grid connected solar panels

Solar Panel Basics: On and Off the Grid

By Wayne Groszko Rise Renewable Energy Expert
Feb 11, 2020

Would you like to live in a solar-powered home? Want to know where to start? Solar power, or electricity produced from sunlight, can be generated in several different ways, and at any scale from small home-based systems to large industrial solar farms. In this guide, we'll focus on off-grid and grid-connected photovoltaic (PV) systems available for your home or cottage.

Table of Contents

  1. What Does Photovoltaic Mean?
  2. Will Solar Panels Work at My Home?
  3. Which Direction Should Solar Panels Face?
  4. Why Are Solar Panels Angled?
  5. When Do Solar Panels Generate The Most Electricity?
  6. What Is a Grid-Connected Solar Power System?
  7. What Are the Components of a Grid-Tied Solar Power System?
  8. What Is an Off-grid Solar Power System?
  9. What Are the Components of off-Grid Solar System?
  10. What To Look For When Buying Solar Panels
  11. Solar Panel Battery Systems
  12. What Is Deep Cycle Lead-Acid Battery?
  13. Charge controllers
  14. Inverters,Wiring

What Does Photovoltaic Mean?

Photovoltaic means 'voltage from light' and refers to a solid-state semiconductor device, aka solar cell, that produces a potential difference (voltage) and current of electrons (electricity) when exposed to light. PV solar panels, or modules, are solar cells assembled between protective layers of glass and plastic and typically framed in aluminum. Besides the regular solar modules, exciting new kinds of packaging for solar cells are continually being developed, including building-integrated systems like solar PV roofing and windows.

solar panels on roof

Will Solar Panels Work at My Home?

The most important question is whether you have a good, sunny spot on your property to install solar panels. It's not so much about where you are on Earth, as solar panels are being deployed successfully everywhere from Antarctica to Greenland to outer space. Instead, it's more about finding a spot on your building or on your land where the modules can face the sun and not be in the shadows of other things like trees and buildings - open spaces and high places work well.

Which Direction Should Solar Panels Face?

Solar modules are often installed on roofs to give them height above the shadows and keep them out of harm's way. But they don't have to be on a roof. There are some advantages to mounting them on a stand on the ground if you have sunny space in your yard.

Look for a solar professional to assess where shadows of nearby trees and buildings may fall on your solar array in the wintertime. Assessors can use a slick device, such as a Solar Pathfinder, to figure out in just a few minutes where the shadows will fall throughout the day and in all seasons. You can also check and see if your place shows up on Google's Project Sunroof map, which gives solar capacity estimates based on satellite imagery.

You want your PV modules to face as closely as possible the direction towards the equator - south in the northern hemisphere or north if you are in the southern hemisphere. That's the direction that receives the most solar energy over the year. Up to 30 degrees off to the east or west is also acceptable. In some cases, even further off can work if the modules are reasonably flat. However, annual production reduces by being that far off the optimal direction. Be sure not to point them directly away from the equator!

Why Are Solar Panels Angled?

The angle at which PV modules are tilted also makes a difference. As a rule of thumb, if panels face the equator, it's good to have a tilt angle matching the latitude of your property. For example, the latitude of Chicago, USA, is almost 42 degrees North. Modules facing south and tilted up from the horizontal anywhere from 25 to 40 degrees will perform exceptionally well there. If you have a sloped roof close to the correct orientation and slope, it's easier to mount the modules parallel with the roof and, you'll still get proper output.

Solar PV Ground Rack
Solar array rack-mounted on the ground

When Do Solar Panels Generate The Most Electricity?

Using solar power is all about timing. Solar panels produce electricity when sunlight is shining on them, usually between 11 am to 4 pm. They provide more power when the sunlight is more intense and not reduced by cloud cover. They will produce some on a cloudy day, too, but typically less than 10% of what they would on a sunny day. And of course, they don't produce at night.

To make full use of PV’s potential, you need to produce as much electricity during the day as possible. If you have battery storage, this can provide power when the sun goes down. This timing issue affects you differently, depending on if you are on or off the grid.

