Hay dryer

This is a simple idea and relatively cheap for a farmer who likes hay milk : a hay dryer with a greenhouse making it possible to make hay without thinking about  rain. With that method, we can make hay in Belgium begin May when the wheater is still very changing. We then become hay as rich as silage but without the drawbacks

A dream of ecologist people ? However greenhouses which dry sludge exist :




We will see later that a greenhouse can dry the same grassland surface as a big barn dryer.

Hay has more qualities than silage : it is lighter and more funny to handle than silage and there is no risk of listeriose nor butyric germs in the  cheese. Farmers make silage because the silage can be made when the grass is not totally dry.

Drying hay on the ground needs a long period without rain and that doesn't arrive when the grass is the most rich. Hay can be dryed in a barn but it needs then fossil energies or the biomethanization. What I will explain is better than a dryer with biomethanization of manure because it is not made at the expense of the soil humus. With the biomethanization, the soil becomes poorer. Presently there are dryers with a dehumidifier using a  heat pump : the humidity of the air is condensed  on the cold wall of the heat pump and is eliminated. This dry air will then heat on the warm wall of the heat pump, and becomes so still dryer. That heat pump needs energie, much more thant my dryer which has only fans. In France, farmers are drying with air which is heated under the roof of the barn warmed up with the sun. But it is not enough in Belgium and the roof is very expensive..

What we seek is to make hay without rain.  In Belgium,  2 days sunny weather are frequent. More than 2 days is doubtful. It is better to have the hay inside into 2 days.

After tedding on the ground, the hay is harvested with 40 % humidity, like silage. Then it is harvested in a greenhouse where the hay is safe from rain. If after that, the weather is variable, the greenhouse warms up enough during the sunny periods. Of course, it is not possible to ted when there is a long rain period. And if the rain arrives after 2 days drying in the greenhouse, when the hay is not completely dry, it will not rain continuously more than one day and then there are sunny periods again. We only  have to prolong the drying process one of two days and the sunny periods are then enough to dry totally the hay. The sun is free and it kost no cent more.

In a closed greenhouse full in the sun, the temperature reaches more than 50 °C. Hay must stay under 40 °C in order to not destroy its nutritive qualities. So it is necessary to use two fans. The first one is turning permanently and the second one begins to work when the temperature in the greenhouse becomes greater than 37 °C. If those two fans have a different power, there are three possibilities to choose the flow instead of with two fans with the same power, there are only two possibilities.

The benefit of a greenhouse is that we can make hay begin May when the grass is very young and contains much protein.So we can avoid purchasing soya as this farmer who says he doesn't no longer know the price of soya :


Plastic greenhouses 2,7 meter high.

A greenhouse 2,7 m high is not so expensive but a large tractor cannot go inside. Five meters high greenhouses are tremendously expensive but allow to work without leaving the tractor. With a 2,7 m high greenhouse, the hay stay on the grassland one and an half day and is then harvested with 40 % humidity. The farmer places the hay at the entry of the greenhouse on a low tipping trailer moved with a micro-tractor. He can also spread the hay in the greenhouse with a wheel loader. We can also use a manure fork for it as you can see in the video :


But the best is probably to use a loader wagon with the upper structure closed. The loader wagon is then 2 meters high and can inside a greenhouse 2,70 m high. In the two following links, you can see a loader wagon made for low stables :



This loader wagon can be used with a 50 HP tractot which can enter in a greenhouse.such as the Solis 50. Its usual height is 2,49 m, but the crash bar can be lowered and its height is then 1,90 m, which can easily enter in a greenhouse with a height of 2,70 m.

In the greenhouse, the hay must be turned. We can use a little pirouette-tedder with a micro-tractor or this very little tedder :




As the little tedder is 1,4 meter wide, if we run at 2 km/hour, a greenhouse of 7 * 30 meters is turned after 2 * (7 -1,4)/ 1,4 * 30 / 1.000 / 2  * 60 = 7 minutes. With that little tedder the whole surface of the greenhouse can be covered with hay except a strip wide as the width of the little tedder. When the little tedder reaches the end of the strip, it must go back along the same way  where there is no more hay in order to project the hay always in the same direction. So, we lose a minimum amount of space.

If we turn the hay in the greenhouse 3 or 4 times a day, the work in one greenhouse is less than 1/2 hour long a day and we can make 20 ha hay a year with only 2 greenhouses.

