you may estimate itusing energy conversion factors, but you should be aware that these may vary, so you should consider  the limitations of this approach. Perhaps this link will help you (especially useful in the case that you are interested in food values)

http://www.fao.org/docrep/006/y5022e/y5022e05.htm#bm5

Bomb calorimetry analysis can give you the value of the heat of combustion which can estimate the calorific value.

yes, of course Bomb calorimetry is the only way to determine it, However, the question was if it could be calculated, on the basis of the lipid content: it cannot, unless you have also information on the total organic content as well, and assign to the percentage remaining (difference between total organic and total lipids) an equal value to proteins and carbohydrates (see the FAO reference of my previous answer).

Yes, I'm wondering if I can calculate it. That means I can calculate it only for extracted lipids!! The link on FAO is really useful. Thanks @Domenico Voltolina

sorry I cannot do more, although I have a suggestion. if you take a sample and obtain its organc content by ignition (first dry to constant weight at 60-65 °C, then incinerate it in a muffle furnace and weigh again to obtain the inorganic contents. Once you have this information, the organic content of the sample is obtained by difference between total dry weight and ash weight. Since the lipid content is known, the rest of the biomass is mainly protein and carbohydrate. If you use the same caloric equivalent for both, as suggested in  FAO among others (actually, proteins have a slightly higher content, but for most applications this approach is considered acceptable), you can estimate the total caloric (energetic) value of your biomass.

cheers and good luck with your work

domenico