PV Panel Options-Output wattage of pv panels are typically available in the range 270 Watt, 340 Watt, 375 Watt, 455 Watt. A manufacturer’s brand name will add to the price. Some brands names are LG, QCELL, LONGI, REC etc. A manufacturer warranty can be up to 25 years. A performance warranty of up to 25 years is available.
Example -A Qcell 340 W , 25 year manufacturer warranty and performance warranty can be purchased for €60 ex vat, a REC 365W for €165, a LG 440W for €261. Some manufacturers are now including a labour warranty of between 10 and 25 years.
Inverters Options-The standalone single inverter price varies from around €160 for a 1.5kw system and increases to approximately €1,300 for a 10kw inverter for the domestic market (single phase). The number of MPPT channels provided in the inverter changes the price-a single MPPT channel inverter will usually be cheaper than a dual MPPT channel inverter. MPPT methods also affect the price (a list of the mppt types available are listed here–for the techies.) As above the manufacturer brand name and the length of the manufacturers warranty also dictate the price you pay.
Hybrid Inverters (those that charge batteries) start at around €600 for a 3kw system and increase to €1600 for a 5kw system. The warranty varies from about 2 years to 25 years. When purchasing an inverter one must ensure that it has a certificate of compliance to match the national grid profile (a grid profile determines when the inverter should switch off and on if there was a power failure) . So purchasing a cheaper inverter online might not be compatible with the national standards required in each country. This grid profile is usually programmed/selected when installing the inverter.
Another option when purchasing a central inverter is to install optimizers . These provide as a means to improve the solar output if shading exists when using a central inverter. These cost around €50 each.
Microinverters prices start at around €100 for a 350 watt pv panel and increase to approximately €160. Warranty’s vary from 10 years to 25 years. Some brand names that exist are Enphase, TSUN , BPE. They require a single management control unit that controls, configures and allows one to monitor the performance remotely on a desktop or mobile phone App. The brand name also carries a cost. The microinverter is able to monitor the performance of each individual solar panel and inform you about an individual failure or issues. They also offer one of the best ways to manage shading from trees, chimneys, etc., or different orientations as stated earlier. This single control unit costs approximately €140 to €280 depending on the functions you require. These unit types generally have an AC charging function similar to the Tesla battery systems.
When the sun is close to the horizon Solar PV Panels generate less energy than when the sun is directly over the Solar Panel.
The reason for this is that the sun’s rays pass through more of the atmosphere thus reducing the sun’s energy (photon energy) on the PV panel. If it is an overcast day they will produce less energy. To translate this into numbers- in the winter when the sun is low in the sky (say 14 degrees from the horizon ) the total irradiance from the sun measures around 780 W/m2 (watts per meter square) with a clear sky. In the summer one would expect to see 1100 W/m2 (55 degrees from the horizon). The bottom line is that if one can point the solar panels perpendicular to the sun one will get a higher electrical output power.
In order for consumers to purchase and compare solar PV panels manufacturers have agreed a way to compare the output power of Solar PV panels and this test is referred to as Standard Test Conditions (STC) . The test is done at an irradiance of 1000w/m2, at a air mass of 1.5 (approximately 42 degrees from the horizon) and at a temperature of 25 degrees. The value w/m2 is how solar irradiance is measured while the PV panel output power is measured in watts. The following calculator will help you understand how the output power of your PV System (in watts) is affected by solar irradiance and other factors. Check your Solar PV Output Power in watts.