When the hay is dry, we can make little bales with this little baler :


The width of that little baler is 1,80 meter and it is used with a 20 to 25 HP tractor. It makes 3 to 9 bales in on minute, or 360 bales of 15 kg in one hour. As we can put 3.000 kg dry hay in a greenhouse of 30 m * 7 m,  we need 3.000 kg / 15 kg  = 200 bales and 60 minutes * 200 / 360 = 33 minutes. To finish the work in 2 serres (which permit a 20 hectares a year harvest), we need one hour..

Other mini-balers exist. They make round bales of 15 kg, but their productivity is low, as they make 50 to 80 bales per  hour. To make 200 bales in two greenhouses, they need 2 * 200 bales / 70 bales/hour = 6 hours to work. It is too much. You can see those mini round balers here :





Those mini round balers cost 7.000 € HTVA. Their useful width is 80 cm. They work with a 20 CV tractor.

The budget to be provided is then (price without VAT) :   

Loader wagon Pöttinger Boss Junior 17T :   21.500 €

Loader wagon Pöttinger Boss Junior 22T :   24.000 €

Tractor Solis 50 2WD :   12.000 €

Tedder Molon 1M40 :   1.314 €

Square baler Abbriata M.60 Mini :   11.529 €

2 greenhouses Filclair RK7 7m * 30 m * 2,70 m :   13.000 €

Total : 60.000 €

With those two greenhouses we can yearly dry 20 hectares if we first dry on the grassland during 1,5 days in order to have 40 % humidity. With a surcharge of 13.000 €, in order to have 4 greenhouses, we can yearly dry 40 ha !

When the hay is dry, we can make swaths with the little tedder and push that swath with a manure fork on the front of a micro-tractor. When it is on the ground outside the greenhouse, a big tractor with a baler dan make 200 kg round bales with it.

And when we work with a horse, it likes as this :


Farmers can wonder whether ultraviolet rays from the sun will not detroy the vitamins in the hay in the greenhouse. Let us compare one hectare hay on the grassland and what its becomes in the greenhouse. On the grassland, 100 ares are subjected to direct sunlight. In the greenhouse, it is 2 ares because only the upper lay is reached with the sun rays. The amount ultraviolet rays received by the hay in the greenhouse are significantly lesser than in the grassland .

With one greenhouse of 30 m * 7 which costs 6.500 €, we can own one hectare at a time.One hectare at a time seems to be too little but with a greenhouse we have to work in another way : instead of one large harvest, we have to make numerous little harvests. Farmers who are drying in a barn with a dehumidifier and cells where the hay reachs 7 meters height are also obliged to make numerous little harvests because they are limited by the surface of the cells where they can put only 1 to 1,5 meter hay. If those farmers make 30 hectares in one year, they will not make more than 1 meter / 7 meter * 30 hectares, or 4 or 5 hectares each time. If we have 3 or 4 greenhouses of 30 m * 7 m, we can do even good but it kosts much less.

The farmer has to follow the weather broadcast to see if there will be two sunny days.

If the hay contained  40 % d'humidity when it was put in the greenhouse, 1 kg hay must evacuate  0,4 kg water. The psychrometric diagram indicates that, when the temperature increases from 18 °C (coming in air) to 34 °C, 1 kg dry air can absorb 17 kcal and 24 gr water.

If the hay is put in the greenhouse  with 40 % d'humidity, 1,66 kg of that grass  contains 0,66 kg water, whereas 1,18 kg dry hay with 16 % humidity  contains 0,18 kg water.  1 kg dry hay contains 0,18 / 1,18 = 0,15 kg water.  To obtain 1,18 kg hay  we must extract 0,66 - 0,18 = 0,48 kg water. For 1 kg hay we must extract 0,48 / 1, 18 = 0, 40 kg water.

If the greenhouse has as dimensions 30 m * 8 * 2,7 (then length of the greenhouse may not be greater the 30 m to have a good ventilation), it has a volume of 648 m³and as the weight of 1 m³ air is 1,2 kg at 20 °C,  the total weight of the air in the greenhouse is 777 kg.

For one m², it receives 5 kWh a day, but all that energie does not come in the greenhouse. Thermal solar panels have an efficiency of  40 %. We will suppose it is the same for the greenhouse.

In one summer day with sun, we have

5 kWh/m² * 40%  * 8,4 m * 30 m = 504 kWh

The greenhouse receives in one hour 504 kWh * 861 kcal/kWh /8 hours = 54243 kcal/hour

But we know that 17 kcal and 24 gr water are absorbed by1 kg dry air

Thus, 1 kcal is absorbed by 1 / 17 kg dry air

54243 kcal/hour need 1 / 17 * 54243 kg dry air sec to be absorbed or 3190 kg dry air

1 kg dry air absorbs 24 gr water

3190 kg dry air absorb 3190 * 24 / 1.000 = 77 kg water 

As the weight of the air in the greenhouse is 777 kg, the air in the greenhouse will be removed 3190 / 777 = 4 times per hour while the air absorbs 77 kg water.

In one day we can extract : 77 kg * 8 = 616 kg water        or, 616 kg water / 0,4 kg water/kg hay with 40 % humidity = 1540 kg hay / day.

4.000 kg hay / ha is a first not too early cut. If we make 4 cuts a year for barn drying, the grassland gives more : making now barn dryiing, a farmer ( https://www.youtube.com/watch?v=y-QH_uLBPJc ) increased his harvest from 7 ton to 11 ton dry material, or 13 ton hay on one hectare. Thus, each of  those 4 cuts produces 3.000 kg hay.

If we put 3.000 kg hay in the greenhouse, it is 3000 kg / (8 m * 30 m) / 30 kg/m³ = 0,4 m high. We can dry those 3.000 kg between 3000 kg / 1540 kg/day = 2 days.  Perhaps are 40 too high for a tedder. We can then dry 1.500 kg, or 50 ares, and they are dry after 1 day.

If we dry 2 times in the week, the greenhouse is used 5 days in the week. Let us take no more because some days will be with rain. Thus, we dry 2 * 1 ha or 2 hectare a week. Between May and September, there are 20 weeks. We can harvest with a greenhouse 2 ha/week * 20 weeks = 40 ha. If we have 2 greenhouses, we can harvest 80 ha. But we make 4 cuts a year on the same surfaces. Thus, 2 greenhouses can annually dry 80 / 4 = 20 hectares

We often hear that hay drying in a greenhouse is only made for very small farms. That is not correct : I found on the internet a farm of 45 ha grassland with an industrial dryer with a surface of 8 meters * 40, or 320 m² for a harvest of about 20 hectares, et normally, the drying process allows only to lay down 1 meter hay at a time In a greenhouse of 8 meters * 30 we lay down a bed of 65 cm hay. Thus, 2 greenhouses dry the same volume as that industrial dryer of 8 * 40 m or 320 m².   Because  8*40*1 = x *8*30*0.65. We conclude x = 2. Thus, 2 greenhouses can dry 20 hectares a year, between May and September.

We supposed the hay was first dryed 2 days on the grassland. We can also place the grass directly in the greenhouse. We have then much less waste of broken leaves than with a tedder. But we cannot then make more than one harvest a week and 2 greenhouses can only dry 5 hectares yearly instead of 20 ha when we use a tedder on the grassland. This swiss farmer uses that method :


I made hay the 10 May 2019 without tedding and the hay was dry after 4 days. It was possible because I put less grass in my little greenhouse. My greenhouse has as dimensions 3 m * 4 m or 10 m² which can be used. The harvested surface was 3 ares. The dimensions of a greenhouse tunnel are 30 m * 6 m because the tedder needs a strip in that 7 m wide greenhouse tunnel. That greenhouse tunnel is 180 m² / 10 m² = 18 times larger than my little greenhouse.

If we put the same proportion in the large greenhouse tunnel as in my little greenhouse, the harvested surface should be 18 * 3 ares = 54 ares, while with tedding we can put 1 hectare. The benefit is that the hay is less high and that will prevent the warming of the grass. The height of the grass in the greenhouse tunnel is 3.000 kg dry hay on 1 hectare * 0,54 hectare / 30 kg/m³ density of hay = 54 m³ and 54 m³ / 30 m long  / 6 m wide = a height of 30 cm when the hay is dry. That is good for the drying process and will prevent fermentations.

Without tedding we dry 54 ares during 4 days instead of tedding 1 hectare during 2,4 days and this allows to make 10 hectares in one year. Without tedding the annual harvest is almost 4 times smaller than with tedding or only 2,5 hectares per year. It is not enough.

I think we should forget the idea to dry without tedding on the grassland during 1,5 day.

17 kcal are absorbed by 1 kg dry air. If the sun gives more calories, we have to blow more otherwise the temperature will increase. We can install two propeller fans : the first one is working continuously and the other one starts when the temperature reachs 37 °C. If the temperature is higher than 40 °C the good things in the hay will be destroyed.

