This is a technical guide for those with a basic understanding of solar and off-grid inverters. For less technical information, see the basic guide to selecting a home grid-tie or off-grid solar battery system. Solar and battery storage systems should always be installed by a licensed electrical professional.

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Basic Steps to Designing An off-grid Solar System

Before purchasing any equipment required for a solar battery (hybrid) or off-grid power system, it is very important to understand the basics of designing and sizing energy storage systems. As explained below, the first part of the process is to use a load table or load calculator to estimate the amount of energy needed to be generated and stored daily. If you cannot develop a load table, a professional solar installer or system designer should be consulted.

Step 1 - Estimate the loads

The most important part of designing any off-grid solar or battery system is calculating how much energy is required per day in kWh. For grid-connected sites, detailed load data can often be obtained directly from your electricity retailer or by using meters to measure the loads directly. For off-grid or stand-alone power systems, always start by using an off-grid load calculator (load table) for summer and winter. The load table can also be used to estimate surge loads, power factors, and the maximum demand required to size an appropriate off-grid inverter.

Step 2 - Battery sizing

Battery capacity is measured in Ah (Amp-hours) or Wh (Watt-hours). Lead-acid (deep-cycle) batteries are sized in Ah, while lithium battery capacity is generally measured in kWh (kilowatt-hours). After using a load calculator to estimate the average daily loads in kWh, you need to determine the number of days of autonomy (continuous days without sunshine) you require the battery to last. Typically, two days is the minimum for lithium battery systems, while the less efficient lead-acid batteries are generally sized for three or more days.

Additionally, all loss factors must be considered to ensure the battery size is adequate to meet the loads, including inverter losses, temperature derating for lead-acid batteries, maximum allowable depth of discharge (DoD) and round-trip efficiency. Also, consider battery type and chemistry, battery voltage range, and maximum battery charge rate (C rating), as explained in Section 6 - Battery Selection and Sizing.

Step 3 - Solar array sizing

A correctly sized solar array is required to charge the battery while also supplying the loads. As explained in more detail below, you must ensure the solar array is large enough while taking into account local conditions, including average solar irradiance throughout the year (peak sun hours), shading issues, panel orientation and tilt angle, cable losses, and temperature derating (loss factors). Our Photonik solar calculator can help estimate solar generation throughout the year, depending on the panel orientation, location and shading losses.

Step 4 - Inverter selection

After steps 1 to 3 have been established, you can select a suitable solar inverter or MPPT Solar Charge Controller to match the solar array depending on the panel and string length, which will determine the string voltage. Always use a string voltage calculator to calculate the maximum and minimum string voltages to ensure the voltage does not exceed the input rating. Next, the primary hybrid or off-grid inverter must be selected to meet the continuous and surge loads, taking into account temperature derating and other loss factors explained in more detail below.

Step 5 - Backup generation source

After your solar system is sized correctly and you have estimated a suitable battery capacity, you need to consider a backup generation source such as a diesel generator, especially if you live in a temperate (colder) location. Even though a backup generator may only be needed for occasional use in winter, it needs to be sized correctly to power the loads and recharge the battery simultaneously, as explained in section 8. However, emerging technologies such as vehicle-to-load (V2L) can offset generator runtime in certain situations, as explained in our guide to using V2L in off-grid systems.

1. Inverter Power ratings

Battery inverters, hybrid or off-grid, are available in a wide range of sizes determined by the continuous output power rating measured in kW or kVA. The inverter power rating depends on the inverter topology or design, the type of power conversion circuitry, whether it uses a transformer, the cooling system, and the operating temperature. Below are two main types of hybrid and off-grid inverters available.

1. Off-grid inverters use heavy-duty transformers, which are more expensive but provide high surge and peak power output and can handle high inductive loads. These inverters typically contain active fan-forced cooling systems to help maintain performance in high temperatures. As explained below, most of these inverters have integrated chargers and are grid-interactive, meaning they can also be used to create micro-grids or hybrid systems.

2. Hybrid inverters and AC-coupled battery systems generally use transformer-less inverters with 'switching transistors'. These compact, all-in-one inverters have lower surge and peak power output ratings but are more cost-effective because they combine the solar inverter (MPPTs) and battery inverter-charger into one integrated unit. They are also typically fully weather-rated, meaning they can be safely installed in more exposed locations, but direct sunlight should always be avoided.

Continuous Power rating

The inverter should be matched (sized) slightly higher than the loads or maximum demand of the appliances it will be powering. Due to temperature de-rating in hot environments, the inverter should be at least 1.2 times larger than the maximum continuous summer demand. Depending on the application, this is often the most important specification to be considered when selecting a hybrid inverter, especially when using a hybrid inverter as a backup power source for dedicated or essential loads. Whether the loads are inductive or resistive is also very important and must be taken into account.

