Your utility bill keeps going up every month for one reason or the other. You have unplugged all the appliances you are not using, switched off lights when you are out of the room and tried to use less power during peak hours. However, with all these efforts, they still don’t seem to make a dent on the power bill not to mention the reliability issues.
So in your quest for a solution, you thought about solar but you are not sure it can help or maybe you dismissed it too soon without a second thought because of the cost. If any of the above describes you even for the least bit, you may want to read through this entire post. If not, UMEME is your friend.
The story of powering your window installation with solar has been there for years but has always been hindered by low efficiency, the prohibitive cost of solar panels and the system at large. Also there is only so much roof space you have available for solar panels not to mention the location and orientation of your house. Of course with more space or good understanding with your neighbour, you could use some of his roof space. In village 2.0 and microgrid posts, suggestions are made for how access to electricity via solar can be a possibility on a community level.
So lets say you want to be independent of the grid (UMEME) or use very little power from the grid. The lingering questions are; how do you go about it and about how much do you need to invest. Am glad you asked, stay with me as I take you through the sizing of your system and approximate it’s cost.
We are assuming your house location has good irradiance levels that allow you get good hours of peak sun. Irradiance on the panel from the sun is what in the end gives you the power output from the panel. Irradiance is a measure of how much power you can get from the sun per unit area, this varies with location.
A typical Ugandan house with no dish washer, washing machine or electric cooker and no heating or cooling needs would have a total load of about 2500 Watts or 2.5kW. Watts is the unit we use for measuring power. Total load in this case means you sum up the power ratings of your all your appliances, devices and electronics basically anything that uses electricity in your house including that 10 watts energy saver bulb in your bedroom. These are usually indicated on the side or back of your appliance. Of course 2.5kW is an approximated value, every household would have a different value depending on what they own.
Having established your load, now we need to know how much energy you use daily. Energy is power used over time (time is usually in hours).This means we need to know your electricity usage patterns, which appliance you use, when and for how many hours. Approximations can also be used where possible.
Energy for a day is then given by the power rating of your appliance known as wattage(W) multiplied by the hours of use for each appliance. We can then sum up the total energy for the entire day by adding up the energy for each device. In this sizing example since we don’t have all the appliances broken down, we can multiply by a factor to give total energy for the day as 12.5kWh or basically 13 units(rounding off). With UMEME Yake system, you can tell how many units you use daily or get an average value per month. This of course makes the consultant’s work easier on sizing your system.
How many panels do you need for a load of 2.5kW? Like you have heard, a panel is not 100% efficient. When they are dirty or covered in dust or overheat the output power is even lower. The wiring also causes some losses in the system. With all these factors in consideration, we need to calculate for a load that’s a lot more than what our house is holding, say 3.5kW. Various panel ratings exist on the market, your choice is usually limited to availability, cost and specs. Lets say you choose 250W 30V panels, you will need about 14 of them.
Panels give us direct current (DC) but our appliances and electronics need alternating current (AC). We need a device that converts this DC to AC, this device is an inverter. The inverter should be able to supply the entire load at once in the event that one day you may be using all your devices at the same time. So the inverter for this load should be 3kW from 24V DC to 240V AC. Remember, It’s always good to get an inverter slightly above your load.
Now we have sized everything we need that will keep your system online when there is sun. But there’s one more thing, if you need to have power in the night when there is no sun or on a cloudy day. You need to store some of the power you generated during the day in batteries for later use. To determine the size of batteries required, starting from the energy per day, and using the system voltage of 24V. We factor in the losses involved, the depth of discharge of the batteries and assuming you want your system to work for two days without being charged, your battery can be calculated to be about 1480Ah. Again based on what is available on the market, If you choose 12V 110Ah batteries you need about 14 of them. For our 24V system, you will need to connect these batteries in series.
Now that we are done with the sizing. How much is this going to cost you? (Disclaimer: the figures used in this cost are based on a supplier of PV systems in the UK, prices may be different depending on the quality and your source of choice)
Batteries = $200 each, but we need 14
Inverter = $760
Panel = $390 each, we need 14
Charge controller = $60
Cabling = $30 (without house wiring)
MPPT = $250
Breakers and Disconnects = $120
Charge controller, helps control the charging of your batteries so they don’t get overcharged and wear out quickly.
Cabling includes all the connections required between the panels, inverter, battery, distribution panel. This assumes your house is already wired for electricity. MPPT is maximum power point tracking. Like the name suggests, its an accessory for solar systems that basically tracks the position of the sun and adjusts your panels accordingly so you always receive the maximum power possible in your location.
Breakers and disconnects add a level of protection to your system. Should a fault occur, they disconnect your appliances to avoid damage on both sides.
All the above gives a Total = $9480, let’s say around $10000 if you include labour and other possible miscellaneous costs.
Seeing that figure, you have already written off solar. Rightfully so, this investment is as large as the last wedding budget you saw. In many countries the government has provided incentives and financing options to help people offset this huge initial investment. Utilities have also stepped up in different ways to make this investment very beneficial to owners of rooftop solar home systems.
Maybe in my next post I will talk about how investment in solar systems can be encouraged on a home to home basis or even micro level. The big question I want to address though is, Is this investment worth it?
These systems usually have a lifespan of 25 years. If we assume you use the same number of units per day for all those 25 years. Assuming a unit with Umeme remains UGX 520, for those years you will pay $24,300. Again this figure is an approximation subject to change based on the rates of power, dollar exchange rate. Now with the solar system assuming you don’t need to replace anything, after 10 years you will be using free electricity. Okay even if you had to buy the whole system again in those 25 years, you would still have about $4, 300 left over.
I guess this is where I ask you, is it worth it? Am an advocate for solar systems if only ways to offset this initial investment were available. Let us know if you would invest in solar.
Editor’s Note: This is post by our contributing writer Jemimah C. Akiror. She is currently a PHD student at Concordia university Canada where her research is mainly in energy efficiency and electrical machine design. She also takes interest in power systems, renewable energy technologies and power electronics. You can follow on Twitter at @JemyConnie or on Linkedin.