Solar energy has been trending upwards for the last decade or so, owing to the new developments in photovoltaic cells and the increase in power generation efficiencies these new developments brought about. Generally speaking for products currently on the market, the efficiency of solar panels will usually be between 10% and 20%, settling at about 15% as far as the average value is concerned. Note that this is true only for commercially available, retail, homeowner application type of panels.
Large or industrial scale solar panels may have a bit higher efficiencies than that, reaching up to 25% owing to the economies of scale for energy production. Furthermore, current research on solar cells have them working at up to 40% efficiency under lab conditions thanks to the new techniques and materials involved (such as GaInP/GaAs/Ge hybrid cells), but more time and testing, as well as a feasible way to produce these novel cells will be required for them to be commercialized effectively in the near future.
Let us do a little calculation to see the cost of meeting the annual power demand of a 1,500 ft2 (about 150 m2) home with the currently available 15% average efficiency solar panels. Assuming 4.8 kWh/ft2/yr as the energy demand for the home, the annual energy demand would be:
Energy demand = 1,500 * 4.8 = 6,400 kWh/yr
In solar energy calculations, one has to factor in the solar irradiance of a given location in order to determine how many hours a day the panel will get unobstructed sunlight. Let us assume the home is in California, and it gets 5.5 hours of unobstructed sunlight daily. Factoring in the efficiency of the panel, and the solar irradiance, we can calculate the total wattage of the solar panels required to keep the house operational:
Daily energy demand = 6,400 * (1/365) = 17.5 kWh
Wattage = 17. 5 kWh * (1/5.5) * (1/0.15) = 21.2 kW
The price for solar panels is usually between $1,200/kW to $1,800/kW, so let us take $1,500/kW as a ballpark figure. The total cost of the solar panel would then be:
Cost = 21.2 kW * $1,200/kW = $25,440
Assuming an annual electric bill of $1,000 (average annual electric bill for homes in the US is about $1,200/yr), it would take the panel 25.4 years to pay for itself, unless there is a rebate or government subsidy of some kind.
The same type of calculations for geothermal or biomass-based solutions, such as anaerobic digestion, will yield about one-half to one-third the rate of return for initial investment as solar panels (limitations of scale may apply). The only caveat is that geothermal is not that great for residential power production, although it can effectively eliminate your cooling/heating energy consumption via heat exchange, and anaerobic digestion will require great amounts of organic solid waste and/or wastewater to work efficiently and be a viable option, considering the startup requirements. That means an anaerobic digester to produce biogas will be required to be set up as a community or neighborhood effort, rather than an individual residential unit. Wind power can also be considered, especially if the location is suitably windy. A good idea would be to combine one or more of these technologies with solar panels to reduce the amount, and therefore, the cost of panels required to meet the projected energy demand.
The efficiency of solar panels is perhaps not their greatest advantage over other forms of alternative energy (yet), but its hassle-free and clean nature. In order to produce biogas using an anaerobic digester, the user has to get in contact with unpleasant waste materials, plus biogas itself poses a constant hazard, and it has to be monitored constantly. Geothermal is better in this regard, but it involves digging the ground down to the water table, and putting pipes there. Plus it requires plumbing to connect with the AC pipes in the house, and it requires the installation of a heat exchanger to function.
In conclusion, although solar panels might not be the most efficient option to generate electricity among different renewable energy alternatives, they certainly are the easiest to install and maintain. Owing to their long service life, solar panels are a “fire and forget” system, which may very well be a viable option if you have the capital to invest in them for the long run.