Maximum Demand explained

Maximum inverter demand is the highest continuous load expected from the inverter, typically over a 30-minute period. If possible, the maximum demand should be based on data measured using a metering device. If load data is unavailable, maximum demand should be estimated based on selected loads in a load table, typically including the highest power rating loads and any other loads likely to be used simultaneously. The selection should be based on a thorough understanding of the load usage patterns to ensure accuracy.

2. Configuration - AC or DC-coupled

As solar battery systems became larger and more advanced, AC-coupled systems became one of the best configurations due to low-cost, easy-to-install string solar inverters. Most modern off-grid AC-coupled systems use bi-directional inverters coupled with one or more compatible solar inverters. AC-coupled systems are generally more efficient during the day when there is high AC power demand, such as air-conditioning systems, modern kitchen appliances and pool pumps. However, high-voltage DC-coupled battery systems (HV) are becoming more popular with the growing range of advanced HV hybrid inverters on the market.

For more information, see our detailed article explaining the difference between AC & DC-coupled systems.

3. Inverter Charge Rating

The battery inverter max charge rating, measured in Amps, needs to be considered to ensure the battery bank capacity and inverter are ‘balanced’ correctly. Ie. In AC-coupled systems, ensure the inverter-charger has enough charging capacity to enable the battery to reach the absorption charge voltage. If the battery bank is too large and the inverter charge rating is too small, the battery will not achieve a complete charge cycle. This will result in unbalanced cells, poor performance, degradation and possible sulfation (if lead-acid batteries are used).

Most modern lithium battery systems can accept a high charge current and can be charged at a higher C rate. If an oversized solar array is used and the inverter charge rate is insufficient, the solar generation may be clipped (reduced), and the system will not perform as efficiently. DC-coupled solar can help overcome this issue as the solar array is directly connected to the battery system and not contained by the inverter charge rating.

4. Solar Array Sizing Guide

Once you have established the average daily energy consumption (kWh), the next step is to determine the solar array size in kW while taking into account the local solar irradiation and any shading losses. The battery capacity (kWh) should also be considered for off-grid systems when sizing the solar array. This is not straightforward, as there are many variables to consider.

Peak Sun Hours Explained

A general guide is to use the minimum peak sun hours (PSH) of your location in Winter. Peak Sun Hours are not the daylight hours but the combined hours when the sun's insolation adds to 1,000 W/m2. This is when your solar panels generate the most electricity, much like measuring the optimum time for solar generation in a specific area. The official PSH figures are unique for every location and are generally provided by meteorological organisations.

The winter Peak Sun Hours or PSH value is typically used to ensure the solar array is large enough to fully charge the battery bank during the shortest sunny day. For example, if you had an off-grid system with a 16kWh battery, you need to generate a minimum of 20kWh during the shortest day, assuming the daytime loads were very low. If the daytime loads are 10kWh, then you will need to generate as much as 30kWh on a sunny day in winter. You can use the Photonik solar design tool to determine how many kWh a solar array will produce throughout the year based on the local PSH, orientation and array tilt angle. Due to the relatively low cost of solar panels, oversizing the solar array is a common practice to ensure the battery is charged even during poor or intermittent weather. In off-grid systems, oversizing will help reduce backup generator runtime.

Lead-acid batteries

For off-grid systems, lead-acid batteries are still a well-proven and reliable technology with a lifespan of up to 15 years when sized and managed correctly. One of the biggest benefits of lead-acid batteries is that, unlike modern lithium batteries, they will not shut down at a low voltage or low SOC. This is important in emergency situations or when a backup generator fails or is not available.

Higher Battery Voltage = Increased efficiency

All hybrid and off-grid inverters are designed to use a specific nominal DC battery voltage, the most common being 48V. Since most lithium battery systems are 48V, this is not a problem. However, many small-capacity inverters use 12V or 24V, so these are only compatible with battery banks of the same voltage. Selectronic, SMA and Schneider have a range of high-end 48V hybrid/off-grid inverters, while Victron Energy and Outback Power supply both dedicated 12V, 24V & 48V off-grid inverters. High-voltage or HV battery systems from 150 to 500V are increasingly common for grid-tied home battery systems, and many hybrid inverters such as the SolarEdge StorEdge, Goodwe EH and Fronius GEN24 Plus all work with high-voltage battery systems. However, it’s worth noting that HV battery systems are not universal and are generally only compatible with a specific hybrid inverter.

Optimum Voltage for Off-grid Systems

For off-grid systems, 48V battery voltages offer many advantages over 12V or 24V batteries, particularly for larger systems. AS shown in the example below, 48V systems result in a reduced current draw for the same power output, leading to lower resistance, cable losses, and voltage drop. This enhances efficiency across all power conversion equipment, including inverters and MPPTs. Low voltage 12V battery systems are generally only suitable for small applications like RVs, caravans or sheds; 12V systems are not recommended for AC power draws exceeding W due to the high current demands. Increased current in electrical systems requires much larger cable (conductor) sizes and can lead to greater heat generation, causing thermal expansion and contraction that can stress components and circuit boards, often resulting in electronic failures.

