Launching my tiny solar power station

I was intending to write about electrical connections, but I think I will let that for another time because I have a recent update on my project.

• Problem in the first solar panel:

I checked earlier on my first solar panel mounted on the roof, and I found that my idea of holding the solar cells to the glass with a PVC tape is a total fail. Unfortunately I did not account for the elasticity of the PVC tape. The PVC tape stretched due to heat during day hours and finally they got dry and crunchy and finally lost its glue and separated from the panel. The result for this problem is the solar cells were sagging and exposed to environmental changes (humidity, dust, rain, ...etc).

• Accounting for the problem in the second panel:
  

I decided to go for another material for insulating the solar cells and holding them straight at the same time. The first material I thought of was the acrylic, but it was very expensive that I could pay EGP 500 (72 USD) for one sheet. Next material I thought of was wood. I wend to the wood store, but I would buy a very big sheet and I would not use half of it. After that I had an idea, what about the thin fiber sheet that is used in aluminium kitchen doors?. I found a leftover at the aluminium workshop that was barely the size I needed. This fiber sheet is thin, somewhat flexible and covered from both sides with a water proof layer and cheap that I paid 110 EGP (16 USD) for both solar panels backing. This was exactly what I wanted.

• Solving the problem in the first panel:

I replaced the new panel with the old one. I took the old one down to the working place and removed as much I could from the ruined PVC backing and mounted the fiber sheet with silicone sealant. Fortunately it was not damaged and it measurements were OK.

• Adding the second panel:

I finally added the old (modified) panel in parallel to the new panel on the roof. I now have a generating power of 140 Watts x 2 = 280 Watts.

Note that I increased the inclination of the solar panels to 45 degrees because we already passed September where the sun goes below the equator. The solar panels are directed to the true South.

• More numbers:
  

I can now operate the TV and the PC+Monitor (166 Watts) easily all day. The extra juice is stored in the battery for some time of night operation, and when these devices are turned off, the battery is charging even more quickly.

I bought the 65 Ah battery to have a total storage capacity of 72 Ah. In ideal case (for calculation) when my panels produce 16 A, then to recharge the battery bank from empty (never happens) to full capacity, then I would need 72 Ah/ 16 A = 4.5 hours. By observing once, it took about 5 hours to charge the battery from 30% to 90%.

Practically, I operated the TV and PC for about four hours on the battery. This really made my day.

The battery bank, when full, holds a usable (30% DOD) power of (72 Ah x 12 V DC ) / 30% = 600 Watts. The solar panels can produce daily (assuming 8 hours of bright sun) 280 Watts x 8 hours = 2.2 KWh.

After two days, I found that I consume daily about 1 KW from solar energy. That is divided between day and night. Then the losses in the system must be 50% (this is a big number, but I don't know if this is normal accounting for efficiency of the battery charger 95% and the power inverter 70% and the battery bank itself 85%. adding theses losses surprisingly results in 50%, but I'm still not sure about this).

I had to go around my basic design more than once to fulfill the budget which has reached now about 8000 EGP (1143 USD).

To conclude this post, I feel special because, in my country no one does as I do. I have my tiny solar power station which produces free clean sustainable energy. I sometimes keep looking at the power meter while it counts the used solar energy and I dream about a bigger station which operates all my home appliances off grid. All my effort in the past four months (whenever I have spare time) were fruitful. I am really happy and have a feeling of accomplishment.

The battery and the charger

I have purchased a cheap Chinese solar battery charger for my system. As I mentioned before this
was not chosen by calculation, but by price. I have a 20A MPPT charger.
20A means that is can handle a max of 20A solar panels input. My panel outputs 8A (by design), so I'm okay if I added another panel, then the current will be 16A, but I can't add a third panel except when I buy a bigger charger. This charger works with input power from the solar panel and charges the battery by regulating this power.

There are two types of battery chargers, PWM and MPPT as mentioned before.

As long as the sun is bright, the battery is charged, and when the sun goes down, the battery charger consumes the battery and routes it to the load.

This type of charger has an instruction that I should first connect the battery then connect the solar panels, but I ignored this instruction and connected only the solar panels, then I had an over current. Fortunately it has an electronic fuse and I haven't burnt anything. I wired the output to my inverter to test the output AC power, but the charger refused to power the load directly from the panels, so I thought the charger was faulty.

I then assumed that the battery has something to do with the operation of the charger, so I went down and bought a test battery of 7Ah (a cheap one of 175 EGP). The make of the battery is MxVolta and it's made in Korea. It is a VRLA (Valve Regulated Lead Acid) battery that can be discharged up to 60% DOD (Depth of discharge) for 2000 cycles. This suits the solar application.
I connected the battery to the charger and to the inverter and I was very pleased when the system worked flawlessly.

Sure a 7Ah has a power of 12V DC x 7A DC = 84 Watts/hour when it is fully charged. I was powering the PC, monitor and fan and the power consumption was 150 Watts, so 84/150=0.56 hours. Adding a losses of 20% then the time this battery can supply is 0.45 hours. But I must take into consideration that I don't want to fully discharge the battery (actually it's a function in the inverter and the battery charger as well). I will aim a 50% DOD, so this battery will have a time of 0.45/2=0.23 hours which is 13 minutes on condition that the battery is fully charged.

The charging time of the battery also counts to decide how big my battery bank will be. I now have a charging capacity of 120 Watts per hour. Considering 10 hours of bright sun I  can get 1.2 Kw of energy everyday. Thus I can charge a battery bank of 1200/12=100Amperes. I intend to buy a 65Ah battery for a start (easily available at my area) and it costs 1150 EGP.

Next time I should write about the cabling and the ATS (Auto Transfer Switch)

Building solar panels

I have stopped writing on my blog for more than two months due to my work heavy load, so I was very tired, but now, I have received the rest of my solar system's components and I again have the urge to write. At this moment when I'm writing these lines, I have my PC fed from solar energy. YES! I have completed my solar UPS and I have made a successful test run.

But first I should resume from where I stopped earlier. I will talk about building my solar panel.

I purchased a a pack of 108 solar cells from ebay (on the right picture and I have to say I expected them to be larger) and I have also purchased tabbing wire to connect solar cell together (this was a time consuming job). The solar cells I bought has a dimensions of 6"x6" each produces 0.5V DC and 8A DC (that what was written on ebay).

I wanted to assemble some of them to produce 18V DC (as standard panels produce) so the calculation will be: 18V DC/0.5V DC = 36 cells. 

Note: These cells are extremely fragile and brittle, I broke about a dozen, but they are still functional.

First thing I did is to put one in the sun and measure how much power does it produce. I measured a 0.55V DC and 1.1A DC. I thought something was wrong as it should produce 8A DC, but I think I could not hold it right or my hand shadow affected the current. Anyway I decided to go on with experimenting. I connected two of them and measured 1.1V DC and also 1.1A. I thought that since they are imported from China, they should be not good, but I couldn't stop at this phase. In the picture the measurement is away from the sun.

I had to connect those 36 cells in a rectangular pattern of 9x4 by connecting each positive side (dark side) to its neighbor's negative side (shiny side)

The frame is made of aluminium angles (3cm x 3cm thickness 3mm) joined together and in the middle is a glass sheet (thickness 6mm) glued to the frame with silicone. I had to line up the cells to be neat and have a nice look. I welded all the 36 cells and extracted the far terminals to be the positive and negative. I covered the back of the cells with a PVC tape to isolate them from humidity (I should use a piece of plexiglass or any isolating sheet for the back of the panel because the PVC tape is not solid, thus sagging a little bit).

The final panel look is in the picture on the right. I measured the voltage output and it was 18.8V DC. I measured the short circuit current and I was very pleased to read 6.5A DC.

My panel initial design was 144 Watts, but practically it is 122 Watts. It's okay for me and this result satisfies me for my first home built solar panel.

After doing some research about which direction to point my panel and which angle is the most suitable to extract the biggest amount of juice from the sun, I reached some very easy numbers. Since I live in Egypt in the Northern hemisphere, then I should point my panel to the true South. Also in Cairo the suitable tilting angle in summer is 15 deg and in winter is 45 deg (I have made an extension leg to increase the tilting angle to 45deg). Sure a tracking device will be much more efficient, but I don't want to bother myself with mechanical designs at this stage yet.

Second practical excercise

For the second day in row, I received the second item I purchased from ebay. Behold the power

inverter. As discussed before, the power inverter converts DC power to AC power to feed the ordinary house appliances. I had already purchased an over-sized inverter for future use. It has a continuous power output of 2000 Watts and surge output of 4000 Watts, that means it can output power of 2000 Watt all the time, but when I turn on my appliances (specially inductive loads like fans), they take a lot of current to start-up then return to their rated current draw. This happens in less than a few seconds, but the inverter should handle this situation or else it will shutdown due to overload or rather be damaged.

As discussed before, I designed my system to use a voltage of 12 V DC, so the input for my inverter is 12 V DC. The output is 220 V DC, as the voltage of the grid in Egypt. This inverter has some capabilities like shutdown on overload, short circuit, very high battery voltage and very low battery voltage. It also has a buzzer to give me a warning to shut down my appliances normally and safely when the battery is critically low.

As soon as I received my inverter, I took it down to my car, opened the hood and connected it to the battery for a test run. I connected the positive (red) terminal of the inverter to the positive terminal of the car battery, and connected the negative (black) terminal of the inverter to the negative terminal of the car battery. I was terrified when I heard a spark when the circuit is closed. I tested it with an AVO and yes!, 240 V AC was on the screen. I haven't tested it on a load, but I will wait till the rest of mt items arrive. I will buy the batteries the last thing, because they tend to lose their charge by time and I don't want them spoiled before using them.

This type outputs a pure sine wave, so that I'm free to power any device as long as it does not draw more than 2000 Watt (1800 for safety) continuously, and also doesn't draw above 4000 Watts (3600 for safety) at start-up.

This power inverter weighs about 5.5 Kg, and is bigger than I imagined, so I have to decide on where to put it. it must be put in a ventilated area to circulate air (it has fans inside), and also it must be put away from batteries to avoid heat or fire due to gasses (very small amount) emitted from the batteries.

• Recalculation

As discussed in the previous post, practically I use 385 Watts to power my target room. It is recommended to design for an inverter double the required power (that will be expensive), so if I would size my system for it's present power, I would have bought a 600 Watt inverter.

My inverter costed me 280$ and shipping 80$ = 360$ which equals 2520 EGP. I was charged 435 EGP for customs and other fees (services), then the total will be 3000 EGP.

A 800 Watt inverter would have costed me about a 130$ less, which will be about 2090 EGP. I will consider that in my calculation irrespective what power inverter I bought, because I want to calculate the real price for my target system.

First practical excercise

At last, today I received the first item from my purchase list from ebay, it's the power meter. That devices is very handy in design an analysis of my system. I bought it from www.eco-worthy.com for 13.55 $ from an auction on ebay. It was shipped to me from Singapore, but I think it's made in China, and I received it after 16 days of my payment. It costed me 135 EGP because of customs and my local mail office also charged me for services (which I don't know).

It is very interesting to watch by my own eyes exactly how much power my appliances are drawing.
This power meter can display Watts, Watt-hours, Amperes, Voltage, Frequency and Power factor. it also displays electricity usage cost, Max power and Min power> It can support a maximum of 3680 Watts before displaying Overload.

I connected my appliances (except the CFL lamp) and I was pretty surprised from what reading appeared on the power meter. I switched on the TV, receiver, fan, PC, monitor and speakers. I started a heavy graphics game (Medal of honor - Warfighter) - very nice game - and the maximum consumption was 350 Watts - 1.6 Amperes. Remember that I calculated my load power of 575 Watts.
These are really good news for me because I will have more juice to use from the batteries for more time. But what mistake did I make in my calculation? I made no mistake, but I have a PC power supply of 500 Watts, and I'm sure I'm not using them all. If I calculated the CFL lamp as 35 Watts, then my true consumption is 350 + 35 = 385 Watts, and 575 - 385 = 115 Watts. Then I can say that I'm using a maximum of 385 Watts from my 500 Watt power supply, but the other appliances I made my calculations from the data on their nameplate.

I'm happy today, I'm going to look at the power meter every now and then to see for real what my consumption costs are, and I'm going to re-size my solar energy system components.

Design - 5

• Inverter

I have now stored power in the form of DC voltage and DC current. I can power some DC devices such as LED lamps, DC motors or some appliances that have DC input. Apart from that, I will need to convert the DC power to AC to power my appliances.

I will divide the types of inveters into two types from the waveform point of view:

1. Modified sine wave: This inverter takes the DC input and converts it to AC output, but with a waveform between the conventional sine wave and the sharp square wave. This can be tolerated by some devices which have their own power supply to change AC to DC like PCs. But most inductive loads like fans or ACs will produce a humming/buzzing sound, produce more heat, draw more power and shorten their life expectancy. Other devices like TVs can have incorrect signal with impure image. This inverter type is the cheaper one.
2. Pure sine wave: This inverter outputs conventional sine waveform that will power anything the grid can power. This type is more expensive.

Inverters can be categorized into two types from the functional point of view:

1. Grid-Tie: This type of inverter has its output can be plugged directly to the grid through any
   
   mains outlet in my apartment. It can synchronize its wave with that of the grid to achieve the same frequency, voltage and angle. This type will take power from the solar energy system to directly power my appliances. If I draw more power than the generated power from solar system, then the extra need is compensated by the grid. If I draw less power than the generated power from solar system, then I actually feed the grid. If I have a mechanical power meter, then it will rotate backwards saving me some money. Some countries (but not Egypt) use this technique to solve a part of energy demand problems, so they encourage people to generate their electricity and sell it to the grid. This type of inverters will cutoff output power if the mains electricity is cut. this is called (islanding technique). This happens for safety because power can be cut off for some electricians need to do some maintenance in the area feeding box, so that they don't get an electric shock from the energy injected by the inverter.
2. Off-grid: This type will not be connected to the grid. It outputs its power to operate appliances
   
   that are connected to it only. This can have backup batteries to extract power when the sun is not in the sky.

Having a grid tie inverter seems to be more reasonable to have because I can sell power when I'm not using it, but I don't need to have power cutoffs. A hybrid system can be achieved by having a grid-tie inverter connected to the grid and another off-grid inverter where some loads (emergency loads that I need to be up all the time like my PC, Internet router and some lighting) connected to it.

As for my calculated load of 575 Watt, I need an inverter with an output that can power that load. Therefore I need at least a 600 Watt inverter. I must take losses into consideration. Adding 20% losses due to inverter efficiency and cabling, then I need at least 575 x 1.2 =690 Watt (700 Watt inverter). i don't think I ever saw an inverter of a power rating between 600 and 800, then the least I can get is a 800 Watt inverter. As per my design, I intended from the beginning to have one room off-grid.

Design - 4

• Batteries

Connecting my panels directly to the inverter to power my appliances means that I can have power only while the sun is shining, so I need to store the excess power for using it at night (or in my case at the time of power outage).

Battery bank should have enough capacity for the designed working hours without charging. The capacity is described as Ah (Amperes hours) which means the amount of amperes I can extract from the battery bank in a time of some hours. If I have a battery of 12 Ah, that means I can get a current of 12 Amperes for one hour, or I can get a current of 1 Ampere for 12 hours, o a current of 6 Amperes for 2 hours, ...etc.

If I'm going to power my 575 Watt/Hour system for 4 hours after sunset, then I will need my batteries to store a power of 575 x 4 = 2.3 kWh. That means 2300 Watt/Hour / 12 V DC = 192 Ah and that is the capacity of the battery bank needed (without calculating losses)

According to my previous calculation in Design - 1, my requirements are day is 3.2 kWh. 3200 / 12 = 266 Ah. Adding losses of 20%, the result is 320 Ah.

If I used a battery bank of 320 Ah, then I will use all of this capacity every day, and I will need to fully recharge the batteries also everyday.

Discharging the batteries to the last drop will damage them, therefore I have to decide on the DOD (Depth Of Discharge). To know how much I can discharge my battery bank, I need to know about:

• Battery types

At first I thought that I can just buy enough car batteries and install them as my battery bank, but then I figured out that they can be used only on certain conditions and they are not recommended. Car batteries are designed to give a very high current in a very short time (cranking the car to start it up), and are designed to be discharged not less than 80% of their capacity or else their life expectancy is shortened much. In the car, after cranking, the dynamo is responsible of charging the battery to 100%.

If I want to use car batteries, then I will use them for a DOD of 20% only, then I need a battery bank of 320 / 20% = 1600 Ah. If the average 100 Ah car battery price is 1,000 EGP, then I need 16,000 EGP.

In my research  I will categorize batteries into two sections; Deep cycle and Shallow cycle (car batteries).

Deep cycle batteries are designed to give constant current while discharging, and to be charged more quickly. These batteries have many types, some of them are:

1. Flooded: These are positive and negative plates which have liquid acid to act as an agent for
   
   moving charges (current). This is the cheapest type of the deep discharge batteries. It has thicker plates to withstand deep discharging without corrosion. The bad thing about these batteries that they produce hydrogen gas when being charged. This makes them not suitable for mounting in a confined area because hydrogen is flammable and poisonous. Also these batteries need constant distilled water refill to compensate the hydrogen (Charging the batteries decomposes the water into hydrogen and oxygen).
2. (Semi)Sealed Lead-Acid: These are as the above type, but are sealed, hydrogen gas is
   
   significantly reduced (not eliminated) and does not need water refill. These are also called VRLA (Valve regulated Lead Acid). These have a moderate price.
3. AGM and GEL: These two have the acid absorbed in a fiberglass mat (AGM) and in the form of gel (GEL). These have the advantage of mounting horizontally or vertically.

Deep cycle batteries can withstand regular DOD of 40% and occasionally DOD of 80%. It is adviced not to go below 50% to lengthen their life expectancy.

• Battery bank capacity

To cope with a DOD of 50%, I need to double my calculated battery bank size, therefore I have to get 320 x 2 = 640 Ah batteries. If the average VRLA battery price of 100 Ah is 2,000 EGP, and I need 640/100 = 7 batteries, they will cost me 14,000 EGP.

Comparing this to a normal car battery, I will need 640/20%= 3200 Ah which will cost me 32,000 EGP.

• Wiring the batteries together

In my design, I went for 12 V DC battery charger and inverter (which was not the best choice). To have

 a battery bank of 12 V DC, just connect all the positive terminals together and all the negative terminals together. I will have then a 12 V DC, 640 Ah battery bank.

To have a  24 V DC battery bank, connect each half of the batteries as a standalone 12 V DC bank, then

connect one positive terminal from bank #2 to one negative terminal from bank #1. I will have a left one positive terminal from bank #1 and negative terminal from bank #2 which will have a potential of 24 V DC, 320 Ah. Note that voltage and current change by changing the battery setup, but the constant is the power. P = V x I (Power = Voltage x Current).

These batteries should be connected to the battery charger and the inverter.

Design - 3

• Battery charger controller
  

The DC voltage coming out from the panels must be higher than the DC voltage of the batteries, so that panels will have more emf than the batteries to push the charges through them. But if our typical 18 V DC panels are connected directly to the batteries, they will eventually overcharge and will cause severe damage to the batteries. Therefore I need a device to control the charges going into the battery bank to prevent overcharging. The charger is required to be three stage charge cycle controller. That means the batteries when they are under a certain voltage are charged applying bulk voltage and the battery draws the maximum current, then absorption voltage is applied and the current gradually decreases as the battery is being charged, then floating voltage is applied.

There are two type of solar battery charge controllers; PWM and MTTP.

• PWM charge controllers

These are the cheaper ones which uses a duty cycle (on time/off time) to regulate the voltage from the panels to the battery bank

• MTTP charge controllers

These are more expensive but usually gives 30% more power than PWM. They reduce the voltage coming out of the panels to reach that of the battery so that maximum current draw is possible

The charger is rated by input voltage (12 V DC in our case) and max current that it can handle ( we have 7 panels each 100 Watts, therefore 700 / 12 = 58.3 Amperes). We must be ready for some phenomena like edge of cloud effect or very bright circumstances, so I will calculate a 30% spare capacity. 58.3 x 1.3 = 75.8 Amperes.