Solar PV Calculator
Most roofs have a pitch of around 35 degrees. The best direction to point the solar panels is usually south but with some solar PV installations, it is possible to have some pointing South and others pointing West in order to collect as much energy as possible during the summer. Meters used to measure solar irradiance are called pyranometers, Solar irradiance meters, or solar radiation meters. An example of how these meters are used to locate, measure, and check if your Solar PV system is working efficiently is shown below. The calculator above can be used with these meters. An affordable pyranometer can be seen here https://pvpanelinnovations.com/
PV Panel Shading
A factor that has a significant impact on the output power of a PV System is shading on an individual Solar PV panel. This can take the form of chimneys, trees or other houses. The reason for this is that if one examines each solar panel one will see that it is made up of individual cells wired together in series to make up a full solar panel (see below). If one or more cells are shaded when installing a traditional solar PV system (One inverter) the output power is reduced for the whole system. There are other solar PV systems that use microinverter’s or DC optimizers that will not be seriously impacted by shading thus the consumer will generate more electricity.
Solar PV
Another factor that significantly reduces the solar panel output power generated is the panel temperature. We are lucky in Ireland to have a mild climate with day temperatures not usually going above 20 degrees (on a good day). What this means from a practical perspective is that a solar panel in Ireland will generate more power than a solar panel in Spain on a cloudless day.
Solar PV Components.
The components that typically make up a solar PV system are PV rails which support the PV panel , roof brackets/hooks that connect the rail to the standard tile or slate roof and clamps that connect directly to a specified roof types such as zinc or steel roofs. There are separate pv panel mounting systems for flat roofs or ground mounting. If one wants to explore PV mounting system suppliers -use a google search for “roof mounting systems for solar panels“. As I used a zinc roof one must ensure expansion joints are installed in the pv rail every 3 meters.
PV Panel Types
There are three types of PV panel cells -monocrystalline (these aesthetically have an even black finish –shown above), Polycrystalline which have an uneven shade of blue crystal cells and CIS types. Monocrystalline are more common and are slightly more expensive than polycrystalline and CIS are now more difficult to purchase (shown in part 1 of the blog). The options available when selecting PV panels other than the type above are length of equipment warranty and length of manufactures performance warranty. The majority of PV panels generate DC (direct current). All PV panels must be angled at least 3 degrees from the horizontal. PV panels produce DC power and to give you an idea of what 4 panels can produce and the energy they can generate for a load, loose connections or cable damage please see this video .
Inverter Options
Inverters are principally available in 3 types -one central inverter for a full PV installation without battery charging, a central inverter that has inbuilt battery charging facility and micro inverters for individual panels or a pair of PV panels.
Central inverters. The important factor here is the warranty length and how many MPPT (maximum power point tracking) channels does the inverter have. If one was installing 8 panels in two rows (strings), two separate MPPT channels would mean that the two rows of 4 panels would have their own ability to generate power independently of the other row (string) so for example if one row of pv panels got dirtier/shaded or a fault occurred on one panel the other row would keep generating at full power. As all PV panels are not exactly the same the separate MPPT channels allow for a higher output yield . When selecting an inverter one must match the PV Panels to a particular Inverter. Once this is done adding more panels can become restrictive and may mean that one needs to change the inverter again. If the inverter fails the whole system fails. If one needs to change a PV panel in the future the central inverter may also need to be changed.
Inverter Options for SOLAR PV
Micro Inverters-simplify the installation of a PV system and permit simple expansion. It is really close to plug and play . Because they are paired with a PV panel they manage shading better than a central inverter. The voltage generated is also different to the central inverter in that it produces low voltage AC -the same voltage as all domestic appliances like fridges, washing machines etc. There is also less of a chance of fires because of loose connections/damaged cables. They offer full management of your PV system with apps and individual panel performance monitoring. Pv panels must also be matched with the individual inverter using the PV panel data sheet. This is one such calculator.
Enphase Calculator
Batteries
As stated before I personally am not in favour of using batteries for PV panel installations. The reason is that batteries are expensive, they are another failure point and I feel they are needed for vehicles more than PV installations. For example, a 300 litre water tank can store 20kw of energy at 60 degrees (a stainless steel water tank would cost around €1000-while a similar battery could cost €10,000 to €15,000 and still would need to be replaced after approximately 6000 cycles). All homes need hot water thus sending any excess electricity from the PV panels could be fed to a hot water tank. So instead of adding batteries why not consider changing the hot water tank and place elements at the bottom of the tank and the middle of the tank.
