How To Size Off Grid Solar System

How To Solar Sizing An Ev

If you can put solar on your EV, where would you put it? On the cars roof, maybe the bonnet too. OK.

How much space have you got? What power level do you get with that space? Does it worth the money? Does it provide a good return on investment? Or just good for the environment?

That is a lot of questions, just for sizing the solar system for your EV.

Ordering The Right Solar System Components

Once you have chosen the placement of the solar panels, you will have an idea of the power power potential of you site, and will be able to choose and order the proper components for your system. There are many choices to make at this point including:

• The number and size of your solar cells
• The type and size of your charge controller
• Your battery bank capacity, while considering battery type
• Choosing the overall voltage of each leg, as well as which loads should be AC vs DC
• The rating of your inverter, if any

We talk about this in part 2 of this series.

How Many Days Of Back Up Should My Batteries Provide

The number of batteries you need in your battery bank will depend on how long they will be needed to back up your system. This will depend on your local climate, your situation, and what other backups you have available.

The battery backup is how long you want to be able to run your house from battery power only. This is used during the night or at times with little sunshine. A standard backup time is between 3 to 5 days, but it can be more or less. The longer you want to be able to back up your system for the larger battery bank you will need.

Some people choose to have a battery backup that can run for a few days and add a generator that can top up the batteries if necessary. This way you can back up your system for several weeks at a time should it become necessary.

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Figure Out How Many Solar Panels You Need

Now that weve determined battery capacity, we can size the charging system. Normally we use solar panels, but a combination of wind and solar might make sense for areas with good wind resource, or for systems requiring more autonomy. The charging system needs to produce enough to fully replace the energy drawn out of the battery while accounting for all efficiency losses.

In our example, based on 2.5 peak sun hours and 240 Wh per day energy requirement:

240 Wh / 2.5 hours = 96 Watts PV array size

However, we need to account for real-world losses caused by inefficiencies, module soiling, aging, and voltage drop, which are generally estimated to be around 15%:

96 array watts / .85 = 112.94 W minimum size for the PV array

Note that this is the minimum size for the PV array. A larger array will make the system more reliable, especially if no other backup source of energy, such as a generator, is available.

These calculations also assume that the solar array will receive unobstructed direct sunlight from 8 AM to 4 PM during all seasons. If all or part of the solar array is shaded during the day, an adjustment to the PV array size needs to be made.

The maximum charge current for lead acid batteries is typically around 20 amps per 100 Ah and somewhere between this range is ideal .

Here are standard configurations of PV arrays with battery banks. The battery capacity calculated in the previous step can be compared against this table to find a suitably sized system:

Will The Size Of Your System Provide Affect Production In Overcast Weather

While panels can produce current at a reduced level during cloudy weather, no current will be produced at night. This means that you will still have to rely on the commercial grid to some extent. However, this doesnt necessarily mean that you will be paying for this current! The reason for this is that your panels will on average be producing much more current than you need. This extra current is automatically banked for you by a system known as Net Metering. Whenever you require additional current during bad weather or at night, you simply draw on this excess current. The way this works is that your system feeds unused current back into the grid, as it is produced, and your utility company banks this current by crediting your account. A well designed system can thus basically reduce your electricity utility bills to zero. Read our post explaining this concept.

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Key Considerations When Sizing Off

• Daily average energy consumption – Summer and winter

• Peak load – The maximum power drawn from loads

• Average continuous load

• Solar exposure – Location, climate, orientation & shading

• Backup power options – During poor weather or shutdown

With the above considerations in mind, the key component of an off-grid power system is the main battery inverter-charger often referred to as a multi-mode inverter as they can usually operate in both off-grid or on-grid modes.

Select Appliances To Run On Your System

*This off grid calculator is indicative only. It is provided to give an estimate only and general guide of the solar system size and solar battery bank required to function free from the electricity grid.

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Determine The Sun Hours

When solar panels are tested and rated, they all undergo testing under standard conditions to produce comparable results. One of the conditions is seeing how much a solar panel can produce when one square meter of that panel is exposed to 1000 watts of sunlight for 1 hour. If the panel produces 300 watts during that hour, then the panel is rated for 300 watts. If it produces 100 watts, then its rated for 100 watts.