For example:

• W @ 12 V = 333 Amps

• W @ 24 V = 166 Amps

• W @ 48 V = 83 Amps

48V battery systems offer numerous benefits compared to lower voltage systems, including more solar power per MPPT, which results in far greater solar capacity per MPPT in DC-coupled systems. Moreover, the reduced chance of failure as the higher voltage and lower current minimise the heating effect caused by resistance in connections and terminals. Finally, 48V systems have a significant cost advantage compared to 12V and 24V due to the higher number of options and increased competition; there are far more 48V battery options, which are generally cheaper than the equivalent (kWh) capacity lower voltage versions. Additionally, 48V inverters cost less per kW to purchase.

Benefits of 48V systems compared to 12/24V

• More solar power capacity per MPPT due to reduced current

• Enhanced efficiency by reducing voltage drop and associated losses.

• Lower wiring costs with smaller gauge cables due to lower current.

• Higher voltage and lower current minimize the heating effect in connections.

• Reduces the risk of overheating and potential failure.

• More options and increased competition - many 48V LFP battery options.

• Reduced upfront cost - 48V inverters cost less per kW to purchase.

Battery Capacity - kWh

Battery capacity is measured in kWh (kilowatt/hours), or Amp-hours (lead-acid), which is the total energy a battery system can store. However, not all available capacity is usable depending on the battery type and specifications. Common Lead-acid deep-cycle batteries (AGM & Gel) should only be discharged to 20-40% of total capacity on a daily basis, whereas Lithium-ion and new-generation battery technologies can be discharged to 80-90% SOC. Therefore, the battery chemistry and capacity must be carefully selected to cater to the user’s energy requirements.

Contact us to discuss your requirements of Hybrid Solar System. Our experienced sales team can help you identify the options that best suit your needs.

Hybrid Vs. Off-grid Example - For a typical grid-connected home with peak (evening) energy use of 10kWh from 5 pm until midnight, a 12-15 kWh lithium battery would be sufficient. However, for off-grid systems, the battery system will need to store enough energy for several consecutive days of bad weather. With an average (efficient) home using 10-15 kWh over a whole day, this will require a much larger, more expensive 30-60 kWh battery system, depending on the days of autonomy required and the size of the solar array.

How to Size an Off-Grid Battery System

To correctly size an off-grid battery system, several factors need to be considered, including the daily load (kWh), inverter power rating, peak loads, and number of days of autonomy. Below are the steps to ensure the battery system is sized correctly to match these requirements.

1. Calculate the Daily Load Requirements:

   • Determine the average daily energy consumption in kilowatt-hours (kWh) per day using a load table. This includes all appliances, loads and devices that will be powered by the system. Generally, the winter load is used when the days are shorter, and the loads are typically higher.
     

2. Determine the Number of Days of Autonomy:

   • Decide how many days your battery system should be able to sustain your loads without recharging from solar or other sources (days of autonomy). This is crucial for periods with limited sunshine or during inclement weather. A general guide is two days for lithium battery systems, while less efficient lead-acid batteries are generally sized for three or four days.
     

3. Battery Storage Capacity (kWh):

   • Size the battery system based on the total energy required per day (kWh/day) multiplied by the number of days of autonomy desired. This gives the total energy storage capacity needed in kWh.
     

     Required Battery Capacity = Daily Load (kWh/day) × Days of Autonomy
     

4. Peak Demand Loads and Power Requirements

   • Using a load table, you can estimate the peak power demand (kW) your inverter and battery system must handle simultaneously. Inverter losses must be taken into account when calculating the peak DC current demand (A). For example, if your peak demand loads were W AC, and the 48V inverter efficiency was 92% (8% loss), then the peak DC battery demand would be calculated as follows:

     W × 1.08 = W (DC load)

     W / 48V = 191 Amps (Battery current)

5. Battery Output Power Rating:

   • The battery must be sized to handle both the peak load demand and the total energy consumption of the connected devices. Ensure it has sufficient power out (in Amps) to meet peak demand without overloading the battery system or the main fuse isolator/breaker. If the number of batteries cannot support the maximum load demand, more batteries must be added, or alternatively, a battery system should be chosen that can meet the power demand.

   • Also, ensure the main battery cables are rated to carry the maximum current with at least a 20% safety factor to allow for higher temperatures.

Modular, Rack-Mount Lithium Battery Systems

Modular lithium battery systems consist of individual battery modules that can be interconnected to scale up capacity as needed. These systems allow flexibility in design and future expansions. They can accommodate changes in energy consumption without requiring a complete overhaul of the system. Using rack-mount lithium battery systems, you can accurately size your off-grid battery system to meet current needs while allowing for future expansion and changes in circumstances over time.