Another good idea is to switch to night time electricity which currently is half the price of the day unit to supplement the lack of PV power during the winter to heat the water tank.
My preference is to install a side arm heat exchangerto the water tank so that I can achieve better hot water stratification. Stratification is the creation of layers of hot water free from movement/mixing when one heats water. What happens for example is when cold water enters the tank at the bottom it can mix the stratified layers of hot water thus reducing the water temperature. It is difficult in Ireland to purchase water storage tanks that have simple devices fitted that maximise stratification with devices such as an inlet baffle on the cold water inlet .
To complement the above use of a water tank one can add a single shower pump and feed all showers from the tank.
Typical Shower Pump around €157
The above will reduce the use of electric showers which are the highest electrical energy consumption devices in a home. From personal experience, I can say that 150 litres of hot water (half a 300 litre tank) can provide 6 showers a day. Currently, I use off-peak electricity to heat half the tank.
If you are a new build one can plan to install the shower pump outside the house in an insulated chamber below ground level near the tank. This is what I have done to reduce the noise as we have a single-story home.
As energy prices increase and the switch from fossil fuels takes place one is left with few options to offset rising electricity costs. In this blog I am going to go through the choices that are available when using Solar PV. Solar PV systems typically generate DC (direct current) power and this is then converted to AC (alternating current) power for use around the home. These systems also synchronise with your own electricity supply grid so that you can use it. The standard system one purchases will automatically disconnect from the national grid if there is a power failure thus ensuring that you do not send power into the national grid. The abbreviation PV stands for Photovoltaics (when light is used to generate electricity from a semiconductor material).
Solar PV Panel
A common-sense starting point before considering Solar PV is to try and reduce your existing electric energy use. This might be as simple as changing old fridges, washing machines, dryers, or pumps. If one uses electricity to heat one’s house then insulating the house and upgrading the hot water tank is also a good starting point. For example, one 300 litre water tank will store 20kw of energy at 60 degrees Celcius (see the previous blog on the water tank). Typical battery systems can not economically or environmentally compete with water as an energy storage system. All homes need hot water and you will not find a safer, more economical, and environmental approach for storing excess energy from Solar PV. One can also opt for reduced price electricity at night (approximately half the price of daytime electricity) which helps the national grid balance its load.
A simple starting point is to visit your home supply meter and work out how much electricity you use per minute on a typical day. This is the load one uses without using main appliances such as kettles, cookers, water heaters, etc. It typically would include fridges, ovens timers, clocks, computers plugged in, modems, etc.
To do this one only needs to look at your meter and it will display a number that tells you how many revolutions or pulses it uses to record one Kw/h (kilowatt per hour) of electricity. One is billed by your electricity supplier for each kw/h you use. Above and below are examples of where you can find the numbers. In the example above the digital meter has 1000 Impules per kw/h and the old type shown below has revolutions -in this case, it is 250 revolutions per kw/h.
To calculate your typical energy use without using main electrical appliances follow this example. Set your phone/ watch to the stopwatch setting. When you see the first pulse start your timer and visually count the impulses in that minute. If you get 10 impulses in 1 minute then multiply 10×60 minutes=600 impulses in an hour. So we know that we now use 600 watts of power in one hour without using main appliances.
In the old type meter, you will notice that there is a red/black mark on the wheel when it revolves in one revolution. In the meter above we can see that it does 250 revolutions in one hour to record 1kw/h use of electricity. So if it does 125 revolutions it is 500 watts of power in one hour or 0.5kw/h. One can use the same principle above and use a two-minute count to increase the accuracy of your calculation. InPart 2 I will look at what PV systems are available to purchase and the parts that make up a good Solar PV system.
Self Build Blog Passive House (Passivhaus) 