There are a number of ways you can calculate your off grid needs:
POWER NEEDS - How much power do you use?
We have a handy basic solar calculator, to give you a rough idea of how much power you use daily, see our calculation tools page, or click here.
PHYSICAL SPACE - What space do you have for panels?
Often there is a restriction on space for panels, so measure this space, or spaces, to help work out what you can physically fit.
FINANCES - Do you have a budget to stick to?
It’s very helpful to give yourself a budget to stick to, often we find that folks have way too much or way too little to achieve their aims, this will help you greatly when working out how much bang for your buck.
Are your items DC or AC or both?
Make a note of which items are DC and AC. Often LED lights, pumps, USB sockets etc are DC powered and can run straight from a battery or charge controller.
AC items, meaning domestic products with a 3 pin plug, will need an inverter to convert the electricity from DC battery power to AC mains power.
Work out what your biggest, or biggest combination of AC items are, to work out your inverter size.
eg A 1200w blender whilst watching a 200w TV... You choose an inverter capable of 1.4kw (1400w) output continuously.
VOLTAGE - What will your System Voltage be?
Most commonly used are 12v, 24v and 48v systems.
Generally, 12v systems used in sheds, motorhomes and boats.
Generally, 24v systems used in smallholdings & larger domestic boats.
Generally, 48v systems used in larger properties, including battery storage systems connected to the grid.
The key to the above is the word generally, there are no rules.
Typically: (PV = PhotoVoltaic, meaning Solar panels)
Under 1kW of PV is best in a 12V system
1kW to 3kW PV is best in a 24V system
3kW+ PV is best in a 48V system
WINTER is coming…!
If you have long dark winters, here in the UK, then you need to consider how reliant you are on your power system. During Winter production can drop by up to 90% on average… Also when working out your solar production with a calculator, the average daily production is just that - an average. In the UK we get days of sun then days of rain and cloud, so be mindful that an average is not realistic, there will be prolonged periods of little to no production.
If you rely on this power, then you will need to consider having a back-up generator to run from time to time, as creating a system to cover your needs through Winter would be horrendously expensive.
Typically there are lead acid and lithium batteries on the market, both are used and both have pros and cons.
Lead Acid - Cheap, Better in cold weather, higher discharge capacity, simple to manage
These take the power from a solar panel or panels and give it to the battery in a meaningful way, to keep the battery healthy and charged.
There are basic versions (PWM) which are cheap, cheerful, but are not great out of the summertime.
MPPTs are the latest incarnation and work very well all year round, especially when you have panels in strings to get a high voltage to the voltage limitation of the controller.
SOLAR PANELS, also known as PV (PhotoVoltaic)
There are a few flavours of panel technologies & the tech is pretty established, so there isn’t a lot in it unless you are buying a lot of panels. Often customers ask about performance but only want one panel, we advise you go for the most power for the space you have. Performance is worth considering when a large array.
SOLAR PANEL TERMINOLOGY
CIGS - Fully flexible and very good when partially shaded.
Glass Foil - Most panels on the market are this type. Glass in front, plastic foil behind.
Glass Glass - The premium of panels in performance and price! Glass in front & behind. (also know as Bifacial)
Half cell - Higher shade tolerance to standard panels.
Mono (black) v Poly (blue) - An old debate, historically Mono were much better when the compared to poly, but often that’s not the case now.
Mono tends to perform a little better now, but a good Poly will out perform a bad Mono…
Frames come in Silver or Black.
Panel fronts tend to be blue/white, black/white or all black depending on your needs.
Parallel or Series or both? - An old adage from a time when panels were made without bypass diodes, meant they used to be wired in parallel to prevent shade issues. Nowadays almost all panels have bypass diodes, so run your panels in series to the limit of your controllers input voltage.
NOTE - Cold weather can increase a panels voltage HIGHER than it’s rated VOC, so ensure when working out your voltages you give a decent buffer for this.
PERC / Percium - Latest tech with high efficiency - “Passivated Emitter and Rear Contact” solar cells, known as PERC solar cells enable the cells to produce 6 to 12 percent more energy than conventional solar panels.
Semi-Flex - Cheap, easy to fit, but not long lasting - typically the adhesive is only rated to ten years and most panels only have 1-2 year warranty for this reason, also many do not allow for running in multiples, so for single use only, generally.
DISTRIBUTION — DC
Generally power for DC items comes either directly from the battery bank or from the charge controller. Many charge controllers have a ‘LOAD OUT’ on them, which is a low load for low power items, like LED lights or similar. This is a simple DC distribution solution.
From the battery bank you must use correct cables, fuses and switches for the system you fit, always consult your installer / electrician.
Don’t be fooled - DC can be as dangerous as AC - beware, please.
