Homeowner Blog

zappi: The Intelligent EV Charger Optimising the Use of Excess Solar

Erica Charles · 11 Oct 2017

Many of our customers have installed an iBoost or Immersun or similar to divert excess solar PV into their hot water tank.

If you have an electric vehicle (EV), it makes sense to divert excess electricity into the EV battery.  In fact if your hot water is heated by gas, oil or biomass, it makes more sense to charge the car than it does to charge the hot water tank. An iBoost is generally displacing fuel costing ~ 5p per kWh, and so 1kWh of diverted electricity is worth ~ 5p. Charging the EV displaces grid electricity at the ‘full value’ ~ 15p per kWh.

Introducing zappi…..

Starting with the formalities, as with many things in this day and age, zappi is one of those 21st century gadgets that doesn’t have a capital letter at the start of its name.  If you're writing a review of the product, you're old fashioned like me, and you want to start a sentence with the product name, the lack of capital really hurts.   At least Apple managed to make the second letter of iPhone etc a capital to give the oldies amongst us something to hang on to…  Oh well, language evolves, apparently.

Apart from this breach of grammatical etiquette which is doubtless entirely lost on the younger generation in our office, the zappi’s a really smart piece of kit, an intelligent EV charger, costing not that much more than a normal EV charger.

zappi is an EV charger with special eco charging modes to optimise self-consumption of on-site solar PV, wind etc.  Specifically it has three charging modes:

  • FAST charge mode - works like an ordinary EV charging station, charging fast (7kW max power), just like an ordinary Mode 3 charging point. The actual charge rate depends on the EV's onboard charger and the grid supply voltage. Typically, vehicles have either a 3.3kW or 6.6kW charger. The actual power can be a little different if the grid supply voltage is not exactly 230V.
  • ECO mode – the car will charge at a minimum rate of 1.4kW, fluctuating above this as surplus solar power allows. The minimum charge rate of 1.4kW will always be achieved, and if surplus power falls below 1.4kW, the shortfall will be drawn from the grid.
  • ECO+ mode - This is similar to the ECO mode in so far as the car will charge at the minimum rate of 1.4KW, fluctuating above this as surplus power allows, however charging will be paused if surplus power falls below the Min Green Level. For example, with the Min Green Level set to 50%, charging will be paused if 700W of power is being imported from the grid and will resume when there is 700W of power being exported.

By setting the Min Green Level to 100%, the car will be charged using only surplus renewable power, providing there is sufficient surplus power to do so.

Note: The EV charging standard does not support charging below 1.4kW.

To supplement the ECO and ECO+ modes, there are various optional boost functions, designed to ensure your car achieves minimum levels of charge whatever the weather.  More on these below.

How much does zappi cost? Only about £150 more than a normal charger...

The average cost of a zappi installed is £900 - £1000, depending on cabling requirements. This is about £150 more expensive than a standard charger.  The zappi is OLEV approved and therefore eligible for the OLEV grant of £500.  You can claim the OLEV grant if you have proof of purchase of an electric vehicle on the eligible vehicle list (must cost less than £60,000).

zappi has a friend called eddi (or Eddi?) ...

eddi is similar to an iBoost or Immersun, in that it diverts excess solar generation to the hot water tank.  If you install zappi and eddi, you can choose whether to prioritise zappi or eddi.

front_2 eddi.jpg

By the way, on the spec sheet Eddi seems fairly ambivalent as to whether he/she uses a capital in his/her name or not. Probably designed by a texter…  or by someone like me who finds it difficult to entirely overturn nearly 50 years of starting proper names with capitals.

What if I have a battery or an iBoost installed?

zappi responds quicker than the iBoost or Immersun, and so the default will be that zappi will be switched on before the iBoost or Immersun.  If you don’t want this to happen, you can set a delay on the zappi to give the iBoost or Immersun time to turn on.

If you have a dc coupled battery system, the battery will always take priority over the zappi.  If you have an ac coupled system (e.g. Tesla Powerwall 2), the battery system is likely to have a similar response time to zappi. Therefore you need to set a delay on the zappi if you want to prioritise charging of your battery over your zappi.  If you want to prioritise the zappi over the battery there is a ‘workaround’ we can install using a CT clamp – this will tell the zappi when the battery is being charged, thus turning on the zappi, subject to sufficient power availability.

Boost functions

To supplement the ECO and ECO+ modes, there are various optional boost functions, designed to ensure your car achieves minimum levels of charge whatever the weather. 

  • Manual boost function - when boosting, the charge rate is set to maximum (just like FAST mode), until a set amount of energy has been stored in the EV's battery. After this, zappi will revert back to ECO or ECO+ mode.

This function is useful if you arrive home with an almost flat battery and would like to charge the vehicle immediately to ensure there is enough charge for a short trip if needed.

  •  Smart boost - the Smart Boost function will charge the EV with a minimum kWh figure by a set time.

Say for example, it’s a sunny Sunday and you wish to ensure there is enough charge in the EV to get to work in the morning (e.g. 15kWh), but in the meantime, you want to use the surplus energy from the PV system to charge the car, so you choose to use ECO+ mode.

At sunset there is only 10kWh of charge accumulated. However, because you activated Smart Boost, and set the time you needed to leave for work, zappi automatically boosts the charge in the night to top up the battery to the required 15kWh by 7am.

  • Boost timer - zappi can be programmed to 'boost' the current charge at certain pre-set times. When boosting, the charge rate is set to maximum (just like FAST mode), regardless of the amount of available surplus power. This means that power may be drawn from the mains grid supply during boost times.
  •  Economy Tariff boosting - boosting only when economy rate electricity is available.


zappi’s a great product with all bases covered – just what you need if you drive an EV and you want to optimise the use of your solar generation. zappi is supplied at a comparatively modest premium to the cost of a standard charger, and qualifies for the OLEV grant where relevant.

Savage, as my teenage sons would say (copied, unfortunately, by their father…)


Topics: EV charging, zappi, Solar PV