Grid-Connected Solar Diagram
Grid-Connected Solar Diagram

What Is a Grid-Connected Solar Power System?

If you have a power line to your building, you can have your solar PV generating system connected directly to the grid in many jurisdictions. It takes care of timing issues by allowing you to export surplus solar power automatically to the grid when it's sunny, powering other homes and businesses. Later on, when the sun isn't shining, you can import electricity to your home from the grid.

The credit you get for the solar energy you export depends on the rules in your area. You can get a "net metering agreement," where you get a credit on your electricity bill in some places. You may be able to get a power purchase agreement to sell solar power for a "feed-in tariff." This tariff is a premium price set by the local, state or provincial government for you to sell your solar energy. Check with the local electric utility to see what's available where you are and how to apply to participate.

What Are the Components of a Grid-Tied Solar Power System?

  • Solar Panels – Solar PV modules used to generate electricity
  • Solar Panel Racks – typically aluminum, solar panel racks are mounting system to secure the modules
  • Inverters – (approved for grid connection) – convert direct current (DC) to grid-suitable alternating current (AC) for your home and export to the grid
  • Wiring – approved and inspected wiring installed by a licensed electrician
  • Optional batteries – You don't need batteries for a grid-connected PV system, but you can add some if you want backup power.

The type and number of modules and inverters (and where they will go) are the primary choices you can make in consultation with a solar professional. The racking and wiring are details that the pro should look after to meet your needs and regulations.

Off-Grid Solar Diagram
Off-Grid Solar Diagram

What Is an Off-grid Solar Power System?

Off-grid means the building or structure has no connection to the electric utility's distribution network. When you go off-grid, you are the power company. Making and storing your electricity using solar photovoltaic (PV) modules and batteries is a great way to achieve this goal. Emission-free and silent, with no fuel needed, solar PV is your best sustainable choice for off-grid electricity.

Off-grid systems need to supply your total energy consumption each day of the year because you don't have access to a utility grid to pull additional energy. It's important to note that your PV array will produce more electricity in summer than in winter.

What Are the Components of off-Grid Solar System?

  • Solar PV modules (generate the electricity)
  • Batteries (store the electricity)
  • Charge controller (regulates the flow of electricity from modules to batteries)
  • Inverter (converts direct current (DC) to alternating current (AC) for appliances)
  • Wiring (distributes the electricity in the house – can be AC, DC, or both)

What To Look For When Buying Solar Panels

The solar PV modules are available in a range of brands, sizes, and output capacity in some ways, the easiest part to source. Look for modules with all the necessary approvals (UL, CE, or CSA labeled) and a 25-year warranty on their power output. It is also your opportunity to explore other products on the market, like solar roofing. Compare costs, benefits, maintenance factors, durability, aesthetics, and any other important attributes.

To properly size your solar array, you have to estimate your monthly electricity consumption. Your usage will dictate how many panels your system will require to supply your energy needs.

"(Annual kWh Usage ÷ 365 days ÷ average sun hours per day) x (1 x efficiency factor) = Required DC Solar Array Size."

It's essential to plan solar production based on the lowest-sun month of the year, which is in early winter. December 21 is the day of the lowest sun in the northern hemisphere (winter solstice), or June 21 if you live in the southern hemisphere. For people looking for a more detailed calculation, PVWatts has an in-depth online calculator.

Solar Panel Battery Systems

Several types of home batteries are available for your off-grid or grid-connected home. Today, the two common types available are deep-cycle lead-acid batteries and lithium-ion batteries. Both types of batteries work well and provide dependable energy storage for off-grid solar power systems.

What Is Deep Cycle Lead-Acid Battery?

Lead-acid batteries have been used for well over a century. They're relatively affordable and can provide plenty of electric currents. Lead-acid batteries last approximately ten years, or 1,500 cycles, providing they are well maintained and used as directed. They are large, heavy, and require periodic maintenance, such as refilling water in the cells. They contain a mix of a recycled and new lead, a toxic metal that must be recycled properly.

What Are Lithium-ion Batteries?

Lithium-ion batteries are lighter and smaller than lead-acid batteries. They are significantly higher in price to purchase than lead-acid batteries but require less maintenance, withstand deeper discharges, and last about 13 or more years, or 2000 cycles. Lithium-ion batteries are made from a mix of recycled and new lithium, a rare and reactive metal that must be recycled properly.

Other new kinds of batteries are evolving in the market, such as salt-water (sodium ion) batteries and redox flow batteries.

Optional Home Storage Batteries

You don't need batteries for a grid-connected solar PV system, but you can choose to add them if you want backup power in the event of a power outage. Conventional grid-connected solar PV systems have no batteries, and their design allows automatic stop producing power during a power outage. It is an essential safety feature to avoid injuring electrical workers who are fixing the wires on the grid. This automatic shut-down has the unexpected result that if the grid power is out, so is your solar power, unless you install backup batteries.

If you want to have solar PV and backup batteries, the most efficient way to use them together is with a grid-interactive inverter. This sophisticated unit will use solar power to charge the batteries. Then it will send the power to your home or the grid as needed. It will then continue to power your home independently from the batteries in the case of a grid power outage.

It takes a large battery to run a whole home for more than a few hours. Batteries cost quite a bit of money, so calculating an appropriate size for a battery bank is something to decide with advice from your solar professional. Many people choose ' critical loads' to keep it to a reasonable size (things you absolutely must have running). Then they connect those loads through a sub-panel and power only the critical loads from the battery bank. These are things like a well pump, refrigerator, and the fans, pumps, and controls that run your furnace, boiler, wood pellet stove, a few lights, and a couple of plugs for internet connection and charging phones. You can choose the things that are essential to you for home resilience in an emergency.

Tesla Powerwall 2 Installation
Tesla Powerwall 2 Installation. Photo Credit: Tesla Energy

What Is the Ideal Home Battery Capacity?

If you are off the grid or experiencing a power outage, you might need your battery bank to get you through a few cloudy days in a row when there is little solar energy coming in to charge them. How do you figure out what size (capacity) of battery you need?

Battery capacity is measured in Amp-hours (one amp of current for one hour), which you can convert to the more common unit of kilowatt-hours (kWh). Just multiply the amp-hours by the voltage and divide by 1000. For example, to convert a 500 amp-hour, 12-Volt battery to kWh, do the following calculation:

"500 amp-hours x 12 Volts/1000 = 6 kWh"

You need to know how many kWh per day you will use and have enough battery capacity to supply that for several days until the next sunny day comes.

Considering the example house using 600 kWh per month, it would take four batteries, like the one described above, to store enough energy to operate the house daily (20 kWh). You probably want to be able to run for at least three cloudy days in a row (60 kWh), so at least 12 of the example battery would be needed. Adding extra batteries above the minimum is a good idea because the batteries will last more years if they are not worked as hard or discharged so deeply.

For comparison, the recently-launched second-generation Tesla Power Wall contains 13 kWh of electricity, so you would need about 6 of those to keep the example house going for three days without sunshine. As a single Power Wall will cost you more than $10,000, the expense of large batteries very quickly shows why off-grid homes use far less electricity than on-grid homes. It's common for people to happily live off-grid while using just one-tenth of the electricity of an ordinary home so that they don't need a large battery bank. A modest and well-designed off-grid home can work with as little as 20 kWh of battery storage, equivalent to two Tesla Power Walls.

Besides the type and size of the battery, you and a designer also choose the voltage. A wide range of battery voltages can be created by wiring batteries together in series and combining the series banks in parallel. Some of the most common battery voltages in use are 12V, 24V, and 48V. It matters which voltage you choose because the charge controllers, inverters, and wiring are rated for specific voltage, current, and power levels.

Charge Controller for Solar Panel Systems
Charge Controller. Photo Credit: Suder

Charge controllers

The primary function of a charge controller is to regulate the flow of electric current from the array of solar modules to the batteries. This ensures the batteries are correctly charged and prevents damage from over-charging. Charge controllers come in a range of capacities based on the voltage and current they can handle. A great feature to look for is high-voltage maximum power point tracking (MPPT). An MPPT charge controller can accept the input from the solar modules at high voltage and charge the batteries at an appropriate lower voltage, using an optimization algorithm to maximize the amount of power going to the battery bank.

OutBack Power Solar Inverter
Solar Inverter. Photo Credit: OutBack Power

Inverters

PV modules and batteries produce electricity in the form of direct current (DC). This can charge devices that use DC, like phones, tablets, and battery maintenance chargers. You can get DC lighting and appliances for your off-grid place, especially at motorhomes and sailing boat shops. But the most commonly available and affordable appliances run on alternating current (AC), and the wiring for AC in a building is more standard for electricians. A highly efficient device called an inverter can convert DC from your batteries to AC for your house wiring. For home use, there are two basic kinds of inverters: micro-inverters and string inverters.

Microinverters

Microinverters are small inverters underneath each solar module or every two or three modules. They convert the solar module's output from DC power to grid-suitable AC power directly in the solar panel. There are two advantages to this:

  1. AC wiring is more common than DC wiring so that installation labor can be cheaper.
  2. A module or small group of modules is independent of the others so that if a shadow or malfunction cuts the output from one micro-inverter, the others will keep performing their best.

However, be aware that if your array is broad, you need many micro-inverters, and the cost can add up to be more than string inverters.

String inverters

String inverters are larger inverters installed either outdoors near the array or inside your electric utility room. They convert the DC electricity from many solar modules into grid-suitable AC power. A string inverter can be a more affordable option and works well when there are no shadows over portions of the array. If the array is partly shaded, partly covered in snow, or has one module with a malfunction, the string inverter output will drop significantly.

Modified Sine Wave vs. Pure Sine Inverters

Both types of wave inverters will provide AC power to appliances that require it. Modified wave inverters are less expensive and adequate to power basic electronics like tablets, cell phones, space heaters, or window air conditioning units. Given the lower quality of power, even smaller appliances or CFL and LED lighting can exhibit poor performance or make buzzing sounds.

However, televisions, computers, fridges, microwaves, and other sensitive products require a clean, consistent power source. Pure sine wave inverters use advanced technology to produce power equal to or better than standard grid-connected power. They are therefore recommended for reliable power throughout your home.

What Size Inverter Do I Need?

For small cottages where you are just running a small AC fridge, lighting a few lights, and plugging in a laptop and phone to charge, a 1,000 W inverter could be enough. A larger 6,000 or even 10,000 W inverter may be needed for a full-sized house with substantial electrical loads. The output voltage matters too – either 120 or 240 Volt, single phase is typical for household use. Remember to account for the voltage required for your well pump, as most off-grid homes use a pumped well for water. A standard well pump is often 240 Volts, which requires a 240 Volt inverter. Many off-grid homes use a DC well pump, so they are not dependent on the inverter to get water.

Wiring

If you use a large enough inverter, you can supply the whole house with AC power and use ordinary interior AC wiring, most familiar to electricians. Electrical contracting and inspection will be easier this way. A popular alternative approach is to wire some portions of the building with DC wiring, which is slightly different from AC wiring. The advantage of DC wiring is you don't have to turn on your inverter to use the DC systems – the power comes straight from the batteries. Using some DC can be advantageous, especially for small cottages or tiny homes. When it comes to a larger home, most people wire up for AC to use AC appliances that are easy to obtain.

Solar Rooftop

Only a small portion of homes in North America have installed solar systems - but this number is rising quickly. Will you be part of the change?

Disclaimer: This article does not constitute a product endorsement however Rise does reserve the right to recommend relevant products based on the articles content to provide a more comprehensive experience for the reader.Last Modified: 2022-10-07T16:10:05+0000