The greenhouse has a volume of 648 m³ which are ejected 20 times a hour. The flow of the propeller fans is 648 m³ * 4 times / hour = 3.000 m³/hour. A propeller fan with 3.000 m³/hour often has a power of 0,3 kW. For on cut of 3000 kg hay, the propeller fan needs  0,3 kW * 24 hours * 2 days * 0.25 €/kWh electricity = 3,6 €. If we have to make 20 hectares in one year producing 10000 kg hay / hectare, the yearly cost to dry the hay is 6 € * 20 * 10000 / 3000 = 240 €, or  3,6 / 3000 = 0,0012 €/kg hay. In energie expressed : 3.000 kg hay need 0,3 kW * 24 hours * 2 days = 14,4 kWh.  Thus, 20 ha giving 10.000 kg hay/year need 960 kWh. This is right if we permanently blow during 24 hours a day. But if we blow only when there is sunshine, it will use annually 320 kWh.

Glass greenhouses 5 meter high.

Plactic greenhouses factory say that a greenhouse more than 4m high can be broken with the wind and that they need beton foundations. However, those foundations are very expensive : one m³ cotst 400 €. Those greenhouses often have horizontal staves at 3,5 m height. It is too low for a tractor or a loader wagon.

Much more expensive is a 5 m high glass greenhouse. It is tremendously more expensive than a plastic 2,7 m high greenhouse, but it stay cheaper than a barn dryer . Such a 30 m * 16 m * 5 m high greenhouse costs 115.000 € (133.000 € when polycarbonate) and a little barn dryer costs 250.000 €. Further, the electricity used in a greenhouse costs yearly 150 € when the ventilators blow only during the day while a barn dryer with the same capacity needs 6.000 € electricity a year for its ventilator and 6.000 € again if there is a dehumidifier.

Fortunaly, there is a less costly solution : a hangar completely closed with the same dimensions but covered with deep black sheet metal (RAL 9005) in order to absorb the warmth  and with a limited number of polycarbonate tranlucent sheets on the roof and in the South side wall. This hangar costs 60.000 €. But I have no experience with a greenhouse made with a limited number of tranlucent sheets. If inside the température reaches 30 °C, it is perfect, and if there are less sunbeams on the hay, it is still better..

If the greenhouse has only one entry, a big tractor and its machines have to go foreward and backward to move in the greenhouse. With 2 doors in the same front wall , it is possible to move without going backward.

The farmer can harvest the grass with a loader wagon and lay it in the hangar as swath. He must return the swath 3 or 4 times a day. That machine projects the hay backward. Three hours later, the farmer come back to make the same work but he will enter by the other door and drive along the opposite way. So, the hay will  not move. It is a little work the farmer has to repeat twice a week during hole the good season.

If the dimensions of the glass greenhouse are 30 m long, 16 m wide, 5 m hgh, its volume is 2.400 m³ and we know that the weight of one m³ air is 1,2 kg at 20 °C, the weight of air in the greenhouse is 2880 kg.

For one m², it receives 5 kWh a day, but all that energy does not come in the greenhouse. Thermal solar panels have an efficiency of  40 %. We will suppose it is the same for the greenhouse.

5 kWh/m² * 40%  * (1 m + 16 m) * 30 m = 1000 kWh

The greenhouse receives in one hour  1000 kWh * 861 kcal/kWh /8 hours = 107625 kcal/hour

But we know that 17 kcal and 24 gr water are absorbed by1 kg dry air

Thus, 1 kcal is absorbed by 1 / 17 kg dry air

107625 kcal/hour need 1 / 17 * 107625 kg dry air sec to be absorbed or 6330 kg dry air

1 kg dry air absorbs 24 gr water

6330 kg dry air absorb 6330 * 24 / 1.000 = 152 kg water 

As the weight of the air in the greenhouse is 2880 kg, the air in the greenhouse will be removed 6330 / 2880 = 2,2 times per hour while the air absorbs 152 kg water. The greenhouse has a volume of 2.400 m³ renewed 2,2 times per hour. The propeller fan has a flow of 2,2 * 2.400 m³ = 5.000 m³ / hour

In one day we can extract : 123 kg * 8 hours = 1000 kg water         or, 1000 kg water / 0,4 kg water/kg hay with 40 % humidity = 2500 kg hay / day.

4.000 kg hay / ha is a first not too early cut. If we make 4 cuts a year for barn drying, the grassland gives more : making now barn dryiing ( https://www.youtube.com/watch?v=y-QH_uLBPJc ), a farmer increased his harvest from 7 ton to 11 ton dry material, or 13 ton hay on one hectare. Thus, each of  those 4 cuts produces 3.000 kg hay.

The dry hay on the ground weighs 30 kg/m³. If we put 2 hectares hay in the greenhouse, it is 2 * 3000 kg / (16 m * 30 m) / 30 kg/m³ = 0,4 m high. The hay is 40 cm high spread on hole the surface of the greenhouse. The tractor which works with a tedder in the greenhouse can easily ride on 40 cm hay.

We dry 2 * 3000 kg hay or a cut of two hectares in the greenhouse between 2 * 3000 / 2500 = 2,5 day when the grass had 40 % humidity. As 1,8 day is very short we should lay the grass in the greenhouse directly after the cut, without tedding in order to avoid leaf leaks and dry during 4 or 5 days. The annual quantity is twice smaller.

With a grass with 40 % humidity, we can make 2 dry process a week and the greenhouse is busy 4 days a week. If we consider the bad weather periods, it is suitable. We then dry 4 hectare a week. May till September  is 20 weeks. We can harvest in one greenhouse 4 ha/week * 20 weeks = 80 ha. But we make 4 cuts on the same grass-land. Thus, 1 greenhouse can annually dry 80 / 4 = 20 hectares a year.

With other words : 20 hectares produce 10.000 kg hay/hectare/year which are dry after 20 ha * 10000 kg hay/ha / 3040 kg/days drying = 66 days drying in one year in the greenhouse when the season is 140 days long..

Summary :

The working approach with a greenhouse is different from a barn dryer. Presently, farmers work with large engines to harvest a large surface in one shot, when the weather is suitable during a long period. With my greenhouse dryer, you must make plenty of little harvests, but very often, because we are limited by the dimensions of the greenhouse, beginning in May when it is still raining and cold, and ending in September. So, we will have a rich and very palatable hay. The only downside is that the hay is highly digestible and the fat percentage in the cow milk is lower. That hay is too rich for horses but we can cut the hay later to have a poorer hay.

Does the sun destroy the vitamins in the hay in the greenhouse ? . In a the 2 ares of the greenhouse we can put 100 ares of the meadow or 1 hectare. When the hay is entirely dryed on the grassland, the hay is 50 times more exposed under the sun than in the greenhouse. In the greenhouse, only the upper lay is in contact with the sunrays. There is no problem with the vitamins.

I use such a dryer, but very small, because I have only 6 ewes. The dimensions of the greenhouse are 4 m * 3 m, and I have to move the hay with my hands. I am very pleased with it. My only difficulty is to move the hay. I made that hay on 10 May 2019. The hay was dry after 4 days without using a tedder on the meadow. The hay was composed of couch-grass. Outside we had 15 °C and 31 °C in the greenhouse. During 6 years I mad hay with that greenhouse, the dry process never failed.

You can see my greenhouse here :




You can see the propeller fan. The white engine above the fan is a dehumidifier De Longhi. It works with a heat pump. It absorbs ideally (at 30 °C)  25 liters water in 24 hours and  has a power of 400 W. As to make 1 kg hay from grass at 40 % humidity 0,4 kg water must be extract, that means that to dry 4.000 kg hay, thus the cut of one hectare, we have to pay for the electricity  :

25 liters / 24 hours * 0,4 kWh/liter water * 1.600 kg water to be extracted from 4.000 kg hay * 0,25 €/kWh = 166 € to dry one hectare with a cut of  4.000 kg dry hay. A dehumidifier is a good method to dry hay night and day, because it costs  4,15 €cent electricity/kg hay. It is not so much but if the farmer makes 10000 kg hay on 20 hectare each year, he will have to pay 8.300 €. In a Austrian farm of 30 hectares, the dehumidifier and the fan have, together, a power of 28 kW. The fan alone is 15 kW because it must cross 7 m hay, dry at the bottom but wet on the top.With a dehumidifier it is nevertheless more expensive than my greenhouse with two propeller fans with less power (360 € for 20 hectares). But let us talk energy : 25 liters / 24 hours * 0,4 kW is the same as using 0,39 kWh to extract 1 kg water. We find that in the documentation of large industrial barn dryers. 1.600 kg water * 10.000 kg hay/ha / 4.000 kg hay *0.39 kWh/kg water * 20 ha = 31.200 kWh annually used in the farm. In the Austrian farm, the ventilator has more or less the same power as the dehumidifier. We can conclude that 60.000 kWh are used on that farm annually. That is not ecologically very responsable. And we said that a dehumidifier is a reasonable solution. Think about dryer which are constructed at the present time and which use fuel !  We can compare those 60.000 kWh with the 1.440 kWh. needed by the greenhouse for the same volume hay.

We found this very interesting canadian document about the dehumidificers :  https://www.agrinova.qc.ca/wp-content/uploads/2016/09/Fiche_Sechage_foin_Agrinova_2oct2014.pdf     We see in it a farm which dries 700 ton hay in one year with 165.000 kWh with a dryer which costed 1.000.000 $ and its dehumidifier has a power of 48 kW. If we count with the Belgian electricity price, it costs as energy 165.000 kWh * 0,25 €/kWh = 40.000 € each year. That dehumidifier extract 36 kg water / kW / day. 1 kWh can extract 36/24 = 1,5 kg water. Ideally, a dehumidifier extracts 25 kg water in 24 hours with a power of 0,4 kW, which means 25 / 24 / 0,4 = 2,6 kg water. We see the great difference between those 2,6 kg and the 1,5 kg water actually extracted.

That canadian document explains that there are compact forage parcels in a barn dryer where the air doesn't go through. As in a greenhouse, the hay is regularly returned, compact parcels cannot exist.

With grass at 40 % humidity, 1.000 kg hay give 400 kg water and as to extract 25 kg water during 24 heures we need a power of 0,4 kW, we use 9,6 kWh, or 9,6 / 25 = 0,384 kWh / kg water. So, 1 ton hay requests 400 * 0.384 = 153 kWh.

It is funny to note that the little home dehumidifiers have het same performance as the big industrial dehumidifiers : 25 liter water extracted between 24 hours with a power of 400 W.

Those figures are valid when the conditions are ideal : temperature 30 °C and humidity 70 %. A factory gives the absorption capacity for different tempeératures, for a dehumidifier of 20 kW :

30 °C    60 % humidity   760 kg captured in 24 hours.

27 °C    60 % humidity   680 kg captured in 24 hours.

20 °C    60 % humidity   501 kg captured in 24 hours.

We see that, if the temperature is  lower than 30 °C, the dehumidifier is less efficient. We must know that, if the temperature goes  above 32 °C, the dehumidifier stops working because the air temperature is higher than the plate delivering the heath. The heath goes from a warm surface to a cold surface, not the contrary. If the humidity of the air decreases under 40 %, the dehumidifier no longer will work correctly. At the end of the dry process, drying will cost a lot more.

If a 20 kW dehumidifier is working in ideal conditions, it must can extract in 24 hours : 25 kg water / 0,4 kWh/kg eau * 20 kW = 1.282 kg water. However, we see that the best performance is 760 kg water. We see there is a great difference.

We can compare a barn dryer with a dehumidifier with our greenhouse. If the cells of the barn dryer are 8 m large and 40 m long and if a lay of 1 m hay is put on it, we put 320 m³ hay. If we have 2 greenhouses 8 m large and 30 m long with a lay of 60 cm, we have 288 m³, which is nearly the same. If the density of hay in the barn dryer is 50 kg/m³, the weight of 1 meter hay is 16.000 kg. With 40 % humidity, we must extract 0,4 kg water/kg hay * 16.000 kg hay = 6.400 kg water. With a dehumidifier with a power of 15 kW, we know that it needs 0,39 kWh / kg extracted water. It needs 6,400 kg water * 0,39 kWh / kg extracted water = 2496 kWh. The dehumidifier works permanently. Between 24 hours, it needs 15 kW * 24 hours = 360 kWh. To dry 16.000 kg hay, it needs 2496 / 360 = 7 days. And we sayed that the dehumidifier needs 0,39 kWh / kg water, it was an ideal never reached..On the other hand,  the 30 m * 7 m * 2,7 m greenhouse dries 1.560 kg hay / day as we saw above. Two greenhouses dry 3.120 kg / day and 16.000 kg hay are dry with 2 greenhouses in 5 days, which is better than the 7 days with the dehumidifier which uses 7 days * 24 hours *15 kW = . 2.500 kWh while the 2 greenhouses uses for their ventilators 2 greenhouses * 5 days * 8 hours * 0,5 kW = 40 kWh. With the greenhouses, we make 2 drying processes in 5 days, while the dehumidifier makes 1 drying process in 7 days. If one cut on one hectare gives 3.000 kg hay, 16.000 kg hay correspond to 5 hectares.

