Hi,
Moving to Economy 7 would reduce your night rate for each unit and that maybe when you want to plug your hybrid in. However, your day rate will also go up (versus a non-Economy 7 contract).
The only way to establish a 'best' package will be to estimate your overall cost under an Economy 7 regime and compare it to single rate use profile.
If you're out of the house during the day, have few appliances on all the time (including fridge, freezer, computers, entertainment systems and heating etc.) then Economy 7 is most likely to be better value.
If your home is occupied during the day and/or you can program appliances to work during that time and your car will be on charge during the day, the single rate deal will probably be best. Bearing in mind most of your daytime use will be in low daylight periods when your panels are not working to the optimum.
If you have a full household with plenty of laundry, you could install solar thermal as well, set your washing machines to run at midday, run on hot and cold then get the best of all worlds.
With no gas (so no central heating) we've just installed air to air source heating in place of old storage heaters and switched away from Economy 7 despite having an EV and solar PV. We do have multiple freezers etc. her's hoping we made the right choice but, changing the meter only costs £50...