW. The Tesla Powerwall is a top of the market example of home battery technology; with a capacity of 13.5kWh and a maximum discharge is 7kW. The battery has dimensions 115cm*75cm*14.7cm, a total volume of 0.127m3 and weighs 114kg (Tesla, 2022c). So the energy density by volume of the Powerwall battery is 13.5/0.127 = 106.3kWh/m3. The battery charges at a rate of 3.68kW, so around half its maximum discharge rate. 

A tree of radius 15cm and height 20m has a volume of 1.413m3. Assume the tree takes 40 years to grow to this size. The mean annual increment is therefore 0.0353m2/year. The energy density of air seasoned wood in general is approximately 1500kWh/m3 (Forest Research, 2022b). Therefore our fully grown tree stores 1500*1.413= 2120kWh of energy and it ‘charges’ at a rate of 0.0353*1500 = 52.95kWh/year, therefore at a ‘wattage’ of 52.95/(365*24) = 0.00604kW or 6W.

If we then take one 30cm*10cm*10cm log we have a 0.003m3 volume of wood and an energy content of 4.5kWh, this energy can be released by combustion, conservatively, in half an hour, therefore the power output of the log as it burns is 4.5kWh/0.5 hours = 9kW. The wood has an energy density of 4.5kWh/0.003m3 = 1500kWh/m3. 

So wood has a much higher energy density than the latest lithium battery, and even just one log has a greater power rating than the Tesla Powerwall, wood can also usually be stored in very large quantities, particularly in rural areas. Wood is used once, although a new tree can grow to replace it, whereas a battery is used many times. A tree charges at around one thousandth the rate of a Powerwall and takes up considerably more space. 

The energy consumption from gas for the average uk home in 2014 was 12,400kWh (thegreenage, 2015). This would include heating and hot water applications and averages at 34kWh per day (bearing in mind heating consumption is likely to be significantly higher during the winter months.) So the Tesla Powerwall with a capacity of only 13.5kWh cannot replace the gas boiler. But we know that wood can provide energy needs for heating and hot water and there are a variety of stoves and boilers on the market that will provide these functionalities. 

And if we look at the costs involved, installation of a wood burning boiler stove that provides hot water and central heating might cost in the region of £2000 including installation (stovesareus.co.uk, 2022), not that dissimilar to a new gas boiler installation (GreenMatch, 2022). In terms of the yearly fuel consumption, 12,400kWh at a current British Gas Tariff of 7.37p/kWh equates to £914 per year. Wood logs are quoted mostly between 7.6p/kWh and 10p/kWh (Lekto Wood Fuels, 2022, arbtalk, 2022). 

The answer is perhaps not so much that energy sources other than gas are too expensive, but moreso that gas is still too cheap when compared with, for example, an electricity tariff of 28.34p/kWh. Gas can also provide near instant heat on demand. Indeed these characteristics probably go a long way to explaining the overwhelming preference for gas when it comes to unpredictable heat demands for central heating and hot water. 

A question is whether the price of gas will continue to rise, and then, if so, then will the price of biomass fuels increase in line with that of gas? Of course if you have your own forested land and wood is available on your doorstep, then all you have to pay for is the labour of harvesting. If a forester cuts half a cord of wood in an hour for £10 (1 cord = 3.6m3) then this is 1.8m3 of wood with an energy content of 1.8m3 *1500kWh = 2700kWh. Then £10/2700kWh gives a cost per kWh of 3.70p, less than half the current price of gas. 

References:

arbtalk 2022, , New energy price cap and fire wood prices. Available: https://arbtalk.co.uk/forums/topic/128619-new-energy-price-cap-and-fire-wood-prices/.

GreenMatch 2022, , How Much Does a New Boiler Cost in 2022?. Available: https://www.greenmatch.co.uk/blog/2018/08/new-boiler-cost.

Lekto Wood Fuels 2022, , UK Energy: How Much Does a kWh of Wood Fuel Heat Cost?. Available: https://www.lektowoodfuels.co.uk/blogs/news/uk-wood-fuel-costs-2022.

stovesareus.co.uk 2022, , Boiler and Central Heating Stoves. Available: https://www.stovesareus.co.uk/stoves/wood-burning-stoves/boiler-stoves.html.thegreenage 2015, , How Much Energy Does My Home Use?. Available: https://www.thegreenage.co.uk/how-much-energy-does-my-home-use/.