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This is solar energy collector/storage when solar energy is high, and I use it in other part of year.

This energy will be store in water inside isolating cistern. I am redirect input water from house roof, and build this from old cistern storage.

My heat storage cistern is 3m x 4m x 3m dimension, and high energy can be stored (about 2-3 MWh).

I am finished this and works fine.

In summer I heat this storage with my solar system (3m x 4m collector, 35 cm high), and use this energy in winter.

Insulator in cistern is 10 cm (2 x 5 cm) 'stiropor' and 2 cm 'stirodur' (on top of stiropor).

'Stiropor' has 70 C, and 'stirodur' has 80 C temperature resistance. Polyurethane foam is used glue (80 C resistance).

Solar collector is build from stiropor too. Polyurethane-foam is used glue too.

Inside collector I put combination of cement/water/parquet-glue. I am use paint-brush with it.

Now I do some experiments with cement/water/polyurethane, and it has interesting characteristics.

On top of collector I put PVC UV resistant 1 cm plate. ( 4 plates of 3x1 m)

Inside collector is 200 m PVC pipe (1/4). Sand (about 1000 kg and must be dry) is above, and on top is roof tile (black color).

PVC on top of collector must be bevel, because of rain. I glue this with polyurethane-foam.

Maybe polyurethane rubber will be another choice (in combination with cement). I will try it in this summer.

Aluminum foil can be used for reflection on sides (less heat on it).

Collector work OK. It is cheap (relative), and collect high energy. I use digital thermometer.

Sensor is inside sand.

Usage of stored energy has two system:

1. Water from standard water supply passing thru cistern about 200 m PVC water pipe, and temperature input for dish-washer, washer and boiler is highest than standard water supply. Electric heater need less energy because of that. PVC pipe need good isolation.

2. Pump and radiator system is used for heating my home. Isolation of home places is important.

I has 2-3 cm stiropor isolator. PVC mesh and standard cement mixture on top of polyurethane-foam glued stiropor.

Good isolation is very important for solar house.

Pump thru collector is 500W and 1000 lit/h, and I use in impulse regime. One hour stop, 15 min start, and so on.

But some automated system will be best approach. Sand in collector can accumulate energy, and this need to be investigate.

E = m*dT/860 [kWh] is used formula. Example: energy stored in 1000 lit water (about 1000 kg) in 10 C difference dT = (T2-T1) is 11.6 kWh.

My cistern with 3m x 4m x 3m is around 35 000 kg of water. If T2=60 C and T1=30 C (dT=30) 1220 kWh can be stored.

It will be minimum.

This summer I will know more...

I am build this in 2 months. It was hard work.

It is 'solar free energy' and has some COP because of pumps, but we need something pocket size device, like 'energy from space' in other part of this web pages.

If I found something useful, you will found this on my pages.

All this investigation need money, and I leave in Croatia, you know...

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Time of year: March/April 2007. (about 2 week of Sun, from 24 C to >40 C in collector).

Water: m = 24000 kg.

Temperature: Tstart = 12 C.

I use that 1 liter of water is equal 1 kg.

Pump work (1/2 hour), stop (1/2 hour)...(from 1 PM to 8 PM, start/stop with mechanical timer). About 1200 liters/hour. About 4 hour of work. This start/stop is the best approach, because of sand hysteresis.

Need about 2 day for 1 C go up in storage water. Energy for 1 C is E = 24000kg * 1C / 860 ~ 28 kWh.

Energy in collector when temperature in collector go to 40 C, and discharge to 20 C (4 hour of impulse pumping on 1200 lit/h) will be for sand if storage capacitance is like water (it is not, 860 constant come for water): Esand ~ 1000kg * 20C / 860 ~ 23 kWh.

When water pass through collector, it come out about 2 C more (average approximation: 3 C on start, 1 C on stop point of 1/2 hour).

Energy will be E ~ 1200 kg * 4 hour * 2 C / 860 ~ 11 kWh. Two day will be 22 kwh.

Conclusion: For this part of year (March/April) on sunny days, I get about 10 kWh per day minimum.