DISTRIBUTION — AC
Small inverters have a standard 3 pin socket on them, and you can easily use them to power low wattage AC devices. They also should have correct wiring, fusing and switches, read the manual and consult your installer / electrician if you are unsure how to fit them safely.
Larger inverters have to be wired directly to a consumer unit and then to various sockets - which your electrician must do for you.
Don’t mess around, AC can kill - always use an electrician.
Remember, it takes a remarkably small amount of current across the human heart to stop it.
BATTERY TO BATTERY CHARGERS (also called B2Bs)
These typically fit between a starter battery and leisure battery. When you charge your starter battery with an alternator (your engine is running) - then the B2B will charge your leisure battery when appropriate to do so.
Many questions asked by experienced and qualified installers can be answered within Victron’s Wiring Unlimited.
In this section we look at what scenarios result in an “off-grid” system, then go on to list the basics elements that make up a simple off-grid solar power installation, as well as a brief look at larger, residential/commercial off-grid set-ups. Finally we will show some examples of how to calculate daily load requirements which helps with inverter sizing and PV array sizing.
An off-grid system is simply defined as a system where there is no permanent grid connection available. This includes: caravans, camper-vans or motorhomes with/without EHU (electric hook-up), canal boats or sailing boats with/without EHU, holiday cabins, yurts, mobile festival stalls, sheds or summer houses or any other permanent or temporary structure without a mains power supply to it.
[It is also important to note that if you have a system with an AC input connection from the grid, e.g. a garden office, where you only expect/plan to use the grid in emergencies to re-charge the batteries, if the grid supply is permanently connected to the inverter (i.e. hardwired in), it is not considered to be truly ‘off-grid’ and so DNO notification and approval may still be required.]
The simplest off-grid system comprises of a solar panel (for harvesting solar energy), a solar charge controller (to regulate battery charge current and voltage) and a battery. The panel charges the battery during sunny periods, via the charge controller, and the battery stores the energy generated from the solar panel until it is needed to run the loads. Loads can be either direct DC loads, like a 12V light or pump, or 230V AC loads which require an inverter to change the DC electricity to AC electricity.
There would also be other components included in the system to ensure safety and reliability, and these will depend on the system’s size, purpose, voltage, battery chemistry, and other characteristics, but the main ones are: solar panel, charge controller, battery and inverter.
Larger residential or commercial off-grid systems will have a back-up generator for re-charging the batteries and supplying the loads when the batteries are low and there is no solar production. These generators are often set-up to start automatically when the batteries get down to a certain voltage or state of charge (SOC). Many systems also use a wind turbine to generate electricity to supplement the solar panels, especially in locations where there is plenty of wind during the long winter months, during which the sun rarely appears!
When choosing the system size needed for your application, there are a number of factors that need careful consideration. All of these are based on what your load profile looks like. A load profile is a closer look at how much power your devices/equipment need to run and how long they run for during a typical day. Power is measured in watts (W), or kilowatts (kW), where 1000W = 1kW. The longer something is on for, using power, the more energy it requires. Energy is measured in Wh (watt-hours) or kWh (kilowatt-hours) and is the result of multiplying the power something uses, by the time it is used for:
e.g. 1 A single 50W light running for 10 hours will use 50W x 10h = 500Wh of energy.
e.g.2 A 1000W pump running for 30 minutes (0.5h) will use 1000W x 0.5h = 500Wh of energy.
From the examples above you can see that two quite different loads can require the same total amount of energy to run them.
When you have a list of all your loads, and how long you need to run them for, you can determine the minimum inverter size needed for your system if you have AC loads, as well as the minimum battery capacity needed for seeing you through periods of bad weather/no solar production. In combination with the load profile and battery capacity, it is then possible to work out the size of the solar array needed to re-charge the batteries quickly and efficiently, as well as meet the daily load requirements. We have a very useful Calculator Tool that helps you with this part of the system design.
The main system sizing parameters that need to be determined are:
Inverter output, in W or kW
Battery capacity, usually in amp-hours (Ah), for your chosen battery voltage
Solar array size, in W or kW
An off-grid system is a system where there is no fixed connection to the mains/grid, and is made up of various components that depend on the size and type of the loads that need electricity. Smaller systems may or may not need an inverter for 230V AC loads, and larger systems will need at least one inverter (more than one in parallel or 3-phase for bigger systems) and will also use a back-up generator. Load calculation is a very important part of the system design, and is the first step in knowing what are the main components you will need to buy.
We are a main distributor for Victron Energy equipment and our team has a wealth of knowledge, expertise and installation experience which we can use to help guide you in your purchase of appropriate equipment for your needs.
Here’s a good starting point to see the range of materials we can offer: