Solar Drier

A VERY GOOD SOLAR FOOD DRIER

The easiest and most efficient solar food drier possible made from recycled objects.

Solar Drier

View of the Solar Drier

I spent many hours looking on internet for plans on how to make a solar drier. There are hundreds of different designs on pinterest and on homesteading sites. I almost started to make a couple of the most promising ones but fortunately I waited.  I eventually found one that I considered to have the best concept at  Elder Grove Homestead (see link below)  I then realized that I already had all the materials needed to make a solar drier without buying  anything and without building or constructing anything. My version uses a clear  window with most of the heating happening on the bottom corrugated iron  plate which generates a slow hot convectional current of air. 

Materials

A piece of corrugated iron painted black.
Some metal mesh with fairly small holes wired down to panels of an old chicken run.
Some circular sand sieves. (builders use them for sieving sand)
Some old windows.
Some ground which has a slight slope.

Solar Drier with windows

The above photo shows the solar drier in use:

How it works.

The sun shines through the window and heats up the black corrugated iron base. The heat and air is trapped in by the glass. As the solar drier is on a slope, the hot air moves slowly upwards  and then escapes from the top of the window. New air is constantly drawn in from the bottom. The food does not burn because as the temperature gets hotter the air moves faster. If it rains it is no problem the food is protected and it does not need to be brought in. The temperature is too hot for insects and even ants do not stay long.

Efficiency.

We have two or 3 electric food  driers but after a few days using this one I packed them away because this works so much better. In the hot sun of August most things were bone dry in one day. I even used this system to dry a load of comfrey leaves so that I don’t have to put up with the smell of rotting comfrey. I can just add the dried comfrey powder directly to the plants.

Advantages.

The main advantage is that no construction is required. If the drier is not in use you can just pick up the pieces and stack them somewhere. No electricity. No moving parts. A lot of the solar driers you see on internet have one window leading to a whole stack of food trays. Even in hot weather this must be slow. With our design the food is dried very quickly, at first you can even see the moisture condensing  on the window. 

Cost.

If you have to buy the windows it could be quite expensive however old windows are quite easy to get hold of. Other websites say that the mesh should be made out of food grade stainless steel. This is probably correct but I think I will risk it. If you paint the corrugated iron you should probably leave it out for a few days to drive off any volatile chemicals. (I did not actually paint mine) . The builder’s sieves can be bought from any builder’s merchant alternatively you can make some wooden frames and staple mesh onto them.

Notes.

As you can see we have  two options of placing the food. On the sand sieves or on the mesh grids. Either work perfectly but the sieves are easier to load with produce and bring to and from the kitchen. The windows are not connected with hinges they can be lifted up with one hand while the food is slipped in with the other. If they get dirty they can be picked up and blasted with water.

Dried Food

Dried Food

The photo above are some of the dried foods on the kitchen shelf ready to be added to many dishes during the winter months. The Tsunami by the way is a failed attempt to make marmite from wine yeast. In the end I dried it out and decided that it will add some umami taste to some foods (hence the name)  In the year of COVID just the two of us managed to dry a massive amount of food during the summer.

For loads of technical details and useful information go to Elder Grove Homestead You don’t need all the hinges and fancy construction techniques that they use you can just do it like mine on the floor with a few old windows.

Review of GeoTech PCS70 BS Shredder

I decided to buy a shredder or a wood chipper.  When we prune the olives and other trees we have a lot of waste  branches that are too small for firewood. We normally burn them. Olive branches have a lot of oil and they make a massive very hot fire. It is a shame that all the carbon that has been captured from the atmosphere is returned  so quickly as carbon dioxide which is a green house gas. The idea of buying a shredder is so that  the waste wood is turned into useful compost and mulch. The shredded output of the shredder is ideal for spreading around the garden to suppress weeds, keep the moisture in and keep the worms happy.