Temperature is going up (for about 2 week, it was cloudy too, but has good sun condition too, air temperature was from 15 C to 19 C)

Yesterday measurement in storage water was 17 C.

All collecting energy is E = 24000 * (17C - 12C) / 860 ~ 140 kWh

COP = 10kWh / (0.5kW * 4h) = 5 minimum (because of pump)

It works very nice, I think, for this part of year!

I can't wait for summer sun...

This week will be sunny too, and I will inform you for next numbers.

Is it posible that I go to summer with hot water?

Time of year: April (16) 2007. (temperature for last few days in collector was about 38 C to 42 C before first start of pump).

We have weeks of sun here in my country. Temperature in storage go up every day.

I need 2 days for 1 C (on about 24000 litres of storage water).

Pump still works on 1/2 hour start and 1/2 hour stop regime (4 hours effectively).

Temperature come from 12 C to 19 C for that few weeks.

Its progress is very nice.

Energy is about 14 kWh per day. Pump use 2 kWh (4 hour with 500 W). Its COP is 7 (700%).

It is good starting point of energy collect (it is middle of april yet).

Total of collecting energy for this few weeks is E = 24000 * (19-12) / 860 = 195 kWh.

Backup night power can be use for reduction on pump consuption (maybe with some solar panel).

1. Night timer (for about 50% price reduction)

2. Battery charger (or solar panel charger)

3. 200 Ah / 12V deep cycle solar battery.

4. More then 600 VA sinus converter.

It is expencive (battery lifetime...), but can be done, of course.

Time of year: May (23) 2007. (from 42 C to 48 C in collector when was sunny day).

I am on 28 C of water (24 000 liters). Coldwater detergent (Tide...) will be nice, but in my country I can't buy it (only sugestion for you).

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Inside view.

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Temporary pressing PVC roof after polyurethane foam glue, before outside finishing work.

It need corner mesh and polyurethane foam protection, because UV protection.

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Interesting material:

I read (one year ago) about building canoe with material (latex and cement). I try something similar, and searching this kind of latex source, now I found useful product in my part of world.

It is "Sika latex" and it can be put with cement stuff. It is great combination (latex and cement), and it can improve my home building stuff. I want testing this, and it can improve building of this kind of collector. Material which I was use is good, but it will be better (I think). And it is cheap enough. Who knows what can else be build with this combination...

Notes about pumping:

Long time ago I was trying to build summer solar heater from roof of my house. On top of house I put pipe with holes on it, and standard water supply was connected on.

Few hundred liters of water is coming back, and temperature goes up for 10-15 C. This first old system I use for adding water in storage tank, in summer, when energy on roof is high.

I remember few mistake:

1. Pipe on top was horizontal line, and water comes from holes from the beginning, but after few meters not. And I put pipe in V formation, with input on both end. It works OK. Eight meters of roof was covered.

2. When change water supply with pump (100 W for central heating system), and try pumping from storage tank (cistern), no water was come to roof. It was too high for pumping. I buy 500 W pump, and it was working good. Mass of water is too high for little pump.

3. That system was work 2 weeks, and collect high energy in summer, from all house roof, but when I was open storage tank... surprise: water was disappear. Evaporation problem! Few thousand liters of water was gone. Then I build closed system, which I explain before. It work OK, but I think 500 W for pumping is too much. Efficiency is 7 times, and I don't care. Now is hard to change system, but if I start build from beginning, I will do some changes.

Closed pumping system:

If little pump is in closed pipes system (and with antifreeze in it), mass for pumping, and gravitational mass (water which coming back) are in balance. Pump has not problem for pumping on high level, and can be using standard pump (low power consumption). Efficiency will be greatest.

I am explain some new ideas for roof style (low price) collector in 13 part of my web pages.

Using closed pump system, has possibility of solar cell power supply (and low price night charging of battery, and daily usage through converter).

Relatively cheap roof system can be build. New ideas are here: 13.

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Time of year: July (1) 2007.