Let us still dream about dehumidifiers. Suppose a farmer installs several dehumidifiers in a barn completely closed and thermical insulated to keep night and day a temperature between 25 et 30 °C. This room can be first warmed up till 25 °C so that the dehumidifier has then its most efficiency.  It must not exceed 30 °C because the warm panel of the heat pump cannot yet deliver its heat to the air of the room which has to refresh it. For 4.000 kg dry hay,  1.600 kg water have to be extracted, during 3 days, night and day, or 500 kg water in on day. As the dehumidifiers extract 25 kg a day, 20 dehumidifier for one hectare are necessay and 60 for 3 hectares. My own dehumidifier costs included VAT 400 € for one piece from a dealer. Exclusive VAT and for many pieces, it cost no more than 250 €, or 15.000 € for 60 dehumidifiers while I read in the farmer press that a dehumidifier for a little farm costs minimum 65.000 € . Where is the mistake ?

Farmers who likes a dehumidifier have to keep in mind that electricity price increases very much when the grass is very wet.We can calculate it :

This are some rates of humidity in grass and the corresponding wheight of water each time for 1 kg dry matter, and the price of electricity for one hectare in a year when 40 % costs 400 € for on hectare, as explained above :

16 % wet :       0,19 kg water 1 kg dry matter        price 1 ha

20                             0.25                                        151 €

30                             0,43                                        260

40                            0,66                                        400

50                            1                                             606

60                            1,5                                         909

70                            2,33                                      1.412

80                             4                                         2..424

90                              9                                        5.454

If the grass is cut without any tedding, it contains 80 % humidity and using a dehumidifier costs 2.424 € for one hectare in a year.

If the farmer harvests 30 ha such grass, it costs 72.720 €. It is absolutely uneconomic.

If it rained on the grass, it costs then 5.454 € for one hectare during one year.

We explained that a greenhouse of 7 * 30 meter can extract 512 kg water a sunny day. A dehumidifier with a heat pump extracts 25 kg water a day with an electric power of 0,4 kW. To extract 512 kg water between 24 hours, it needs as power 512 / 25 * 0,4 = 8 kW. The Austrian farm had a dehumidifier of about 13 kW. Thus, 1,6 greenhouses extracts the same as a dehumidifier of 13 kW which is in service in a 28 hectare farm.

Another example found on the internet : a farmer dries 142 ton in 3 cells of 300 m³ each. Together, those cells have a volume of 900 m³. Those cells are 7 m high. The surface of the cells is 128 m². That farmer puts 3 hectares with 3.000 kg hay in 2 cells with a surface of 86 m². The density hay is 3 * 3.000 / 86 = 100 kg/m³. If  the total surface of the dryer (128 m²) is used, the weigtht of stored hay is 128 m² * 1 m high * 100 kg/m³ = 12.800 kg. We said that we must extract 0,4 kg water / kg hay if the hay has 40 % humidity. In that barn dryer we must extract 12.800 kg hay * 0,4 kg water/kg hay = 5.120 kg water. If that farm has a dehumidifier, we need 0,39 kWh to extract 1 kg water. To extract 5.120 kg water, we need 5.120 kg water * 0,39 = 2.000 kWh. If the power of the dehumidifier is 15 kW, in 24 hours it needs 15 * 24 = 360 kWh/day, because a dehumidifier is working 24 hours a day, instead of a greenhouse which is working 8 hours a day, only during the day. The barn dryer needs 2.000 kWh / 360 kWh/day = 5,5 days to dry. We know that 2 greenhouses dry in 1,5 day  --> 2 greenhouses * 2.500 kg hay placed as windrows in the greenhouse = 5.000 kg hay. In 5,5 days, those 2 greenhouses dry 5.000 kg hay * 5,5 / 1,5 = 18.500 kg hay. Two greenhouses of 30 m * 7 have a greater efficiency than a dryer with dehumidifier of 15 kW because we saw it dries only 12.800 kg.in the same delay. However, we must compare similar things because a dehumidifier is permanently working , night and day, instead of the greenhouse working only during the day when there is sun..If I made this comparison, it is to demonstrate that the the greenhouses are very efficient, contrary to what is often assumed, and not only used by hobby farmers.

