An online solar panel calculator is one of the most common tools nowadays for consumers looking to go solar. Online solar tools have become mainstream in countries like the USA, Australia, UK, etc. enabling many online users to make online decisions to go solar. For instance, EnergySage has one of the most popular online solar calculators in the States, and millions of people use this platform each year to research and shop for solar through their network of pre-screened, local installers.

However, not all consumers have access to online tools to help them make online solar decisions because such tools require a lot of investment to create them. For instance, most of these tools have been developed or informed from solar mapping research conducted using Light Detection and Ranging (LIDAR) technology. These tools can determine the specific solar potential for rooftop solar for both residential and commercial places. The cost for LIDAR remains high and it will perhaps take time before it can be reduced.

Many solar consumers in countries without site-specific solar data can still determine their solar potential manually by performing a few calculations although it can be time-consuming and tedious. As such, this blog attempts to capture the process or steps for how to determine whether solar is right for your house or business, manually without the use of online solar tools which we promote here.

1. Determine the electrical load for your household or business
A very straight forward way to determine the electrical load for your household or business is from your monthly utility bills. You can pick out the number of kilowatt-hours of electricity consumed in your household on a yearly basis and then get the average by dividing by 12 to get the monthly electricity consumption and then divide that figure by 30 to get the daily kWh usage.

To be more specific, you can list all your heavy electrical appliances such as your refrigerator, washing machine, etc. Determine their wattage and how many hours are used by them to determine the number of watt-hours.

Once you complete this step, this will give you a general estimate of your energy consumption. At this point, you can decide whether you need to do something with regards to lowering your energy consumption by implementing energy efficiency measures. For instance, one of the low hanging fruits can be changing all your incandescent bulbs to LEDs. LED bulbs use more than 75% less energy than incandescent lighting which means you can save a huge significant of energy by just switching to LEDs if you are currently using incandescent bulbs.

2. Solar Insolation
Solar insolation is the incident solar radiation onto some object or specifically the measure of the solar energy that is incident on a specified area over a set period. Solar insolation
can be expressed in two ways, that is:

• Kilowatt-hours per square meter (kWh/m2) per day which represents the average amount of energy hitting an area each day.
• Watts per square meter (W/m2) which represents the average amount of power hitting an area over an entire year.

The importance of knowing the values of solar insolation at certain positions on the Earth is to help determine the size and output of your Solar PV system. As such, based on the solar insolation of your location, these values will help to determine the expected output for your solar panels and determine whether your specific location will be good for solar power. There are other factors such as obstructions to your rooftop like trees or building design that will affect solar insolation for your PV system.

There are various ways to determine solar insolation for your building ranging from weather databases in your area. As early mentioned on this blog, today there are various tools that use the LIDAR technology that has simplified this process. However, these tools are country-specific, but some tools like Google Project Sunroof are aiming to have global coverage to have online users just plug their address into the tool to determine solar potential. Google Project Sunroof in addition to providing with your solar insolation calculates how much money a user can expect to save yearly by making use of solar power

Until, we have a resource that can provide online users with specific rooftop solar insolation like the Google Project Sunroof, online users without this specific information can use for instance the Global Solar Atlas
which was developed by the World Bank and the International Finance Corporation (IFC) to support the scale-up of solar power around the world. The primary aim of this Global solar Atlas is to provide quick and easy access to solar resource and photovoltaic power potential data globally, at a click of a mouse.

The methodology for the Global Solar Atlas is location-specific that involves three main different models i.e. solar radiation model, air temperature model, and PV power simulation model. Solar radiation and air temperature modeling result in a series of pre-calculated data layers that can be retrieved at (almost) any location on the map. Additional information about a possible PV system type and configuration are used for the PV power simulation, which is calculated on-demand using Solargis internal algorithms and databases. For more information, see the details of the methodology of the Global Solar Atlas.