The current carrying capacity, often referred to as ampacity, is the maximum current a cable can safely conduct without overheating. Matching the cable’s ampacity to the calculated maximum current draw ensures that the cable operates within safe thermal limits, reducing the risk of insulation degradation or fire hazards. Factors main that affect CCC include:

• Cable Cross-Sectional Area: Larger cables (with greater mm² or lower AWG numbers) can carry more current.

• Installation Conditions: Ambient temperature, conduit fill, and cable bundling affect heat dissipation. For example, cables enclosed in walls, conduits, or within insulation will run hotter than cables mounted on a wall.

• Material and Construction: Different conductor materials and cable designs offer varying heat resistance. For example, flexible (multi-strand) cables offer a greater CCC compared to regular building wire used in AC applications.

Insulation Temperature Rating

Insulation temperature rating refers to the maximum continuous operating temperature at which a cable’s insulation can perform reliably without degradation. This is a crucial factor because elevated temperatures can affect the cable voltage drop (efficiency), its lifespan and the system's overall safety. Generally, the minimum temperature for power systems at which a cable should be rated is 90°C (194°F).

• V90 Rated Cable: This cable has insulation designed to operate at temperatures up to 90°C (194°F). It is suitable for many standard applications with moderate ambient temperature and operating conditions.

• V110 Rated Cable: Cables with insulation rated for up to 110°C (230°F) are ideal for high-temperature environments or applications where cables may be bundled closely together, limiting heat dissipation. This is the preferred cable for battery installations, especially where high continuous current flow is expected.

Double-insulated flexible cables (often used in welding applications) are typically rated at a minimum of 110°C (230°F) and are an excellent option for battery cables due to their high quality and durability. The flexibility also allows for bending, making them ideal for installations where cable routing is tight. DC welding generally has a very high insulation rating (from V110 up to V300) and improved safety, as the double insulation provides an extra layer of protection.

Online cable size calculators

Online cable size calculators are invaluable tools for both professionals and DIY enthusiasts when designing solar and battery systems. These calculators allow users to quickly input key parameters—such as maximum current draw, system voltage, cable length, and permissible voltage drop—to determine the optimal cable size for a given installation. By automating complex calculations, these tools help ensure compliance with safety standards and efficiency requirements. Note different countries and jurisdictions may have different cable standards and requirements.

Below are links to some of the best online cable calculators:

• jCalc - Australian AS/NZS cable size calculator - https://www.jcalc.net/cable-sizing-calculator-as

• Southwire - North American Wire Gage Calculator - https://www.southwire.com/calculator-vdrop

• Elandcables - International and British standards - https://www.elandcables.com/cable-calculator

As a general rule, all combustion (diesel/petrol) generators are most efficient if operated at 70 to 80% load. For example, if you have a 10kVA generator, you would want to operate at a load of 7kVA to 8kVA, which equates to 6 - 7kW. Operating at the optimal load will dramatically improve fuel efficiency and reduce runtime. This will also improve the generator's lifespan and ensure it is not overloaded and damaged, or underloaded, which can cause premature wear and increased emissions.

Another factor you need to consider is the battery bank type, capacity and overnight load (kWh). For example, if you have a lithium battery, you may only need to run the generator for long enough to charge the battery with enough energy to get you through to the next day. In this situation, you would not charge the battery 100% or even 90%. You might only need to charge 60% state of charge to get you through to the following day, especially if the weather forecast is good. When charging lead-acid batteries, charging the battery to 100% using a generator is not recommended, as the charging current required for the last 10% of charging is very low and will severely underload the generator for a prolonged time.

Backup power using Vehicle-to-load (V2L)

Vehicle-to-load (V2L) technology is also being explored in off-grid systems, potentially reducing or replacing backup generators in certain scenarios. An electric vehicle (EV) equipped with V2L could serve as a backup power source due to its large battery capacity, typically 70kWh, around double that of an average residential off-grid solar system. This large capacity allows EVs with sufficient V2L capability to store surplus solar energy and provide backup power when needed.

The feasibility of using V2L hinges on two main factors:

1. The EV must generally have sufficient battery capacity for backup power, which may be constrained if it is regularly used for long-distance travel. Alternatively, if the EV is used for shorter trips and remains parked at home during the day, a portion of its battery capacity could be allocated to backup power.

2. The effectiveness of using V2L is based upon adequate solar availability, particularly in winter, when solar energy may be insufficient due to factors like shading, snow cover, or poor weather. Oversizing the solar array can mitigate these challenges by ensuring ample energy production for household needs and EV charging. Learn more in our detailed V2L explained article.

   For more information, please visit PERC PV Module.

Hello

I live in a village in the UK. My goal is self sufficiency before retirement. I am in the planning stages of sorting out solar and batteries. My end goal is to be off grid, but this will take time due to funds allocation! I need to build the system slowly.