Water is 35 C now, and I don't need heater for shower. It is more than 50 in collector. It is not summer time heating yet. But it is good for swimming in the sea.

It is around 2 days per 1 C (if is sunny days) of 24 000 liters of water. Like before, because discharges of collector go from >50 C to few (1-2) C up of water temperature.

Sunny days and raining was changing all time of this month, but I am satisfied with results.

Time of year: August (14) 2007.

High solar energy month was passing away. I was add more water, and now I have 30 000 liters of water tank. Before I was add water, I put this water at roof of my house, in impulse regime, because it is discharge heat in tank. Water is coming from roof with about 30 C. Tank if full (30 cm air gap), and temperature was go down from 37 C to 34 C. And after I was heating this with collector, now is around 35 C.

Changing rain and sunny days are come, and with using this water heat (all summer showing, washing...), temperature is stabilize on 35 C. It go down when raining, and go up when is sunny days. Collector temperature is less then 50 C (some days it go to 45-47 C). I found problem with condensing of water from sand (it was not dry, when I put it in collector). It reduces energy which going in, and I put 4 little holes, and clean this water inside collector. Temperature in collector after that going up again.

I don't expect much more of 35 C in tank. This capacity of water is too much for my collector. For better system it will need bigger collector (2x), and 50-60 C will be possible.

Time of year: September (24) 2007.

Temperature in tank is now around 31 C. Weeks of changing sun and rain. Maximum in collector is around 40 C (on sunny days). Hours of discharge with pump going down (I put timer to 01-06 hour, with 1/2 hour pause interval). Night are cold, days are sunny (with weeks of rain too). Collecting energy and using are in balance (but temperature in tank going slowly down). I switch on water heater. Heater with flow-heater will be more appropriate, but I have standard 50 lit. boiler. Valve for summer/winter with some automatic redirect cold pipe water (few liters) before input in heater will improve efficiency (50% more energy is using for this losses, than heat 10 liters of water for differences between 31 to 35 C (example from present situation).

Automatic temperature switch water redirect to some cold tank ( water for WC?), and 'on-fly' boiler will be nice device here. Standard boiler has lot of losses.

Time of year: November (10) 2007.

Usage of water and natural losses make temperature in tank to go down to around 20 C. This summer collecting energy is not enough for heating home. But energy is useful for preheating water from water supply system. Effect of difference in temperature (temperature in tank going down, but temperature in water supply going down too). Differences stay constant, and this reduce heater work in hot water consumers.

I will use this system only for preheating water from water supply (for now). It reduce energy consumption, and all summer I have hot water. I am only 50% satisfy. This system with 2x more space in collector and in combination with windmill will be good. But it is not so cheap system. It is only one battle, and fight for finding useful energy source will continue...

Time of year: January (3) 2008.

Temperature in tank is 12 C. It is winter time, and outside temperature is between -5 to 8 C (around 3 C in morning is common). Inside pipe water supply temperature is around 6 C. That temperature difference phenomena is here (water supply temperature in winter go down, tank temperature too, but difference is here around 6 C). Not much energy, but it is still positive. This year I will not give some aditional input source of energy (windmill), because I would like to know how this system work with solar energy only. Combination of solar/wind will be best aproach. Windmill design is on other part of this web, and idea is collection of high energy wind and direct temperature adding to water tank. For that purpose standard windmill are bad and thay need to be disconnected, when highest energy is here. Because of that, Tesla's style windmill is on my web.

Time of year: June (26) 2008.

Temperature in tank is 31 C. Few week of sunny days with temperature between 22 to 32 C. It is good for swimming in the sea. I have 31 C inside the tank (around 25 000 liters of water). This year I start pump in 3 PM and stop in 7 PM. Before that, sand inside collector accumulate energy of Sun. 55 C in collector is common in the 3 PM.

I see some problem with outside cement mix that I was use. It has little cracks. Acrylic color protection is crack with it. I think that my new silicone/soda-bicarbonate/cement mix will be better approach. It is more elastic. But price will be higher. Inside of collector, it look OK.

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