In the real world, we all get varying degrees of direct sunlight depending on seasonality and location. Regions near the equator typically get more solar energy than places that are near the poles during winter. Other factors such as pollution, local climate can result in very different levels of sun exposure.

Data has shown that sunlight can vary a great deal even amongst places with the same latitude. Sun hours tell us how many hours a day solar panels can expect to receive 1000 kilowatts. To get accurate sun hours for your location, our tool below pulls historical data from the National Solar Radiation Database based on your address or zip code.

The average daily solar radiation gives you an estimate of the daily peak sun hours for the address you entered. Peak sun hours is defined as the number of hours in a day where the sun is intense enough to reach 1000 watts per hour. The table above gives you a breakdown of how average peak sun hours vary by month.

What Are Your Options For Feeding Electricity Back To The Grid

Depending on where you live, you will be faced with different rules around how you will be compensated for feeding electricity back to the grid. These rules are determined by your state, or by your utility and can have a large impact on the size of your PV system

The three most common scenarios are net metering, a feed-in tariff, or no compensation.

Net meteringNet metering is when any additional energy you dont use is fed back into the grid and you are given credits for this energy, almost like winding your meter back. This allows you to use the grid like a giant battery, storing your solar energy for use after the sun goes down.

Feed-in tariffA feed-in tariff is when you are paid a specific amount for the energy you dont use and feed back to the grid. Originally feed-in tariffs were quite high, to encourage the growth of the solar industry. Now in some countries such as Australia, the tariff can be much lower than what you normally pay for your electricity.

No compensation for exportingIn some areas, you wont be compensated at all for any electricity you feed back into the grid. It is still useful to be connected so you can use the grid at night without installing a battery, but any electricity that is generated by your solar system and not used by your household is essentially wasted.

A few useful websites to start:

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Ballparking A Solar System Size With Your Annual Usage

Based on your annual electricity and monthly consumption pattern, we can ballpark a general system size for you. To do this, we use a rule-of-thumb number for solar production in NC to estimate your needed system size. Based on our experience, our rule of thumb is that 1 kilowatt of solar installed in NC will produce 1,300 kilowatt hours per year. So if your home uses 12,000 kWh per year, wed estimate you need around a 9.2 kW solar system to meet 100% of your energy needs .

Remember, this is just an initial rough estimate. We always refine your system size with more accurate annual production estimates based on the exact solar potential of your site after we perform a full site evaluation of your home, discuss your goals of going solar, and work through any limitations if encountered. With that said, this graph shows how this rough estimation translates to solar kW and number of solar panels.

Roof space needed for a solar system

If a space meets all those criteria, then it is ready to shine. For a roof mounted solar system, each panel takes up an area of approximately 18 square feet. So for the 100% energy offset 9.2 kW solar system we have been using as an example, we would need 31 panels or 470 sq feet of eligible roof space .

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What Size Battery Charger Do I Need

As a general rule, lead acid batteries need a solar charger with output in amps 20% of the battery bank amp-hour capacity.

For my example off grid installation that would be:

Battery capacity 1041 x 20% = charger output size = 208 amps

The input volts should be matched to the solar panel output volts and output volts to the battery volts.

For lithium batteries output current of 30% battery capacity is recommended.

Important: All batteries have a Maximum Charge Voltage and Maximum Charge Current, which can be found in the specifications. These should not be exceeded ot the battery life may be significantly reduced.

Most good quality chargers used in off grid solar power installations can be set for voltage and also have variable current output.

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What Is An Off

An off-grid solar system is a stand-alone solar power system that provides electricity to a home or business independently from the grid. It is different from a standard residential solar power system in that there are specific components that apply to this type of system. Multi-mode inverters and adaptable batteries are the main difference. The beauty of an off-grid system is that the site is generating and storing its electricity from the sun, and the occupant/owner will not be receiving a quarterly power bill.

How To Size And Choose Off

While most solar-powered houses are grid-tied setups, many people enjoy the benefits of being completely disconnected from the city power grid. However, designing an off-grid solar power system is very different from a grid-tied system. You need to select equipment that can keep up with the endless demands of an off-grid setup. One key piece of equipment that you should take into consideration is your solar inverter. Which one is best for an off-grid solar application?

