Plug-in solar - Terminology (the boring but important bit 🤣)
When I started I found the terminology very confusing. However it is important as some of the terminology if not used correctly could result in the wrong system selection or setup.
So let's clarify a few terms. These are general terms that apply equally to professionally installed or plug-in solar
In simple terminology a household appliance uses Power to get it going and keep it going. Power is measured in Watts (W) or Kilowatts (kW). As an example a 3kW kettle generally needs 3kW of power to run it when it's switch on.
The amount of power consumed by an appliance during its operation is known as Energy it's used and it's measured in Watt hours (Wh) or Kilowatt hours (kWh). So a 3kW kettle that was boiling constantly for 1 hour would have used 3kWh of energy. If it had only boiled for 20 minutes it would have used 1kWh of energy, if it only boiled for 5 minutes it would have used 250Wh of electricity
Knowing specific measures of your household consumption is key to sizing your system. In any household there is a background consumption that runs 24x7 (eg fridges). This load is known as your households Base Load. The Base Load contributes to your households Average Daily Consumption. An average base load is around 200w which can mean it makes up around 4.8kwh of your Average Daily Consumption. Both of these can be measured using the Sizing your solar and battery system page.
Solar arrays are sized based upon Kilowatt at peak (kWp). It tells you how much power they will generate under peak conditions. So a 1kWp system (eg 2 x 500w panels) would generate 1kW of power under optimum conditions.
Batteries are sized based upon the amount of Energy they can store. So a 3kWh battery can store 3kWh of energy. Batteries generally have recommended Depth of Discharge (DoD) which describes how much of the batteries capacity can be discharged. For example a DoD of 90% means that it is recommended only to discharge 90% of the battery. DoD can limit how much of the batteries capacity is usable. For example a 10kwh battery with a 90% DoD may only have 9kwh of usable capacity.
An Inverter converts power generated from solar panels from Direct Current or DC to Alternating Current or AC so it can be used by household appliances. It can also convert from AC to DC to allow power to be stored in a battery. Inverters have an input power limit (eg how many solar panels they can take) and an output power limit. For example a 1kW inverter with 2kWp of solar panels connected could generate 2kW of power at peak generation, however as the inverter is only rated at 1kw, it will only output 1kW of power. In that case it wouldn't be able to run a 3kW kettle on it's own. So if the solar was generating the inverter would only provide 1kW and you would need an extra 2kW from the grid to boil that kettle. Similar limits apply to battery inverters, so if the battery was 3kwh and the inverter was limited to 1kW then that is maximum power it could discharge, so again your 3kw kettle would need more than just the battery to run it.
We pay for electricity based upon a price per kWh used. So if the tariff was 25p per kWh and that 3kw kettle boiled for 20 minutes and used 1kWh of energy, that would cost around 25p. An average household uses around 8kWh per day, so the average household daily charge for electricity consumed (excluding standing charge) would be £2.
Solar systems (Plug-in, DIY or professionally installed) are generally Grid Tied. This means they will only work when the household has grid power. This is a safety mechanism designed to stop them working if the grid goes down or if they are unplugged. Some systems with batteries can operate in Island Mode which means they can continue to power devices through an Emergency Power socket (EPS) built into the device.
All solar and battery systems connected to the grid are required to be notified to your Distribution Network Operator (DNO). The type of notification depends on the total capacity of all inverters in your household connected to the grid. If the total is under 3.6kw then notification is known as G98 and can be done after the equipment is installed. If the total is over 3.6kw then it's known as G99 and approval must be obtained before the equipment is connected to the grid.
Is your mind boggled yet 😂🤣
If this blog has helped and you go on to installing a solar or battery solution, please let me know by leaving a comment and sharing this page as I really like to know I've been able to help.
If you're considering a move to Octopus to charge your batteries in the darker months, please consider using my referral link below (click on the Octopus) as it will give each of us £50 off our Octopus bill.
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