What would be an ultimate system that incorporates solar panels (ground mount I’m in thatched house) batteries (Fogstar 15.5kwh) and a backup generator. Short term I know off peak electricity cheaper than diesel. But I want to get rid of utilities companies one day.

In my mind there is a brain box inverter (?) that everything could run off which is app controlled with data logging live and historical. Hopefully I buy this first then as funds permit start to buy everything else. What is important is the flexibility to easily drop in new equipment.

At the heart of everything I’d like a power management system that doesn’t require lcd menus on the equipment itself, some kind of cloud or iPad type control.

In terms of my usage I would say 15.5kwh x 2 be optimal or 1 to get going with grid or generator backup.

Is there a design software available? You need a hybrid inverter. Batteries and panels. And some varies disconnects/switches/fuses based on the design and your local code. I wouldn’t buy anything until you know exactly what it will look like initially and what you want to ultimately achieve. Buying things now locks you in to using that component. Battery prices are dropping, new inverters coming to market. Ideally you want to buy everything you need to initially have a complete system that you can use but still then expand later without wasting or having to replace the components you already bought. Buying just panels or an inverter or batteries now that cannot be used makes no sense other than losing value. You need all 3 to have a functioning system. You could also initially run the system without any batteries. Batteries have a management system that manages the battery. The inverter does everything else. Most of the big name inverters will also have apps and websites so you can see what’s happening and also historical data.
Sit down, think about your objectives, both short and long term. Get some of your power usage data from your house from your utility bills. Think about how much you want to spend. Think about your timelines.

Short term I know off peak electricity cheaper than diesel. But I want to get rid of utilities companies one day.

I think that the first step is is to make an Audit of your consumption, maybe use a device like Emporia.

Then, if you plan to make your own DIY system, you could start making a small off grid system with a 48V battery
that you charge using off peak power (maybe Octopus rate) and use the battery and an inverter during peak hours.

You could make a separate subpanel to which you connect some particulars devices, such as your refrigerator,
and use a transfer switch to feed your subpanel either using the grid or using your battery and inverter.

You could use maybe a timer to control your transfer switch, so during off peak hours you will use the grid
to recharge your battery and to feed your subpanel, and during peak hours you turn off the charger and
feed the sub panel using your battery and inverter.

Later on, then you can start to install some solar panels and a Solar Charge Controller to charge your battery
instead of using your charger. But if the weather is bad you still have the possibility use your charger instead.

And gradually your can add more solar panels and additional SCC. So with more solar panels you will start to have
more solar energy to charge another battery and even use a second more powerfull inverter, to run
some appliances, like an heat pump.

Note: If you really want to get rid of utilities companies, you need to plan making a full off grid system
able to handle in-rush current when starting a motor, like a refrigerator, HVAC, water pump. And have
enough storage energy in case of bad weather. In the case hybrid system, you will be still using the
grid to handle in-ruch current and bad weather situations. So you have to determine if the extra cost
of a full off grid solution is worthwhile or if still using the grid with an hybrid solution will be more cost-effective. Rewrite of your goals:
- build the system slowly: batteries, solar panels (ground mount) batteries, backup generator; get rid of utility one day.
- everything manageable by power management system that doesn’t require lcd menus on the equipment
- my usage: 15.5kwh x 2 be optimal or 1 to get going with grid or generator backup.
- Is there a design software available?

As you are already grid-connected, I'd leave that connection in place and use it as alternate charging source. Choose a system reference voltage (probably 48v). As I'm not in the UK, find out from UK folks what the requirements are for permitting, installation, wiring, etc.

1. Research and implement the Victron Cerbo (management system), as this is pretty comprehensive (if you buy into Victron).

2. Research and implement a backup generator; could be inverter-gen, could be open-frame non-inverter gen with a "ChargeVerter". Putting this in place now, sized for future needs, and you have backup for when grid goes down.

3. research and implement Inverter/charger + battery-bank. This runs parallel to your grid connection and current wiring (so no inspections or permitting (yet). Ties into management system if victron inverter, and would be sized to your current or future usage requirements.

At this point, you have a system running in the garage or on the bench, and it can power loads you hook up to it, and be recharged either by a grid-connected device (at night if lower costs) or by generator.

4. implement solar panels on ground mount. Tie in to victron mppt, and rest of system.

5. plan wiring to reduce/remove grid connection. Leave in just enough grid connection to provide that alternate charging device support.

At this point, you are hopefully running on all your equipment, purchased slowly and piecemeal, each being managed by Victron Cerbo as each comes online.

Design software still seems iffy to me, if the goal is to get it to help you put together all of these pieces; there are online design packages that help solar installers, but not end users or DIY (easily). Good news is that with Victron's book "wiring unlimited" and other such resources, and Visio or other diagramming software (paid or free), you can get pretty close.

You could also have Victron sales org (whoever that is in your region) put together a quote, and this would start you off with a reference design.