 

The shredder is quite good. So far we have used it with olive prunings and poplar branches with a diameter of up to about 3cm. The shredder comes with a small metal bar in the middle of the exit chute. I think this is due to safety to stop anyone putting their hand down. It caused a lot of blockages because once a small twig had been blocked it rapidly stops any more material from being ejected. Once I had removed this small metal bar the blockages were less frequent. At the end of this video there is actually a blockage caused by pine needles. When there is a blockage it takes a couple of minutes to unscrew the 13 milimetre bolts, unscrew the expulsion chute and clear the blockage. Blockages happen when too many leaves or pine needles are put in at the same time. This machine is not designed for lots of small leaves it, prefers long straight branches.

 

When does grid parity happen in the south of Spain?

A view of grid parity from someone who has been living off grid for 10 years.
The date of writing this post is 8th July 2017.

What is Grid Parity?

Grid parity  occurs when an alternative energy source can generate power at the same  price as buying power from the electricity grid. Or to put it another way: After installing an alternative energy system how long will it take the before the cost of installation will be the same as if the house had been connected to an electric company. This is called pay back time.

The Quick Answer

In case you just want a quick answer in my opinion it would take 8 and a half years.
Below I will explain how I calculated this figure.

Calculations

Our annual electricty usage is 2005 kWh per year.
This is in our  house which is not connected to the grid.
The average occupation is about 4 people.
We do not use electrity for heating, cooking or AC.
The biggest electricty use we have is the swimming pool pump.
We live a fairy normal life and we have a freezer and  fridges.
We very occasionally have to use a generator when there is a prolonged cloudy spell but the cost is minimal. Maybe 20 euros per year.

We calculate the costs of the electric company by looking at the electricty bill we have for another house. The name of the company is Iberdrola.

We use the figure of 3000 watts as the maximum amount of power that can be used at any one time. (la potencia) The figure we use for the price of electrity is 0.16 euros per  kWh. There are other expenses such as electricty tax (impuesto), equipment hire (alquiler) and VAT (IVA).

The price per year of electricity from the GRID.

The cost if we bought the electricty from the grid would be 598 euros per year.
224 for additional costs and 374 euros for the electricity.

How much our solar electrical installation would cost.
To replicate our system you would need
1250 watts of panels – 840 euros 
50 amp combined inverter charge controller 750 euros
12 x 2v Lead Acid batteries 800 amp hours. 3500 euros.

Total cost 5090 euros

Total installation cost divided by GRID cost is 8.5

So time to parity is 8.5 years

Conclusion:
There are lots of other variables such as battery life and efficiency of the batterys which we have not considered here but 8.5 years  is a good basic figure and it feels about right..  

If I lived in a city would I cut off from the grid?
No probably not. If you have solar power  you always have to be a bit conscious of the time of day and if there is sun or not. The battery technology is the most important factor.  Batterys like the TESLA powerwall sound very promising and could provide about the bare minimum which would satisfy most people. I imagine that within 10-15 years in the future we will see a green energy revolution with excellent power storage and the  demise of the internal combustion engine.

The best thing about this situation for me is that we have been here for 10 years so our electricty is now effectively free. I just hope that our existing batterys can hold out long enough so that there are very good possibilities are available when the time comes to replace them.  

Aparently  450g  of carbon dioxide is put into the atmosphere per Kwh for electricty bought from the grid.

According to these figures we have not caused 9 metric tons of C02 to be released into the atmosphere.

 

 

 

Batch Water Heater – Free Hot Water

Batch Water Heater – Free Hot Water

batch_water_heater_on_roof

Probably the cheapest, simplest way of getting free hot water from the sun is a solar batch heater.  All you have to do is use a tank of water placed in the sun which will act as a pre-heater for the water which normally goes into the  hot water system.

In our case we used a 150 litre immersion heater tank which had stopped working. I am sure that in many countries there would be recycling centres which would let you have old immersion heaters for free. You can even chain them together in order  to make a very large capacity pre-heating system. The only possible drawback could be that if you live in a very cold climate they could freeze up in a prolonged cold spell.  In this case it would be a good idea to disconnect them during the coldest months.