In this case I need either one 80 A charge controller or two 40 A charge controllers wired in parallel.

Another option is raise the voltage to 24 V DC and use only one charge controller of 40 A.

Design - 2

Types of solar energy systems

• 1. Grid-Tie
  

In this system, the DC power comes out of the solar panels directly to the inverter (grid-tie inverter). This type of inverters convert the DC power to AC power and plugged directly in the mains and it synchronizes its wave form with that of the grid. It supplies your home with its nominal power (e.g. 500 Watts). If you are using more than 500 Watts than the rest is fed to your home from the grid. if you are not using all the 500 Watts, then you are feeding the grid itself. Your utility meter runs in backward direction. This happens as long as the sun shines, but after the sun sets, you are using the grid power only. Another feature in that inverter is when the grid power cuts off, the inverter power cuts off also. this is to prevent the inverter to feed the grid while workers are working and assuming no power is in the lines.

• 2. Grid-Tie with batteries
  

This is like the grid-tie system, but there are backup batteries that are charged using the charger inside the inverter and are used mainly to feed your DC loads, or can be connected to another (not a grid-tie) inverter to feed some AC loads

• 3. Off-Grid

In this system, the panels feed DC power to a battery charger which is connected to the battery bank to charge it while the sun is shining. An off-grid inverter is connected to the batteries to use their stored power to convert it to AC and feed AC loads. This type of inverters con not be plugged into the mains.

Components of solar energy system

• Solar Panels

The sun sends in one hour an amount of energy enough for human consumption for a full year. We need to collect that energy and make use of it either directly or indirectly. Solar panel is one way to do so. Solar cells which form solar panels are like a transistor. They are made from high purity silicon that has impurities to form a P-N junction.A P-N junction that has positive and negative charges on the barrier of that junction. These charges are waiting for excitation to move around forming electrical current. The excitation comes from the power of the sun in the form of photons.

There exists 3 commercial types of solar cells; mono-crystalline, poly-crystalline and amorphous.

The mono-crystalline are the most efficient and also most expensive. Efficiency 17-20%

The poly-crystalline are the mid-range in terms of efficiency and price. Efficiency 12%

The amorphous are the least efficient and least expensive. Efficiency 8%

More efficient cells means that they collect more solar energy in the same area. Amorphous has an advantage that they are like a thin film and can be put on any shape without breaking and they can resist heat, but also they are very inefficient, lose efficiency by time and I will need more space to mount them.

I found that the most suitable type is the poly-crystalline in terms of performance and price.

As I said before that the average price of a mono-crystalline panel of 100 Watts is about 200$, so if I used a poly-crystalline panel it will cost me less. A more better idea that I can buy single solar cells and wire them together and put them into a frame to compose my custom solar panel which will save me some money.

If I'm going to power my requirements of 575 Wh directly from the solar panels (without using batteries) then I will have to get a 575 Watts panels. Calculating losses for inverter of 20% : 575 x 1.2 then I require panels power of  690 Watts panels. This will enable me to extract electricity only during sunlight hours.

• Wiring solar cells
  

A solar cell of size 6" x 6" gives a typical of 0.5 V DC and 8 Amperes max (that equals 4 Watt). A solar panel gives a typical of 18 V DC. Then wiring 36 solar cell in series gives me that volt and keeping the current a 8 Amperes. This panel gives a maximum of 18 x 8 = 144 Watts. Therefore, I will need 900 / 144 = 7 panels of those. Wiring the panels together in parallel give me 18 V DC, 8 x 7 = 56 Amperes. That is equal to 56 Ah.

The solar cell has two sides, one is the negative (shiny side), and the one which is positive (matt). Wiring the positive side of  the cell to the next cell's negative side in series forms a panel. I can choose to either arrange than as 6 x 6 cells or as 4 x 9 cells. the latter will be better to save space.

I will the cells together under a protective surface such as glass or thick acrylic and over another piece of acrylic and insulate them to protect them from weather harshness like rain and dust. I will also put that setup inside an aluminium frame and fix them to another aluminium setup on the roof (my roof is horizontal, so I need to tilt them).

• Mounting solar panels
  

To get the maximum efficiency I can from solar panels, I must mount them either on an adjustable base or on a fixed base. Adjustable base moves through the day using servo motors and a tilting controller that calculates the position of the sun to direct the panels towards it to collect as much power from the sun as it can. this systems cost too much and I'm not going to use them in my system.

Putting panels on a fixed base requires calculating horizontal and vertical angles. Because Egypt is in the northern hemisphere, then my panels should be directed towards the South. Cairo lies geographically in the latitude line number 30. As a general rule, in the winter when sun is far on the South, the panels needs a tilting angle of (Latitude + 15 = 45) and in summer where the sun is over our heads (Latitude - 15 = 15). I have to make my base adjustable with two positions to change them once every 6 months to get the max power from the sun.

Design - 1

I had to switch my goal for the reason of a low budget that I have, so I decided to power only one room in my apartment using solar energy. My goal is to have sustained power feeding to this room from the sun with the possibility to use it partially with the grid.

