It seems that battery users are effectively excluded from this scheme. Assuming that these users do their charging during off-peak periods, the 'Baseline' against which their "skill of reducing electricity import" is compared will be zero.
Seems discriminatory to exclude those of us who - at our own expense of buying batteries - save peak hour electricity every day. Might even encourage us to establish a new 'Baseline' by charging during peak hours in the hope of a £1000 reward!
I think what you could do to take part is actually export your battery energy onto the grid during the period which might count. Might mean you have to mess up your usual charge discharge schedule but could mean you have a large "reduction" in your consumption even if it's negative. Probably worth checking with Glow support though so I'd drop them an email. If not you can complain to National Grid who've set this up and try get them to fix it, at least for the next trial period if they do it.
I've got a small solar and small battery installation. I've signed up for Glow Delight not expecting to save very much energy or win the prize.
The first event, 13th Feb I set the batteries to charge from 16:20 for an hour but my batteries were fully changed from solar so no charging from the main took place and the house simply ran off the mains supply for that period. During the 17:30 to 18:30 time slot the house ran almost completely from the batteries and I managed a reduction of 92% which amounted to a saving of 0.287 kWh hardly significant but every little helps.
For the second event, it had been a dull day and there was very little stored in the batteries, so this time using the same time slot as above, the batteries pulled power from the mains which then provided sufficient to get me though the 17:30 to 18:30 period. This time the saving was 0.286 kWh a reduction of 95%
Future saving (if any) will likely be of a similar size. From my PoV it's an interesting experiment and whilst my savings are small I will continue to take part.
Just my two pence worth!