There is some promise of Solar PV getting a another small leap in efficiency soon , the perskoyvite , has had the headlines recently but some talk of graphene based one has been around also , but no real life test results , but been doing a little comparison thinking to perhaps some eco thinking isnt as daft as it sounds.
If it takes 2 Hectares of land to have a solar PV array of peak 1MW output and estimated CO2 per kwh over a 25yr life span is 0.5g and if we have an average annual output of around 835,000 kwh for the 2 hecatre (will be more for high solar sites) then a CO2 cost of 417.7 kg a year (x25 year life span = 10,437.5 kg and perhaps if replaced 4 times in 100 yrs =41,750 kg)
Useful comparison point is 41,750kg of CO2 being produced in 100yrs by using them , but obviously quite good where they replace fossil fuel., they dont recycle , but bar the metals/doping pretty inert and probebly not too much of a problem , although sheer volume will be a problem , if we cant reccyle them.
If we plant the 2 hectares with trees for 100yrs and use the timber for building e.g houses lets see how this looks
A conifer forest will be absorbing around 0.8-2.5 tonnes of CO2 per hectare so 1.6-5 tonnes of CO2 per year for our 2 hectare plot and as we might harvest every 100yrs as useable timber somthing like 450,000kg will have been absorbed , and if we use to make houses , we also negate some of the CO2 of certain construction materials. Couldnt fing a kg wt for a single house using timber frame, so dont know how many houses it would make , also measuring timber is a bit of an art , fresh cut timber will lose about half its weight to become construction grade , and actual species has surprising differences in density.
If we think as biomass then before we started really mining coal , coppiced wood really was the energy mainstay for at least 1000yrs in the UK, charcoal enabling the bronze and iron smelting , and a 2 hectare coppice (if managed well and suitable species) could be absorbing 10-12 tonnes of CO2 per hectare , so 20-24 tonnes of CO2 per 2 hectares , over 100yrs is an astonishing 2,200,000kgs of CO2 absorbed.
Its true solar PV doesnt need water to grow and they are for now considered a good renewable , but the trees do go onto storing there captured CO2 much further as a building material , and of course when the woods life as a building material is done , we can burn it as biomass.
By comparison to , and to show just how important the tropical rainforests really are , a conifer forest that we typically see in N America and N Europe will absorb 0.8 to 2.5 tonnes of CO2 per hectare , the rainforests (as forest) absorbs 10 tonnes of CO2 per hectare per year ...
