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Hybrid portable generator cuts costs and CO2

Rugby-based Off Grid Energy claims its hybrid system for portable generators achieves fuel savings and CO2 reductions of up to and beyond 75 per cent.

“Often people don’t know the exact load on a generator so each person in the supply chain adds a bit more capacity to be on the safe side,” Off Grid director Danny Jones tells CN.

“So you end up with a generator that is significantly overrated, meaning it runs for long periods with very low loads and that’s not good for the generator’s reliability or fuel efficiency.”

Smarter power cuts noise and emissions

To overcome this problem, the new Grid To Go unit is essentially a smart battery pack that can either be used on its own to power items for short durations or, more usually, it will be connected between the generator and the load.

In the latter configuration, if the electrical load requirement is low the power can be supplied from the batteries without the need to constantly run the generator, meaning the operation is silent and there are no emissions.

When the battery charge falls below a pre-determined level, the generator is automatically started and run at a high output for a short duration to recharge the battery pack.

Mr Jones says this operation dramatically reduces generator running time, cuts fuel and service cost as well as CO2 emissions, while also extending refuelling intervals.

If the electricity demand from the load rises above the output of the battery pack, the generator automatically restarts and the power is fed straight through the Grid To Go unit to the load.

Any excess power from the generator is used to keep the Grid To Go’s batteries fully charged and once the peak demand has passed the system automatically reverts to battery power.

Efficient running makes more savings

Mr Jones points out that further savings are possible, as generators are normally sized to cover peak demand, meaning that for most of the time they are running inefficiently at less than a third of their rated capacity. “As the Grid To Go unit helps cover peaks, the generator can be sized closer to the average demand with a little extra to allow for recharging the battery pack,” he says.

“As the Grid To Go unit helps cover peaks, the generator can be sized closer to the average demand with a little extra to allow for recharging the battery pack”

Danny Jones, Off Grid

If a smaller generator is specified and the peak load exceeds its capacity, the Grid To Go unit automatically goes into ‘power assist’ mode and adds battery power to that developed by the generator to cover the shortfall. When the peak subsides, the unit will revert to normal operation.

Off Grid Energy has identified a 33 kWh trailer-mounted Grid To Go unit as optimum for the construction industry (although it also produces other power ratings as trailer mounts or with a lifting eye).

The standard 33 kWh uses lead-acid batteries, while a more expensive lithium-ion version has a 50 kWh capacity, is lighter and recharges more quickly.

A-Plant trial gets big results

Through working with A-Plant, a Grid To Go unit was on trial at the end of 2012 at a Balfour Beatty site in a residential area. It was being used in conjunction with a 33 kVA generator to power a site welfare unit and overnight security.

Normal practice would have been to run the generator continuously, but with the Grid To Go unit in place, the generator was running for less than a third of the time and was programmed to avoid overnight running.

According to Mr Jones, over 10 days this resulted in a fuel saving of 460 litres (or around £367) and 1,216 kg of CO2. “Over a year that equates to a saving of more than £13,000 and 43,000 kg of CO2 – and that’s just on site,” he says.

Furthermore, the data logger showed the average daytime load was 3-4 kW and overnight it was less than 2 kW, while the peak load was no more than 10 kW. “So the generator is three times bigger than is actually required,” Mr Jones says.

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