Brr, it's that time of year to get out the puffa jackets and pull on the thermals.
The advance of Winter brings with it reduced solar irradiation levels, the summer peak can drop by 70-90% to that of the lowest level experienced in December/January. This means solar-only solutions can struggle to deliver all the power needed to keep off-grid equipment running. Or the system must be drastically over-sized for the summer months so it can deliver what's required in the winter.
The solution is to have a hybrid system where solar and wind compliment each other.
In most parts of the world, winters are noticeably windier, perfect for wind turbines. When we advise customers on the most cost effective combination of solar and wind to meet their specific power requirements, we size the system by looking at the worst case scenario and that's Winter.
Wind plays a particularly important role in temperate zones above a latitude of 55oN because the solar levels are significantly reduced in the winter. Take a look at the mean monthly sunshine levels on Lerwick, Shetland Islands in Scotland which is 60oN. Winter levels are about 12% of the summer peak. Compare this now with mean monthly wind speed - during January wind speeds are nearly twice that of July and August.
So we can accurately size an off-grid power system, the first thing we need to do is capture the details about the power load and proposed location. Is the power requirement continuous or for a defined number of hours per day? What is the peak and standby power of the equipment? What voltage is each piece of equipment? Where is the site - GPS or post/zip code is useful here? Is it on hill, in a valley or with trees/buildings nearby? All this is important as it affects which wind turbine we'd choose from our range.
Using a combination of different wind speed and solar irradiation databases, we can estimate the power production of a bespoke system as seen below.
Here the equipment is drawing 28W continuously - it's radio repeater equipment located in south-west England (50.7oN) where the annual average wind speed is 4.8m/s. Allowing for a 20% safety margin (see the red line), this installation requires an LE-300 wind turbine and 2 x 70W monocrystalline solar panels from our DC-Solar range featuring 21.5% efficient Sunpower cells.
Where the off-grid system is mission critical, a generator or methanol fuel cells, are recommended as a back-up. Solar and wind provide the bulk of the power with fuel cells kicking in when batteries reach a pre-defined level of discharge.
Contact us if you are planning on installing off-grid equipment, we'd be pleased to recommend a reliable hybrid power solution.