Off-grid Inverter Sizing

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What Does It Mean To Go Off

Off-grid living is a characteristic of housing and lifestyle.

The term off the grid can be associated with people that decide to disconnect their homes from the national electrical grid.

Today, going off grid is still considered the ultimate path to living rough, but it does not have to be all that serious though.

Off-grid living can also mean people create and utilize their own utilities, like gas, water and electricity generated from solar systems .

In general, self-sustainable off grid homes tend to be popular in locations that are more isolated from common governmental utilities like electricity.

However, isolated homes are not the only ones that make use of solar panels to generate their own electricity.

Off-grid living also attracts environmentally conscious, forward thinking individuals who want to reduce their ecological footprint while saving on monthly utility costs.

• In summary, taking your home off-grid means you are able to create/supply energy, drinkable water, grow food and manage waste/wastewater for yourself.

Example : A Simple Set Up In A Small Home

• The solar system requires 9.26kW.
• This system will need 31 x 300watt panels which will give a total of 9300kW

A large home using 17.8kWh, with a 48-volt battery system and a backup for three days, needs 31 x 300watt solar panels.

As you can see from these examples, the smallest adjustments to the hours of sunlight, the voltage of the batteries, and even the temperature you can store them can have a considerable effect on the number of panels your home needs.

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Often The Only Feasible Option

When youre seeking to power a building in a really remote location – say a hunting cabin out in the woods – theres a good chance theres no grid to connect to at all.

If you contact the utility for a connection, they will probably tell you that you are out of their coverage area. Alternatively, they could offer to lay the wire to connect you to the grid but only at an astronomical cost.

That means that youll have to produce your own power. You could use a backup generator, but fuel for it is expensive, while renewable energy like hydropower and wind arent available most places. This leaves solar as the only practical option for off-grid power.

A beautiful off-grid A-frame cabin in the Catskill Mountains. Image source: Chris Daniele via OffGridWorld

Freedom From The Grid

This is the primary reason why people in blackout-prone regions are interested in off-grid solar. When connected to the grid, you are dependent on an external supplier the utility company for all your power.

When the grid shuts off, so does your power supply. This dependence doesnt seem to be a problem until you are hit with blackouts and power failures, as those who suffered through the California blackouts of 2019 can attest.

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Solar Panel Size Dimensions

If you refer to the physical solar panel size dimensions, we can start off by saying that each manufacturer has its own optimal dimensions. This largely depends on their own technology.

As you might already know, solar panels are comprised of an arrangement of cells. Depending on the number of cells in the panel they are larger or smaller.

Traditionally, solar panels come in two different configurations: 60-cell and 72-cell. However, if you go to Panasonic or SunPower, they offer 96-cell panels.

But solar energy does not stop in large rigid solar panels.

You can also find small solar panels, and they are ideal to mount on motorhomes, boats, and caravans. Check out our guide on the best boat solar panels.

Solar panels also come in flexible and foldable configurations, making them more practical and easy to carry in case youd like to take them on your hiking or camping trips.

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What To Do If Your Solar System Doesnt Produce Enough Energy

You may wonder, what do I do if my existing solar system doesnt produce enough electricity to cover my needs. In that case you have two options reduce your usage or increase production.

Before investing on more power input, it is always prudent to investigate whether an upgrade of appliances, more efficient lighting, or completely removing an unnecessary power consumer would solve the problem. For many off grid homes, saving power is much cheaper than increasing production.

However, you may find yourself in the situation where you need to increase your overall power production. The first thing to do is to make sure you are getting the most out of your existing panels . After that, it is time to consider adding additional solar panels to your system.

To add more solar panels, if your system is relatively new, maybe a year or less, then the simplest thing to do is to buy more of the identical solar panels that you already have, and add additional parallel strings. Check out my solar free designers guide if you are not clear on series and parallel solar panel wiring

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Make Sure Your Solar Panels Are Accessible

Lastly, solar panels need to be clean and cool to work a maximum efficiency, and have a nice long life. Dust, dirt, and snow will naturally accumulate on solar panels, which need to be cleaned off periodically. Snow accumulation on your solar panels will reduce their life. Placing your panels closer to the ground where they are easier to access can go along way towards making routine solar panel maintenance actually get done in a timely manner.