However, like every online tool, the Global Solar Atlas can only provide solar estimates and the figures you get are preliminary to provide you with an estimation about your solar potential. It is always advisable to obtain the final word of a licensed and experienced solar installer to make an actual assessment for your solar PV system. Online materials suggested on this platform only provide estimates. For instance, the objective of the Global Solar Atlas is to provide reliable introductory-level data to help policymakers, researchers, and commercial solar companies take better decisions. For project-specific analysis of large -power plants, the data available via the Global Solar Atlas is suitable only for preliminary analysis.

The Global Solar Atlas provides an opportunity to do site prospection and pre-evaluation of the potential of solar energy in different countries and areas. For instance, in our context, you can check the solar energy potential for a specific site for instance for your home or business. In this case, you can determine how much electricity will be generated and in what time. Also, analysis of the averaged solar radiation components for specific locations helps with planning and pre-evaluation of opportunities for solar energy projects.

3. Determine capacity of solar panels or how many solar panels you need
Once you have determined the solar insolation which is sometimes referred to as “peak sun hours” measured in kWh/m2 per day, it is easy to estimate the capacity of solar panels or how many solar panels are needed. The term “peak sun hours” refers to the solar insolation which a particular location would receive if the sun were shining at its maximum value for a certain number of hours. Each peak sun hour is defined as one hour when the intensity of sunlight (solar irradiance) reaches an average of 1,000 watts of energy per square meter (roughly 10.5 feet). Since the peak solar radiation is 1 kW/m2, the number of peak sun hours is numerically identical to the average daily solar insolation. For example, a location that receives 8 kWh/m2 per day can be said to have received 8 hours of sun per day at 1 kW/m2. Being able to calculate the peak sun hours is useful because PV modules are often rated at an input rating of 1kW/m2.

Also, there are various solar panels out there of different sizes ranging from 500-watt solar panels, 300-watt solar panels, 250-watt solar panels to 1watt solar panels, and so on. However, it is good to know what size of solar panels to pick depending on the size of your rooftop or anywhere that you want to place them to harvest solar energy.

Once you have estimated your average kWh used monthly in step one (1) above, it is easy to estimate the capacity of solar panels needed in your building. Let us say that you use an average of 1000kWh per month, to get the daily kWh usage divide 1000kWh by 30 to get about 34 kWh daily usage. Assuming you want to off-set the 34 kWh daily electricity usage with solar panels at 100%, using a 250-watt solar panel and your site location is getting 4 hours of sunlight per day that means 250W multiplied by 4 hours which is 1000 watt-hours per day or 1kWh a day.

Since you are consuming 34kWh daily, then you need 34 solar panels each with a 250-watt power rating. This is just a rough estimate and a lot of other factors such as cloud cover, system design, etc. will affect the sizing of your system. However, to help you make the decision to contact a solar installer in your local area, doing a preliminary feasibility study will help you to make a good decision on whether to pursue solar for your home or business. Other factors such as solar panel efficiency and whether your solar panels come with warranties are important while conducting your research.

Remember, the above example assumes you are going solar 100% however, considering you have a net-metering arrangement in your area, you can decide to off-set your current usage at 75%, 50%, 30%, and so on. For instance, if you decide to off-set your current electricity usage at 50%, this means 34kwh/day multiplied by 0.50 which is equal to 17kWh/day which means you will only need 17 solar panels each with a 250-watt power rating.  

Depending on the amount of electricity usage you want to offset using solar panels, you will probably need to invest in some additional equipment often referred to as balance-of-system
to condition the electricity, safely transmit the electricity to the load that will use it, and or store the electricity for future use. For off-grid systems or those not connected to the grid, you will need batteries and a charge controller to store excess power produced during the day and use it at night when there is no sunshine. Grid-connected PV systems you will need power conditioning equipment such as solar inverters to convert your DC generated power to AC to comply with your power provider’s grid connection requirements.

This article just provides the initial steps that can help you figure out how to go solar. To get specific information about solar panels and balance of system, please contact a solar installer in the local area. If you are in the USA, this solar calculator can help you locate a solar panel cost calculator and obtain multiple solar quotes from your local area. Learn more here.