Calculation of solar and wind generator in a combined off grid solution

With this guide, you can figure out how much solar and what type of wind generator you need in a combined installation.

You can jump directly to the joined calculator for photovoltaic and wind generators, but we recommend that you read this article first.

It will always be your own decision how much solar vs. wind you want. To help you with decision this guide starts with the basic.

What are your power needs?

The calculation of your total power requirements, is based on a review of your electrical appliances consumption of power (Watts) and how many hours they are running every day. Put this into the calculator. This gives you your total needs per day (in Wh and Ah).

Then select how many watts of solar you initially wants to do the calculation on (can be changed on the fly!) and select a wind generator in the graph below. Read how much power per day (Ah / day), at a given m/s. Put also this into the calculator.
Finally you can, based on what the power needs are, see if the selected solar/wind generator combination will be sufficient.
The result will show if you are supplied with power, month by month. Most all year installations need more power in winter than in summer, this is not in the calculation! This often points towards a larger wind generator.

When you need to weigh the sun and wind against each other, be sure to think of this relation between solar power and wind generator performance over the year.
If your needs are in the summer, you should have a lot of solar and in the winter the wind generator are typically more productive.

Solar and wind generator calculator for boat, caravans cottages and offgridPower Needs distributed throughout the year

If you have power needs all year, you must have a balanced power production where you primarily use solar in the summer and primarily wind generator in winter (Northern Europe).
It also means that your PV and wind generator in theory have a production capacity that can deliver significantly more than your daily needs, in periods of the year. However, since they produce in different periods, it is often a necessity.
Example: You need 120 Ah/day. In June/July this can be provided by 350 Watt solar panels facing south. But when there is no wind (it’s rare, but it happens), the 350 watts is required.
Unlike in December, when it would require 4200 watts of solar (it is not a calculation error! …) To provide the same 120 Ah/day. A wind generator in december makes more sence, when there is more wind in the winter than in the summer months.
You therefore need to “over covered” you your needs. That is having a bigger production unit than would be required under ideal conditions.

Solar and wind generator calculator for boat, caravans cottages and offgridWind is Difficult!

You need to know something about your local wind conditions. We can’t know the local conditions for your wind generator. You need to know your local wind index over a year.
You may need to google a bit to find it. It’s the wind index per month, you need, not the m/s per month. The difference is that when you double the m/s there will be 8 times more energy in the wind. Therefore it’s the wind energy index you need to find.
Are you going to drive/sail with your wind generator, look at this rough European map (click it to see it larger).

But no matter how you look at it, it’s hard to predict how much wind you have to produce electricity from. The graph below shows the production from Rutland wind generators from the wind that actually hits the generator blades. The statistics you can see I’m referring to here is often based on height of XX meters and maybe without trees and buildings that provide shelter and turbulence. That’s why you should always get a wind generator that is “too big” to covered your power needs. The best thing to do, is measure the actual wind conditions over a year, but it is rarely a practical thing to do.
A wind generator produce theoretically 8 times as much power every time the wind speed is doubled (in reality it’s a bit less). Also therefore it is typical in the winter a wind generator produce best, since there is significantly more wind and the wind is colder. Cold wind has a higher density than hot air.

If you are sailing or live somewhere windy, it may well be that the wind generator will supply plenty of power in the summer months as well, but solar should also be considered for even at the coast there is no wind sometimes, but typically along with a high sun … .;)
On the other hand, it is typically the lowest cost in financially terms, to produce a watt hours (Wh) by wind, than it is by solar. Simply because when there is wind enough, the wind generator will produce around the clock and solar are peaking in mid day.

Conclusion: A combined installation are very often the right choice to achieve security of supply. However, it should be slightly oversized, in both solar and wind generator sizes.

The battery must be large!

Another thing that is necessary, is a good and large battery. We refer you to our battery guide where you can read more about battery choices, but we will strongly recommend a battery that has at least 5-day needs in storage.
You will find the recommendations and minimum size for your battery in the bottom of the calculator.

At the bottom of this page you can see the wind generators and package solutions for your needs. Should you not find what you seek, then we could make it, please write or call us.

Using the calculator.

The green fields in the calculator can modify as needed. It is not certain that it is necessary, but you have the opportunity.
You must use dot instead of a comma in the calculator! otherwise it will fail.

We use external data to show what you can expect of production in your locale. There are links to this data into the calculator and it can be a little nerdy to find the right data, but you have the possibility and can achieve a more accurate result. BUT We don’t have the data for your country pre typed and there fore Google is your friend 🙂
IMPORTANT !!: With a calculator like this you must remember, that it is not better than the figure you give it to calculate on. The models are good, but if, for example. you enter an overly optimistic view of what a given wind generator can produce at your site, then the whole result will look to good and you are kidding yourself. So remember to be realistic. It can also be difficult to know which wind one can expect at a given location. The solar data are a lot more trustworthy
There are intermediate computations and results. They are probably not all so interesting for you, but they are there so you can see them. Those who are interesting, are those that are highlighted in bold.

Whether you think this is just a calculator after your head and you master it great, or you scratch your neck and need help, you are always welcome to write or call us (+45 70 500 999) . We can help you and it’s free 🙂

irradiation on the solar.

In the calculator we use a source for finding solar radiation at a particular place in Europe. The source is the European Union which publishes the data we need. You can click on the link and find the data you think suits you best. The one we have pre typed, is Aarhus, Denmark and these data can be found by plotting your location in the map and click the tab called “Monthly radiation” We used the first column “Hh” in the results you get up when you press the “Calculate “. The “Hh” column show the result for horizontally mounted solar, as usually used on ships and caravans. The next column shows the result if you have the optimal tilt angle toward the sun (and your plant is directly south facing). In Aarhus, the optimal angle is 42 degrees. If you have a defined slope (eg. Your roofs angle) for your solar you can enter it into the calculator under “Irradiation at chosen angle:” and you’ll get your very own customized result.
The result for the 12 months you can enter in the calculator and get a more accurate result.

The wind on your generator

It is somewhat difficult to find free information available online that are precise enough. The figures for wind index we have pre typed into the calculator, is the average over 10 years (2005-2015) in Denmark.

You can find wind index number for your area with a little help from Google and your local weather service. You can type the wind index directly into our calculator. Remember! That it’s only wind index figures on the distribution over a year you can change the calculator. How much your generator produces is specified from the graph of Rutland wind generators and your choice of m/s.

Solar and wind generator calculator for boat, caravans cottages and offgrid

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