Hope this helps ... Up here going totally off grid would mean a drastic reduction of my daily consumption. My 44kWp system produces 350kWh on a perfect day, but there was few 2kWh days in December with many under 10kWh. At the same time my consumption was 180-250kWh/day depending how cold it was. There's no way to add enough panels to compensate poor Nov-Dec-Jan production here. The only way would be getting rid of ground source heating and going back to oil/wood AND still use generator all the time for those three months. Here it's much cheaper to be grid tied but of course it can change in the future.

I'm live much more north than you, but If you want to go totally off grid, you should plan how to keep your winter consumption low.

I'm using Deye (=Sunsynk) and can recommend it. With it don't need anything extra, just install app and you have remote control over your system.

I'd would start with hybrid inverter (big enough to go off-grid eventually) with some panels while being still grid tied. This way you can start "saving" on electric bill immediately. Then add battery and more panels as funds allow. Generator would be my last purchase before pulling the plug.

I have no experience being off-grid and only one year with solar so far, but that's how I'd do it. Think as most folks are saying, for possibly 7 or 8 months of the year, you will be essentially off grid once you have a reasonable solar, inverter and battery setup, but for 3 or 4 months when you really need to heat your home in winter, run a tumble dryer ect then you hit a roadblock vs being "entirely off grid", Thatched roof implies an older house so perhaps not quite as good as a new build at keeping the heat in and the weather out.

Your target ideal state maybe off grid 100% of the time, you can do that with other heating means, Bottled gas or Oil in Winter, but that would be investing and spending cash to meat the goal rather than aiming for lowest run rate cost.

I would love to be off grid, especially when the Energy companies are lifting the standing charges, but its difficult in the UK. My goal has been to get to the lowest run rate, I do that by leveraging the solar through 8 months of the year with the excess heating water or charging car, in Winter I use the batteries as a storage tank for over night cheap electricity, which I use for the other 20 hours of the day. But in Winter there is little option but to switch the central heating on even in a well insulated modern house.

Rewrite of your goals:
- build the system slowly: batteries, solar panels (ground mount) batteries, backup generator; get rid of utility one day.
- everything manageable by power management system that doesn’t require lcd menus on the equipment
- my usage: 15.5kwh x 2 be optimal or 1 to get going with grid or generator backup.
- Is there a design software available?

As you are already grid-connected, I'd leave that connection in place and use it as alternate charging source. Choose a system reference voltage (probably 48v). As I'm not in the UK, find out from UK folks what the requirements are for permitting, installation, wiring, etc.

1. Research and implement the Victron Cerbo (management system), as this is pretty comprehensive (if you buy into Victron).

2. Research and implement a backup generator; could be inverter-gen, could be open-frame non-inverter gen with a "ChargeVerter". Putting this in place now, sized for future needs, and you have backup for when grid goes down.

3. research and implement Inverter/charger + battery-bank. This runs parallel to your grid connection and current wiring (so no inspections or permitting (yet). Ties into management system if victron inverter, and would be sized to your current or future usage requirements.

At this point, you have a system running in the garage or on the bench, and it can power loads you hook up to it, and be recharged either by a grid-connected device (at night if lower costs) or by generator.

4. implement solar panels on ground mount. Tie in to victron mppt, and rest of system.

5. plan wiring to reduce/remove grid connection. Leave in just enough grid connection to provide that alternate charging device support.

At this point, you are hopefully running on all your equipment, purchased slowly and piecemeal, each being managed by Victron Cerbo as each comes online.

Design software still seems iffy to me, if the goal is to get it to help you put together all of these pieces; there are online design packages that help solar installers, but not end users or DIY (easily). Good news is that with Victron's book "wiring unlimited" and other such resources, and Visio or other diagramming software (paid or free), you can get pretty close.

You could also have Victron sales org (whoever that is in your region) put together a quote, and this would start you off with a reference design.

Hope this helps ...

Sorry I missed this post, much appreciated and great advice

Rewrite of your goals:
- build the system slowly: batteries, solar panels (ground mount) batteries, backup generator; get rid of utility one day.
- everything manageable by power management system that doesn’t require lcd menus on the equipment
- my usage: 15.5kwh x 2 be optimal or 1 to get going with grid or generator backup.
- Is there a design software available?

As you are already grid-connected, I'd leave that connection in place and use it as alternate charging source. Choose a system reference voltage (probably 48v). As I'm not in the UK, find out from UK folks what the requirements are for permitting, installation, wiring, etc.

1. Research and implement the Victron Cerbo (management system), as this is pretty comprehensive (if you buy into Victron).

2. Research and implement a backup generator; could be inverter-gen, could be open-frame non-inverter gen with a "ChargeVerter". Putting this in place now, sized for future needs, and you have backup for when grid goes down.

3. research and implement Inverter/charger + battery-bank. This runs parallel to your grid connection and current wiring (so no inspections or permitting (yet). Ties into management system if victron inverter, and would be sized to your current or future usage requirements.

