Energy yields fluctuate on a monthly basis
Each geographic location has specific climate and environmental circumstances making different forms of renewable energy generation more efficient. During the year, seasonal patterns can shift the main benefits from one energy form to another, the energy consumption might be subject to fluctuation, or there are restrictions in terms of assets positioning. All those factors should be considered before investing time and money in any specific technology.
Solar energy is becoming increasingly attractive even for higher latitude locations like North-USA, Canada and Northern Europe. Thus, in this brief article we look at the impact of ice and snow on the yields of solar modules. As an aid, we are using a Site Environmental Awareness report, which can be easily obtained for any geographical location worldwide.
Estimating the losses due to ice and snow
Our atSEA report has a handy table showing the annual sum of available solar energy in kilowatt hours (kWh) per square meter for different mounting angles of solar panels. In another graphic, it shows the relative losses as percentage if we are unable to mount at the most efficient tilt and orientation.
What an interesting outcome for our location! In spring and fall, we could produce about as much electricity using wall mounted panels with 90 degrees tilt as from panels mounted at optimum 50 degrees tilt. It is interesting, since vertical wall mounted panels would be much less affected by snow accumulation.
Let’s quantify the issue. If we assume that snow and ice accumulation would make the modules unproductive over winter months and early spring, the annual loss would be an average of 240 kWh/m2, the sum of the output for late fall and spring months.
However, for vertical mounting the production would be significantly lower in summer months compared to optimum tilt. Counting the monthly difference in our plot we find that it amounts to about 260 kWh/m2 loss over a six-month period. Which is like the losses of optimum mounting tilt due to snow and ice.
What an interesting outcome for our location! In spring and fall, we could produce about as much electricity using wall mounted panels with 90 degrees tilt as from panels mounted at optimum 50 degrees tilt. It is interesting, since vertical wall mounted panels would be much less affected by snow accumulation.
Let’s quantify the issue. If we assume that snow and ice accumulation would make the modules unproductive over winter months and early spring, the annual loss would be an average of 240 kWh/m2, the sum of the output for late fall and spring months.
However, for vertical mounting the production would be significantly lower in summer months compared to optimum tilt. Counting the monthly difference in our plot we find that it amounts to about 260 kWh/m2 loss over a six-month period. Which is like the losses of optimum mounting tilt due to snow and ice.
Assessment of different mitigation scenarios
We could just accept that nothing is perfect and simply evaluate which mounting positions require least investment and would have lower maintenance costs during the life cycle of the modules. Or we look at simple mitigation possibilities.
To mitigate the losses of vertical mounting, simple engineering solutions exist, for example, lifting the panels 30-40 degrees away from the wall in the spring to achieve the optimum 50-60 degrees tilt angle for the summer season. It would mean repositioning the panels twice a year, probably a couple of minutes effort per module assuming cheap engineering. 20 modules would translate to about 2 hours labor per year.
For the mounting at the optimum tilt, we are facing the ice and snow clearing issue, which might be particularly challenging on a steep roof top. Climbing on icy roofs is extremely dangerous and should not be attempted! Thus, safe access is something to consider when selecting the position for the modules. The one-off access when modules are mounted is not the same as regular maintenance access. It is the main reason many use their garden space rather than the roof-top for solar modules. Obviously, this depends on the availability of such space and the expected frequency that maintenance is needed, for example cleaning in very dusty areas or like in our case, removal of ice and snow.
To estimate the frequency of the snow problem, we look at the number of wet days in combination with frost days for different months which suggest that precipitation is in the form of snow and there is ice buildup. It seems that we have a remarkably high fraction of days with precipitation suggesting small amounts of snow every other day (on average). A nightmare from the snow clearing perspective…. But each location is different, and it is always worth evaluating on a case-by-case basis.
Estimating the losses due to ice and snow
Let’s translate the ice and snow issue into monetary terms.
At the optimum mounting tilt of 50 degrees and orientation of 20 degrees to the west, (because our location has better afternoon sun!), we could be getting 1165 kWh/m2/year assuming accessible position where ice and snow can be cleared regularly.
With even a very modest electricity cost of 40 cents per kilowatt hour and average panel efficiency of 30%, our location could produce about 140 euro (150 USD) per square meter per year worth of electricity. If snow and ice clearing is not addressed or wall mounted panels are not tilted for the summer our losses would mean minus 30 euro. Which for a total module surface of 40 square meters translates already to a loss of 1200 euro (1300 USD) per year. The cost of quality location intelligence from atsea.fi helping us to quantify and mitigate the losses was just a fraction of it.
The numbers from the Site Environmental Awareness report are based on a combination of satellite and ground-based measurements with physical models resulting in highly localized data. Locations just 50 km (about 31.07 mi) away may have different available solar energy levels, but the approach on how to use data to optimize the positioning remains the same.
Final position choice will be strongly affected by the availability of suitable mounting points within the property.
