The following viewpoint is from Victor Hill, an engineer at DENSO. For our viewpoint guidelines, please go here.
Going off-grid refers to relying on a system that generates and uses electricity to run all appliances at home or business. For a system to be truly off the grid, there should be absolutely no connection with it. The phrase is not only possible and practical, but also beneficial in very many ways. Benefits include the absence of utility bills and life becoming free and easy. There are many motivations behind generating your own energy such as:
- Environmental concerns, a desire to consume maximum renewable energy
- Independence from the utility, either to eliminate inconveniences due to power blackouts or for philosophical reasons
- Social values, that is, being accountable to effects of your energy use, and
- Cost, if you live too far from the grid, living off grid makes economic sense.
If you live far from the grid (or the grid is entirely unavailable in your locality), your only viable option is an independent off-grid system. However, if extending the utility grid to your property is possible, find out the cost of making the connection, and what the cost will cover. Be sure to make a reasonable comparison that you can base your decision on. These are the factors to consider before going off-grid.
1. Cost
If you live far from the utility grid and not yet connected, living your life off the grid makes economic sense. You should also be planning to stay there long enough to recover costs incurred buying system components and installing it.
2. The electric energy your roof can generate
To go off the grid and still retain your present electricity consumption rate, you will have to buy sufficient energy taping and storage capacity. However, for homes built on a quarter acre block, the rooftop may not provide enough space to mount enough number of solar panels. If enough roof space is not available either you should buy high-efficiency solar panels or reduce electricity consumption to a level where the rooftop arrays can suffice.
3. The possibility of energy usage increasing suddenly
Ordinarily, your household’s electric consumption isn't constant. There is a possibility of some high-energy consuming appliances being switched on at the same time. Be sure to engineer your off-grid system to handle such spikes by constructing it with extra capacity.
4. Battery safety
Batteries need to be installed, operated and services following certain principles to minimize risks. Find out about security requirements of your batteries either from honest best home generator reviews or the manufacturer. Strategize you will ensure they are safe for the system to also remain 100 percent safe. Avoid shortcuts at all costs at any stage of its installation.
5. Maintenance costs
Don't forget to factor in the maintenance costs of the system you are about to install. Solar panels typically have a 25-year maintenance warranty, while batteries and inverters both need replacement after between 5 to 10 years.
How to size your solar system
1. Sizing the PV panels
Different sizes of (PV) Photovoltaic modules generate different amounts of electric power. The climatic conditions of the locality also play a role. Consequently, you should consider (PGF) PV generation factor, which takes into account climatic conditions and panel size. (Refer the map below for the corresponding PGF of each state). Use PGF to determine the sizing of your generator as follows.
- Step 1: Calculate total daily Watt-Hour required from the panels by multiplying total daily appliances Watt-Hour by 1.3 to get the total Watt-Hours you need on a daily basis. (1.3 caters for the energy lost during conversion and along the connecting cables. )
- Step 2: Divide the figure you obtain from the preceding step by PGF to obtain the Watt-Hour ratings of the PV modules necessary to power all your appliances.
- Step 3: Divide the number from the previous step by the rated Watt-Peak output of the PV panels available to you. If the result has a fractional part, raise it to the next highest number full number to get the number of modules needed for your establishment.
For example, if the total daily appliances are 1000 kWh, and PGF is 4.5, this will lead to the total watt peak requirement is 1000*1.3/4.5 = 288.9 Watt-peak (i.e. Wp).
Further depending on the solar panel capacity available, the number of panels are derived. For instance, if the required solar energy is required to be generated from 100 Watt-peak solar panel, so the number of solar panels is 288,9/100 = 2.89 or ~ 3 panels.
2. Inverter sizing
Sizing an inverter depends on the wattage of the appliances connected to it. The input power ratings of the inverter should not exceed the total watt-hour of the appliances. Since most inverters are rated on kilovolts ampere, (kVA), size your inverter as follows:
The power factor is less than 1 (between 0.85 and 0.99). So, you can assume 1.18VA is equal to 1 Watt. So, if have a situation where the total watt-hour is 1000, for example, multiply that figure by 1.18 to get 1180 VA (1.18 kVA) as the size of your inverter. (You should add some extra, or simply settle for the inverter whose rating is slightly higher, by about 25 percent, than the figure you obtain for safety purposes)
3. Battery sizing
Use a deep cycle battery for your solar PV system. The capacity of your battery should also be enough to run all your appliances during cloudy seasons and at night. Size your battery as follows;
- Calculate the total Watt-Hours enough for all your appliances as explained above.
- Divide the figure by 0.85 to cater for battery loss
- Divide the answer in the preceding step by 0.6 to cater for depth of discharge
- Divide the resulting answer by the minimal battery voltage.
- Multiply the result with the number of days of autonomy to get the necessary Ampere-Hour of your deep cycle battery. Days of autonomy refers to the days you will want to use your system when the PV panels are not producing energy.
4. Controller sizing
To size your controller, multiply the number of panels by the watts-hour to obtain the total wattage of your system. Divide the answer by the total voltage of your batteries to get current that will be flowing at any one time. Then add 25 percent to the value you get in the preceding step to allow for low temperatures before rounding it up to get the controller size you should use. Obviously, the sizing process is unique to every situation, and there is no standard answer for different situations and or regions.
Reality check
Owners connected to the grid can obtain their energy from the utility when the resource is unavailable. Off-grid system owners, on the other hand, have to generate the energy they need all the time, and that makes dealing with an inconstant resource challenging.
Designing an off-grid system to overcome variations come at an increased cost of more electricity generating capacity and larger storage capacity. Such a system is more environmentally friendly and efficient
Typically, battery maintenance involves adding water, checking connections and cleaning. Setting up a charging routine correctly is equally important since batteries last longer when fully charged on a regular. You must not leave your battery in an uncharged state for more than a few days.
For most off-grid systems near balanced resources, a fuel-powered battery is crucial. The best system incorporates a modest home backup generator, which should be used as seldom as possible.
Some off-grid systems are, however, are located near the perfect balanc of resources, such as sun/hydro and sun/the windm or year-round hydro, thus eliminating the need for a backup generator.
Should you leave your off-grid system design and installation to the professionals or do it yourself? The option of doing it yourself may compel you to attend some classes. Once you complete the training, buy the equipment from a reliable source (preferably local). Alternatively, you could engage the services of a pro, but first establish if they have experience working on off-grid solar systems.To get the best results in your off-the-grid system, do not take chances. Be realistic, acquire the necessary training and source for reliable help. Ensure your system is rightly installed and enjoy your independence as you use renewable energy.