With the greenhouse, the grass may be wet : the dry process has only to be  prolonged one or two days. The sun is free. I already had that case with my greenhouse of 3 meters on 4. It rained on the grass just after I cut it but with the greenhouse it was dry without any problem..

The harvest on the grass-land is easier with a greenhouse than with a deshumidifier because the dehumidifier must start with a hay at 40 % wet, 2 days tedding, while we can put hay in the greenhouse which stayed on the grass-land not so long. The hay is earlier save against the rain and will dry in the greenhouse instead of on the grass-land. So, we have more time to harvest and we can do it more relaxed.

A dryer with a greenhouse is more or less similar to a dryer where the air is heated under the roof of the barn. However, the greenhouse warms up more quickly when there is a a rift in the sky because with a barn, the sun must first warm up the roof..

In its magazine of september 2019, the magazine Wallonie Elevages talks about the Inno4Grass Awards. One of the laureate is a german farmer which has a barn dryer and who says "During May, the electricity increased with 8.000 €. We hope to limit the cost of hay barn drying at 10 cents per liter, which is an amount often published." That farm has 200 hectares grassland and 180 milk cows giving 800.000 liters. With 10 cents per liter, its costs yearly : 800.000 liters *0,1 € = 80.000 € yearly. If he would dry with 5 greenhouses of 30 * 16 * 5 m and propeller fan receiving the electricity from solar panels placed near the greenhouse, it costs then 0 €. Those german farmers will live poor and die rich because they are above those 10 cents.

Presently, the milk is payed 0,37 € / kg. Farmers say it is absolutely not sufficient. And if 10 cents are needed for the barn dryer, the actual price of the milk is 0,27 €  ...

With such a big farm, the cows may not yet go to the grassland : one farmer cannot guide a herd with 180 cows. Other reasons therefore : if the farmer has an installation for biomethanization (cost : 2 millions de euros), the cow have to stay in the stable in order to keep their slurrys. With a milking robot, the cows have to stay near it, thus in the stable.

And when all those farmers will be pensioned , who iis the young people who can afford such expensive farms ? Perhaps investment funds but if the price of the milk stay low, they will not be interested.

Machine-intensive agriculture which is presently promoted is possible thanks to cheap energy. But we don't know till when that model  of agriculture will exist.

It makes us think : what kind of agriculture do we want, what kind of society do we want ? A society with one farmer for 1.000 cows. A society where very few people have work and the others are homeless. I prefer this little breton farmer who has 8 very small breton cows on 7 hectares who has no financial worries and no debt and he and his family are entirely happy :



In a documentary film on the television, the RTBF says that in Belgium , during 2017, 40 % farmers earn less than 1.000 € a month. How much a very little farmer can earn ? Let us take a farmer with 10 Belgian Blue dual purpose cows. That cattle gives meat and milk. The calves are of good conformation. Their sales can cover the cost of that farm. Those cows give 4.000 liters milk a year while a Holstein cow gives 8.000 liters. That farmer can make direct selling because his production is limited. If he receives 0,75 € / liter, with other words 7,5 € / kg hard cheese, what is very few, his ten cows give him 10 cows * 4.000 liters * 0,75 €/liter = 30.000 €/year. In one month, he has 2.500 €.. It is more better than the 1.000 € of the RTBF.

It demonstrate in which gridlock the political leaders of the European Union and the banks are leading us. It is a headlong rush to become bigger and bigger in order to collect more incentives, because those incentives are payed per hectare.

A "normal" farmer will think a cow giving 8.000 liters milk in one year earns twice more than a cow of 4.000 liters. That is note right. Both earn more or less the same per hectare because, which is important is the food quantity given by the grassland. A cow which gives less milk has to eat less, we see it in the food tables. We can keep more cows on the same hectare when they gives less milk. That means that the milk quantity on one hectare is more or les the same as with specialised breeds. Dual purpose cows give more calves with better quality. Finally, the income is more or les the same with the two breeds, but the farmer has to look after more dual purpose cows, but cows which can be easilier feeded.

Moreover, the most popular milk breed in the world after the Holstein is the Jersey cow, a very little cow producing no more than 3.500 à 4.000 liters a year. But its popularity attests that it is very cost-effective.

You will say I am very "Martine on the farm" and you are  right, but I like it better than a concentration camp for cows.

Hay milk : delicious !