To make some sort of calculation about the energy that my batch heater could expect to absorb I asked a question on a forum. The answer is here My tank is about 50cm radius by 1 metres length so it probably has a power intake of around 400 watts.

According to my own energy calculator it would take over 11 hours  to get the water to shower temperature.

“It would take 11 hours 27 minutes to heat 150 litres of water from a starting temperature of 15 C to a final temperature of 40 C when 400 watts is applied. The energy consumed is 4.58 kWh. The cost in Spain would be  0.87 euros.”

It is not possible to give exact figures but  our current setup consists of a 50 litre black PVC pre-heat tube, the 150 litre batch heater in this post and a 150 litre thermosiphon solar heater.
One one day last week that was  enough for 5 powerful hot showers at the end of a full day of sun. After that the water ran cold.

Batch water heater creation

Hannah preparing the hot water heater

The first thing to do with an immersion heater is to strip off the insulation. I decided to only strip off the insulation which is facing the sun and leave the rest.  I cut off the mild steel covering with an angle grinder then hacked away at the foam insulation with chisels. In the photo above Shep is helping Hannah (our very pleasant Canadian volunteer) to strip the foam off.

Batch water heater in cold frame

Batch water heater in cold frame

I put the tank in an old cold frame made out of plywood. I sprayed expanding builders foam behind the tank.

Solar water heating system

Solar water heating system. 150 litre  thermosiphon, batch heater and PVC plastic tube

The window pane is from an old house before we had double glazing. It was very simple to connect the water to the tank using flexible plumbing fittings. The water that goes into the tank is pre-heated in a long piece of pvc tubing mentioned in another post

The only cost involved was the flexible plumbing tubes for just a few euros.
I estimate that this could save us over  120 euros per year.

 

50 litre solar hot water heater for only 71 euros.

Black platic tubes

32mm tubes for solar hot water

 The temperature of our cold water supply is very cold maybe 5C. When this water is mixed into the solar hot water tank it cools the rest of the water down considerably.

We got ripped off for 1200 euros by a company called http://tutiendasolar.com/ (We paid them for a solar hot water system which they were never able to deliver.) So I did not have an appetite to spend any more money.

I realised  that if we could increase the temperature of the water supply it would increase the efficiency of the hot water system.

I bought 100 metres of black 32mm PVC agricultural tubing which can withstand 8 atmopheres for 57 euros. The two brass connectors cost 7 euros each so that brings the total to 71 euros.

To calculate the amount of water in the tube you use this formula.

Length of pipe x Pi x Radius of pipe

In our case:

100m x 3.142 x 1.6cm = 502.72 cc

That is 50 litres.

According to my calculations:
If the water in the tube could get to 38C it would be enough for an  8 minute shower at 6 litres per minute.

Here are some other calculations:

To compare the cost of heating the water in this tube with an electric water heater we need this calculation:
We are heating 50 litres of water by 35C (from 5C to 40C)

The formula I have is imperial:
weight of water in pounds x  temp increase in deg Farenheit /3413 = KWH used by an electric heater.

The metric figures are:
55 kilos = 110 pounds
35C = 95 farenheit

SO
110 x 95/3413 = 3.061822 KWH

The average price of electrity in Spain is  0.19 per KWH
SO
3.061822 x 0.19 = 0.58

Each time the tubes heat enough water to have an 8 minute shower it theoretically saves 58 euro cents.
The supplementary water system will pay for itself after 122 showers.
Let’s assume that there are always 5 people here and they have showers on average 5 times per week. That is  25 showers per week.

This system should pay for itself in about 5 weeks.

According to carbonfund.org the carbon emissions of electricity are :-
0.0005925 metric tons CO2 per kWh

If there are 5 people here having 5 showers per week that is 1300 showers per year
If each shower uses 3.061822 KWH that is 3980 KWH saved per year (or 756 euros)

This means that we theoretically  save 2.35 metric tons of CO2 being emitted per year.

Maybe you can find an error with my figures but it seems that solar water heating makes sense.

See another solar water: How to make a batch water heater