At this point, you have a system running in the garage or on the bench, and it can power loads you hook up to it, and be recharged either by a grid-connected device (at night if lower costs) or by generator.

4. implement solar panels on ground mount. Tie in to victron mppt, and rest of system.

5. plan wiring to reduce/remove grid connection. Leave in just enough grid connection to provide that alternate charging device support.

At this point, you are hopefully running on all your equipment, purchased slowly and piecemeal, each being managed by Victron Cerbo as each comes online.

Design software still seems iffy to me, if the goal is to get it to help you put together all of these pieces; there are online design packages that help solar installers, but not end users or DIY (easily). Good news is that with Victron's book "wiring unlimited" and other such resources, and Visio or other diagramming software (paid or free), you can get pretty close.

You could also have Victron sales org (whoever that is in your region) put together a quote, and this would start you off with a reference design.

Hope this helps ...

Would you elaborate on the generator options to research? I work from home part of the week in a workshop which uses high wattage tools. I was thinking of separating this off as a separate circuit on a diesel Hyundai generator which could form the backup generator with auto switch somehow? "2. Research and implement a backup generator; could be inverter-gen, could be open-frame non-inverter gen with a "ChargeVerter". Putting this in place now, sized for future needs, and you have backup for when grid goes down."

You'll want to figure out your requirements (things this gen has to power, if all else fails), your fuel of choice (we use propane, but don't know what you've got available), and type of gen (inverter-gen closed frame, open-frame inverter-gen, open-frame non-inverter gen). I tend to stay away from inverter-gen's, as these are very expensive overall, too compact to work on, have expensive parts embedded in them, and so on. An open-frame inverter-gen bucks this trend, and a few manufacturers are coming out with them. An open-frame non-inverter-gen (tri-fuel), but still with low THD levels approaching an inverter-gen, are coming on the market ... these seem to be the sweet-spot for me. Otherwise, add a chargeverter to the non-inverter-gen models, if your chosen inverter needs it (most AIO's would need it).

Then, size the gen to operate everything you want to power (inverter-charger, tools, appliances) at no more than 75% of gen capacity (the sweet spot here for gen watts). It will recharge the battery-bank through inverter-charger, whenever that gets low. If you have complex shop tools with huge power draws, or other large loads, you can always fire up the gen and run it for that load. We run everything through the inverter & battery-bank, but depending on shop needs, you could get fancy with circuits powering both inverter-charger, and heavy shop loads.

But, gen is there mainly for backup duty if grid down, or solar output (in winter months) isn't where you want it. If you can get a large propane site tank, and propane delivered, now you've got a reliable source of backup power, with little to no fuel mess ... propane also runs clean through the carb, so better for reduced maintenance.

For me, the gen would have to be auto-start, auto-choke (start with a remote fob), and have a "smart port" on it for later ATS integration into automated start/stop based on grid up/down or inverter/battery-bank power levels. You don't want to trudge out to the gen shed thru snow and pull on the starter rope; a gen shed keeps things quiet, and hidden, depending on your 'hood. A westinghouse model fills all my requirements, although I don't really know what's available in the market on your side of the pond.

We are totally off-grid, and run the gen whenever we have more than a few days of cloud cover; still runs no more than a few hours/day, as it refills the battery-bank (buffer), and we run off battery-bank beyond that. Really nothing to it ... we are our own power grid (we can't get a grid connection where we are, without a winning lottery ticket), and it's assembled from off-the-shelf stuff ...

Hope this helps ...

"2. Research and implement a backup generator; could be inverter-gen, could be open-frame non-inverter gen with a "ChargeVerter". Putting this in place now, sized for future needs, and you have backup for when grid goes down."

You'll want to figure out your requirements (things this gen has to power, if all else fails), your fuel of choice (we use propane, but don't know what you've got available), and type of gen (inverter-gen closed frame, open-frame inverter-gen, open-frame non-inverter gen). I tend to stay away from inverter-gen's, as these are very expensive overall, too compact to work on, have expensive parts embedded in them, and so on. An open-frame inverter-gen bucks this trend, and a few manufacturers are coming out with them. An open-frame non-inverter-gen (tri-fuel), but still with low THD levels approaching an inverter-gen, are coming on the market ... these seem to be the sweet-spot for me. Otherwise, add a chargeverter to the non-inverter-gen models, if your chosen inverter needs it (most AIO's would need it).

Then, size the gen to operate everything you want to power (inverter-charger, tools, appliances) at no more than 75% of gen capacity (the sweet spot here for gen watts). It will recharge the battery-bank through inverter-charger, whenever that gets low. If you have complex shop tools with huge power draws, or other large loads, you can always fire up the gen and run it for that load. We run everything through the inverter & battery-bank, but depending on shop needs, you could get fancy with circuits powering both inverter-charger, and heavy shop loads.