• Before converting to solar energy

Being an automation engineer, and through my 9 working years, I gained a parameter in my personality which is "passion for efficiency and optimization". I make electrical designs and programs for machines and factory processes which are not tolerant to mistakes. These programs must run the equipment efficiently to save power and to output maximum production rate.

That made me always check the power consumption for the home appliances before buying. So I changed most of my 40 Watt incandescent light bulbs to  26 Watt and 35 Watt CFL bulbs. LED bulbs are yet better, and I intend to use them soon.

I also changed my CRT TV to an LCD 23" TV which was adequate for my small living room and for the price at the purchasing time.

Also trading my CRT 17" PC monitor for a LCD 19" one, these actions saved my a few EGP every month.

What I benefit from using energy efficient appliances is that I can use a bigger solar energy system with my available budget aside from saving me a little cash in the previous three years.

Note: when buying electrical appliances, look for the energy consumption grade. A grade is the better.

• Basic load calculations

To decide how much power my living room requires, I must calculate the power drawn by every piece of electrical equipment in that room. I need to know the total power in terms of watt hours to size my solar energy system.

I have the following appliances:

1. 23" LCD TV that draws 50 Watts
2. A dish receiver that draws 25 Watts
3. A fan that draws 137 Watts
4. A CFL lamp that draws 35 Watts
5. A flourescent lamp that draws 38 Watts
6. A computer with power supply which draws 1 A = 1 x 220 V AC = 220 Watts
7. A computer LCD monitor that draws 45 Watts
8. Computer speakers that draws 25 Watts

That will result in a total power of  575 Watts. That is the power drawn by these devices when they are all on for one hour. Therefore I need 575 Watt/Hour (that is different from my previous calculation of 1.6 kWh, and that makes sense because it is about one third of my total power consumption and it's in the living room where me and my family stay most of the time. Aside from that, the fridge, microwave, washing machine, water heater, lighting and air condition consumes the rest)

Every device will be used for a certain hours per day, so let's calculate.

1. 23" LCD TV is on for 6 hours
2. Dish receiver is obviously on for the same 6 hours
3. Fan will be on for 10 hours
4. CFL lamp will be on for 6 hours
5. Flourescent lamp will be discarded
6. Computer+monitor+speakers will be on for 4 hours

The calculation will be: 50x6 + 25x6 + 137x10 + 35x6 + 290x4 = 300 + 150 + 1370 + 210 + 1160 = 3.2 kWh/day. I need a system that can supply that power and recharges itself from the sun for free.

What are the components of solar energy system?

To be continued...

Study - 4

• Market research

It was not convincing for me to pay that much for only 2-3 Hrs of power usage per week. So I took two decisions, the first is that I chose solar energy to rely on for reaching my goal. The second is I changed my goal.

Living in a dream of free power supply forever, without cutoffs within a small money resources is not just a

dream, it's a fantasy. Solar energy cost per kWh has gone down through the past few years, but still not good enough for mid-range people in a third-world country like Egypt.
Prices have gone from 11$ per kWh in 1998 to 4$ per kWh in 2012. That is about 77 EGP at 1998 to 28 EGP per kWh in 2012.
Comparing this to the grid electricity of 19 Pt / kWh, solar energy cost is 147 times that of the grid cost.
If taking into consideration that solar energy provides free power, and needs maintenance of  8000 EGP every 5 years (average battery life), therefore the running cost per month for using solar energy is 8000 / 5 = 1600 EGP per year equals 133 EGP per month. That's double the grid electricity costs. But take into consideration that the fossil fuel energy resources are limited, and electricity costs will not stop increasing. Also the power cutoff problem in Egypt is not anywhere near to be solved. So I think solar energy is not yet ready to be used in a wide scale in Egypt, but in the near future it will be.
Many people say that the investment in a good solar energy system starts paying for itself after 10 years, and I think it is true.

• Who is the target of solar energy systems?

Paying a big sum of money for an investment which will return benefit after 10 years is not for regular citizens in Egypt. A person who decides to use solar power must have a good motive to justify his choice. For people living in Sinai (Eastern Egypt), Alwahat (Western Egypt) and Upper Egypt (Southern Egypt), the grid electricity supply is very difficult to be found in most places, so they live off-grid. They usually use diesel generators to power their houses. Many other places have limited hours of electrical supply per day. Those people are the most who are in need for solar energy, yet they don't usually have the sufficient financial resources. Also persons who have villas, chalets or weekend houses who also power them using diesel generators are in need for solar energy systems.

Note: I'm not mentioning industrial solar energy usage here. For instance, all communications equipment that are far from the grid are either solar or diesel powered. Diesel powered equipment needs a constant refill, but solar needs nothing.

There can be at least three ways to use solar energy:

1. Off-grid: That is when I rely on solar power totally without the need for power from the grid.
2. Grid-tie: That is when I rely on solar power and grid power both.
3. Hybrid: That is when I use the two previous ways together.

I intend in my research to focus on people who have frequent power cutoffs and intend to use the solar system as a UPS only (those people are my case), and not totally rely on it.

I also had to do my calculations to find that I will dedicate a budget of 8,000 EGP for my system. I'm curious what can I achieve from that relatively small sum of money in terms of my requirements.

Study - 3

• 2. Investment and value for money (continued)

SOLAR ENERGY

A typical solar energy system components are:

1. Solar panels to harvest the sun's energy and change it to power.
2. Solar charger/controller to regulate the rate of charging for batteries and prevent overcharging.
3. A battery bank to store harvested energy.
4. An inverter to convert DC voltage to AC voltage for powering the home appliances.

As for the UPS, I will need the same battery bank, but what about the other components?

I have to choose solar panels with enough current to charge my battery bank as fast as possible. If I have a typical solar panel of 100 Watt and output voltage of 18 V DC, then the current output is about 5.5 Amperes. Charging 400 Ah batteries from 5.5 A solar panels requires 73 hours (if I assume that I will not discharge the batteries more than 50%, then the charging time will be calculated for only 200 Ah and will be equal to 36 hours). I must here account for the fact that sun does not rise at night, so every day I have limited amount of hours for charging my batteries.

In Cairo, Egypt, we are blessed by long solar radiation hours (hours that the sun is visible in our sky) which are an average of 9 Hrs per day (6.4 Hrs in December and 11.7 Hrs in July).

This results in about 9 hours of charging per day. For 36 hours of charge to fill the 200 A, I need 25 / 9 = 4 days. So I will be able to use my solar energy for one day (1.5 Hr) and keep it charging for 4 days.

If I doubled, tripled or multiplied my solar panels, the charging time will be reduced, but note that an average monocrystalline solar panel (types will be discussed later) costs about 200$ (add 30% for customs and shipping) equals 1820 EGP.

The voltage output for the solar panel is 18 V DC. Connecting that voltage directly on a battery pf 12 V DC

will ceratinly overcharge it, then the battery will be damaged (The damage ranges from overheating to explosion according to battery type which will have it's own discussion later). A charger controller is then needed to regulate the output voltage from the panel to charge the battery in a safe way.

Battery charger controllers are selected according to their input voltage and current. A typical charger controller for one panel is a 12 V DC, 10 A solar charger controller and can be bought for 15$ to 20$ for a basic function (without LCD or other options) equals about 180 EGP.

The last component is the inverter. I needed an inverter of 12 V DC inpuut and 220 V AC output and with

power enough for my 1.6 kW calculation. An 2000 kW off grid inverter (types will be discussed later) which outputs pure sine wave costs 280$ + shipping 80$ = 360$ equals about 3100 EGP.

To sum up the cost, I need at least a solar panel (1820) + charger controller (180) + inverter (3100) + the same battery bank (8000) = 13100 EGP

Take into consideration that I will get my power for free and that will be cut off my electricity bill (not too much but better than nothing)

I was very surprised to see that the cost of the solar energy system was less than that of a plug and play UPS by about 20% plus the fact that the power is for free.

At this point, both systems are not coping with my goal yet (I can't rely on a system that is powered once or twice a week for that price), so I decided to make some assumption/modifications/estimations/requirements.

Study - 2

• 2. Investment and value for money

Either using the UPS or solar energy, I would pay a considerable sum of money, but I need to study both cases well.

At first I have to decide upon what load I want to have powered without any downtime due to power shortage. I began with a very big fancy dream of powering all my apartment without downtime. That means that I need enough power for all the electrical appliances for at least 1.5 Hr daily. With a simple calculation, I consume an average of 250 kWh monthly and I will assume I use them in the period of 6 hours daily. Therefore my month will have 26 days (because of weekends) x 6 Hr = 156 hours of electrical usage a month. that means that I need an average net power output about 1.6 kW, and I need it for 1.5 Hr.

In Egypt the voltage reaching domestic areas for home usage is 220 V AC. That means that I need a current of  1600 Watt / 220 V AC = 7.3 Amperes. Converting the voltage to 12 V DC (which is the batteries' voltage that I assume to use either in the UPS or solar energy system), therefore the current rises to about 133 Amperes (that is calculated by dividing the required power 1600 Watt by 12 V DC, because the power is constant). This is roughly calculated because both systems have losses which will be discussed later.

Assuming that I need this power for 1.5 Hr, therefore I need a power storage of 133 x 1.5 = 200 Amperes.

UPS

A typical UPS of 2000 VA = 1200 Watt has two batteries of  12 V DC, 9 Ah. That's a total of 18 Ah.

Dividing 18 Ah by 133 Ah, the UPS battery will be completely consumed in about 8 minutes (taking into consideration that batteries should never be completely discharged, I will assume it will be discharged to 30% then the power will cutoff, I will only have about 5 minutes.

That UPS from GE (pure sine wave) will cost me 840$ = 5880EGP + 30% customs and shipping = 7644 EPG, and the surprise is that is not enough to power my full load, but that is the nearest one I could get a price for. By common sense, the sufficient UPS (from power output perspective, not from time perspective) will cost me at least 1000$ = 7000 + 30% = 9100EGP .

I certainly can get extra batteries to prolong the time for working in power outage. I will need 133 Ah plus taking into consideration that I will keep the batteries charged above 50% (to prolong their lifetime), I will need a battery bank of 266 Amperes for every hour of power outage (in my assumption of 1.5 Hr, I will need 400 Ah) This will cost me an extra of 2000 EGP per 100 Ah (batteries type are either Trojan or Bosch). The system cost will reach about 17100 EGP. (that's a big sum of money).

The second noticeable thing is that all the stored power inside batteries is charged from my grid and is not free.

Another important point to be taken into consideration that the battery charger built in the UPS has a maximum charging current, and that affects the charging time of the batteries. My example UPS  claims to have a recharge time of 6 Hrs. By calculation, my 400 Ah batteries will need (400 Ah / 18 Ah) x 6 Hr = 133 hours. In this case, I can use my UPS with the large battery bank once or twice a week.

to be continued...

Study - 1

After having defined the problem, I had to study the alternatives for solutions. I had several solutions to think about, the first of them is to do NOTHING :). This way I will save the cost for my backup system, the time to study and implement it and also I will not pay for the time when I used no electricity.
My engineering hunger didn't left me do so, unfortunately.
So I had to think about UPS to power my devices for the power outage time. It will cost much for a big enough UPS and will need batteries replacement every about 3 years. It charges from electricity (the grid), but it is a tested and proven solution with plug and play feature.
Second thing I thought about is to use renewable energy source as my UPS system. It will also require also enough batteries (which needs replacement every 4-5 years) for powering my devices for the power outage time. It will require another hardware that will cost in total more that an equivalent UPS. It is not considered a plug and play like the UPS, and it charges for free
Solar energy and wind energy were the available and feasible solutions to use. Knowing the fact that wind is not too much in my area, and also knowing that sun is shining almost all year round, then solar energy will have a plus.

I can do a small comparison according to criteria as follows:

• 1. Feasibility

UPS is used mostly to save a backup power for PCs or lighting. To be able to power a fan, AC or any inductive load, I need to get a true sine wave output UPS, which is more expensive in contrast to square wave output or modified sine wave output.

Solar energy also will need a power inverter to change the DC voltage from the panels to AC voltage to power my normal home appliances. Also power inverters' output is divided into square wave, modified sine wave and pure sine wave.

So, both systems are applicable and can be inline with my goal. Also both systems can supply enough power to my target appliances as I will discuss later.

What are the available wave forms?

Most of PCs and devices have power supply that change AC to DC and can take square wave or modified sine wave without problems. Other devices like fans and pumps can also be powered using square wave or modified sine wave, but they will draw much power, heat much more, buzz much louder and shorten their lifetime. Devices like TVs can have distorted image.

Switching on the blog lights

I'm Ahmed Amer, and I live in Cairo, Egypt. I'm holding a BSc in electrical engineering and I'm willing to change the world around me, even within a small radius. If it wasn't for my limited resources, I would've built a far bigger project, but I will go with what I can afford. I'm doing this research to help people looking for the same idea, and I hope people who have experience can help me too.

Problem description:

• 1. Cost 
  

Electrical energy cost in Egypt has been raised at the beginning of 2013 for about 15% according to the following list:
1 EGP = 100 Pt
1 USD = 7 EGP (Today)
Monthly usage up to 50 kWh: Rate is 5 Pt / kWh
Monthly usage up to 200 kWh: Rate is 12 Pt / kWh
Monthly usage up to 350 kWh: Rate is 19 Pt / kWh
Monthly usage up to 650 kWh: Rate is 29 Pt / kWh
Monthly usage up to 1000 kWh: Rate is 53 Pt / kWh
Monthly usage more than 1000 kWh: Rate is 67 Pt / kWh

I took into consideration that the dollar price will not stop rising in the near future.
I took into consideration also that our economy is not growing in the near future, thus buying fuel for power stations puts a great headache on the country's income.
New fuel prices (higher) will be applied by the end of 2013 which shall raise the prices of everything.
My average usage of power lies between 200 and 350 kWh/month, thus I pay between 30 to 70 EGP/month, (which is not too much, but cost was not the main problem). That because i took some steps in saving energy which I will discuss later.

• 2. Availability
  

Normally in winter, there are few power outages, because we have a moderate climate and don't usually use heaters. But in summer, the power outage is frequent (daily) and during the coming 5-7 years, Ramadan month is coming in the summer, where a peak electricity usage occurs during Iftar period which is at dusk. With all those lights on, ACs, TVs, electric stoves, kitchen machines, dish receivers and PCs, the power outage due to load shedding becomes more frequent and lasts longer. In summer it is very hot at 6-7-8-9, where we suffer a lot if there isn't at least a fan to give some breath.

• 3. Appliances switching
  

When the power outage has ended, some of the left-on devices keep their last state, thus going on again as soon as power has been restored. This definitely shortens the device age. In some areas, the power does fluctuate until it is stable again. This includes overvoltage and undervoltage which if the power supply of the device can't handle, it will be damaged. Also motors and pumps can suffer damage from this behavior.

• Environment
  

Extracting power from fossil fuel causes a lot of damage for the environment in the form of increased carbon emissions, thus increases the global warming due to green house effect. In Egypt, the idea of saving the environment is not very popular due to the level of education and poverty, but as a collage-degree holder, I should put that into consideration.

• Social responsibility
  

Well, saving some kilowatts from my side does mean that some poor guys living in a small rooms with one lamp in each room can use this extra power that I saved. A small contribution for the community is better than nothing at all.