But, gen is there mainly for backup duty if grid down, or solar output (in winter months) isn't where you want it. If you can get a large propane site tank, and propane delivered, now you've got a reliable source of backup power, with little to no fuel mess ... propane also runs clean through the carb, so better for reduced maintenance.

For me, the gen would have to be auto-start, auto-choke (start with a remote fob), and have a "smart port" on it for later ATS integration into automated start/stop based on grid up/down or inverter/battery-bank power levels. You don't want to trudge out to the gen shed thru snow and pull on the starter rope; a gen shed keeps things quiet, and hidden, depending on your 'hood. A westinghouse model fills all my requirements, although I don't really know what's available in the market on your side of the pond.

We are totally off-grid, and run the gen whenever we have more than a few days of cloud cover; still runs no more than a few hours/day, as it refills the battery-bank (buffer), and we run off battery-bank beyond that. Really nothing to it ... we are our own power grid (we can't get a grid connection where we are, without a winning lottery ticket), and it's assembled from off-the-shelf stuff ...

Hope this helps ...

Best summary of "how to think about your generator needs" I've read. Well done.

"2. Research and implement a backup generator; could be inverter-gen, could be open-frame non-inverter gen with a "ChargeVerter". Putting this in place now, sized for future needs, and you have backup for when grid goes down."

You'll want to figure out your requirements (things this gen has to power, if all else fails), your fuel of choice (we use propane, but don't know what you've got available), and type of gen (inverter-gen closed frame, open-frame inverter-gen, open-frame non-inverter gen). I tend to stay away from inverter-gen's, as these are very expensive overall, too compact to work on, have expensive parts embedded in them, and so on. An open-frame inverter-gen bucks this trend, and a few manufacturers are coming out with them. An open-frame non-inverter-gen (tri-fuel), but still with low THD levels approaching an inverter-gen, are coming on the market ... these seem to be the sweet-spot for me. Otherwise, add a chargeverter to the non-inverter-gen models, if your chosen inverter needs it (most AIO's would need it).

Then, size the gen to operate everything you want to power (inverter-charger, tools, appliances) at no more than 75% of gen capacity (the sweet spot here for gen watts). It will recharge the battery-bank through inverter-charger, whenever that gets low. If you have complex shop tools with huge power draws, or other large loads, you can always fire up the gen and run it for that load. We run everything through the inverter & battery-bank, but depending on shop needs, you could get fancy with circuits powering both inverter-charger, and heavy shop loads.

But, gen is there mainly for backup duty if grid down, or solar output (in winter months) isn't where you want it. If you can get a large propane site tank, and propane delivered, now you've got a reliable source of backup power, with little to no fuel mess ... propane also runs clean through the carb, so better for reduced maintenance.

For me, the gen would have to be auto-start, auto-choke (start with a remote fob), and have a "smart port" on it for later ATS integration into automated start/stop based on grid up/down or inverter/battery-bank power levels. You don't want to trudge out to the gen shed thru snow and pull on the starter rope; a gen shed keeps things quiet, and hidden, depending on your 'hood. A westinghouse model fills all my requirements, although I don't really know what's available in the market on your side of the pond.

We are totally off-grid, and run the gen whenever we have more than a few days of cloud cover; still runs no more than a few hours/day, as it refills the battery-bank (buffer), and we run off battery-bank beyond that. Really nothing to it ... we are our own power grid (we can't get a grid connection where we are, without a winning lottery ticket), and it's assembled from off-the-shelf stuff ...

Hope this helps ...

Hyundai DHYSELR Diesel Generator Long Run - Generators Direct

*Please be advised that Hyundai Power Products now have an extended lead time and you may not receive them next day. The current delivery time is estimated at 2-4 working days.* The DHYSELR is the long running version of the DHYSE, with a large 25L fuel tank which boosts the maximum...
This is what I am thinking. I would probably not ever run more than 3kw at same time in workshop.. is it an inverter gen or do I need that as an extra? An air-cooled, diesel gen at rpm ... looks to be non-inverter-gen type. Interesting, and not what I would've expected out of a diesel genset, but, it is inexpensive. Can't give any advice on this, other than find the manuals & warranty, and read up on it. Can't yet find THD values for it ...

As this seems to be non-inverter type (can't find inverter or THD in the one manual I have found), you might have to place a chargeverter in front of it. Next problem might be availability of an EU (230v specific) version of the chargeverter ... if this isn't available, or the US model isn't compatable with your country's power, then you'll have to research the inverter model long before purchasing a generator, as some AIO's might not like the output of this (or any non-inverter) gen. AIO's tend to want very grid-like power (low-THD) on their AC input ...

To size the gen, you'll have to carefully sum up your shop's (and any other) tool power loads, and size the gen larger than that ... use only 50 to 75% of the power from it for all of your loads, and you'll have "stiff" grid-like power from it.

Hope this helps ...